That portion of optical attenuation in optical fiber resulting from the conversion of optical power to heat. Caused by impurities in the fiber such as hydroxyl ions.
A material such as silicon carbide, aluminum oxide, silica, cerium oxide, emery, or rouge is used to figure, shape, or finish optical elements. Abrasives differ from polishing materials mainly in particle size.
A device that accepts inputs (optical or electrical) from a primary path and a secondary path to provide automatic or manual switching in the event that the primary path signal is broken or otherwise disrupted. In optical A/B switches, optical signal power thresholds dictate whether the primary path is functioning and signals a switch to the secondary path until optical power is restored to the primary path.
A device that requires a source of energy for its operation and has an output that is a function of present and past input signals. Examples include controlled power supplies, transistors, LEDs, amplifiers, and transmitters.
A multiplexing function offered in connection with SONET that allows lower-level signals to be added or dropped from a high-speed optical carrier in a wire center. The connection to the add/drop multiplexer is via a channel to a central office port at a specific digital speed (DS3, DS1, etc.)
Abbreviation for the add-drop multiplexer. A device that adds or drops signals from a communications network.
Abbreviation for asynchronous digital subscriber line. See DSL.
Yellow fibers provide cable tensile strength, support, and additional protection for the optical fiber bundle. Kevlar® is a particular brand of aramid yarn.
The angle over which the core of an optical fiber accepts incoming light; usually measured from the fiber axis. Related to the numerical aperture (NA).
Part of the telecommunication network that connects to individual and corporate users.
An adapter is a mechanical device designed to align fiber-optic connectors. It contains the split sleeve, also known as the interconnect sleeve, that holds the two ferrules together. Adapters can help mate or connect a variety of fiber optic cables together.
A mechanical fixture within an adapter body that aligns and holds two terminated fiber connectors. The adapter sleeve material is typically phosphor bronze, ceramic, or polymer.
A device that drops and/or adds one or more optical channels to a signal.
Cable made entirely of dielectric (insulating) materials without any metal conductors, armor, or strength members.
All Silica Fiber
Also known as all-glass fiber. A fiber with both a silica core and a silica cladding, regardless of the presence of a polymer overcoat or buffer.
A signal that varies continuously (e.g., sound waves). Analog signals have frequency and bandwidth measured in hertz.
Angle of Incidence
The angle between an incident ray and the normal to a reflecting or refracting surface.
Angled physical contact (APC)
A polishing technique for fibers/ferrules that minimizes reflective light. A style of the fiber-optic connector with a 5 -15 degree able on the connector tip for the minimum possible back reflection. Usually used in AM or DWDM single-mode transmission systems using laser light sources. Typically 65-70 dB.
The cable that is suspended in the air on the telephone or electric utility poles.
Abbreviation for automatic gain control. A process or means by which gain is automatically adjusted in a specified manner as a function of input level or another specified parameter.
Abbreviation for amplitude modulation. A transmission technique in which the amplitude of the carrier varies in accordance with the signal.
American National Standards Institute (ANSI)
The American National Standards Institute (ANSI) is the official American standards body through which standards are published, and various other standards-setting committees are accredited.
A device, inserted within a transmission path, that boosts the strength of an electronic or optical signal. Amplifiers may be placed just after the transmitter (power booster), at a distance between the transmitter and the receiver (in-line amplifier), or just before the receiver (preamplifier).
The loss at a connector due to fiber end face angles being misaligned.
Abbreviation for American National Standards Institute. An organization that administers and coordinates the U.S. voluntary standardization and conformity assessment system.
APC (Angled Physical Contact)
Abbreviation for angled physical contact. A style of fiber optic connector with a 5°-15° angle on the connector tip for the minimum possible back-reflection.
APD (Avalanche Photodiode)
A photodiode that exhibits internal amplification of photocurrent through avalanche multiplication of carriers in the junction region.
Application-specific optical fiber (ASOF)
Fibers built for specific applications such as erbium fibers used in EDFA optical amplifiers. Other types include high N.A. fibers used for manufacturing filters and gratings, etc.
Arrayed waveguide grating (AWG)
A device that allows multiple wavelengths to be combined and separated in a DWDM system. An array of planar waveguides diffracts light at angles that depend on the wavelength. The central element is an array of narrow, curved waveguides that run parallel to each other between a pair of mixing regions. The waveguides differ in length by an increment that is much larger than the wavelength. The input signal enters the first mixing region and is coupled into the waveguides to pass into the second mixing region.
Antireflection coating. A thin, dielectric, or metallic film applied to an optical surface to reduce its reflectance and thereby increase its transmittance.
A ruggedized fiber optic test adapter designed to loop a signal from the Tx side of a port to the Rx side, simulating a complete connection.
A protective layer, usually metal, wrapped around a cable.
ASE (Amplified Spontaneous Emission)
A background noise mechanism common to all types of erbium-doped fiber amplifiers (EDFAs). It contributes to the noise figure of the EDFA which causes loss of signal-to-noise ratio (SNR).
Abbreviation for an application-specific integrated circuit. A custom-designed integrated circuit.
Abbreviation for American Society for Testing and Materials. An organization that provides a forum for the development and publication of voluntary consensus standards for materials, products, systems, and services that serve as a basis for manufacturing, procurement, and regulatory activities.
Data that is transmitted without an associated clock signal. The time spacing between data characters or blocks may be of arbitrary duration. Opposite of synchronous.
ATM (Asynchronous Transfer Mode)
A digital transmission switching format, with cells containing 5 bytes of header information followed by 48 data types. A transmission standard widely used by the telecom industry. A digital transmission switching format with cells containing 5 bytes of header information followed by 48 data bytes. Part of the B-ISDN standard.
Reduction of signal magnitude, or loss, normally measured in decibels. Fiber attenuation is normally measured per unit length in decibels per kilometer. The decrease in signal strength along a fiber optic waveguide caused by absorption and scattering. Attenuation is usually expressed in dB/km.
A device used to measure power loss in fiber optic connectors, cables, or systems.
1) In electrical systems, a usually passive network for reducing the amplitude of a signal without appreciably distorting the waveform. 2) In optical systems, a passive device for reducing the amplitude of a signal without appreciably distorting the waveform
The condition in a fiber optic link when the operation is limited by the power of the received signal (rather than by bandwidth or distortion).
Passive components that produce a controlled signal attenuation in an optical fiber transmission line.
Automatic test equipment (ATE)
Test equipment that is computer programmed to perform a number of test measurements on a device without the need for changing the test setup. Especially useful in testing components and assemblies.
Avalanche Photodiode (APD)
A semiconductor photodetector with integral detection and amplification stages. Electrons generated at a p/n junction are accelerated in a region where they free an avalanche of other electrons. APDs can detect faint signals but require higher voltages than other semiconductor electronics.
The average level of power in a signal varies with time.
AWG (Arrayed Waveguide Grating)
An array of curved planar waveguides that separates many optical channels at once. Also called Waveguide Array. A device, built with silicon planar lightwave circuits (PLC), that allows multiple wavelengths to be combined and separated in a dense wavelength-division multiplexing (DWDM) system.
Axial Propagation Constant
For an optical fiber, the propagation constant evaluated along the axis of fiber in the direction of transmission.
The center of an optical fiber.
A transmission network that carries high-speed telecommunications between locations. This is normally the main portion of a telecommunication network, with branches going to individual buildings. In a local area network, this is usually the link between routers, switches, and bridges.
The inter-building and intra-building cable connections between entrance facilities, equipment rooms, and telecommunications closets. Backbone cabling consists of the transmission media, main and intermediate cross-connects, and terminations at these locations.
A percent of the transmitted signal reflected back towards the source from a fiber-optic interface. Referenced in dB.
The ratio of the optical pulse power (not energy) at the OTDR output to the backscatter power at the near end of the fiber (z=0). This ratio is inversely proportional to the pulse-width because the optical pulse power is independent. It is expressed in dB.
A transmission network that carries high-speed telecommunications between regions (e.g., a nationwide long-distance telephone system). Sometimes used to describe the part of a local area network that carries signals between branching points.
Scattering of light in the direction opposite to that in which it was originally traveling. The return of a portion of scattered light to the input end of fiber; the scattering of light in the direction opposite to its original propagation.
A term applied to any process in the cable plant that causes light to change directions in fiber and return to the source. Occurs most often at connector interfaces where a glass-air interface causes a reflection.
The highest frequency that can be transmitted by an analog system. Also, the information-carrying capacity of a system (especially for digital systems). The range of frequencies within which a fiber optic waveguide or terminal device can transmit data or information.
A design that uses a birefringent crystal. They are used in optical couplers, optical switches, and optical isolators.
The condition in a fiber optic link when bandwidth, rather than received optical power, limits performance. This condition is reached when the signal becomes distorted, principally by dispersion, beyond specified limits.
A method of communication in which a signal is transmitted at its original frequency without being impressed on a carrier. The number of signal level transitions per second in digital data. The term is often confused with bits per second. Telecommunications specialists prefer to use “bits-per-second” to provide an accurate description.
The number of signal-level transitions per second in digital data. For some common coding schemes, this equals bits per second, but this is not true for more complex coding. Bits per second is less ambiguous. A unit of signaling speed equal to the number of signal symbols per second, which may or may not be equal to the data rate in bits per second.
A device that divides incident light into two separate beams. An optical device, such as a partially reflecting mirror, that splits a beam of light into two or more beams. Used in fiber optics for directional couplers.
Attenuation caused by high-order modes radiating from the outside of a fiber optic waveguide which occurs when the fiber is bent around a small radius. See also macro bending, microlending.
The smallest radius an optical fiber or fiber cable can bend before excessive attenuation or breakage occurs.
The fraction of bits transmitted that are received incorrectly. The number of coding violations detected in a unit of time.
Operating in both directions
A device that sends information in one direction and receives information from the opposite direction.
Base two numbers with only two values, 0 or 1.
A type of fiber optic connector consisting of two cone-shaped ferrules aligned by a mating sleeve.
Operating in both directions. Bidirectional couplers split or combine light the same way when it passes through them in either direction. The bidirectional transmission sends signals in both directions, sometimes through the same fiber.
Having a refractive index that differs for the light of different polarizations.
The smallest unit of information upon which digital communications are based; also an electrical or optical pulse that carries this information.
The number of levels that a pixel might have, such as 256 with an 8-bit depth or 1,024 with a 10-bit depth.
Bit Period (T)
The amount of time required to transmit a logical one or a logical zero.
Bit Error Rate (BER)
The fraction of bits transmitted incorrectly. The fraction of bits transmitted that are received incorrectly.
Bit error rate tester (BERT)
Test equipment that measures the bit error rate (BET) of digital transmission systems.
Popular coax bayonet style connector Often used for baseband video.
An abbreviation for broadband on a passive optical network.
A technique for building optical filtering functions directly into a piece of optical fiber-based on interferometric techniques. Usually, this is accomplished by making the fiber photosensitive and exposing the fiber to deep UV light through a grating. This forms regions of higher and lower refractive indices in the fiber core.
A high-speed switch to transfer an optical signal to an alternate fiber.
Scattering of light caused by a change in refractive index, as used in Fiber Bragg Gratings and Distributed Bragg Reflectors.
An essential part of many fiber-optic cable designs, consisting of a layer of woven yarn. Note: In the case of single-fiber loose-buffered or two-fiber “zip-cord” loose-buffered fiber-optic cables, the braid is situated between the buffer tube and jacket. In the case of cables having multiple buffer tubes, the braid is usually situated between the inner jacket and outer jacket.
To separate the individual fibers or buffer tubes of a fiber-optic cable for the purpose of splicing or installing optical connectors.
A type of fiber optic cable containing several fibers, each with its own jacket and all of them surrounded by one common jacket. Breakout cables are designed for convenient installation of fiber optic connectors but tend to have high transmission losses due to bends in the fibers.
Covering a wide range of frequencies or having a high data rate. The broadband label is sometimes used for a network that carries many different services or for video transmission.
Sending the same signal to many different places, like a television broadcasting station. Broadcast transmission can be over optical fibers if the same signal is delivered to many subscribers.
Bundle of Fibers
A rigid or flexible group of fibers assembled in a unit. Coherent fiber bundles have fibers arranged in the same way on each end and can transmit images.
Material that is used to protect an optical fiber or cable from physical damage and to provide mechanical isolation or protection. Fabrication techniques include both tight jacket or loose tube buffering, as well as multiple buffer layers.
A protective tubing used to protect the exposed fiber. Commonly used in terminating multi-fiber cable or “fan-out” situations. Also known as furcation tubing.
The operation of a laser diode or other component prior to its use in its intended application, as a means of testing and stabilizing it.
A network topology in which all terminals are attached to a transmission medium serving as a bus. Also called a daisy-chain configuration.
A joining of two fibers without optical connectors arranged end-to-end by means of a coupling. Fusion splicing is an example.
Eight bits of digital data. (Sometimes parity and check bits are included, so one “byte” may include 10 bits, but only 8 of them are data.)
One or more optical fibers enclosed, with strength members, in a protective covering.
A cable that is connector terminated and ready for installation.
The cable plant consists of all the optical elements including fiber, connectors, splices, etc. between a transmitter and a receiver.
A communications system that distributes broadcast and non-broadcast signals as well as a multiplicity of satellite signals, original programming, and other signals by means of a coaxial cable and/or optical fiber.
In technology, the wave is modulated with a signal carrying information. In business, a company that provides telecommunication services.
Carrier-to-Noise Ratio (CNR)
The ratio, in decibels, of the level of the carrier to that of the noise in a receiver’s IF bandwidth before any nonlinear process such as amplitude limiting and detection takes place.
Category 5 (CAT5) cable is a popular twisted-pair copper cable. It is used for Ethernet cable applications. Category 5e (CAT5e) can support short-run Gigabit Ethernet (1000 Mbps) networking, unlike CAT5 which supports Fast Ethernet (100 Mbps).
An acronym for cable television, derived from Community Antenna TeleVision.
Wavelengths of about 1530 to 1565 nm, where erbium-doped fiber amplifiers have their strongest gain. Normally erbium-fiber amplifiers operate in either C- or L-band. The wavelength range between 1530 nm and 1562 nm used in some CWDM and DWDM applications.
Abbreviation for Consultative Committee on Radio. Replaced by ITU-R.
