4 nm (100 GHz/50 GHz grid). This small channel spacing allows to transmit simultaneously more information. Currently a restriction on wavelengths between 1530 nm and 1625 nm exists which corresponds to the C and L band. In fiber-optic communications, wavelength-division multiplexing (WDM) is a technology which multiplexes a number of optical carrier signals onto a single optical fiber by using different wavelengths (i. Instead of transmitting one signal per fiber, WDM systems combine multiple optical carriers. FS DWDM transceivers are available with C17-C61 100 GHz DWDM wavelengths, and C17-C61 50 Ghz DWDM wavelengths, including DWDM SFP, DWDM SFP+, DWDM XFP, and Tunable DWDM transceivers that support transmission distance up to 100 km.