Optical FDM switch experiments with tunable fiber Fabry-Perot filters

The authors discuss results of research aimed at understanding the use of monolithic tunable lasers and fiber Fabry-Perot filters in implementing an optical cross-connect switch. The switch architecture uses optical frequency division multiplexing where laser signals are transmitted at different frequencies and then summed in a star coupler. At each star coupler output, a tunable receiver is used to retrieve any input signal of choice. The experimental receiver consists of an optical tunable filter followed by a direct-detection receiver. The laboratory demonstration consists of four frequency-locked transmitters with monolithic tunable lasers, each dithered with a slightly different frequency for the dual purpose of frequency locking and positive channel identification upon signal reception. The tunable filter is a tunable two-stage fiber Fabry-Perot filter design consisting of a narrow filter followed by a wide filter. The tuning of the filters is computer controlled, and the combined filter has a tuning range of 15,000 GHz with a finesse ≈5170. Therefore, it is capable of covering over 1000 channels of 2.9-GHz each. Receiver sensitivity was measured to be -30 dBm at 1.7 Gb/s and -29 dBm at 2.5 Gb/s (bit error rate = 10^-10).