L Band
L band: Long wavelength band, wavelength range 1565nm-1625nm, it is the second lowest-loss wavelength band, often used when the C-band is not enough to meet bandwidth requirements. With the widespread use of EDFA, DWDM systems have been scaled up to the L-band, and were initially often used to extend the capacity of terrestrial DWDM optical networks. Now, it has been introduced to submarine cable operators to expand the total capacity of submarine cables. Because the transmission attenuation loss of the C-band and L-band transmission windows is the smallest, the signal light in the DWDM system is usually selected in the C-band and L-band.