Abbreviation for Consultative Committee on Telephony and Telegraphy. Replaced by ITU-T.
Abbreviation for code-division multiple access. A coding scheme in which multiple channels are independently coded for transmission over a single wideband channel using an individual modulation scheme for each channel.
A fixed-length data packet transmitted in certain digital systems such as ATM.
In a laser, the nominal value central operating wavelength. It is the wavelength defined by a peak mode measurement where the effective optical power resides (see illustration). In an LED, the average of the two wavelengths measured at the half amplitude points of the power spectrum.
A telephone company facility for switching signals among local telephone circuits; connects to subscriber telephones. Also called a switching office.
The center component of a cable provides strength. Commonly referred to as “Central Strength Member.”
A communications path or the signal sent over that path. Through multiplexing several channels, voice channels can be transmitted over an optical channel.
Data encoding and error correction techniques used to protect the integrity of data. Typically used in channels with high bit error rates such as terrestrial and satellite broadcast and videotape recording.
A/B Markers easily identify the TX and RX connector on each end of a fiber optic cable assembly. These channel markers assure that the proper connections are made between the transmitting and receiving ports of a transceiver.
The amount of bandwidth allocated per channel.
In laser diodes, the shift of the laser’s center wavelength during single pulse durations.
Chromatic dispersion (CD)
The variation in the velocity of light (group velocity) as a function of wavelength. It causes pulses of a modulated laser source to broaden when traveling within the fiber, up to a point where pulses overlap and the bit error rate increases. CD is a limiting factor in high-speed transmission and must be properly compensated, which implies proper testing.
The optical circulator allows for optical add/drop multiplexing in conjunction with integrating a fiber Bragg grating (FBG) and is commonly used in the long haul, metropolitan area networks, and networks. In a circulator, the internal passive components are arranged so that light passes from port 1 to 2, from port 2 to 3, and from port 3 to 4 while preventing it from traveling in the opposite direction. Because each level of the circulator is identical, the steps can be repeated as many times as necessary.
A pulse in which the wavelength changes during the duration of the pulse.
Wavelength-dependent pulse spreading in optical fibers, measured in picoseconds (of pulse spreading) per nanometer (of source bandwidth) per kilometer (of fiber length). It is the sum of waveguide and material dispersion. Reduced fiber bandwidth caused by different wavelengths of light traveling at different speeds down the optical fiber. Chromatic dispersion occurs because the speed at which an optical pulse travels depends on its wavelength, a property inherent to all-optical fiber. May be caused by material dispersion, waveguide dispersion, and profile dispersion.
Passive three-port devices that couple light from Port 1 to 2 and Port 2 to 3 and have high isolation in other directions.
Originally a physical connection that transmits electricity or signals. Now also a communication channel that guarantees a fixed transmission capacity.
making temporary physical or virtual connections between two points, which guarantees a fixed transmission capacity.
The layer of glass or other transparent material surrounding the light-carrying core of an optical fiber. It has a lower refractive index than the core and thus confines light in the core. Coatings may be applied over the cladding. Material that surrounds the core of an optical fiber. Its lower index of refraction, compared to that of the core, causes the transmitted light to travel down the core. This is glass or plastic, having a low refractive index, that surrounds the core of a fiber. Optical cladding promotes total internal reflection for the propagation of light in a fiber.
A mode confined to the cladding; a light ray that propagates in the cladding.
The process of separating an optical fiber by a controlled fracture of the glass, for the purpose of obtaining a fiber end, which is flat, smooth, and perpendicular to the fiber axis.
CLEC (Competitive Local Exchange Carrier)
A company that offers local telephone service in competition against dominant phone companies.
Abbreviation for cable modem termination system.
Coarse Wavelength-Division Multiplexing (CWDM)
Transmitting signals at multiple wavelengths through the same fiber with wide spacing between optical channels. Typical spacing is several nanometers or more. Also called wide wavelength multiplexing. CWDM allows eight or fewer channels to be stacked in the 1550 nm region of optical fiber, the C-Band.
An outer plastic layer applied over the cladding of fiber for mechanical protection. The material surrounding the cladding of a fiber. Generally, a soft plastic material that protects the fiber from damage.
Coaxial cable – cable with a central metallic conductor surrounded by an insulator that is covered by a metallic sheath that runs the leg nth of the cable. 1) A cable consisting of a center conductor surrounded by an insulating material and a concentric outer conductor and optional protective covering. 2) A cable consisting of multiple tubes under a single protective sheath. This type of cable is typically used for CATV, wideband, video, or RF applications.
A device, also called an encoder that converts data by the use of a code, frequently one consisting of binary numbers, in such a manner that reconversion to the original form is possible.
Coherent Bundle of Fibers
Fibers packaged together in a bundle so they retain a fixed arrangement at the two ends and can transmit an image.
In fiber optics, a communication system where the output of local laser oscillator is mixed with the received signal, and the difference frequency is detected and amplified.
That length over which energy in two separate waves remains constant. With respect to a laser, the greatest distance between two arms of an interferometric system for which sufficient interferometric effects can be obtained.
1. The process of aligning the optical axes of optical systems to the reference mechanical axes or surfaces of an instrument.
2. The adjustment of two or more optical axes with respect to each other.
An optical instrument consisting of a well-corrected objective lens with an illuminated slit or reticle at its focal plane. Collimators are used in lens testing to determine focal lengths, and in other metrological applications where a distant object at a known location is required.
Reducing the number of bits needed to encode a digital signal, typically by eliminating long strings of identical bits orbits that do not change in successive sampling intervals (e.g., video frames).
A cable containing both fiber and copper conductors. Also known as hybrid cable.
The process of connecting pieces of fiber together.
A device mounted on the end of a fiber-optic cable, light source, receiver, or housing that mates to a similar device to couple light into and out of optical fibers. A connector joins two fiber ends, or one fiber end, and a light source or detector. A mechanical or optical device that provides a demountable connection between two fibers or a fiber and a source or detector.
The maximum value in dB of the difference in insertion loss between mating optical connectors (e.g., with remating, temperature cycling, etc.). Also called optical connector variation.
The measurement of how well-centered the core is within the cladding.
Any interference that increases the amplitude of the resultant signal. For example, when the waveforms are in phase, they can create a resultant wave equal to the sum of multiple light waves.
Industry slang for metal wire, either twisted-pair or coaxial cable.
Copper vs Fiber
In general, fiber has many advantages over copper. In copper networks, loss increases with signal frequency- High data rates increase power loss and therefore decrease transmission distances. In fiber-optic networks, the loss does not change with signal frequency.
The central part of an optical fiber that carries light. The light-conducting portion of fiber, defined by its higher refraction index. The core is the center of a fiber, surrounded by a concentric cladding of lower refractive index.
In fiber optics, a mode that shares energy among one or more other modes, all of which propagate together. Note The distribution of energy among the coupled modes changes with propagation distance.
A device that connectors three or more fiber ends, dividing one input between two or more outputs or combining two or more inputs into one output.
The total optical power loss within a junction, expressed in decibels, attributed to the termination of the optical conductor.
Coupling ratio is a measure of how a device distributes light from its inputs to its outputs. It is expressed as either a percentage or in dB.
Transfer of light into or out of an optical fiber. (Note that coupling does not require a coupler).
The fraction of available output from a radiant source is coupled and transmitted by an optical fiber.
A crimped metal cylinder that holds the connector to the cable through the cable’s strength member.
The angle at which light in a high-refractive-index material undergoes total internal reflection. In geometric optics, at a refractive boundary, the smallest angle of incidence at which total internal reflection occurs.
Carrier suppressed return-to-zero differential quadrature phase-shift keying. These technologies make it possible to generate DWDM signals with bit rates of 100 Gbps and beyond per channel and transmit them over long distances.
Connections between terminal blocks on the two sides of a distribution frame or between terminals on a terminal block (also called straps). Also called cross-connection or jumper.
Cross-gain Modulation (XGM)
A technique used in wavelength converters where gain saturation effects in an active optical device, such as a semiconductor optical amplifier (SOA), allow the conversion of the optical wavelength. Better at shorter wavelengths (e.g. 780 nm or 850 nm).
Cross-phase Modulation (XPM)
A fiber nonlinearity caused by the nonlinear index of refraction of glass. The index of refraction varies with an optical power level which causes different optical signals to interact.
1) Undesired coupling from one circuit, part of a circuit, or channel to another. 2) Any phenomenon by which a signal transmitted on one circuit or channel of a transmission system creates an undesired effect in another circuit or channel.
Abbreviation for carrier sense multiple access with collision detection. A network control protocol in which (a) a carrier sensing is used and (b) while a transmitting data station that detects another signal while transmitting a frame, stops transmitting that frame, waits for a jam signal, and then waits for a random time interval before trying to send that frame again.
Customer Premises Equipment (CPE)
Terminal, associated equipment, and inside wiring located at a subscriber’s premises and connected with a carrier’s communication channel(s) at the demarcation point (demarc), a point established in a building or complex to separate customer equipment from telephone company equipment.
Measurement of optical loss made by cutting a fiber to compare the loss of a short segment with loss of a longer one.
A destructive technique for determining certain optical fiber transmission characteristics, such as attenuation and bandwidth, by (a) performing the desired measurements on a long length of the fiber under test, (b) cutting the fiber under test at a point near the launching end, (c) repeating the measurements on the short length of the fiber, and (d) subtracting the results obtained on the short length to determine the results for the residual long length.
The highest order mode will propagate in a given waveguide at a given frequency.
The longest wavelength at which a single-mode fiber can transmit two modes, or (equivalently) the shortest wavelength at which a single-mode fiber carries only one more.
Abbreviation for continuous wave. Usually refers to the constant optical output from an optical source when it is biased (i.e., turned on) but not modulated with a signal.
Cycles per Second
The frequency of a wave, or the number of oscillations it makes per second. One cycle per second equals one hertz.
A format for component digital videotape recording working to the ITU-R 601, 4:2:2 standard using 8-bit sampling.
The VTR standard for digital composite (coded) NTSC or PAL signals that use data conforming to SMPTE 244M.
A composite digital video recording format that uses data conforming to SMPTE 244M.
An uncompressed tape format for the component digital video which has provisions for HDTV recording by use of 4:1 compression.
The noise current generated by a photodiode in the dark.
Optical fiber installed without transmitter and receiver, usually to provide expansion capacity. Some carry lease dark fibers to other companies that add equipment to transmit signals through them.
Data Dependent Jitter
Also called data-dependent distortion. Jitter related to the transmitted symbol sequence. DDJ is caused by the limited bandwidth characteristics, non-ideal individual pulse responses, and imperfections in the optical channel components.
The number of bits of information in a transmission system, expressed in bits per second (b/s or bps), and which may or may not be equal to the signal or baud rate.
A logarithmic unit describing the ratio of loss of power per kilometer distance
Abbreviation for decibel relative to a carrier level.
Decibels relative to 1mW.
Decibels relative to 1 µW.
Reflection of light caused by periodic changes in refractive index in a stack of layers of different composition or-equivalently-by a corrugation at the boundary between two semiconductor layers. The period and the refractive index select one wavelength.
Abbreviation for data circuit-terminating equipment. 1) In a data station, the equipment that performs functions such as signal conversion and coding, at the network end of the line between the data terminal equipment (DTE) and the line, and maybe a separate or an integral part of the DTE or of intermediate equipment. 2) The interfacing equipment that may be required to couple the data terminal equipment (DTE) into a transmission circuit or channel and from a transmission circuit of a channel into the DTE.
A logarithmic comparison of power levels, defined as ten times the base-10 logarithm of the ratio of the two power levels. One-tenth of a bel.
A device used to delay transmission of a signal for functions such as memory loops, sequential processing or built-in testing. The delay can be achieved by coiling long lengths of coaxial cable or optical fiber.
A device that separates a multiplexed signal into its original components; the inverse of a multiplexer.
Dense Wavelength-Division Multiplexing (DWDM)
Transmitting signals at multiple wavelengths through the same fiber with close spacing. Channel spacing usually is 200GHz or less in frequency units, corresponding to 1.6nm in wavelength units at 1550nm. The transmission of many closely spaced wavelengths in the 1550 nm region over a single optical fiber. Wavelength spacings are usually 100 GHz or 200 GHz which corresponds to 0.8 nm or 1.6 nm. DWDM bands include the C-Band, the S-Band, and the L-Band.
Any interference that decreases the desired signal. For example, two light waves that are equal in amplitude and frequency, and out of phase by 180°, will negate one another.
A device that generates an electrical signal when illuminated by light. The most common fiber-optic detectors are photodiodes.
Differential group delay (DGD)
A delay caused by different arrival times of optical signals, which causes dispersion. In multimode fibers, it is the delay difference of the various modes, whereas in single-mode fibers it is the delay caused by chromatic, waveguide, and polarization mode dispersion.
Differential mode delay (DMD)
A distortion of the signal-bearing light-pulse over lengths of multimode optical fiber. The light paths traveling the full width of the core will take longer to get to the receiver than those closer to the core.
Feedback arising from reflection distributed through a structure.
The loss of power at a joint occurs when the transmitting fiber has a diameter greater than the diameter of the receiving fiber. The loss occurs when coupling light from a source to fiber, from fiber to fiber, or from fiber to detector.
An optical fiber that selectively transmits one wavelength and reflects others based on interference effects inside the structure. Also called an interference filter.
An array of fine, parallel, equally spaced reflecting or transmitting lines that mutually enhance the effects of diffraction to concentrate the diffracted light in a few directions determined by the spacing of the lines and by the wavelength of the light.
A data format that uses discrete varying signals to contain information.
Digital Subscriber Line (DSL)
A service that transmits digital signals to homes at speeds of hundreds of kilobits to tens of megabits per second over twisted-pair wires at higher frequencies than voice telephone signals. There are several variations.
An electronic device that lets current flow in only one direction. Semiconductor diodes used in fiber optics contain a junction between regions of different doping. They include light emitters (LEDs and laser diodes) and detectors (photodiodes).
A semiconductor diode that generates laser light. A current flowing through the diode causes electrons and holes to recombine at the junction layer between p- and n-doped regions, producing excited states that can release energy in the form of light.
Abbreviation for the dual in-line package. An electronic package with a rectangular housing and a row of pins along each of two opposite sides.
