Erbium-doped optical fiber amplifiers (EDFAs) provide an efficient wideband amplification for the C-band, Raman amplification adds a mechanism for amplification in the L-band. For CWDM, wideband optical amplification is not available, limiting the. 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. This technique enables bidirectional communications over a. and semiconductor optical amplifiers (SOA), are utilized to extend transmission range. The main concept underlying the WDM technique is.