Pdh vs sdh describes difference between pdh and sdh

DWDM Channels Frequencies

DWDM operates in the range between 1530 and 1565 nm, the so-called C-band that corresponds to the low-loss window of the optical fiber. This is the range where the Erbium-Doped Fiber Amplifier (EDFA) is operative. A grid of allowable wavelengths/frequencies of operation is per ITU-T, centered in a frequency of 193.1 THz, or a wavelength of 1553.3 nm, and all sorts of frequencies spaced at multiples of 25 GHz (=0.2 nm) around that center frequency. Commercial systems might have channels at 2.5 Gbps, 10 Gbps, and 40 Gbps (in which the latter are recently becoming commercial) in addition to combinations of these in the same system. The higher the bit rate, the larger needs from the power budget meaning that the lasers must have better signal to noise figures, the amplifier spacing needs to be reduced, amplification must be higher for example, by employing two DWDM Optical Amplifiers in series. Typically 64 DWDM channels at 10 Gbps reach a maximum distance of around 1,500 km with an amplifier spacing close to 100 km. Long-distance transmission systems beyond 1,500 km and up to 4,500 km will also be commercially available using advanced and much more expensive systems.