A device that combines two or more types of signals into a single output. Usually incorporates a multiplexer at the transmit end and a demultiplexer at the receiver end.
A couple in which light is transmitted differently when it goes in different directions.
The suppression back reflections, generally measured in dB. If a 0 dBm signal passes through a coupler with 50 dB directionality, only -50 dBm will pass in the wrong direction.
The stretching of light pulses as they travel in an optical fiber, which increases their duration. The temporal spreading of a light signal in an optical waveguide caused by light signals traveling at different speeds through a fiber either due to modal or chromatic effects.
Offsetting the dispersion of one fiber by using different fibers or other components that have a dispersion of the opposite sign. Usually done for chromatic dispersion; compensation for polarization-mode dispersion is in development.
Dispersion-compensating Fiber (DCF)
A fiber that has the opposite dispersion of the fiber being used in a transmission system. It is used to nullify the dispersion caused by that fiber.
Dispersion-compensating Module (DCM)
This module has the opposite dispersion of the fiber being used in a transmission system. It is used to nullify the dispersion caused by that fiber. It can be either a spool of a special fiber or a grating-based module.
Dispersion-Shifted Fiber (DSF)
Optical fiber with a nominal wavelength of zero chromatic dispersion shifted away from 1310nm. Often used for zero dispersion-shifted fiber, which has zero chromatic dispersion at 1550nm and is not used in the DWDM system.
A change in the shape of a signal’s waveform.
Distributed feedback (DFB)
A type of laser using an internal grating to reduce the line width of the laser that may be used for analog applications, e.g., AM/FM/DWDM applications.
Distributed feedback (DFB)
A type of laser using an internal grating to reduce the line width of the laser that may be used for analog applications, e.g., AM/FM/DWDM applications.
A technique used in a fiber optic system design to cope with the dispersion introduced by the optical fiber. A dispersion slope compensator (illustrated) is one dispersion management technique.
The result of dispersion in which pulses and edges smear making it difficult for the receiver to distinguish between ones and zeros. This results in a loss of receiver sensitivity compared to a short-fiber and measured in dB. The equations for calculating dispersion penalty are as follows:
The change in dispersion with a wavelength
Distributed Bragg Reflection
Reflection of light caused by periodic changes in refractive index in a stack of layers of different composition or-equivalently-by a corrugation at the boundary between two semiconductor layers. The period and the refractive index select one wavelength.
Distributed Feedback Laser (DFB Laser)
A diode laser with a corrugation in the electrically pumped part of the laser, which selects the laser wavelength by reflecting that wavelength back into the active layer.
Part of a cable system consisting of trunk and feeder cables used to carry signals from headend to customer terminals.
The mode in an optical device spectrum with the most power.
Thick liquid or paste used to prepare a surface or a varnish-like substance used for waterproofing or strengthening a material.
An impurity added to an optical medium to change its optical properties. EDFAs use erbium as a dopant for optical fiber.
Double-window Fiber (Dual Window Fiber)
1) Multimode fibers optimized for 850 nm and 1300 nm operation.
2) Single-mode fibers optimized for 1310 nm and 1550 nm operation.
Doubly Clad Fiber
An optical fiber that exhibits wide transmission bandwidth and low bending loss to the reduction of guided modes as a result of the high-refractive-index external cladding and the tight confinement within the core regions.
A system for fabricating optical fiber, consisting of a furnace that heats the materials, a polymer coating stage, a capstan-pulling apparatus that free-draws the preform into a fiber, and a drum on which the finished product is wound.
Abbreviation for data signaling rate. The aggregate rate at which data pass a point in the transmission path of a data transmission system expressed in bits per second (bps or b/s).
A cable that delivers service to an individual customer.
A transmission rate in the North American digital telephone hierarchy. Also called T-carrier.
Abbreviation for data terminal equipment.
1) An end instrument that converts user information into signals for transmission or reconverts the received signals into user information.
2) The functional unit of a data station that serves as a data source or a data sink and provides for the data communication control function to be performed in accordance with link protocol.
Abbreviation for data terminal ready. In a communications network, a signal from a remote transmitter that the transmitter is clear to receive data.
Abbreviation for digital television. Any technology, using any of several digital encoding schemes, used in connection with the transmission and reception of television signals. Depending on the transmission medium, DTV often uses some type of digital compression to reduce the required digital data rate. Except for artifacts of the compression, DTV is more immune (than analog television) to degradation in transmission, resulting in a higher quality of both audio and video, to the limits of signal reception.
Dual Attachment Concentrator
A concentrator that offers two attachments to the FDDI network which are capable of accommodating a dual (counter-rotating) ring.
Dual Ring (FDDI Dual Ring)
A pair of counter-rotating logical rings.
In cables, one that contains two fibers. For connectors, one that connects two pairs of fibers. For data transmission, full-duplex transmitters and receivers simultaneously send and receive signals in both directions, but half-duplex cannot do both at the same time.
A two-fiber cable is suitable for duplex transmission.
Transmission in both directions, either one direction at a time (half-duplex) or both directions simultaneously (full-duplex).
For an optical instrument, defined as the ratio (in dB) of the smallest signal that can be observed at a specified wavelength separation in the presence of a strong, nearly-saturating signal.
The E2000/LX-5 is like an LC but with a shutter over the end of the fiber.
Edge-Emitting Diode (LED)
An LED that emits light from its edge, producing more directional output than LEDs that emit from their top surface.
A semiconductor laser that emits light in the plane of its junction from the edge of the chip.
The area of a single-mode fiber that carries the light.
An acronym for Electronic Industries Alliance.
Describes the fact that the core or cladding may be elliptical rather than circular.
A semiconductor diode reverse-modulated so it modulates light passing through it.
Electromagnetic Interference (EMI)
Noise generated when stray electromagnetic fields induce currents in electrical conductors.
A solid-state optical switch with no moving parts and a very fast response time.
Waves made up of oscillating electrical and magnetic fields perpendicular to one another and traveling at the speed of light. Can also be viewed as photons or quanta of energy. Electromagnetic radiation includes radio waves, microwaves, infrared, visible light, ultraviolet radiation, X rays, and gamma rays.
A cabinet used to organize and enclose cable terminations and splices for use within main equipment rooms, entrance facilities, main or intermediate cross-connects, and telecommunications closets.
A means of combining clock and data information into a self-synchronizing stream of signals.
A fiber-optic bundle used for imaging and viewing inside the human body.
The term often used to describe the end of a ferrule. The end face is finished or polished to have a smooth end, which can minimize connector loss or back reflection. Typical polish types are PC, UPC, and APC.
The quality of the end surface of a fiber prepared for splicing or terminated in a connector. For an optical fiber, the optical quality of the surface at the end of the fiber.
End separation loss
The optical power loss caused by the distance between the end of a fiber and a source, detector, or another fiber
Abbreviation for the electrical-to-optical converter. A device that converts electrical signals to optical signals, such as a laser diode.
Equilibrium Mode Distribution (EMD)
The steady modal state of a multimode fiber in which the relative power distribution among modes is independent of fiber length.
Erbium-Doped Fiber Amplifier (EDFA)
An optical fiber doped with the rare earth element erbium, which can amplify light at 1530 to 1610nm when pumped by an external light source.
Used in wavelength lockers, the etalon is a Fabry-Perot filter paired with a beamsplitter cube.
In digital transmission systems, a scheme that adds overhead to the data to permit a certain level of errors to be detected and corrected.
Checking for errors in data transmission. A calculation based on the data being sent; the results of the calculation are sent along with the data. The receiver then performs the same calculation and compares its results with those sent. If the receiver detects an error, it can be corrected, or it can simply be reported.
Abbreviation for enterprise systems connection. A duplex optical connector used for computer-to-computer data exchange.
A local-area network standard. The original Ethernet transmits 10 Mbit/s. Other versions are Fast Ethernet at 100 Mbit/s, Gigabit Ethernet at 1Gbit/s, and 10 Gigabit Ethernet. A standard protocol (IEEE 802.3) for a 10-Mb/s baseband local area network (LAN) bus using carrier sense multiple access with collision detection (CSMA/CD) as the access method. Ethernet is a standard for using various transmission media, such as coaxial cables, unshielded twisted pairs, and optical fibers.
Guided light waves that extend beyond the boundary of a fiber core into the cladding. Evanescent waves can transfer energy between waveguides. Light guided in the inner part of an optical fiber’s cladding rather than in the core, i.e. the portion of the light wave in the core that penetrates into the cladding.
Loss of a passive coupler above that inherent in dividing light among the output ports. In a fiber optic coupler, the optical loss from that portion of the light that does not emerge from the nominal operation ports of the device.
Modulation of the output of a light source by an external device.
Splice losses arising from the splicing process itself.
The ratio of the low, or OFF optical power level (PL) to the high, or ON optical power level (PH).
The ratio of the power of a plane-polarized beam that is transmitted through a polarizer placed in its path with its polarizing axis parallels to the beam’s plane, as compared with the transmitted power when the polarizer’s axis is perpendicular to the beam’s plane.
A pattern formed by overlaying traces of a series of transmitted pulses in a visual display. The more open the eye, the sharper the distinction between on and off pulses. A diagram that shows the proper function of a digital system. The “openness” of the eye relates to the BER that can be achieved.
A standard laser diode consisting of a semiconductor cleaved on each end forming a resonant chamber to create the lasting effect. Used in digital applications.
Fabry Perot Laser
A laser oscillator in which two mirrors are separated by an amplifying medium with an inverted population, making a Fabry-Perot cavity. Standard diode lasers are Fabry-Perot lasers.
Also called turn-off time. The time required for the trailing edge of a pulse to fall from 90% to 10% of its amplitude; the time required for a component to produce such a result. Typically measured between 90% and 10% points or alternately the 80% and 20% points.
In a birefringent material, the index of refraction varies with the direction of vibration of a lightwave. That direction having a low refractive index is the fast axis; at right angles to it is the slow axis, with a high index of refraction.
A phenomenon that causes some materials to rotate the polarization of light in the presence of a magnetic field parallel to the direction of propagation. Also called the magneto-optic effect.
A multi-fiber cable constructed in a tight-buffered tube design. At a termination point, cable fibers must be separated from the cable to their separate connection positions.
FC stands for Fixed Connection. It is fixed by way of a threaded barrel housing. FC connectors are typical in test environments and for single mode applications.
Abbreviation for Federal Communications Commission. The U.S. Government board of five presidential appointees has the authority to regulate all non-Federal Government interstate telecommunications as well as all international communications that originate or terminate in the United States.
See FC. A threaded optical connector that uses a special curved polish on the connector for very low back-reflection. Good for single-mode or multimode fiber.
Abbreviation for frame check sequence. An error-detection scheme that (a) uses parity bits generated by the polynomial encoding of digital signals, (b) appends those parity bits to a digital signal, and (c) uses decoding algorithms that detect errors in the received digital signal.
Abbreviation for Food and Drug Administration. Organization is responsible for, among other things, laser safety.
Frequency-division Multiplexing (FDM)
A method of deriving two or more simultaneous, continuous channels from a transmission medium by assigning separate portions of the available frequency spectrum to each of the individual channels.
A tube within a connector with a central hole that contains and aligns a fiber.
An optical fiber doped to amplify light from an external source. The most important type is the erbium-doped fiber amplifier.
The lowest frequency at which the magnitude of the fiber transfer function decreases to a specified fraction of the zero frequency value. Often, the specified value is one-half the optical power at zero frequency.
Fiber Bragg Grating (FBG)
An optical fiber in which the core refractive index varies periodically, causing Bragg scatting at wavelengths selected by the period and refractive index. A fiber Bragg grating reflects the selected wavelength and transmits others.
Fiber-optic test procedure (FOTP)
Specific substandard within the TIA/EIA 455 standard, used predominantly for test and measurement.
Light transmission through optical fibers for communications purposes.
A sensing device in which the active sensing element is an optical element attached directly to an optical fiber. The measured quantity changes the optical properties of the fiber so that it can be detected and measured.
Fiber to the building/business (FTTB)
A topological reference to a PON network that supports multiple subscribers in a single structure, i.e., a business or a building.
Fiber Distributed Data Interface (FDDI)
A standard for a 100 Mbit/s fiber optic local-area network. Abbreviation for fiber distributed data interface.
1) A dual counter-rotating ring local area network.
2) A connector used in a dual counter-rotating ring local area network (illustrated).
A mechanism whereby the core of a single-mode fiber can be destroyed at high optical power levels.
An optical fiber in which the refractive index of the core varies periodically along its length, scattering light in a way similar to a diffraction grating, and transmitting or reflecting certain wavelengths selectively.
Fiber Optic Attenuator
A component installed in a fiber optic transmission system that reduces the power in the optical signal. It is often used to limit the optical power received by the photodetector to within the limits of the optical receiver.
A coil of optical fiber that can detect rotation about its axis.
Fiber Optic Cable
A cable containing one or more optical fibers.
Fiber Optic Communication System
The transfer of modulated or unmodulated optical energy through optical fiber media which terminates in the same or different media.
Fiber Optic Link
A transmitter, receiver, and cable assembly that can transmit information between two points.
Fiber Optic Modems
Fiber optic modems are used in fiber optic networks for sending and receiving data.
Fiber Optic Ribbon
A coherent optical fiber bundle in which the configuration is flat rather than round, giving an output in a line.
Fiber Optic Sensor
Any device in which variations in the transmitted power or the rate of transmission of light in optical fiber are the means of measurement or control. Fibers can be used to measure temperature, pressure, strain, voltage, current, liquid level, rotation, and particle velocity
Fiber Optic Span
An optical fiber/cable terminated at both ends which may include devices that add, subtract, or attenuate optical signals.
Fiber Optic Subsystem
A functional entity with defined bounds and interfaces which is part of a system. It contains solid-state and/or other components and is specified as a subsystem for the purpose of trade and commerce.
An optical instrument consisting of an objective lens, a coherent (usually flexible) fiber bundle, and an eyepiece to examine the output of the fiber bundle.
Fiber to the Curb (FTTC)
Fiber optic service to a node that is connected by wires to several nearby homes, typically on a block.
Fiber to the desk (FTTD)
Transmission system using fiber-optics as the medium throughout, from the transmitter to desktop.
