Tunable optical filters for dense WDM networks

WDM is currently taking over as the leading technology in point-to-point tr ansmission links. For optical implementation of WDM networks, logical funct ionalities such as wavelength (channel) selection should be carried out in the wavelength domain; thus, development of dynamic optical devices is requ ired. One key device is a tunable optical filter. Important features of suc h a filter include low insertion loss, narrow bandwidth, high sidelobe supp ression, large dynamic range, fast tuning speed, a simple control mechanism , small size, and cost effectiveness. Here, an extensive overview of the di fferent technologies used to produce tunable optical filters is presented. Among them, fiber filters such as fiber Bragg gratings and fiber Fabry Pero t are the most commercialized, yet inherently limited in their dynamic spee ds. For high demanding dynamics, micromachined and acousto-optic filters ca n offer a good solution in the microseconds tuning speeds. Faster tunable d evices, in the nanosecond tuning speeds, might emerge out of microresonator s, electrooptic filters, and active DBR filters.