Optical modules are one of the core components of optical communication equipment. Its main function is to complete the conversion between electrical signals and optical signals (ie "photoelectric conversion"). It consists of receiving and transmitting components, functional circuits, optical interfaces and surface accessories. Common optical module types are 200-400Gb / s (Note: Gb / s, hereinafter referred to as "G") applicable OSFP, 50G-100G applicable QSFP +, 25G applicable SFP +, SFP and lower speed applicable XFP, SFF, GBIC, 1x9, etc., different packaging types correspond to different speeds.
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The optical module is composed of optoelectronic devices, functional circuits, and optical interfaces. Optoelectronic devices include two parts: transmitting and receiving.
The transmitting part is: an electric signal with a certain bit rate is input and processed by an internal driver chip to drive a semiconductor laser (LD) or a light emitting diode (LED) to emit a modulated optical signal of a corresponding rate, and an internal optical power automatic control circuit is provided to enable the The output optical signal power remains stable.
The receiving part is: an optical signal of a certain code rate is input into the module and converted into an electrical signal by a light detection diode. After the preamplifier outputs an electric signal with the corresponding bit rate, the output signal is generally PECL level. At the same time, an alarm signal is output after the input optical power is less than a certain value.
Parameters and meaning of optical module
Optical modules have many important optical and electrical technical parameters, but for hot-swappable optical modules such as SFP, the following three parameters are of most concern when selecting:
1 Center wavelength
Unit nanometer (nm), there are currently three kinds:
l 850nm (MM, multimode, low cost but short transmission distance, generally only 500M);
l 1310nm (SM, single-mode, large loss but small dispersion during transmission, generally used for transmission within 40KM);
l 1550nm (SM, single-mode, small loss but large dispersion during transmission, generally used for long-distance transmission above 40KM, and can transmit 120KM directly without repeating)
In addition to the above several conventional wavelengths, CWDM wavelengths (SM, single-mode, IP module) and DWDM wavelengths (SM, single-mode, IP module) are used in multi-channel transmission.
2 Transmission rate
The number of bits of data transmitted per second (bits).
There are currently 7 types commonly used: 155Mbps, 1.25Gbps, 2.5Gbps, 10Gbps, 25Gbps, 40Gbps, 100Gbps, etc. The transmission rate is generally backward compatible, so 155M optical modules are also called FE (100M) optical modules, 1.25G optical modules are also called GE (Gigabit) optical modules, and 10G optical modules are also called 10GE (10G) optical modules. The most widely used modules in optical transmission equipment. In addition, it has 2Gbps, 4Gbps, and 8Gbps transmission rates in fiber optic storage systems (SANs).
3 Transmission distance
The distance that an optical signal can be transmitted without relay amplification, in kilometers (also known as kilometers, km). Optical modules generally have the following specifications: multi-mode 550m, single-mode 20km, 40km, 80km, 120km and so on.