SFP Module
An SFP module is a hot-pluggable, small form-factor transceiver that plugs into switch, router or OLT ports to provide a fiber or copper link.
Stands for: Small Form-factor Pluggable
SFP is a transceiver form factor standardised through industry multi-source agreements (MSAs). Because modules for different distances and media fit the same port, the link type can be chosen without replacing the network device. The main family members are SFP (1 Gbit/s), SFP+ (10 Gbit/s), SFP28 (25 Gbit/s), QSFP+ (40 Gbit/s) and QSFP28 (100 Gbit/s).
Modules differ by medium and reach. Multimode fiber uses 850 nm SR optics (about 300 m on OM3 at 10G). Single-mode fiber uses 1310 nm LR (10 km), 1550 nm ER (40 km) and ZR (80 km) optics. BiDi modules use two different wavelengths (for example 1310/1550 nm or 1270/1330 nm) over a single fiber and must be installed as matched pairs. For short runs there are DAC (direct-attach copper) and AOC (active optical cable) assemblies, and RJ45 SFPs for copper Ethernet. In PON networks, OLT ports also use SFP optics rated by optical class, such as B+ and C+.
The DDM/DOM feature defined in SFF-8472 exposes module temperature, supply voltage and transmitted and received optical power through the device interface. These readings are very useful for validating the optical budget and troubleshooting. When selecting a module, check speed, wavelength, fiber type, connector (usually LC, SC for PON) and that the modules at both ends match.
Some vendors' equipment accepts only modules carrying their own coding, which is why compatible modules coded for the target platform are widely used. 10GBASE-T (RJ45) SFP+ modules run hot and, when many are installed side by side, can push a device past its thermal limits. Not every SFP+ port accepts a 1G SFP module.
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