Optical multiplexers and amplifiers
The large bandwidth of fiber can be made full use of by transmitting several channels simultaneously on a single-mode fiber using multiplexing techniques. The multichannel light wave systems that result can provide savings. The four major techniques used for optical signal multiplexing are wavelength-division multiplexing (WDM) or optical frequency division multiplexing (OFDM), optical time division multiplexing (OTDM), subcarrier multiplexing (SCM), and optical code division multiplexing (OCDM), also known as spread spectrum. This chapter presents these four types of multiplexing methods and two types of optical amplifiers. Although fiber has low loss, amplifiers are still required to regenerate the optical signal when transmitted over long distances. A regenerator is essentially a receiver-transmitter pair that recovers the electrical bit stream from the incoming optical signal, amplifies it, and converts it back into optical form. The emergence of dense wavelength division multiplexing (DWDM) is one of the most recent and important phenomena in the development of optical transmission technology.