Fiber to the Home (FTTH)
A network in which optical fibers bring signals all the way to homes.
A standard for transmitting signals at 100 Mbit/s to 4.25 Gbit/s over fiber or (at slower speeds) copper. An industry-standard specification that originated in Great Britain which details computer channel communications over fiber optics at transmission speeds from 132 Mb/s to 1062.5 Mb/s at distances of up to 10 kilometers.
An instrument that couples visible light into the fiber to allow visual checking of continuity and tracing for correct connections.
A device that clamps onto a fiber and couples light from the fiber by bending, to identify the fiber and detect high-speed traffic of an operating link or a 2 kHz tone injected by a test source.
Figure 8 Cable
An aerial cable configuration in which the conductors and the steel strand which supports the cable are integrally jacketed. A cross-section of the finished cable approximates figure 8.
A device that transmits only part of the incident energy and may thereby change the spectral distribution of energy.
A cable construction in which the cable core is filled with a gel material that will prevent moisture from entering or passing through the cable.
The fiber in the loop. Fiber-in-the-loop (FITL): Fiber optic service to a node that is located in a neighborhood.
A substance surrounding the buffer tubes of a fiber-optic cable, to prevent water intrusion into the interstices in the event of a breach of the jacket.
Materials that have the amorphous structure of glass but are made of fluoride compounds (e.g., zirconium fluoride ) rather than oxide compounds (e.g., silica). Suitable for very long wavelength transmission. This material tends to be destroyed by water, limiting its use.
FM (Frequency Modulation)
A method of transmission in which the carrier frequency varies in accordance with the signal.
Forward Error Correcting (FEC)
A communication technique used to compensate for a noisy transmission channel. Extra information is sent along with the primary data payload to correct for errors that occur in transmission.
FOTP (Fiber Optic Test Procedure)
Standards developed and published by the Electronic Industries Association (EIA) under the EIA-RS-455 series of standards.
FWM – Four-Wave Mixing (FWM)
A nonlinearity common in DWDM systems where multiple wavelengths mix together to form new wavelengths called interfering products. Interfering products that fall on the original signal wavelength become mixed with the signal, mudding the signal, and causing attenuation. Interfering products on either side of the original wavelength can be filtered out. FWM is most prevalent near the zero-dispersion wavelength and at close wavelength spacings.
A single optical transmission element characterized by a core, a cladding, and a coating.
Abbreviation for Fabry-Perot. Generally refers to any device, such as a type of laser diode, that uses mirrors in an internal cavity to produce multiple reflections.
Also called free-space photonics. The transmission of modulated visible or infrared (IR) beams through the atmosphere via lasers, LEDs, or IR-emitting diodes (IREDs) to obtain broadband communications.
A fixed-length block of data transmitted as a unit; SONET transmits frames. In the video, one of a series of images shown in sequence.
The number of times an electromagnetic wave oscillates in a second, or the number of wave peaks that pass a point in a second; measured in hertz.
FDM – Frequency-Division Multiplexing (FDM)
Combining analog signals by assigning each a different carrier frequency and merging them in a single signal with a broad range of frequencies
Frequency-shift Keying (FSK)
Frequency modulation in which the modulating signal shifts the output frequency between predetermined values. Also called frequency-shift modulation, frequency-shift signaling.
Fresnel Reflection Loss
Reflection losses at the ends of fibers caused by differences in the refractive index between glass and air. The maximum reflection caused by a perpendicular air-glass interface is about 4% or about -14 dB.
Full-spectrum WDM (FSWDM)
A technology platform based on the use of spectrally enriched optical pulses for signal transmission at speeds of 10 Gbps and higher.
Abbreviation for full-service access network. A forum for the world’s largest telecommunications services providers and equipment suppliers to work define broadband access networks based primarily on the ATM passive optical network structure.
Fiber to the Building. This is in reference to fiber optic cable, carrying network data, connected all the way from an Internet service provider to a customer’s physical building.
An abbreviation for fiber to the curb.
An abbreviation for fiber to the desk.
An abbreviation for fiber to the home.
Stands for Fiber to the Premises.
An abbreviation for ‘Fiber to the x’. The ‘x’ is a variable that can mean fiber to the: premises, curb, home, business, or desk, for example.
In data transmission, transmitters and receivers simultaneously send and receive signals in both directions.
The lowest order mode of a waveguide. Note: In optical fibers, the fundamental mode is designated LP01 or HE11.
A bundle of fibers melted together so they maintain a fixed alignment with respect to each other in a rigid rod.
A method of making a multimode or single-mode coupler by wrapping fibers together, heating them, and pulling them to form a central unified mass so that light on any input fiber is coupled to all output fibers.
A splice made by melting the tips of two fibers together so they form a solid junction.
An instrument that permanently bonds two fibers together by heating and fusing them.
A protective tubing that protects the exposed fiber. Commonly used in terminating multi-fiber cable or “fan-out” situations. Also referred to as buffer tubing.
Abbreviation for fiber under test. Refers to the fiber being measured by some type of test equipment.
Abbreviation for full width half maximum. Used to describe the width of a spectral emission at the 50% amplitude points. Also known as FWHP (full width half power).
Gallium Aluminum Arsenide (GaAlAs)
A semiconductor compound used in LEDs, diode lasers, and certain detectors.
Gallium Arsenide (GaAs)
A semiconductor compound used in LEDs, diode lasers, detectors, and electronic components.
Loss resulting from the end separation of two axially aligned fibers.
Gap Loss Attenuator
An optical attenuator that exploits the principle of gap loss to reduce the optical power level when inserted in-line in the fiber path. e.g., to prevent saturation of the receiver.
A beam pattern used to approximate the distribution of energy in a fiber core. It can also be used to describe emission patterns from surface-emitting LEDs. Most people would recognize it as the bell curve (illustrated).
An abbreviation for Gigabit Ethernet. Gigabit networking, or commonly called 10-Gigabit Ethernet (10GBASE-T), is a communications technology that offers data speeds up to 10 billion bits per second.
Gigabits (billion bits ) per second
Abbreviation for germanium. Generally used in detectors. Good for most fiber optic wavelengths (e.g., 800-1600 nm). Performance is inferior to InGaAs
A substance, resembling petroleum jelly in viscosity, that surrounds a fiber, or multiple fibers, enclosed in a loose buffer tube.
Abbreviation for gigahertz. One billion Hertz (cycles per second) or 109 Hertz.
A fiber in which the refractive index changes gradually with distance from the fiber axis, rather than abruptly at the core-cladding interface.
A graded-index lens, a lens where the refractive index varies along its length.
Graded-Index Fiber Lens
A short segment of a graded-index fiber that focuses light passing through it.
Abbreviation for gradient index. Generally refers to the SELFOC lens often used in fiber optics.
The rate of change of the total phase shift with respect to angular frequency, d /d, through a device or transmission medium, where is the total phase shift, and is the angular frequency equal to 2f, where f is the frequency.
Group Delay Time
The difference in travel time through fiber for the light of different wavelengths.
Also called the group refractive index. In fiber optics, for a given mode propagating in a medium of refractive index (n), the group index (N), is the velocity of light in a vacuum (c), divided by the group velocity of the mode.
1) The velocity of propagation of an envelope produced when an electromagnetic wave is modulated by, or mixed with, other waves of different frequencies.
2) For a particular mode, the reciprocal of the rate of change of the phase constant with respect to angular frequency.
3) The velocity of the modulated optical power.
In data transmission, a system in which transmitters and receivers cannot simultaneously send and receive signals.
Hard-Clad Silica Fiber
A fiber with a hard plastic cladding surrounding a step-index silica core. (Other plastic-clad silica fibers have a soft plastic cladding.)
Abbreviation for high data-rate digital subscriber line. A DSL operating at a high data rate compared to the data rates specified for ISDN.
Abbreviation for high-definition television. Television that has approximately twice the horizontal and twice the vertical emitted resolution specified by the NTSC standard.
1) A central control device required within some LAN and MAN systems to provide such centralized functions as remodulation, retiming, message accountability, contention control, diagnostic control, and access to a gateway.
2) A central control device within CATV systems to provide such centralized functions as remodulation (illustrated). See also local area network (LAN).
The most commonly used gas laser. The HeNe laser has an emission that is determined by neon atoms by virtue of a resonant transfer of excitation of helium. It operates continuously in the red, infrared, and far-infrared regions and emits highly monochromatic radiation.
HFC – Hybrid Fiber/Coax (HFC)
The use of fiber to distribute cable-television signals to nodes, which in turn distribute them to homes over coaxial cable.
A telecommunication technology in which optical fiber and coaxial cable are used in different sections of the network to carry broadband content. The network allows a CATV company to install fiber from the cable headend to serve nodes located close to business and homes, and then from these fiber nodes, use coaxial cable to individual businesses and homes.
Index of refraction (I)
The ratio of the speed of light in a vacuum to the speed of light in a material. When light strikes the surface of a transparent material, some light is reflected while some is bent (refracted) as it enters. I am used to calibrating OTDRs for measuring fiber length.
A set of transmission speeds arranged to multiplex signals at successively higher data rates.
High Loss Fiber
Optical fiber in which the attenuation exceeds the normally acceptable level for long-haul or data communications use.
Abbreviation for the high-performance parallel interface as defined by the ANSI X3T9.3 document, a standard technology for physically connecting devices at short distances and high speeds. Primarily to connect supercomputers and to provide high-speed backbones for local area networks (LANs).
A polishing fixture used to facilitate the manual finishing of the end faces of certain types of optical fiber connectors.
1. A fiber optic cable containing two or more different types of fiber, such as 62.5µm multimode and single-mode.
2. A cable containing both optical fiber and copper wire. Also known as composite cable.
Increases in fiber connector attenuation that occur when hydrogen diffuses into the glass matrix and absorbs some light.
Abbreviation for Insulated Cable Engineers Association. A technical professional organization that contributes to the standards of insulated cable in these four areas: power cables, communication cables, portable cables, and control and instrumentation. Within this organization, there are subcommittees that concentrate on one of the four areas.
Abbreviation for Institute of Electrical and Electronics Engineers. A technical professional association that contributes to voluntary standards in technical areas ranging from computer engineering, biomedical technology, and telecommunications, to electric power, aerospace, and consumer electronics, among others.
Abbreviation for Intermediate Frequency. A frequency to which a carrier frequency is shifted as an intermediate step in transmission or reception.
Index-Matching Gel (Index-Matching Fluid)
A gel or fluid with a refractive index close to the glass reduces refractive-index discontinuities that can cause reflective losses.
Index Matching Material
A substance, usually a liquid, cement (adhesive), or gel, has an index of refraction that closely approximates that of an optical fiber, and is used to reduce Fresnel reflection at the fiber end face.
In an optical fiber, an undesired decrease in the refractive index at the center of the core.
Index of Refraction
The speed of light in a vacuum divided by the speed of light in a material, abbreviated n, which measures how materials refract light.
The refractive index of a fiber as a function of the cross-section.
Indium Gallium Arsenide (InGaAs)
A semiconductor material used in lasers, LEDs, and detectors.
Indium Gallium Arsenide Phosphide (InGaAsP)
A semiconductor material used in lasers, LEDs, and detectors.
Light with wavelengths longer than 700nm and shorter than about 1mm, invisible to the human eye, which we can feel as heat. Glass optical fibers transmit infrared signals at 700 to about 1650nm in the infrared.
Infrared Emitting Diodes
LEDs that emit infrared energy (830 nm or longer).
Colloquially, optical fibers with the best transmission at wavelengths of 2µm or longer, made of materials other than silica glass.
Integrated Services Digital Network (ISDN)
Originally a standard to transmit two digital voice lines at 64 kbit/s and one 16 kbit/s data channel. Now repackaged as IDSL, a form of DSL, transmitting 128 kbit/s over distances beyond the reach of DSL.
An EDFA or other type of amplifier placed in a transmission line to strengthen the attenuated signal for transmission onto the next, distant site. In-line amplifiers are all-optical devices.
Optical devices that perform two or more functions and are integrated on a single substrate; analogous to integrated electronic circuits.
Power per unit solid angle.
Indium Phosphide. A semiconductor material used to make optical amplifiers and HBTs.
The loss of power that results from inserting a component, such as a connector, coupler (illustrated), or splice, into a previously continuous path.
Telecommunications facilities placed inside a building.
A material having high resistance to the flow of electric current. Often called a dielectric.
Integrated Detector/Preamplifier (IDP)
A detector package containing a PIN photodiode and transimpedance amplifier.
The square of the electric field strength of an electromagnetic wave. Intensity is proportional to irradiance and may get used in place of the term “irradiance” when only relative values are important.
Intensity Modulation (IM)
In optical communications, a form of modulation in which the optical power output of a source varies in accordance with some characteristic of the modulating signal.
The ability to prevent undesired optical energy from appearing in one signal path as a result of coupling from another signal path. Also called crosstalk.
For light, the way that waves add together, depending on their phase. Constructive interference occurs when the waves are in phase and their amplitudes add. Destructive interference occurs when the waves are 180 degrees out of phase and their amplitudes cancel.
An optical filter that selectively transmits one wavelength and reflects others based on interference effects inside the structure. Also called a dielectric filter.
An instrument that employs the interference of light waves to measure the accuracy of optical surfaces; it can measure a length in terms of the length of a wave of light by using interference phenomena based on the wave characteristics of light. Interferometers are used extensively for testing optical elements during manufacture. Typical designs include the Michelson, Twyman-Green, and Fizeau interferometers.
An optical device that separates a series of optical channels so alternating wavelengths emerge out its two ports. The best-known type is a Mach-Zehnder interferometer.
A fiber nonlinearity mechanism caused by the power dependant refractive index of glass. Causes signals to beat together and generate interfering components at different frequencies. Very similar to four-wave mixing.
Internet Protocol (IP)
Standard packet-switched transmission format for the Internet; uses variable-length packets.
International Telecommunications Union (ITU)
A civil international organization, headquartered in Geneva, Switzerland, established to promote standardized telecommunications on a worldwide basis. The ITU-R and the ITU-T are committees under the ITU, which is recognized by the United Nations as the specialized agency for telecommunications.
Loss due to inherent traits within the fiber; for example, absorption, scattering, and splice loss.
