Fiber optics glossory

O

OADM – Optical Add/Drop Multiplexer

A device that adds or drops individual wavelengths from a DWDM system.

OAM

Abbreviation for operation, administration, and maintenance. Refers to telecommunications networks.

OAN

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.

OCx

Optical Carrier, a carrier rate specified in the SONET standard.

ODN

Abbreviation for the optical distribution network. The term for optical networks being developed for interactive video, audio, and data distribution.

O/E

Abbreviation for the optical-to-electrical converter. A device used to convert optical signals to electrical signals. Also known as OEC.

OEIC

Abbreviation for an optoelectronic integrated circuit. An integrated circuit that includes both optical and electrical elements.

OEM

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.

OFNG

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.

OFNP

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.

OFNR

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.

OLT

Abbreviation for optical line termination. Optical network elements terminate a line signal.

OLTS

Abbreviation for the optical loss test set. A source and optical power meter combined are used to measure optical loss.

OMS

Abbreviation for optical multiplex section. A section of a DWDM system that incorporates an optical add/drop multiplexer.

ONI

Abbreviation for the optical network interface. A device used in an optical distribution network to connect two parts of that network.

ONT

Abbreviation for optical network termination. An optical network element that terminates a line signal in installations where the fiber extends into the customer premises.

ONU

Abbreviation for optical network unit. A network element that is part of a fiber-in-the-loop system.

OOI

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).

Optical Amplifier

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.

Optical Bandpass

The range of optical wavelengths that can be transmitted through a component.

Optical Channel

An optical signal is 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.

Optical Circulator

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.

Optical Fiber

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.

Optical Isolator

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.

Optical Networking

Processing and switching signals in optical form as well as transmitting them optically.

Optical Node

The point where signals are transferred from optical fibers to other transmission media, typically twisted-pair wires or coaxial cables.

Optical Path Power Penalty

The additional loss budget is 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 is 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.

Optical Waveguide

Technically, any structure 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 are located between a demarcation point in a switching facility and a demarcation point in another switching facility or customer premises.

Overfilled Launch

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.

OXC

Abbreviation for optical cross-connect. See cross-connect.

P

PABX

Abbreviation for private automatic branch exchange. See PBX.

Packet

In data communications, a sequence of binary digits, including data and control signals, is transmitted and switched as a composite whole. The packet contains data, control signals, and possibly error control information, arranged in a specific format.

Packet Switching

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.

PAL

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 Fiber

Panda is a common style of PM fiber, using round and symmetrical stress rods on either side of the core to induce polarization.

Parabolic Profile

In an optical fiber, a power-law index profile with the profile parameter, g, equal to. Synonym: quadratic profile.

Passband

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.

Passive Component

A component that doesn’t require outside power.

Passive Device

Any device that does not require a source of energy for its operation. Examples include electrical resistors or capacitors, diodes, optical fiber (photo), cables, wires, glass, lenses, and filters.

Pay-Per-View (PPV)

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 landline 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.

PBX

Abbreviation for private branch exchange. A subscriber-owned telecommunications exchange that usually includes access to the 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.

Peak Power

Highest instantaneous power level in a pulse.

Peak Wavelength

In optical emitters, the spectral line has the greatest output power. Also called peak emission wavelength.

PFM

Abbreviation for pulse-frequency modulation. Also referred to as square wave FM.

Phase

The position of a wave in its oscillation cycle.

Phase Constant

The imaginary part of the axial propagation constant for a particular mode is usually expressed in radians per unit length. See also attenuation.

Phase Noise

Rapid, short-term, random fluctuations in the phase of a wave are caused by time-domain instabilities in an oscillator.

Phase-shift Keying (PSK)

1) In digital transmission, angle modulation is 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 the 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, and phase-shift signaling.

Photoconductive

Losing an electrical charge on exposure to light.

Photodetector

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.

Photonic

A term coined for devices that work using photons or light, analogous to “electronic” for devices working with electrons.

Photovoltaic

Providing an electric current under the influence of light or similar radiation.

Photons

Quanta of electromagnetic radiation. Light can be viewed as either a wave or a series of photons.

Pigtail

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.

pin Photodiode

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.

Planar Waveguide

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.

PLC

Abbreviation for planar lightwave circuit. A device that incorporates a planar waveguide.

Plenum

An air-handling space such as that found above drop ceiling tiles or on raised floors. Also, a fire code rating for indoor cable.

Plenum 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.

Point-to-Point Transmission

Carrying a signal between two points, without branching to other points.

Polyethylene (PE)

A type of plastic material used for outside plant cable jackets.

