Chapter 9.1 - Basic WDM Scheme

9.1 Basic WDM Scheme

The WDM technique corresponds to the scheme in which the capacity of a lightwave system is enhanced by employing multiple optical carriers at different wavelengths. Each carrier is modulated independently using different electrical bit streams (which may themselves use TDM and FDM techniques in the electrical domain) that are transmitted over the same fiber. Figure 9.1 shows schematically the layout of such a dispersion-managed WDM link. The output of several transmitters is combined using an optical device known as a multiplexer. The multiplexed signal is launched into the fiber link for transmission to its destination, where a "demultiplexer" separates individual channels and sends each channel to its own receiver. The implementation of such a WDM scheme required the development of many new components such as multiplexers, demultiplexers, and optical filters (see Chapter 8 of LT1), all of which became available commercially during the 1990s.

Figure 9.1: Schematic of a WDM fiber link. Each channel operates at a distinct wavelength through transmitters operating at different wavelengths. Pre-, post-, and in-line compensators are used to manage the dispersion of fiber link.