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Tutorial/Optical Transceivers

Optical Transceivers

What are an optical transceiver and its functions?

The optical transceiver module, referred to as an optical module or fiber module, is an important device in optical fiber communication systems.

As an important part of optical communication transmission, the optical transceiver module is composed of an optoelectronic device, functional circuit, and optical interface. The optoelectronic device includes two parts: transmitting and receiving. The main function is to realize photoelectric/electrical optical conversion, including optical power control and modulation transmission. Signal detection, IV conversion, and limited amplification decision regenerative function, in addition to anti-counterfeiting information query, TX-disable, and other functions. The common Optical transceivers: SFP, SFF, SFP+, GBIC, XFP, 1x9, etc.

Classification of Optical Transceivers

Classification of Optical Transceivers

Classified by package: 1*9 、GBIC、 SFF、SFP、XFP、SFP+、QSFP28QSFP+CFP 、CFP2 、 X2、XENPARK

Classified by rate: 155M、622M、1.25G、2.5G、4.25G、10G、25G 、 40G 、 100G 、 200G 、 400G

Classified by wavelength: 850nm 、 1310nm、1490nm 、 1550nm 、 CWDM、DWDM

Classified by mode: Single-mode fiber (yellow), multimode fiber (orange)

Classified by the number of inserted fibers: Single Fiber (BIDI), dual fiber, parallel

Classified by usability: Hot-plug (GBIC, SFP, XFP, XENPAK) and not-hot plug (1*9, SFF)

Transmission of 100/Gigabit Ethernet and SDH network

Application of Optical Transceivers

Special Optical module – PON

PON adopts point-to-multipoint network topology, and the use of WDM technology enables different directions to use different wavelengths of optical signals. In order to separate the signals on the same fiber with the direction of the multiple users, the following two multiplexing technologies are used: the downlink data stream uses TDM technology, and the upstream data stream uses TDMA technology.

The development roadmap and scale deployment process of PON

The block diagram of a typical PON system working principle

Special Optical module –CWDM SFP

Adopts CWDM technology, optical signals of different wavelengths can be combined and transmitted through one optical fiber by external wavelength division multiplexer, thereby saving fiber resources. At the same time, the receiving end needs to decompose the complex optical signal using a wave decomposition multiplexer. The CWDM SFP optical module is divided into 18 bands, from 1270nm to 1610nm, separated by 20nm between every two bands. CWDM SFP has speed and protocol transparency. CWDM provides a protocol-transparent transmission channel that provides different rates on a single fiber, allowing users to directly go up and down a certain wavelength without converting the original signal format. Commonly used 8 bands, from 1470nm to 1610nm, each channel is separated by 20nm. Colors are often used to distinguish between different band optical modules.

When is CWDM SFP used?

One fiber can be used for multiple fibers, which can realize multi-service transmission at the same time. The services are completely independent. Even then, independent broadband can be guaranteed.

Special Optical module –DWDM SFP

DWDM SFP is a dense wavelength division multiplexing technology that can couple different wavelengths of light into a single-core fiber for transmission. The channel spacing of the DWDM SFP is 0.4 nm, 0.8 nm, 1.6 nm, etc., and the spacing is small, requiring additional wavelength control devices. A key advantage of the DWDM SFP is that its protocol and transmission speed are irrelevant.

The introduction of Data Center Interconnection

What's in the data center? In the data center, it is actually a neatly arranged server and various switches/routers. The servers and switches are filled with various optical modules for data transmission and exchange.

The data exchange capacity within the data center accounts for more than 70%, and the data communication between different data centers interconnection is only about 13%. This explains why the data center business is in the development stage, and the corresponding optical module has developed so rapidly.

Early optical modules used 155 Mb/s (1.5 million bits per second), 622 Mb/s, 1.25 Gb/s, 2.5 Gb/s up to 10 Gb/s, using time-division multiplexing. That is, TDM (Time Division Multiplexing), which transmits more bits per unit time. However, the transmission rate of an optical module is fast, and it is not as good as several simultaneous transmissions. Then there is a parallel transmission, called parallel, four parallels called QSFP, and 12 parallels called CXP.

Optical module package