Devices for wavelength multiplexing and demultiplexing

There is renewed interest in wavelength division multiplexing as a technique to upgrade the transmission bandwidth capacities of existing systems together with the possible future provision of broadband multichannel systems. A critical review of the component technology to enable wavelength division multiplexing is therefore useful at this stage. The major implementations of wavelength multiplexer/demultiplexer devices are discussed and compared with particular emphasis placed on their optical efficiency, spectral stability, crosstalk performance and the number of channels that may be provided. Passive devices ranging from the bulk optical implementations (i.e. prisms, grating, filters) to integrated waveguide and fibre directional coupler realisations are considered. In addition developments associated with active devices including integrated source and detector arrays, wavelength tunable devices and optical amplifiers which may be employed within wavelength multiplexed systems are outlined to provide an insight into possible future directions within the field