Evolution of the acousto-optic wavelength routing switch

Through the efforts of many research groups and consortia over the last several years, the acousto-optic tunable filter has evolved into a device capable of high-performance wavelength-selective optical switching and wavelength routing in dense WDM systems. The distinguishing feature of the AO switch is its ability to sustain many independent coexisting passbands, thus allowing in a simple integrated-optic device, the parallel processing capability of much more complex designs. The AOTF has also found a role in active gain equalization of optically amplified networks. In this paper, we review the design of both hybrid and fully integrated AO switches. The theory of operation is reviewed and recent advances in passband engineering are described which have made low-crosstalk, wavelength misalignment-tolerant switches to be possible. Advanced issues such as mechanisms of interchannel crosstalk and its reduction are also discussed. Both device and system issues are covered.