Abbreviation for Internet protocol. A standard protocol, developed by the DOD, for use in interconnected systems of packet-switched computer communications networks.
An arbitrary unit created by the Institute of Radio Engineers to describe the amplitude characteristic of a video signal, where pure white is defined as 100 IRE with a corresponding voltage of 0.714 Volts and the blanking level is 0 IRE with a corresponding voltage of 0.286 Volts.
Abbreviation for Instrumentation, Systems, and Automation Society. An international, non-profit, technical organization. Society fosters the advancement of the use of sensors, instruments, computers, and systems for measurement and control in a variety of applications
Abbreviation for International Standards Organization. Established in 1947, ISO is a worldwide federation of national standards committees from 140 countries. The organization promotes the development of standardization throughout the world with a focus on facilitating the international exchange of goods and services and developing the cooperation of intellectual, scientific, technological, and economic activities.
Abbreviation for an Internet service provider. A company or organization that provides Internet connections to individuals or companies via dial-up, ISDN, T1, or some other connection.
The outer, protective covering of the cable. Also called the cable sheath.
Small and rapid variations in the timing of a waveform due to noise, changes in component characteristics, supply voltages, imperfect synchronizing circuits, etc. See also DDJ, DCD, and RJ. Also called phase jitter, timing distortion, or inter-symbol interference. The slight movement of a transmission signal in time or phase can introduce errors and loss of synchronization. The amount of jitter will increase with longer cables, cables with higher attenuation, and signals at higher data rates.
A short single fiber cable with connectors on both ends used for interconnecting other cables or testing.
A very strong, very light, synthetic compound developed by DuPont which is used to strengthen optical cables.
One thousand cycles per second.
Abbreviation for kilometer. 1 km = 3,280 feet or 0.62 miles.
An emitter that radiates according to Lambert’s cosine law, which states that the radiance of certain idealized surfaces depends on the viewing angle of the surface. The radiant intensity of such a surface is maximum normal to the surface and decreases in proportion to the cosine of the angle from the normal. Given by:
Usually, a fiber with a score of 200µm or more.
Large Effective Area Fiber (LEAF)
An optical fiber, developed by Corning, designed to have a large area in the core, which carries the light.
From Light Amplification by Stimulated Emission of Radiation, one of the wide range of devices that generates light by that principle. Laser light is directional, covers a narrow range of wavelengths, and is more coherent than ordinary light. Semiconductor diode lasers are the usual light sources in fiber optic systems.
Laser Diode (LD)
A semiconductor that emits coherent light when forward biased.
Lateral Displacement Loss (Lateral Offset Loss)
The loss of power that results from lateral displacement of optimum alignment between two fibers or between a fiber and an active device.
Launch Fiber (Launch cable)
An optical fiber used to couple and condition light from an optical source into an optical fiber. Often the launch fiber is used to create an equilibrium mode distribution in multimode fiber. Also called launching fiber.
A standard or protocol for signal transmission or processing to perform certain functions. It includes standard interfaces with other layers, which perform other functions.
LC stands for Lucent Connector. The LC is a small form-factor fiber optic connector.
Wavelengths of about 1570 to 1625nm where some erbium-doped fiber amplifiers operate. Separate from C-Band.
In an optical fiber, a mode having a field that decays monotonically for a finite distance in the transverse direction but becomes oscillatory everywhere beyond that finite distance.
LEC (Local Exchange Carrier)
A local telephone company, i.e., a communications common carrier that provides ordinary local voice-grade telecommunications service under regulation within a specified service area.
Abbreviation for local exchange. Synonym for the central office.
The plot of optical output (L) as a function of current (I) which characterizes an electrical-to-optical converter. A typical L-I curve is shown on the right.
Light ARMOR Cable
A fiber optic cable assembly with ruggedized plastic jacketing providing fiber protection for the semi-harsh environment, commercial, or industrial applications.
Light Emitting Diode (LED)
A semiconductor diode that emits incoherent light at the junction between p- and n-doped materials.
An optical fiber or fiber bundle.
Use of fibers to illuminates.
An adjective, a synonym for optical, often (but not always) meaning fiber-optic. The path of a point on a wavefront. The direction of the lightwave is generally normal (perpendicular) to the wavefront.
The basic measurement of how well analog-to-digital and digital-to-analog conversions are performed. To test for linearity, a mathematically perfect diagonal line is converted and then compared to a copy of itself. The difference between the two lines is calculated to show the linearity of the system and is given as a percentage or range of least significant bits.
The range of wavelengths in an optical signal sometimes called spectral width.
A defect in the cleaved end face of an optical fiber, in the form of a sharp protrusion at the edge of the fiber.
A network that transmits data among many nodes in a small area (e.g., a building or campus). A communication link between two or more points within a small geographic area, such as between buildings. Smaller than a metropolitan area network (MAN) or a wide area network(WAN).
The part of the telephone network extending from the central (switching) office to the subscriber.
LH – Long Haul (LH)
Abbreviation for the long-haul. Classification of video performance under RS-250C. Lower performance than medium-haul or short-haul.
LOMMF Laser Optimized Multimode Fiber
LOMMF is the highest capacity medium for 10-gig optical transmission. LOMMF was developed for use with VCSEL lasers. With laser-optimized multimode fiber, no special terminations or connectors are necessary.
1. In public switched networks, regarding circuits that span long distances, such as the circuits in inter-LANA, interstate, and international communications.
2. In military use, communications among users on a national or worldwide basis. Long-haul communications are characterized by a higher level of users, more rigorous performance requirements, longer distances between users, including worldwide distances, higher traffic volumes, and densities, larger switches and trunk cross-sections, and fixed and recoverable assets. Usually pertains to the U.S. Defense Communications System.
A commonly used term for light in the 1300 and 1550 nm ranges.
Oscillation modes of a laser along the length of its cavity. Each longitudinal mode contains only a narrow range of wavelengths, so a laser emitting a single longitudinal mode has a narrow bandwidth. Distinct from transverse modes.
A protective tube loosely surrounding a cabled fiber, often filled with gel. A type of fiber optic cable construction where the fiber is contained within a loose tube in the cable jacket.
Loose Tube vs Tight Buffered
Fiber optic cables are constructed in two ways: loose tube and tight buffered. Both contain a type of strengthening members, such as aramid yarn, stainless steel wire strands, or gel-filled sleeves. Each, however, is designed for very different environments.
Attenuation of the optical signal, normally measured in decibels. The amount of a signal’s power expressed in dB, that is lost in connectors, splices, or fiber defects.
Loss of Budget
An accounting of overall attenuation in a system.
Primarily used for indoor applications, Low Smoke Zero Halogen (LSZH) cable is designed to reduce toxic emissions in event of a fire.
An optical device that separates a series of optical channels so alternating wavelengths emerge out its two ports sometimes called an interleaved.
In a fiber, all macroscopic deviations of the fiber’s axis from a straight line, that will cause light to leak out of the fiber, causing signal attenuation.
In multimode fiber optics, a technique used to modify the modal distribution of a propagating optical signal.
Metropolitan Area Network (MAN)
A telecommunication system serving a metropolitan area, typically with cable lengths to 200km. A network covering an area larger than a local area network. A series of local area networks, usually two or more, that cover a metropolitan area.
Allowance for attenuation in addition to that explicitly accounted for in a system design.
Splicing of many fibers in a cable.
Pulse dispersion caused by variation of a material’s refractive index with wavelength.
A splice in which fibers are joined mechanically (e.g., glued or crimped in place) but not fused together. An optical fiber splice accomplished by fixtures or materials, rather than by thermal fusion. The capillary splice, illustrated, is one example of a mechanical splice.
Mean Launched Power
The average power for a continuous valid symbol sequence coupled into a fiber.
Medium Access Control (MAC)
1) A service feature or technique used to permit or deny the use of the components of a communication system.
2) A technique used to define or restrict the rights of individuals or application programs to obtain data from, or place data onto, a storage device, or the definition derived from that technique.
MEMS (Micro-electro-mechanical systems)
Tiny moving mirrors fabricated from semiconductor materials.
A network that makes multiple interconnections between different points.
The linear supporting member, usually a high strength steel wire, used as the supporting element of a suspended aerial cable. The messenger may be an integral part of the cable, or exterior to it.
Tiny bends in fiber that allow light to leak out and increase loss. Mechanical stress on a fiber introduces local discontinuities, which results in light leaking from the core to the cladding by a process called mode coupling.
One-millionth of a meter or 10-6 meters. Abbreviated µm.
Microscope Fiber Optic Inspection
A microscope used to inspect the end surface of a connector for flaws or contamination or a fiber for cleave quality.
One-millionth of a second or 10-6 seconds. Abbreviated µs.
One-millionth of a Watt or 10-6 Watts. Abbreviated µW.
Abbreviation for the military specification. Performance specifications issued by the Department of Defense that must be met in order to pass a MIL-STD.
Abbreviation for military standard. Standards issued by the Department of Defense.
Minimum Bend Radius
The smallest radius an optical fiber or fiber cable can bend before increased attenuation or breakage occurs.
The loss of power resulting from angular misalignment, lateral displacement, and fiber end separation.
Dispersion arising from differences in the times that different modes take to travel through the multimode fiber.
The noise that occurs whenever the optical power propagates through mode-selective devices. It is usually only a factor with laser light sources.
An electromagnetic field distribution that satisfied theoretical requirements for propagation in a waveguide or oscillation in a cavity (e.g., a laser). Light has modes in fiber or laser. A single electromagnetic wave traveling in a fiber.
The transfer of energy between modes. In a fiber, mode coupling occurs until equilibrium mode distribution (EMD) is reached.
The dynamic process a multi longitudinal mode laser undergoes whereby the changing distribution of power among the modes creates a continuously changing envelope of the laser’s spectrum.
Mode-Field Diameter (MFD)
The diameter of the one mode of light propagating in a single-mode fiber, slightly larger than the core diameter.
A device that removes higher-order modes to simulate equilibrium mode distribution. A mode filter is most easily constructed.
Acronym for modulator/demodulator. 1) In general, a device that both modulates and demodulates signals. 2) In computer communications, a device used for converting digital signals into, and recovering them from, quasi-analog signals suitable for transmission over analog communications channels such as telephone lines.
A device that mixes modes to uniform power distribution.
MH – Medium Haul (MH)
Abbreviation for medium-haul. Classification of video performance under RS-250C. Higher performance than long-haul and lower performance than short-haul.
A device that removes high-order modes in a multimode fiber to give standard measurement conditions. A device that removes cladding modes.
The process by which the characteristic of one wave (the carrier) modifies another wave (the signal). Examples include amplitude modulation (AM), frequency modulation (FM), and pulse-coded modulation (PCM).
In an intensity-based system, the modulation index is a measure of how much the modulation signal affects the light output.
A device that imposes a signal on a carrier.
Abbreviation for multiple service operators. A telecommunications company that offers more than one service, e.g. telephone service, Internet access, satellite service, etc.
Multi-fiber connector housing up to 24 fibers in a single ferrule.
MT RJ Connector
MT-RJ stands for Mechanical Transfer Registered Jack. MT-RJ is a fiber-optic cable connector that is very popular for small form factor devices due to its small size. Housing two fibers and mating together with locating pins on the plug, the MT-RJ comes from the MT connector, which can contain up to 12 fibers.
MU is a small form factor SC. It has the same push/pull style but can fit 2 channels in the same footprint as a single SC. MU was developed by NTT.
Multilongitudinal Mode (MLM) Laser
An injection laser diode has a number of longitudinal modes.
Transmits or emits multiple modes of light. An optical waveguide with a much larger core (50µm +) than the single-mode waveguide core (2µm to 9µm) and which permits approximately 1,000 modes to propagate through the core compared to only one mode through a single-mode fiber.
Dispersion resulting from the different transit lengths of different propagating modes in a multimode optical fiber. Also called modal dispersion.
Multimode Fiber – MM
An optical fiber that has a core large enough to propagate more than one mode of light The typical diameter is 62.5 micrometers or 50 micrometers.
Multiple Reflection Noise (MRN)
The fiber optic receiver noise resulting from the interference of delayed signals from two or more reflection points in a fiber optic span. Also known as multipath interference.
A device that combines two or more signals into a single output.
The process by which two or more signals are transmitted over a single communications channel. Examples include time-division multiplexing (TDM) and wavelength-division multiplexing (WDM).
Abbreviation for Mach-Zehnder, a structure used in fiber Bragg gratings and interferometers. Named for the two men who developed the underlying principles of the structure.
NA Mismatch Loss
The loss of power at a joint occurs when the transmitting half has a numerical aperture greater than the NA of the receiving half. The loss occurs when coupling light from a source to fiber, from fiber to fiber, or from fiber to detector.
National Electric Code® (NEC)
A standard governing the use of electrical wire, cable, and fixtures installed in buildings; developed by the American National Standards Institute (ANSI), sponsored by the National Fire Protection Association (NFPA), identified by the description ANSI/NFPA 70-1990.
Abbreviation for National Cable Television Association. The major trade association for the cable television industry.
NDSF – Non Dispersion-Shifted Fiber
The most popular type of single-mode fiber deployed. It is designed to have a zero-dispersion wavelength near 1310 nm.
NEXT , RN – Near-end Crosstalk (NEXT, RN)
The optical power reflected from one or more input ports, back to another input port. Also known as isolation directivity.
The part of the infrared near the visible spectrum, typically from 700 to 1500 or 2000nm; is not rigidly defined.
Abbreviation for National Electrical Manufacturers Association. The organization responsible for the standardization of electrical equipment, enabling consumers to select from a range of safe, effective, and compatible electrical products.
Near Field Scanning
A technique for measuring the refractive-index profile of an optical fiber by using an extended source to illuminate an end face and measuring the point-by-point radiance at the exit face.
A system of cables or other connections that links many terminals or devices, all of which can communicate with each other through the system.
The specific physical, i.e., real, logical, or virtual, the arrangement of the elements of a network. Common network topologies include a bus (or linear) topology, a ring topology, and a hybrid topology, which can be a combination of any two or more network topologies. Illustrated to the right is a bus topology utilizing tee couplers to connect a series of stations that listen to a single backbone of cable.
Neutral Density Coating
A coating that appears gray to the eye and has a flat absorption curve throughout the visible spectrum. Metals are generally used for this purpose.
