The SFP Module consists of optical device, functional circuit and optical interface. The optical device consists of transmitting and receiving parts.
The transmitting part is: the input of a certain code rate of electrical signals, through the internal driver chip processing, driving semiconductor laser ( LD) of light emitting diode ( LED) to send out the corresponding code rate modulation optical signal, light internal is provided with an automatic power supply control circuit. The output optical signal power remains stable.
The receiving part is: the optical signal input module of a certain code rate is converted into an electrical signal through the optical detection diode. After the preamplifer, the output signal of the corresponding bit rate is PECL level. When the input optical power is less than a certain value, an alarm signal is generated.
Parameters and meaning of the optical modules
The Optical modules had any important optical technical parameters. However, for GBIC and SFP hot-plug SFP Modules, you need to pay attention to the following three parameters.
Based on nanometer(nm), there are three main types at present.
850nm ( MM, multi-mode, low cost but short transmission distance, generally only 500M).
1310nm ( SM, Single Mode, small transmission loss, large dispersion, generally used for long distance transmission over 40KM, no relay can directly transmit 120KM).
1550nm ( SM, Single Mode, small transmission loss, large dispersion, generally used for long distance transmission over 40KM, no replay directly transmit 120KM).
Transmission Rate
The numbers of bits ( BPS) of data transmitted per second.
Currently. There are four commonly used SFP Modules. 155Mbps, 1.25Gbps, 2.5Gbps, 10Gbps and so on. The transfer rate is usually backward compatible. Therefore, a 155M SFP Module is also called an FE ( 100Mbit/s) SFP Module, and a 1.25G SFP Module is also called a GE( Gigabit) optical module.
This is the most widely used SFP in the optical transmission equipment. In addition, its transmission rates in fiber optic storage systems ( SAN) are 2Gbps, 4Gbps, and 8Gbps.
Transmission distance
Optical signal do not need to be relayed to the distance where they can be transmitted directly. In kilometers ( also called kilometers, KM). The specifications of SFP Modules are as follows: Multi-Mode 550M, Single-Mode 15KM, 40KM,80KM,and 120KM, etc.