Polyvinyl-chloride (PVC)

A type of plastic material used for cable jacketing. Typically used in flame-retardant cables.

PVDF (Kynar®)

Abbreviation used to denote polyvinyl difluoride. A type of material used for cable jacketing.

Polarization

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 maintain 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 arises from random fluctuations in how fibers transmit light in vertical and horizontal polarization.

Polishing

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.

Polishing Jig

In fiber optics, a device is used to polish a biconic plug to a specified length and surface finish. Also called a polishing disc.

PON

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.

p-p

Abbreviation for peak-to-peak. The algebraic difference between extreme values of a varying quantity.

Perform

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.

Profile Dispersion

Dispersion attributed to the variation of refractive index contrast with wavelength.

ps

Abbreviation for a picosecond. One trillionth of a second or 10-12 seconds

Pulling Eye

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.

Pulse

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.

Pulse Dispersion

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 is 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.

Pump Laser

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, is used in EDFA applications.

PW

Abbreviation for picowatt. One trillionth of a Watt or 10-12 Watts.

Q

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.

QDST

Abbreviation for quaternary dispersion supported transmission. See DST.

QoS – Quality of Service

1. The performance specification of a communications channel or system 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.

Quantization

The process of converting the voltage level of a signal into digital data before or after the signal has been sampled.

Quantizing Error

Inaccuracies in the digital representation of an analog signal. These errors occur because of limitations in the resolution of the digitizing process.

Quantizing Noise

Noise results from the quantization process. In serial digital video, a granular type of noise occurs only in the presence of a signal.

Quantum Efficiency

The fraction of photons that strike a detector that produces electron-hole Paris in the output current.

Quaternary

A semiconductor compound made of four elements. (e.g., InGaAsP).

Quaternary Signal

A digital signal has four significant conditions.

R

Radiation-hardened Fiber

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.

Radiometer

An instrument, distinct from a photometer, to measure the power (watts) of electromagnetic radiation.

Raman Amplifier

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.

Rayleigh Scattering

The scattering of light that results from small inhomogeneities of material density or composition.

Rays

Lines that represent the path taken by light.

Receiver

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.

Receive Cable

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.

Receiver Overload

The maximum acceptable value of average received power for an acceptable BER or performance.

Receiver Sensitivity

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.

Recombination

Combination of an electron and a hole in a semiconductor that releases energy, sometimes leading to light emission.

Refraction

The bending of light as it passes between materials of different refractive index.

Refractive Index

The speed of light in a vacuum is divided by the speed of light in a material, abbreviated n, which measures how materials refract light.

Refractive-Index Gradient

The change of refractive index with distance from the axis of an optical fiber. Also called the refractive index profile.

Regenerator

A receiver-transmitter pair that detects a weak signal cleans it up, then sends the regenerated signal through another length of the fiber.

Repeater

A receiver-transmitter pair that detects and amplifies a weak signal for retransmission through another length of optical fiber.

Responsivity

The ratio of detector output to input, is usually measured in units of amperes per watt (or microamperes per microwatt).

Residual Loss

The loss of the attenuator at the minimum setting of the attenuator.

Return Loss

See optical return loss.

Return Path

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.

RF

Abbreviation for radiofrequency. Any frequency within the electromagnetic spectrum is normally associated with radio wave propagation.

RF Carrier

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.

RFI

Abbreviation for radio frequency interference. Synonym for electromagnetic interference.

Ribbon Cables

Cables in which many parallel fibers are embedded in plastic material, forming a flat ribbon-like structure.

RIN

Abbreviation for relative intensity noise. Often used to quantify the noise characteristics of a laser.

Ring

A cable forms a closed loop connecting two or more points, so all points remain connected if the cable breaks at one point.

Ring Network

A network topology in which terminals are connected in a point-to-point serial fashion in an unbroken circular configuration.

Rip Cord

Of an optical cable, is 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.

Riser

A pathway for indoor cables that pass between floors, normally a vertical shaft or space. Also a fire-code rating for indoor cable.

Rise Time

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

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.

Router

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.

RTS

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.

Ruby Laser

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.

RZ

Abbreviation for return to zero. A common means of encoding data is 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.

S

Sampling Rate

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).

Saturation

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 chroma or purity of a color.

S-Band

A proposed designation for wavelengths of 1460 to 1530nm, where optical amplifiers based on thulium-doped fibers are in development.

SC Connector 

Abbreviation for subscription channel connector. A push-pull type of optical connector that features high packing density, low loss, low back reflection, and low cost.

