Detailed analysis of SFP optical module interface indicators and components

The speed of the optical module SFP+ is: 10G SFP+ optical transceiver is an upgrade of SFP (sometimes called “mini-GBIC”). SFP has been widely used on Gigabit Ethernet and 1G, 2G, and 4G Fibre Channel. In order to adapt to higher data rates, SFP+ has designed enhanced electromagnetic shielding and signal maintenance characteristics than SFP, and has formulated new electrical interface specifications.

Interface index of SFP optical module

1. Output optical power Output optical power refers to the output optical power of the light source at the sending end of the optical module, unit: dBm.

2. Received optical power Received optical power refers to the received optical power at the receiving end of the optical module, unit: dBm.

3. Receive sensitivity Receive sensitivity refers to the minimum received optical power of the optical module at a certain rate and bit error rate, in dBm. Under normal circumstances, the higher the rate, the worse the receiving sensitivity, that is, the larger the minimum received optical power, the higher the requirements for the receiving device of the optical module.

4. Saturated optical power, also known as optical saturation, refers to the maximum input optical power when a certain bit error rate (10-10～10-12) is maintained at a certain transmission rate.

It should be noted that the photodetector will saturate the photocurrent under strong light. When this phenomenon occurs, the detector needs a certain time to recover. At this time, the receiving sensitivity decreases and the received signal may be misjudged. It causes bit errors, and it is very easy to damage the receiver detector. In use, it should try to prevent exceeding its saturated optical power.

Note that for long-distance optical modules, since the average output optical power is generally greater than its saturated optical power, please pay attention to the length of the fiber when using it to ensure that the fact that the received optical power reaches the optical module is less than its saturated optical power. The optical module is damaged.

Components of SFP optical modules

The composition of the SFP optical module is: laser: including the transmitter TOSA and the receiver ROSA circuit board IC, and the external accessories are: shell, base, PCBA, pull ring, buckle, unlocking piece, rubber plug. In addition, for easy identification, Generally, the parameter type of the module is identified by the color of the pull ring. For example: the black pull ring is multi-mode, the wavelength is 850nm; the blue is the module with the wavelength of 1310nm; the yellow is the module with the wavelength of 1550nm; the purple is the module with the wavelength of 1490nm.

SFP, SFF and GBIC optical module relationship

SFP is the abbreviation of Small Form-factor Pluggables, that is, small package pluggable optical module. SFP can be regarded as a pluggable version of SFF. Its electrical interface is a 20-pin gold finger. The data signal interface is basically the same as the SFF module. The SFP module also provides an I2C control interface, compatible with SFP-8472 standard optical interface diagnostics. Both SFF and SFP do not include the SerDes part, and only provide a serial data interface. The CDR and electrical dispersion compensation are placed outside the module, making small size and low power consumption possible. Due to the limitation of heat dissipation, SFF/SFP can only be used for ultra-short distance, short distance and medium distance applications at 2.5Gbps and below.

SFP optical modules now have a maximum speed of 10G, and most use LC interfaces. It can be simply understood as an upgraded version of GBIC. The volume of SFP optical modules is reduced by half compared with GBIC optical modules, and more than double the number of ports can be configured on the same panel. In terms of other functions, the basic of SFP module is the same as GBIC. Therefore, some switch manufacturers call SFP optical modules miniaturized GBIC.