Neutral Density Filter
Also known as a gray filter. A light filter that decreases the intensity of the light without altering the relative spectral distribution of the energy.
NF – Noise Figure (NF)
The ratio of the output signal-to-noise ratio to the input signal-to-noise ratio for a given element in a transmission system. Used for optical and electrical components.
Abbreviation for National Fire Protection Association. Publisher of the National Electrical Code®, and 300 other codes and standards through a full, open-consensus process.
An acronym for National Institute of Standards and Technology.
1) A terminal of any branch in network topology or an interconnection common to two or more branches in a network.
2) One of the switches forming the network backbone in a switch network.
3) A point in a standing or stationary wave at which the amplitude is a minimum.
1) An undesired disturbance within the frequency band of interest; the summation of unwanted or disturbing energy introduced into a communications system from man-made and natural sources.
2) A disturbance that affects a signal and that may distort the information carried by the signal.
3) Random variations of one or more characteristics of any entity such as voltage, current, or data.
Noise Equivalent Power (NEP)
The optical input power to a detector needed to generate an electrical signal equal to the inherent electrical noise.
No Return to Zero (NRZ)
A digital code in which the signal level is low for a 0 bit and high for a 1 bit and does not return to 0 between successive 1 bits.
The deviation from linearity in an electronic circuit, an electro-optic device, or a fiber that generates undesired components in a signal. Examples of fiber nonlinearities include SBS, SRS, FWM, SPM, XPM, and Intermodulation.
Perpendicular to a surface.
Abbreviation for nonreturn to zero. A common means of encoding data that has two states termed “zero” and “one” and no neutral or rest position.
The analog video broadcast standard used in North America, set by the National Television System Committee.
Numerical Aperture (NA)
The sine of half the angle over which a fiber can accept the light. Strictly speaking, this is multiplied by the refractive index of the medium containing the light, but for air the index is almost equal to 1. The light-gathering ability of fiber; the maximum angle to the fiber axis at which light will be accepted and propagated through the fiber. NA = sin a, where a is the acceptance angle. NA also describes the angular spread of light from a central axis, as in exiting a fiber, emitting from a source, or entering a detector.
NZ-DSF – Nonzero Dispersion-Shifted Fiber (NZ-DSF)
Single-mode fiber with the wavelength of zero chromatic dispersion shifted to just outside of the erbium-fiber amplifier region. Some types have zero dispersion near 1500nm, others near 1625nm. Types with zero dispersion at 1580nm are not usable in the L-band of erbium-doped fiber amplifiers.
OADM – Optical Add/Drop Multiplexer
A device that adds or drops individual wavelengths from a DWDM system.
Abbreviation for operation, administration, and maintenance. Refers to telecommunications networks.
Abbreviation for the optical access network. A network technology, based on passive optical networks (PONs), that includes an optical switch at the central office, an intelligent optical terminal at the customer’s premises, and a passive optical network between the two, allowing services providers to deliver fiber-to-the-home while eliminating the expensive electronics located outside the central office.
OCH – Optical Channel
An optical wavelength band for WDM optical communications.
Optical Carrier, a carrier rate specified in the SONET standard.
Abbreviation for the optical distribution network. The term for optical networks being developed for interactive video, audio, and data distribution.
Abbreviation for the optical-to-electrical converter. A device used to convert optical signals to electrical signals. Also known as OEC.
Abbreviation for an optoelectronic integrated circuit. An integrated circuit that includes both optical and electrical elements.
Abbreviation for an original equipment manufacturer. The manufacturer of any device that is designed and built to be distributed under the label of another company.
Optical Fiber Nonconductive General Purpose. Type OFNG cable must be resistant to the spread of fire and suitable for general-purpose use, with the exception of risers and plenums.
Optical Fiber Nonconductive Plenum. Cable installed in ducts, plenums and other spaces used for environmental air must be listed as having adequate fire-resistant and low smoke-producing characteristics.
Optical Fiber Nonconductive Riser. Optical fiber cable used in vertical shafts, or in runs between floors, must have fire-resistant characteristics capable of preventing the spread of fire from floor-to-floor.
Abbreviation for optical line termination. Optical network elements that terminate a line signal.
Abbreviation for the optical loss test set. A source and optical power meter combined used to measure optical loss.
Abbreviation for optical multiplex section. A section of a DWDM system that incorporates an optical add/drop multiplexer.
Abbreviation for the optical network interface. A device used in an optical distribution network to connect two parts of that network.
Abbreviation for optical network termination. An optical network element that terminates a line signal in installations where the fiber extends into the customer premises.
Abbreviation for optical network unit. A network element that is part of a fiber-in-the-loop system.
Abbreviation for open optical interface. A point at which an optical signal is passed from one equipment medium to another without conversion to an electrical signal.
Open Systems Interconnection (OSI)
Pertaining to the logical structure for communications networks standardized by the International Organization for Standardization (ISO).
A device that amplifies an input optical signal without converting it into electrical form. The best developed are optical fibers doped with the rare-earth element erbium.
The range of optical wavelengths that can be transmitted through a component.
An optical signal transmitted at one wavelength. WDM systems transmit multiple channels at separate wavelengths.
Optical Channel Spacing
The wavelength separation between adjacent WDM channels.
Optical Channel Width
The optical wavelength range of a channel.
Optical Continuous Wave Reflectometer (OCWR)
An instrument used to characterize a fiber optic link wherein an unmodulated signal is transmitted through the link, and the resulting light scattered and reflected back to the input is measured. Useful in estimating component reflectance and link optical return loss.
A device that transmits light only in one direction through a series of ports, so light can go from port 1 to port 2 and port 2 to port 3, but not from port 2 to port 1.
Optical Directional Coupler (ODC)
A component used to combine and separate optical power.
Optical Fall Time
The time interval for the falling edge of an optical pulse to transition from 90% to 10% of the pulse amplitude. Alternatively, values of 80% and 20% may be used.
A glass or plastic fiber that has the ability to guide light along its axis. The three parts of an optical fiber are the core, the cladding, and the coating or buffer.
A component used to block out reflected and unwanted light. Also called an isolator.
Optical Link Loss Budget
The range of optical loss over which a fiber optic link will operate and meet all specifications. The loss is relative to the transmitter output power and affects the required receiver input power.
Processing and switching signals in optical form as well as transmitting them optically.
The point where signals are transferred from optical fibers to other transmission media, typically twisted-pair wires or coaxial cable.
Optical Path Power Penalty
The additional loss budget required to account for degradations due to reflections, and the combined effects of dispersion resulting from intersymbol interference, mode-partition noise, and laser chirp.
Optical Performance Monitor
A device installed in a WDM system to monitor signals at the transmitted wavelengths.
Optical Power Meter
An instrument that measures the amount of optical power present at the end of a fiber or cable.
Optical Pump Laser
A shorter wavelength laser used to pump a length of fiber with energy to provide amplification at one or longer wavelengths. See also EDFA.
Optical Return Loss (ORL)
The ratio (expressed in dB) of optical power reflected by a component or an assembly to the optical power incident on a component port when that component or assembly is introduced into a link or system.
Optical Rise Time
The time interval for the rising edge of an optical pulse to transition from 10% to 90% of the pulse amplitude. Alternatively, values of 20% and 80% may be used.
Optical Spectrum Analyzer (OSA)
An instrument that scans the spectrum to record power as a function of wavelength.
Optical Signal-to-Noise-Ratio (OSNR)
The optical equivalent of SNR.
Optical Time-Domain Reflectometer (OTDR)
An instrument that measures transmission characteristics by sending a short pulse of light down a fiber and observing back-scattered light.
Technically, any structure that can guide light. Sometimes used as a synonym for optical fiber, it can also apply to planar light waveguides.
Outside Plant (OSP)
In telephony, all cables, conduits, ducts, poles, towers, repeaters, repeater huts, and other equipment located between a demarcation point in a switching facility and a demarcation point in another switching facility or customer premises.
A condition for launching light into the fiber where the incoming light has a spot size and NA larger than accepted by the fiber, filling all modes in the fiber.
Abbreviation for optical cross-connect. See cross-connect.
Abbreviation for private automatic branch exchange. See PBX.
In data communications, a sequence of binary digits, including data and control signals, that is transmitted and switched as a composite whole. The packet contains data, control signals, and possibly error control information, arranged in a specific format.
Organizing signals by dividing them into data packets, each containing a header that specifies its destination and a packet of data intended for that destination. Separate data packets then are directed to their destinations.
Abbreviation for phase alternation by line. A composite color standard used in many parts of the world for TV broadcast. The phase alternation makes the signal relatively immune to certain distortions (compared to NTSC). Delivers 625 lines at 50 frames per second. PAL-plus is an enhanced-definition version.
Panda is a common style of PM fiber, using round and symmetrical stress rods on either side of the core to induce polarization.
In an optical fiber, a power-law index profile with the profile parameter, g, equal to. Synonym: quadratic profile.
The region of usable frequency in electronics or wavelength in optics.
Passive Branching Device
A device that divides an optical input into two or more optical outputs.
A component that doesn’t require outside power.
Any device that does not require a source of energy for its operation. Examples include electrical resistors or capacitors, diodes, optical fiber (photo), cable, wires, glass, lenses, and filters.
An event that has an associated viewing cost, and which may be purchased separately from any package or subscription. The ordered events could include movies, special events, such as sports, or adult programming. The event could be purchased by either impulse PPV by using a television remote (this application requires a continuous land line phone-based connection), or over the phone PPV (this application may have additional costs for processing).
Passive Optical Network
A fiber-optic distribution network with no active components between the switching point and the customer.
Abbreviation for private branch exchange. A subscriber-owned telecommunications exchange that usually includes access to public switched networks.
PC (Fiber Connector Polish)
Abbreviation for physical contact. Refers to an optical connector that allows the fiber ends to physically touch. Used to minimize back reflection and insertion loss.
PCS Fiber – Plastic Clad Silica
Also called hard clad silica (HCS). A step-index fiber with a glass core and plastic or polymer cladding instead of glass.
Highest instantaneous power level in a pulse.
In optical emitters, the spectral line having the greatest output power. Also called peak emission wavelength.
Abbreviation for pulse-frequency modulation. Also referred to as square wave FM.
The position of a wave in its oscillation cycle.
The imaginary part of the axial propagation constant for a particular mode usually expressed in radians per unit length. See also attenuation.
Rapid, short-term, random fluctuations in the phase of a wave caused by time-domain instabilities in an oscillator.
Phase-shift Keying (PSK)
1) In digital transmission, angle modulation in which the phase of the carrier discretely varies in relation, either to a reference phase or to the phase of the immediately preceding signal element, in accordance with data being transmitted.
2) In a communications system, the representation of characters, such as bits or quaternary digits, by a shift in the phase of an electromagnetic carrier wave with respect to a reference, by an amount corresponding to the symbol being encoded. Also called bi-phase modulation, phase-shift signaling.
Losing an electrical charge on exposure to light.
An optoelectronic transducer such as a PIN photodiode or avalanche photodiode. In the case of the PIN diode, it is so named because it is constructed from materials layered by their positive, intrinsic, and negative electron regions.
Photodiode – PD
A diode that can produce an electrical signal proportional to light falling upon it.
A term coined for devices that work using photons or light, analogous to “electronic” for devices working with electrons.
Providing an electric current under the influence of light or similar radiation.
Quanta of electromagnetic radiation. Light can be viewed as either a wave or a series of photons.
A short optical fiber permanently attached to a source, detector, or other fiber optic device at one end and an optical connector at the other.
A semiconductor detector with an intrinsic (i) region separating the p- and n-doped regions. It has a fast linear response and is used in fiber-optic receivers.
A flat waveguide formed on the surface of flat material. The zone of high refractive index is rectangular in cross-section and guides light in the same way as the core of an optical fiber.
Plastic-Clad Silica (PCS) Fiber
A step-index multimode fiber in which a silica core is surrounded by a lower-index plastic cladding.
Plastic Optical Fiber (POF)
An optical fiber made entirely of plastic compounds. Optical fibers in which both the core and cladding are made of plastic material. Typically their transmission is much poorer than that of glass fibers, and their lowest losses are in the visible region.
Abbreviation for planar lightwave circuit. A device that incorporates a planar waveguide.
An air-handling space such as that found above drop ceiling tiles or in raised floors. Also, a fire code rating for indoor cable.
Cable made of fire-retardant material that meets electrical code requirements (UL 910) for low smoke generation and installation in air spaces.
Plesiochronous Digital Hierarchy (PDH)
The North American Digital Hierarchy of time-division multiplexing rates.
Carrying a signal between two points, without branching to other points.
A type of plastic material used for outside plant cable jackets.
A type of plastic material used for cable jacketing. Typically used in flame-retardant cables.
Abbreviation used to denote polyvinyl difluoride. A type of material used for cable jacketing.
Alignment of the electric and magnetic fields that make up an electromagnetic wave; normally refers to the electric field. If all light waves have the same alignment, the light is polarized.
Polarization Maintaining Fiber (PM Fiber)
Fibers that maintains the polarization of light that enters it.
Polarization Dependent Loss
In passive optical components, a loss varies as the polarization state of the propagating wave changes. Expressed as the difference between the maximum and minimum loss in decibels.
Polarization Mode Dispersion (PMD)
Dispersion arising from random fluctuations in how fibers transmit light in vertical and horizontal polarization.
The optical process, following grinding, puts a highly finished, smooth, and apparently amorphous surface on a lens or a mirror.
Polishing and Abrasive Material
Any of the numerous powders used for grinding and polishing glass, crystal, or metal, the chief material being emery and carborundum for grinding, and rouge or the oxides of tin, cerium, or other metals for polishing.
In fiber optics, a device used to polish a biconic plug to a specified length and surface finish. Also called a polishing disc.
Abbreviation for passive optical network. A broadband fiber-optic access network that uses a means of sharing fiber to the home without running individual fiber-optic lines from an exchange point, telco CO, or a CATV headend and the subscriber’s home.
POP (Point of Presence)
POTS (Plain Old Telephone Service)
Analog voice telephone line.
Abbreviation for peak-to-peak. The algebraic difference between extreme values of a varying quantity.
A cylindrical rod of specially prepared and purified glass from which an optical fiber is drawn.