Scattering

Loss of light that is scattered off atoms in different directions, so it escapes from the fiber core. A major component of fiber attenuation.

S-CDMA

Abbreviation for synchronous code division multiple access. A synchronized version of CDMA.

Scoring

The cutting of pitch tooling surfaces by an optical technician permits polishing compounds to flow across the surface of the tool.

Scrambler

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%.

Scratch

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 is caused by the nonlinear index of refraction of glass. The index of refraction varies with the 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.

SFP Loopback

A small form factor test fixture is 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.

Selfoc Lens

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.

Semiconductor Laser

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.

SH

Abbreviation for short-haul. Classification of video performance under RS-250B/C. Higher performance than long-haul or medium-haul.

Sheath

An outer protective layer of a fiber optic cable. Also called the cable jacket.

Short Wavelength

A commonly used term for light is in the 665, 790, and 850 nm ranges.

Si

Abbreviation for silicon. Generally used in detectors. Good for short wavelengths only (e.g., < 1000 nm).

Silica

Silicon dioxide (SiO2).

SI Units

The standard international system of metric units.

Signal-to-Noise Ratio (SNR) 

The ratio of signal to noise, measured in decibels; is 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 databases (MIB).

Silica Glass

Glass is made mostly of silicon dioxide, SiO2, used in conventional optical fibers.

Simplex

Single element (e.g., a simplex connector is a single-fiber connector).

Simplex Cable

A term sometimes used for a single-fiber cable.

Single-Frequency Laser

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.

Single Mode

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 core radius approaches the wavelength of the source. Consequently, only a single mode 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 are 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.

Slurry

The name of the mixture of liquid and grinding or polishing compounds used in processing optical materials.

SMA

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.

Soliton

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.

Synchronous transmission

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.”

Source

In fiber optics, a transmitting LED or laser diode or an instrument injects test signals into fibers.

Span Engineering

The process of designing a DWDM transmission span to achieve the required performance based on fiber type, transmission distance, amplifier spacing, noise, power, and channel count.

Spectral Efficiency

The number of data bits per second that can be transmitted in a one Hertz bandwidth range.

Spectral Width

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.

Splice

A permanent junction between two fiber ends.

Splice Organizer

In optical communication, a device facilitates the splicing or breaking out of fiber optic cables.

Splice Tray

A container that prevents spliced fibers from becoming damaged or misplaced.

Splitter

see Coupler.

Splitting Ratio

The ratio of power emerging from output ports of a coupler.

ST Connector 

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, is still widely used.

Star Coupler

A couple with more than three or four ports.

Star Network

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.

Step-index fiber

A type of fiber where the refractive index of the core is uniformly higher than that of the surrounding cladding.

Strain Relief

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 server such as a mid-range or mainframe computer.

Strength Member

The part of a fiber optic cable is composed of aramid yarn, steel strands, or fiberglass filaments that increase the tensile strength of the cable.

Step-Index

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 convert energy from one wavelength to another.

Subscriber Loop

The part of the telephone network from a central office to individual subscribers.

Submarine Cable

A cable designed to be laid underwater.

Surface-Emitting Diode (SLED) 

An LED emits light from its flat surface rather than its side. Simple and inexpensive, with emission spread of a wide angle.

Surface-Emitting Laser

A semiconductor laser emits light from the wafer surface.

Switch

A device that directs light or electricity along different paths, such as fibers or wires.

Switched Network

A network that routes signals to their destinations by switching circuits, such as the telephone system.

Synchronous

A data signal is sent along with a clock signal. A system in which events, such as signals, occur at evenly spaced time durations. Opposite of asynchronous.

T

T1

In telecommunications, the cable is used to transport DS1 service.

Talkset (fiber optic)

A communication device that allows conversation over unused fibers.

Tap Loss

In a fiber optic coupler, the ratio of power at the tap port to the power at the input port is.

Tap Port

In a couple where the splitting ratio between output ports is not equal, the output port contains the lesser power.

Tbit/s

Terabits (trillion, or 1012 bits) per second.

Tee coupler

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.

T Carrier

A system transmitting signals at one of the standard levels in the North American digital hierarchy.

TCP/IP

Abbreviation for transmission control protocol/Internet protocol. Two interrelated protocols 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.

T Coupler

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 control the operation of, the telecommunications network.

Termination

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

Terminating a fiber is accomplished by 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.

Test Cable

A short single-fiber jumper cable with connectors on both ends was used for testing. This cable must be made of fiber and connectors of a matching type to the cables to be tested.

Test Kit

A kit of fiber optic instruments, typically including a power meter, source, and test accessories used for measuring loss and power.

