Optical frequency multiplex technique: principles, applications, and potential

The performance of optical communication systems can be considerably increased by optical frequency multiplexing, and the technique is suitable for the expansion of signal transmission capacity as well as for realisation of more flexible system structures. Principles of the technique in which outputs from frequency shift modulated monomode semiconductor laser channels operating at different stabilised frequencies are multiplexed for transmission by light wave conductors, are described. Channel selection and laser local oscillator heterodyne frequency conversion for signal recovery is effected at the receiving end. Applications and realisation are discussed for long distance signal transmission, broadband distribution systems, passive optical networks, and optical frequency switching systems.