Precision Sleeve Splicing
Optical fiber splicing uses a capillary tube, of suitable material, to align the mating fibers.
Dispersion attributed to the variation of refractive index contrast with wavelength.
Abbreviation for a picosecond. One trillionth of a second or 10-12 seconds
A pulling eye is a device fastened to a fiber cable to which a hook may be attached in order to pull the cable through a duct or small space.
A current or voltage changes abruptly from one value to another and back to the original value in a finite length of time. Used to describe one particular variation in a series of wave motions. The parts of the pulse include the rise time, fall time, and pulse width, pulse amplitude. The period of a pulse refers to the amount of time between pulses.
Pulse-code Modulation (PCM)
A technique in which an analog signal, such as a voice, is converted into a digital signal by sampling the signal’s amplitude and expressing the different amplitudes as a binary number. The sampling rate must be at least twice the highest frequency in the signal.
The Spreading out of pulses as they travel along with an optical fiber.
Public Switched Networks (PSN)
1. Any common carrier network that provides circuit switching among public users.
2. A switched network accessible to the public for originating and terminating telecommunications messages.
3. Any common carrier switched network, whether by wire or radio, including local exchange carriers, interexchange carriers, and mobile service providers, that use the North American Numbering Plan in common with the provision of switched services.
The semiconductor laser provides the light that excites atoms in a fiber amplifier, putting them in the right state to amplify light. A power source for signal amplification, typically a 980 nm or 1480 nm laser, used in EDFA applications.
Abbreviation for picowatt. One trillionth of a Watt or 10-12 Watts.
QAM – Quadrature Amplitude Modulation.
A coding technique that uses many discrete digital levels to transmit data with minimum bandwidth. QAM256 uses 256 discrete levels to transmit digitized video.
Abbreviation for quaternary dispersion supported transmission. See DST.
QoS – Quality of Service
1. The performance specification of a communications channel or system which may be quantitatively indicated by channel or system performance parameters such as signal-to-noise ratio, bit error rate, message throughput rate, and call blocking probability.
2. A subjective rating of telephone communications quality in which listeners judge transmissions by qualifiers such as excellent, good, fair, poor, or unsatisfactory.
Quadrature Phase-shift Keying (QPSK)
Phase-shift keying uses four different phase angles out of phase by 90°. Also called quadriphase or quaternary phase-shift keying.
The process of converting the voltage level of a signal into digital data before or after the signal has been sampled.
Inaccuracies in the digital representation of an analog signal. These errors occur because of limitations in the resolution of the digitizing process.
Noise results from the quantization process. In serial digital video, a granular type of noise occurs only in the presence of a signal.
The fraction of photons that strike a detector that produces electron-hole Paris in the output current.
A semiconductor compound made of four elements. (e.g., InGaAsP).
A digital signal having four significant conditions.
An optical fiber made with core and cladding materials that are designed to recover their intrinsic value of attenuation coefficient, within an acceptable time period, after exposure to a radiation pulse.
An instrument, distinct from a photometer, to measure the power (watts) of electromagnetic radiation.
A fiber that transfers energy from a strong pump beam to amplify a weaker signal at a longer wavelength, using stimulated Raman scattering.
Random Jitter (RJ)
Random jitter is due to thermal noise and may be modeled as a Gaussian process. The peak-to-peak value of RJ is of a probabilistic nature, and thus any specific value requires an associated probability.
Rare Earth Doped Fiber
An optical fiber in which ions of a rare-earth element, such as neodymium, erbium or holmium, have been incorporated into the glass core matrix, yielding high absorption with low loss in the visible and near-infrared spectral regions.
The scattering of light that results from small inhomogeneities of material density or composition.
Lines that represent the path taken by light.
A device that detects an optical signal and converts it into an electrical form usable by other devices.
Reconfigurable optical add/drop multiplexer (ROADM)
Unlike original OADMs, a reconfigurable OADM can be managed via a network connection without need for a truck roll. They function as optical switches, allowing for remote service changes, and provide an express wavelength path and power monitoring.
A known-good fiber optic jumper cable attached to a power meter used as a reference cable for loss testing. This cable must be made of fiber and connectors of a matching type to the cables to be tested.
The maximum acceptable value of average received power for an acceptable BER or performance.
The minimum acceptable value of received power needed to achieve an acceptable BER or performance. It takes into account power penalties caused by use of a transmitter with worst-case values of extinction ratio, jitter, pulse rise times and fall times, optical return loss, receiver connector degradations, and measurement tolerances. The receiver sensitivity does not include power penalties associated with dispersion, or back reflections from the optical path; these effects are specified separately in the allocation of maximum optical path penalty. Sensitivity usually takes into account worst-case operating and end-of-life (EOL) conditions.
Combination of an electron and a hole in a semiconductor that releases energy, sometimes leading to light emission.
The bending of light as it passes between materials of different refractive index.
The speed of light in a vacuum divided by the speed of light in a material, abbreviated n, which measures how materials refract light.
The change of refractive index with distance from the axis of an optical fiber. Also called refractive index profile.
A receiver-transmitter pair that detects a weak signal cleans it up, then sends the regenerated signal through another length of the fiber.
A receiver-transmitter pair that detects and amplifies a weak signal for retransmission through another length of optical fiber.
The ratio of detector output to input, usually measured in units of amperes per watt (or micro amperes per microwatt).
The loss of the attenuator at the minimum setting of the attenuator.
See optical return loss.
A communications connection that carries signals from the subscriber back to the operator. The return path allows for interactive television and on-demand services, such as pay-per-view, video on demand, and interactive games.
Return to Zero (RZ)
A digital coding scheme where the signal level is low for a 0 bit and high for a 1 bit during the first half of a bit interval and then, in either case, returns to zero for the second half of the bit interval.
Abbreviation for radiofrequency. Any frequency within the electromagnetic spectrum normally associated with radio wave propagation.
An AM technique wherein a carrier, with a frequency much higher than the encoded information, varies according to the amplitude of the information being encoded.
Abbreviation for radio frequency interference. Synonym for electromagnetic interference.
Cables in which many parallel fibers are embedded in plastic material, forming a flat ribbon-like structure.
Abbreviation for relative intensity noise. Often used to quantify the noise characteristics of a laser.
A cable that forms a closed loop connecting two or more points, so all points remain connected if the cable breaks at one point.
A network topology in which terminals are connected in a point-to-point serial fashion in an unbroken circular configuration.
Of an optical cable, a parallel cord of strong yarn that is situated under the jacket(s) of the cable for the purpose of facilitating jacket removal preparatory to splicing or breaking out.
A pathway for indoor cables that pass between floors, normally a vertical shaft or space. Also a fire-code rating for indoor cable.
The time it takes output to rise from low levels to peak value. Typically measured as the time to rise from 10% to 90% of maximum output.
RJ-45 is the 8-conductor version of an RJ-11. It looks like a regular modular phone connector, only it’s wider. You need to use RJ-45 for Ethernet because the connection standard puts the Ethernet on some of the outer connectors, not in RJ-11. RJ-11 plugs will fit into an RJ-45 socket, but because the plastic plug is smaller, some of the contacts will get bend back a little more.
A device that directs data packets to their destinations using the information in their headers to pick the best path. Distinct from the wavelength router.
Abbreviation for the request to send. In a communications network, a signal from a remote receiver to a transmitter for data to be sent to that receiver.
The optically pumped, solid-state laser uses sapphire as the host lattice and chromium as the active ion. The emission takes place in the red portion of the spectrum.
Abbreviation for return to zero. A common means of encoding data that has two information states called “zero” and “one” in which the signal returns to a rest state during a portion of the bit period.
The number of discrete sample measurements made in a given period of time. Often expressed in megahertz (MHz) for video.
SAN (Storage Area Network)
Connects a group of computers to high-capacity storage devices. May be incorporated into local area networks (LAN), metropolitan area networks (MAN), and wide area networks (WAN).
1) In a communications system, the condition in which a component of the system has reached its maximum traffic handling capacity.
2) The point at which the output of a linear device, such as a linear amplifier, deviates significantly from being a linear function of the input when the input signal is increased.
3) The degree of the chroma or purity of a color.
A proposed designation for wavelengths of 1460 to 1530nm, where optical amplifiers based on thulium-doped fibers are in development.
Abbreviation for subscription channel connector. A push-pull type of optical connector that features high packing density, low loss, low backreflection, and low cost.
Loss of light that is scattered off atoms in different directions, so it escapes from the fiber core. A major component of fiber attenuation.
Abbreviation for synchronous code division multiple access. A synchronized version of CDMA.
The cutting of pitch tooling surfaces by an optical technician permits polishing compounds to flow across the surface of the tool.
1) A device that transposes or inverts signals or otherwise encodes a message at the transmitter to make the message unintelligible at a receiver not equipped with an appropriately set descrambling device. Scramblers usually use a fixed algorithm or mechanism.
2) A device intended to normalize the duty cycle of a data stream to be close to 50%.
A defect on a polished optical surface whose length is many times its width. Block reek is a chainlike scratch formed in polishing. A runner cut is a curved scratch caused by grinding. A sleek is a hairline scratch. A crush or rub is a surface scratch or scratches usually caused by mishandling.
Self-phase modulation (SPM)
A fiber nonlinearity caused by the nonlinear index of refraction of glass. The index of refraction varies with optical power level causing a frequency chirp that interacts with the fiber’s dispersion to broaden the pulse.
Semiconductor Optical Amplifier (SOA)
A laser diode without end mirrors coupled to the fibers on both ends. The light coming in either fiber is amplified by a single pass through the laser diode. An alternative to EDFAs.
A small form factor test fixture used loop an electrical signal from the Tx side of a port to the Rx side of a port, prior to the population with an optical transceiver.
Synchronous Digital Hierarchy (SDH)
The international version of SONET, the Synchronous Optical Network Standard. The biggest difference is in the names of the transmission rates.
A trade name used by Nippon Sheet Glass Company (NSG) for a graded-index fiber lens; a segment of graded-index fibers made to serve as a lens.
A laser in which injection of current into a semiconductor diode produces light by recombination of holes and electrons at the junction between p- and n-doped regions.
Abbreviation for short-haul. Classification of video performance under RS-250B/C. Higher performance than long-haul or medium-haul.
An outer protective layer of a fiber optic cable. Also called the cable jacket.
A commonly used term for light in the 665, 790, and 850 nm ranges.
Abbreviation for silicon. Generally used in detectors. Good for short wavelengths only (e.g., < 1000 nm).
Silicon dioxide (SiO2).
The standard international system of metric units.
Signal-to-Noise Ratio (SNR)
The ratio of signal to noise, measured in decibels; an indication of analog signal quality.
Simple Network Management Protocol (SNMP)
The Internet standard protocol for network management software. It monitors devices on the network and gathers device performance data for management information data bases (MIB).
Glass made mostly of silicon dioxide, SiO2, used in conventional optical fibers.
Single element (e.g., a simplex connector is a single-fiber connector).
A term sometimes used for a single-fiber cable.
A laser that emits a range of wavelengths small enough to be considered a single frequency.
Single-longitudinal Mode Laser (SLM)
An injection laser diode that has a single dominant longitudinal mode. A single-mode laser with a side mode suppression ratio (SMSR)< 25 dB.
Containing only one mode. When dealing with lasers, beware of ambiguities because of the difference between transverse and longitudinal modes. A laser operating in a single transverse mode typically does not operate in a single longitudinal mode. A type of low-loss optical waveguide with a very small core (2-9 microns). It requires a laser source for input signals because of the very small entrance aperture. The smallest of the core radius approaches the wavelength of the source. Consequently, only a singlemode is propagated.
Single-Mode Fiber (SMF)
A small-core optical fiber through which only one mode will propagate. The typical diameter is 8-9 microns.
Single Polarization Fiber
Optical fibers capable of carrying light in only one polarization.
Slab Dielectric Waveguide
An electromagnetic waveguide (a) that consists solely of dielectric materials, (b) in which the dielectric propagation medium has a rectangular cross section, (c) that has a width, thickness, and refractive indices that determine the operating wavelength and the modes the guide will support beyond the equilibrium length, (d) that may be cladded, protected, distributed, and electronically controllable, and (e) that may be used in various applications, such as in integrated optical circuits (IOCs) in which their shape is geometrically more convenient than the optical fibers that are circular in cross-section, that are used in fiber optic cables for long-distance transmission.
The name of the mixture of liquid and grinding or polishing compounds used in processing optical materials.
A threaded type of optical connector. One of the earliest optical connectors to be widely used. Offers poor repeatability and performance.
SM Zipcord Fiber
Zipcord (or zip-cord) is a two-fiber cable essentially with two single-fiber cables conjoined by their jackets. The jacket strip can be easily separated from one another for the installation of optical connectors. Zip cord cables may include both loose-buffer and tight-buffer designs.
An optical pulse that naturally retains its original shape as it travels along with an optical fiber.
Synchronous Optical Network (SONET)
A standard for fiber-optic transmission. Abbreviation for the synchronous optical network transport system. An interface standard widely used by the telecom industry where OC-3 is the lowest current rate (155.5 Mb/s), and OC-768 is the highest rate being contemplated (39.808 Gb/s). Valid rates increase by a factor of four from the OC-3 rate up to OC-768.
A transmission method in which data characters are synchronized by timing signals generated at the sending and receiving stations (as opposed to starting/stop communications). Both stations operate continuously at the same frequency and are maintained in the desired phase relationship. Several data codes may be used for the transmission as long as the code utilizes the required line control characters. Also called “bi-sync” or “binary synchronous.”
In fiber optics, a transmitting LED or laser diode or an instrument that injects test signals into fibers.
The process of designing a DWDM transmission span to achieve the required performance based on fiber type, the transmission distance, amplifier spacing, noise, power, and channel count.
The number of data bits per second that can be transmitted in a one Hertz bandwidth range.
A measure of the extent of a spectrum. For a source, the width of wavelengths contained in the output at one half of the wavelength of peak power. Typical spectral widths are 50 to 160 nm for an LED and less than 5 nm for a laser diode.
Speed of light
2.998 x 108 meters per second
Spectral Width, Full Width, Half Maximum (FWHM)
The absolute difference between the wavelengths at which the spectral radiant intensity is 50 percent of the maximum power.
A permanent junction between two fiber ends.
