OPTICAL WAVELENGTH CONVERTERS

Devices and techniques for shifting the frequency/wavelength of an opt ical carrier wave are reviewed, with particular reference to applicati ons in wavelength/frequency division multiplexed optical communication systems. Considered first are devices which make use of semiconductor laser amplifiers or oscillators. Some of these techniques come close to satisfying the requirements for a suitable wavelength shifter, thou gh none appear to offer the potential for a transparent network indepe ndent of data modulation format. A second main category, using nonline ar optical materials, promises to satisfy the requirements for frequen cy translation in a network which is fully transparent to the modulati on format. However, the conversion efficiencies currently available ap pear too low for cost-effective communication systems engineering so t hat further advances in nonlinear optical materials/techniques are sti ll required. It seems likely that guided wave techniques will provide the best means of improving the efficiency by increasing the interacti on length and the optical intensity for a given power. Schematic examp les of such a converter are discussed. All of the existing techniques have some deficiencies compared to an ideal system so that wavelength conversion for optical communication systems is still a problem in sea rch of a good solution.