Test Source

A laser diode or LED is used to inject an optical signal into fiber for testing loss of the fiber or other components.

Thermal Noise

Noise resulting from thermally induced random fluctuation in current in the receiver’s load resistance.

Thermo-Optic Switches

Optical switches controlled by temperature-induced changes in refractive index.

Threshold Current

The minimum current needed to sustain laser action in a diode laser.

Throughput Loss

In a fiber optic coupler, the ratio of power at the throughput port to the power at the input port.

Throughput Port

In a couple where the splitting ratio between output ports is not equal, the output port contains the greater power.

TIA

An acronym for the Telecommunications Industry Association.

Terminator

An optical plug with the fiber is 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.

Thermo-electric switch

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 milliseconds, but less costly.

Thermoplastic

A material that will soften, flow or distort appreciably when subject to sufficient heat and pressure, i.e., polyvinyl chloride (PVC) or polyethylene (PE).

TICL

Abbreviation for temperature-induced cable loss. Optical loss as a result of extreme temperatures outside a fiber optic cable’s environmental specifications.

Tight Buffer

A material tightly surrounds a fiber in a cable, holding it rigidly in place.

Tight Buffered Cable

A protective coating is 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.

Token Ring

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.

Transceiver

A combination of transmitter and receiver provides both output and input interfaces with a device.

Transverse Modes

Modes across the width of a waveguide, fiber, or laser. Distinct from longitudinal modes, which are along the length of a laser.

Transducer

A device that converts energy from one form to another, such as optical energy to electrical energy.

Transmitter

A device that includes a source and driving electronics. It functions as an electrical-to-optical converter.

Transponder

The part of a satellite that receives and transmits a signal.

Triplexer

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.

Traveling Wave

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.

Tray

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.

Tree

A network architecture in which transmission routes branch out from a central point.

Trunk

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 that 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.

Trunk Line

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.

Twisted-Pair

Pair of copper wires twisted around each other. The standard way to connect individual voice telephones is widely used for other low-speed communications.

U

U-band

The “ultra-long” DWDM transmission band, occupies the 1625 to 1675 nm wavelength range.

UL

Abbreviation for Underwriter’s Laboratory. An organization that tests product safety for a wide variety of products. UL approved products carry UL symbol.

Ultraviolet (UV) 

Electromagnetic waves are invisible to the human eye, with wavelengths about 10 to 400nm, shorter than visible light.

Unidirectional

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).

UTP

Unshielded Twisted Pair.

V

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.

VDSL

Abbreviation for very high data rate digital subscriber line. A DSL operates at a data rate higher than that of an HDSL. See also DSL.

Visible Light

Electromagnetic radiation is visible to the human eye at wavelengths 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.

Voice Circuit

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.

VPN

Abbreviation for the virtual private network. A protected information-system link utilizing tunneling, security controls, and end-point address translation gives the end user the impression that a dedicated line exists between nodes.

W

WAN

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).

Waveguide

A structure that guides electromagnetic waves along its length. An optical fiber is an optical waveguide.

Waveguide Array

An array of curved planar waveguides separates many optical channels at once. Also called Array Waveguide (AWG).

Waveguide Coupler

A couple in which light gets transferred between planar waveguides.

Waveguide Dispersion

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).

Wavelength

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).

Wavelength blocker

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.

Wavelength locker

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 meter

Wavelength meters provide digital displays of both wavelength and optical power levels 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.

Wavelength Adapter

A device that receives one wavelength and outputs a second wavelength, usually takes a standard signal and converts it to an ITU wavelength.

Wavelength Isolation

A WDM’s isolation of a light signal in the desired optical channel from the unwanted optical channels. Also called far-end crosstalk.

Wavelength Router

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.

Wideband

Possessing a large bandwidth.

Window

A wavelength region where fibers have low attenuation, used for transmitting signals.

Working Margin

The difference (in dB) between the power budget and the loss budget (i.e. the excess power margin).

X

X-Band

The frequency range is between 8.0 and 8.4 GHz.

X-Series Recommendations

Sets of data telecommunications protocols and interfaces defined by the ITU.

Y

Y Coupler

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.

Z

Zero Dispersion-Shifted Fiber

Fiber with zero chromatic dispersion shifted to 1550nm, used before the advent of DWDM.

Zero-Dispersion Wavelength

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 cables with two single-fiber cables having conjoined jackets. The zip cord cable can be easily divided by slitting and pulling the conjoined jackets apart. Zip cord cables include both loose-buffer and tight-buffer designs.