Abstract

Until recently, optical receivers using coherent detection were considered the only alternative for achieving the high sensitivity and selectivity needed for dense WDM systems. Within the last two years high-gain erbium-doped fiber amplifiers (EDFAs) and tunable narrowband fiber Fabry-Perot (FFP) filters have been used at the input of high performance, direct detection receivers and proposed as practical alternatives to coherent detection. Aside from 2- or 3-dB less sensitivity, these direct detection receivers offer significant reductions in complexity and polarization sensitivity and are easily achievable from commercially available all-fiber system oriented components. The FFP filters used in these direct detection receiver experiments combine the extremely high optical resolution of Fabry-Perot interferometry, the subangstrom positioning capability of piezoelectric transducers, and the superior stability characteristics of the rotary mechanical splice. This FFP configuration is mechanically stable and with 97% reflecting multilayer mirrors spaced from 10 to 1,000 pm generates filters with bandwidths from 1 to 100 GHz. Filters with less than 1-dB insertion loss have been reported, and commercially available devices can have less than 2-dB loss. With improved tolerances, a finesse of 200 or greater appears feasible with little or no additional loss penalty. These filters will allow 100 dense WDM channels in the 30-nm gain spectrum of an EDFA.

© 1991 Optical Society of America