What is the difference between the bail colors of SFP CWDM optical transceivers?

The CWDM transceivers are working in a specific optical frequency ranges defined by the ITU-T. In 2002 the ITU standardized a channel spacing grid for use with CWDM (ITU-T G.694.2), using the wavelengths from 1270nm through 1610nm with a channel spacing of 20nm.

Each transceiver module typically contains a laser transmitter circuit capable of converting electrical signals to optical signals, and an optical receiver capable of converting received optical signals back into electrical signals.

Typically, a transceiver module is electrically interfaced with a host device — such as a host computer, switching hub, network router, switch box, computer I/O and the like — via a compatible connection port. Moreover, in some applications it is desirable to miniaturize the physical size of the transceiver module to increase the port density, i.e., and therefore accommodate a higher number of network connections within a given physical space. In addition, in many applications, it is desirable for the module to be hot-pluggable, which permits the module to be inserted and removed from the host system without removing electrical power.

For practical purpose the frequency range has been represented by the equivalent colors according to the spectral color of the light, which can be found at the bail color of an optical transceiver (such as SFP, SFP+, XFP, QSFP, SFP28, QSFP28). In such a way, the technician can identify at the rack and in the spares the desired frequency for the system by picking up the corresponding color.

CWDM Wavelength and Bail Color Definition