Some Knowledge About Optical Transceiver Modules

About Optical Fiber

As the propagation medium of optical communication, optical fiber is divided into multi-mode optical fiber and single-mode optical fiber. The core diameter of multimode fiber (orange-red) is 50um~62.5um, and the outer diameter of the cladding is 125um, which is suitable for short-distance transmission (2KM-5KM); the core diameter of single-mode fiber (yellow) is 8.3um, and the cladding outer diameter is 125um. The outer diameter is 125um, mostly used for medium and long distance transmission (20KM-120KM).

The main advantages of optical fiber communication: large capacity, low loss, long relay distance, strong confidentiality, small size, light weight, and inexhaustible raw materials for optical fiber.

Disadvantages: easy to break, difficult to connect, afraid of bending.

Currently, conventional optical transceiver modules mainly include: optical transmitter, optical receiver, Transceiver (optical transceiver integrated module) and Transponder (optical transponder).

Optical Transceiver Integrated Module

The main function of Transceiver is to realize photoelectric/electro-optic conversion, including optical power control, modulation transmission, signal detection, IV conversion and limiting amplification decision regeneration function. In addition, there are some anti-counterfeiting information query, TX-disable and other functions. Common ones are: SIP9 , SFF, SFP, GBIC, XFP, etc.

Optical Transponder

In addition to the photoelectric conversion function, Transponder also integrates many signal processing functions, such as MUX/DEMUX, CDR, function control, performance energy collection and monitoring functions.

Common transponders include: 200/300pin, XENPAK, and X2/XPAK, etc.

Transmission Distance

The transmission distance of optical modules is divided into three types: short distance, medium distance and long distance. It is generally considered that 2km and below are short distance, 10 to 20km are medium distance, and 30km, 40km and above are long distance.

The transmission distance of optical modules is limited, mainly because there is a certain amount of loss and dispersion when optical signals are transmitted in optical fibers.

Loss is the loss of optical energy due to absorption, scattering and leakage of the medium when light is transmitted in an optical fiber. This energy is dissipated at a certain rate as the transmission distance increases.

Dispersion occurs mainly because electromagnetic waves of different wavelengths propagate at different speeds in the same medium, causing different wavelength components of the optical signal to arrive at the receiving end at different times due to the accumulation of transmission distances, resulting in pulse broadening and inability to distinguish the signal. value.

Loss and dispersion: Loss is the loss of optical energy due to absorption, scattering and leakage of the medium when light is transmitted in an optical fiber. This part of the energy is dissipated at a certain rate as the transmission distance increases. Dispersion occurs mainly because electromagnetic waves of different wavelengths propagate at different speeds in the same medium, causing different wavelength components of the optical signal to arrive at the receiving end at different times due to the accumulation of transmission distances, resulting in pulse broadening and inability to distinguish the signal. value. These two parameters mainly affect the transmission distance of the optical module. In actual application, the link loss of 1310nm optical module is generally calculated as 0.35dBm/km, and the link loss of 1550nm optical module is generally calculated as 0.20dBm/km. Calculation of dispersion value It is very complicated and is generally only used as a reference.

Therefore, users need to choose appropriate optical modules according to their actual networking conditions to meet different transmission distance requirements.

1. Central Wavelength

The center wavelength refers to the optical waveband used for optical signal transmission. There are three main central wavelengths of commonly used optical modules: 850nm band, 1310nm band and 1550nm band.

850nm band: mostly used for short-distance transmission;

1310nm and 1550nm bands: mostly used for medium and long distance transmission.

The unit is nanometer (nm). There are currently three main types:

850nm (MM, multi-mode, low cost but short transmission distance, generally only 500M);

1310nm (SM, single mode, large loss during transmission but small dispersion, generally used for transmission within 40KM);

1550nm (SM, single mode, with small loss during transmission but large dispersion, generally used for long-distance transmission of more than 40KM, and can directly transmit up to 120KM without relay);

2. Transmission Rate

Refers to the number of bits (bits) of data transmitted per second, unit bps. There are currently four commonly used ones: 155Mbps, 1.25Gbps, 2.5Gbps, 10Gbps, etc.

The transmission rate is generally backward compatible, so the 155M optical module is also called FE (100M) optical module, and the 1.25G optical module is also called GE (Gigabit) optical module. These are the most commonly used modules in optical transmission equipment. In addition, its transmission rates in optical fiber storage systems (SAN) are 2Gbps, 4Gbps and 8Gbps;

3. Trtansmission Distance

Refers to the distance that optical signals can be directly transmitted without relay amplification. The unit is kilometers (also called kilometers, km). Optical modules generally have the following specifications: multi-mode 550m, single-mode 15km, 40km, 80km and 120km, etc., .

Optical Transceiver Module Classification

There are many types of optical transceiver integrated modules:

According to packaging, it can be divided into: 1*9, SFF, SFP, SFP+, XFP, GBIC, X2, XENPARK, 300Pin, etc.;

Among them, hot-swappable packages: SFP, SFP+, XFP, GBIC, X2, XENPARK, 300Pin;

Non-hot-swappable package (with pins): 1*9, SFF;

(1) 1*9 package - welding type optical module, generally the speed is not higher than Gigabit, and mostly uses SC interface.

(2) SFF package - welding small package optical module, generally the speed is not higher than Gigabit, mostly using LC interface.

The SFF (Small Form Factor) small package optical module adopts advanced precision optical and circuit integration technology. Its size is only half of the ordinary duplex SC (1*9) fiber optic transceiver module. It can double the number of optical ports in the same space. , which can increase the line port density and reduce the system cost per port. And because the SFF small package module uses an MT-RJ interface similar to a copper wire network, the size is the same as a common computer network copper wire interface, which is conducive to the transition of existing copper cable-based network equipment to higher-speed optical fiber networks To meet the sharp increase in network bandwidth demand.

(3) GBIC packaging-hot-swappable Gigabit interface optical module, using SC interface.

GBIC is the abbreviation of Giga Bitrate Interface Converter, which is an interface device that converts gigabit electrical signals into optical signals. GBIC is designed to be hot-swappable. GBIC is an interchangeable product that meets international standards. Gigabit switches designed with GBIC interfaces occupy a large market share in the market due to their flexible interchangeability.

(4) SFP package - hot-swappable small package module, currently the highest speed can reach 4G, mostly using LC interface.

SFP is the abbreviation of Small Form Pluggable, which can be simply understood as an upgraded version of GBIC. The volume of the SFP module is reduced by half compared to the GBIC module, and more than double the number of ports can be configured on the same panel. Other functions of the SFP module are basically the same as those of the GBIC. Some switch manufacturers call SFP modules miniaturized GBIC (MINI-GBIC).

(5) XENPAK encapsulation--applied to 10 Gigabit Ethernet, using SC interface.

(6) XFP packaging-10G optical module, can be used in 10 Gigabit Ethernet, SONET and other systems, mostly using LC interface.

According to the rate, it can be divided into units Mb/s or Gb/s. It mainly covers the following rates: low rate, 100M (155M, 622M), Gigabit, 1.25G, 2.5G, 4.25G, 4.9G, 6G, 8G, 10G and 40G, etc.

According to wavelength, it can be divided into conventional wavelength, CWDM, DWDM and other categories;

According to color, it can be divided into single-mode fiber (yellow) and multi-mode fiber (orange-red);

3 Introduction to optical fiber interface:

The fiber optic interface is a physical interface used to connect fiber optic cables. Usually there are several types such as SC, LC, FC, ST and so on.

Optical fiber interface: SFP optical modules are all LC interfaces, GBIC optical modules are all SC interfaces, and other interfaces include FC and ST.