In optical communication, a device that facilitates the splicing or breaking out of fiber optic cables.
A container that prevents spliced fibers from becoming damaged or being misplaced.
The ratio of power emerging from output ports of a coupler.
Abbreviation for straight tip connector. Popular fiber optic connector originally developed by AT&T.
Stainless Steel Cable
A fiber optic cable with flexible stainless steel jacketing for increased fiber protection
Standard Single-Mode Fiber
Step-index single-mode fiber with zero dispersion at 1310nm; the first type used in fiber-optic communications, still widely used.
A couple with more than three or four ports.
A network in which all terminals are connected through a single point, such as a star coupler or concentrator.
Steady State Modal Distribution
Equilibrium modal distribution (EMD) in a multimode fiber, achieved some distance from the source, where the relative power in the modes becomes stable with increasing distance.
A type of fiber where the refractive index of the core is uniformly higher than that of the surrounding cladding.
A method of controlling the bend of a fiber as it exits the connector. Available in various sizes depending on the cable size. 900um, 1.6mm, 2.0mm, and 3.0mm, or even the Timbercon Armadillo cable (custom integrated boot shell design).
Storage area network (SAN)
A network that links host computers to storage servers and systems. The network protocols can include FC-AL, SSA, ATM, and Fast Ethernet. The storage technology can be a collection of servers on a network or a more complex and expensive host storage servers such as a mid-range or mainframe computer.
The part of a fiber optic cable composed of aramid yarn, steel strands, or fiberglass filaments that increase the tensile strength of the cable.
An optical fiber, either multimode or single mode, in which the core refractive index is uniform throughout so that a sharp step in refractive index occurs at the core-to-cladding interface. It usually refers to a multimode fiber. Such fibers have a large numerical aperture, are simple to connect, but have lower bandwidth than other types of optical fibers.
Step-Index Multimode Fiber
A step-index fiber with a core large enough to carry light in multiple modes.
Step-Index Single-Mode Fiber
A step-index fiber with a small core capable of carrying light in only one mode; this type has zero dispersion at 1310nm.
Stimulated Raman Scattering
Interactions between light and atoms in a transparent material that converts energy from one wavelength to another.
The part of the telephone network from a central office to individual subscribers.
A cable designed to be laid underwater.
Surface-Emitting Diode (SLED)
An LED that emits light from its flat surface rather than its side. Simple and inexpensive, with emission spread of a wide-angle.
A semiconductor laser that emits light from the wafer surface.
A device that directs light or electricity along different paths, such as fibers or wires.
A network that routes signals to their destinations by switching circuits, such as the telephone system.
A data signal that is sent along with a clock signal. A system in which events, such as signals, occur at evenly spaced time durations. Opposite of asynchronous.
In telecommunications, the cable used to transport DS1 service.
Talkset (fiber optic)
A communication device that allows conversation over unused fibers.
In a fiber optic coupler, the ratio of power at the tap port to the power at the input port.
In a couple where the splitting ratio between output ports is not equal, the output port containing the lesser power.
Terabits (trillion, or 1012 bits) per second.
A fiber-optic coupler in which three fiber ends are joined together and a signal transmitted from one fiber is split between the other two. A conceptual drawing looks like the letter T, which accounts for the name.
Telcordia Technologies (Bellcore)
Formerly known as Telcordia-Bell Communications Research, it is the unofficial standards development body providing technical specifications for the regional Bell operating companies.
A system transmitting signals at one of the standard levels in the North American digital hierarchy.
Abbreviation for transmission control protocol/Internet protocol. Two interrelated protocols that are part of the Internet protocol suite. TCP operates on the OSI transport layer and breaks data into packets. IP operates on the OSI network layer and routes packets. Originally developed by the U.S. Department of Defense.
A couple with three ports.
TEC (TE Cooler)
Abbreviation for the thermoelectric cooler. A device used to dissipate heat in electronic assemblies.
Telecommunications Management Network (TMN)
A network that interfaces with a telecommunications network at several points in order to receive information from, and to control the operation of, the telecommunications network.
Preparation of the end of a fiber to allow connection to another fiber or an active device, sometimes also called “connectorization”.
Termination and Splicing
Termination and splicing equipment for fiber optics include tools or kits for cutting, finishing, positioning, aligning, and joining fiber optic cables.
Terminating a fiber is accomplished through preparing the fiber for connection to another fiber or device such as a connector. The goal when terminating is to produce a perfect end to the fiber. The end should be cleanly cut, clear, and physically connected to the receiving optical device. This can be accomplished through two means; permanently joining the fibers by welding or gluing the ends of the fiber together, or mechanically aligning the fibers and joining them with transparent gel.
A short single fiber jumper cable with connectors on both ends used for testing. This cable must be made of fiber and connectors of a matching type to the cables to be tested.
A kit of fiber optic instruments, typically including a power meter, source, and test accessories used for measuring loss and power.
A laser diode or LED used to inject an optical signal into fiber for testing loss of the fiber or other components.
Noise resulting from thermally induced random fluctuation in current in the receiver’s load resistance.
Optical switches controlled by temperature-induced changes in refractive index.
The minimum current needed to sustain laser action in a diode laser.
In a fiber optic coupler, the ratio of power at the throughput port to the power at the input port.
In a couple where the splitting ratio between output ports is not equal, the output port containing the greater power.
An acronym for the Telecommunications Industry Association.
An optical plug with the fiber dead-ended so that there is no return loss. This is done by breaking the end of the fiber and index matching it inside the connector. As they have to be measured for ORL, it is best to have several types with the measurement value required.
A variation on the electro-optic switch, the thermo-optic switch uses temperature instead of an applied voltage to change the refractive index of the active waveguide arms. Slower than their electro-optic counterparts, with typical response times in the milliseconds, but less costly.
A material that will soften, flow or distort appreciably when subject to sufficient heat and pressure, i.e., polyvinyl chloride (PVC) or polyethylene (PE).
Abbreviation for temperature-induced cable loss. Optical loss as a result of extreme temperatures outside a fiber optic cable’s environmental specifications.
A material tightly surrounding a fiber in a cable, holding it rigidly in place.
Tight Buffered Cable
A protective coating extruded tightly over fiber for mechanical and environmental protection. The coating material is either nylon or PVC. This buffering offers excellent physical and flexing properties, but higher micro-bending sensitivity.
Time-Division Multiplexing (TDM)
Digital multiplexing by taking one bit or byte of data at a time from separate signals and combining them in a single bitstream.
A ring-based network scheme in which a token is used to control access to a network. Used by IEEE 802.5 and FDDI.
Total Internal Reflection
Total reflection of light back into a material when it strikes the interface with a material having a lower refractive index at an angle below a critical value.
A combination of transmitter and receiver provides both output and input interfaces with a device.
Modes across the width of a waveguide, fiber, or laser. Distinct from longitudinal modes, which are along the length of a laser.
A device that converts energy from one form to another, such as optical energy to electrical energy.
A device that includes a source and driving electronics. It functions as an electrical-to-optical converter.
The part of a satellite that receives and transmits a signal.
Commonly known as a passive WDM, which is included in the transceiver package that combines and separates the three common wavelengths of 1490 nm, 1550 nm downstream, and 1310 nm upstream as needed in FTTx networks. Utilizing both lasers and detectors, this provides optical-to-digital and digital-to-optical conversion in the active, three-wavelength transceiver used in the OLT and ONT. Also used to describe the active transceiver as a whole.
A wave that (a) propagates in a transmission medium, (b) has a velocity determined by the launching conditions and the physical properties of the medium, and (c) may be a longitudinal or transverse wave.
A unit or assembly of units or sections, and associated fittings, made of metal or other noncombustible materials forming a rigid structural system used to support cables. Includes ladders, troughs, channels, solid bottom trays, and similar structures.
A network architecture in which transmission routes branch out from a central point.
1) In a communications network, a single transmission channel between two switching centers or nodes, or both.
2) A circuit between switchboards or other switching equipment, as distinguished from circuits which extend between central office switching equipment and information origination/termination equipment. Trunks may be used to interconnect switches, such as major, minor, public and private switches, to form networks.
A transmission line running between telephone switching offices or from a cable-TV head end to a distribution node.
Tunable dispersion compensator
Correctly adapt or compensate for the dynamic change in fiber distance in reconfigurable fiber-optic systems such as long haul and metropolitan area networks. FBG-type dispersion compensators can also be made tunable. Changing the temperature gradient along the length of the grating changes the group delay response of the filter, thus changing the dispersion. Tunable gratings typically have dispersion versus temperature tables so that the user can set the appropriate amount of dispersion by adjusting the temperature to a specific value.
Pair of copper wires twisted around each other. The standard way to connect individual voice telephones, widely used for other low-speed communications.
The “ultra-long” DWDM transmission band, occupying the 1625 to 1675 nm wavelength range.
Abbreviation for Underwriter’s Laboratory. An organization that tests product safety for a wide variety of products. UL approved products carry UL symbol.
Electromagnetic waves invisible to the human eye, with wavelengths about 10 to 400nm, shorter than visible light.
Operating in one direction only.
UPC (Ultra Physical Contact)
Specific to single-mode applications, referring to the end face geometry of a connector ferrule as well as performance characteristics (-55dB Return Loss).
Unshielded Twisted Pair.
VCSEL (Vertical Cavity Surface Emitting Laser)
A semiconductor laser in which light oscillates vertically (perpendicular to the junction plane) and light emerges from the surface of the waver rather than from the edge of the chip.
Abbreviation for very high data rate digital subscriber line. A DSL operating at a data rate higher than that of HDSL. See also DSL.
Electromagnetic radiation is visible to the human eye at wavelengths of 400 to 700nm.
Visual Fault Locator
A device that couples visible light into the fiber to allow visual tracing and testing of continuity. Some are bright enough to allow finding breaks in fiber through the cable jacket.
Virtual Circuit (VC)
A communications arrangement in which data from a source user may be passed to a destination user over various real circuit configurations during a single period of communication, usually on a per-call basis, although permanent connections can be established.
VOA (Variable Optical Attenuator)
An attenuator in which the attenuation can be varied.
A circuit capable of carrying one telephone conversation or its equivalent; the standard subunit in which telecommunication is counted. The US analog equivalent is 4kHz, the digital equivalent is 64 kbit/s.
Abbreviation for the virtual private network. A protected information-system link utilizing tunneling, security controls, and end-point address translation giving the end user the impression that a dedicated line exists between nodes.
Wide area network. A wide area network (WAN) is a geographically dispersed telecommunications network. The term distinguishes a broader telecommunication structure from a local area network (LAN). A wide area network may be privately owned or rented, but the term usually connotes the inclusion of public (shared user) networks. An intermediate form of network in terms of geography is a metropolitan area network (MAN).
A structure that guides electromagnetic waves along its length. An optical fiber is an optical waveguide.
An array of curved planar waveguides that separates many optical channels at once. Also called Array Waveguide (AWG).
A couple in which light gets transferred between planar waveguides.
The part of chromatic dispersion arising from the different speeds light travels in the core and cladding of a single mode fiber (i.e., from the fiber’s waveguide structure).
The distance an electromagnetic wave travels in the time it takes to oscillate through a complete cycle. Wavelengths of light are measured in nanometers (10-9 m) or micrometers (10-6m).
Used in ROADM systems the wavelength blocker rejects dropped wavelengths so they are not expressed through the node.
Wavelength Division Multiplexing(WDM)
Multiplexing of signals by transmitting them at different wavelengths through the same fiber.
Used to prevent optical drifting of sources. DWDM systems can have multiple wavelengths as closely spaced as 0.4 nanometers, or 50 gigahertz. Such narrow spacing requires a precision monitoring circuit to provide error correction in case the laser wavelength begins to drift. The wavelength locker employs a Fabry-Perot filter, or “Etalon” which is paired with a beamsplitter cube, while a tap coupler samples a small percentage of the modulated laser output and passes it through the beamsplitter. The light then passes through the etalon and into both an etalon photodiode and a reference photodiode. As the laser’s wavelength changes, an error signal between the reference and etalon photodiode is generated. This error signal then drives a Peltier cooler, which controls the laser temperature, thus locking the wavelength to the desired value.
Wavelength meters provide digital displays of both wavelength and optical power level and are used in both factory and field testing applications. They are more accurate than OSAs for testing wavelengths.
Wavelength selectable switch (WSS)
A type of ROADM used in DWDM networks to allow a network operator to change the direction of an added or dropped wavelength through the use of mirrors mounted on micro-electrical-mechanical positioners.
A device that receives one wavelength and outputs a second wavelength, usually to take a standard signal and convert it to an ITU wavelength.
A WDM’s isolation of a light signal in the desired optical channel from the unwanted optical channels. Also called far-end crosstalk.
An optical device that directs input signals according to their wavelength.
Wavelength Routing Switch (WRS)
A switch, used in optical networks, that routes wavelengths as required to specific terminals in the network.
Wavelength Selective Coupler
A device that couples the pump laser wavelength to the optical fiber while filtering out all other unwanted wavelengths. Used in erbium-doped fiber amplifiers.
Wide area network (WAN)
A telecommunications or computer network that extends over a wide geographic area (as opposed to local area networks or LANs) and allows business, education or government users to share data regardless of their location.
Possessing a large bandwidth.
A wavelength region where fibers have low attenuation, used for transmitting signals.
The difference (in dB) between the power budget and the loss budget (i.e. the excess power margin).
The frequency range between 8.0 and 8.4 GHz.
Sets of data telecommunications protocols and interfaces defined by the ITU.
A variation on the tee coupler in which input light is split between two channels (typically planar waveguide) that branch out like a Y from the input.
Zero Dispersion-Shifted Fiber
Fiber with zero chromatic dispersion shifted to 1550nm, used before the advent of DWDM.
The wavelength at which the net chromatic dispersion of an optical fiber is nominally zero. Arises where waveguide dispersion cancels out material dispersion.
Zipcord (Zip Cord)
A two-fiber cable consisting of two single-fiber cables having conjoined jackets. A zip cord cable can be easily divided by slitting and pulling the conjoined jackets apart.
Zip Cord Fiber
Two-fiber cable with two single-fiber cables having conjoined jackets. The zipcord cable can be easily divided by slitting and pulling the conjoined jackets apart. Zip cord cables include both loose-buffer and tight-buffer designs.