Two-stage Fabry-Perot filters as demultiplexers in optical FDMA LANs

A high-finesse optical filter can be constructed by cascading two moderate-finesse Fabry-Perot filters of different free spectral ranges. Methods for controlling the undesirable interactions within the interfilter cavity are studied. In particular, the use of an isolator, an attenuator, or a length of fiber longer than the coherence length of the light sources used is considered. The use of a three-mirror filter, which avoids the offending cavity altogether, is also considered. The implications on the number of potential users of optical frequency-division multiple-access (FDMA), local-area networks (LANs) are also addressed.>