Wavelength multiplexer-demultiplexer

A multiwavelength multiplexer-demultiplexer constructed from units each capable of multiplexing or demultiplexing two wavelengths is described. As many such units as required can be interconnected to form multiplexer-demultiplexers of any number of wavelengths. Each two-wavelength multiplexer-demultiplexer unit includes a four-port power divider, a four-port phase shifter having two ports connected to two ports of the phase shifter. The power divider may be a single-mode optical fiber directional coupler, or a half-silvered mirror beam splitter, The phase shifter may include a pair of single mode optical fibers or a pair of oppositely disposed mirrors.