Differential frequency-deviation multiplexing for lightwave networks

In differential frequency-deviation multiplexing (DFDM) systems, information is transmitted as the relative optical frequency difference between optical pulses transmitted in successive time intervals. This difference is detected using a fiber interferometer and a photodiode. Individual channels are defined by a unique frequency deviation in the frequency-shift-keying (FSK)-modulated laser spectrum. Limitations on receiver sensitivity indicate that for 100-Mb/s channels, which require approximately 200-MHz bandwidth, the total usable bandwidth is limited, by thermal noise, to 3.7 GHz per microwatt of received power. A network is proposed which uses a passive star coupler to interconnect approximately 12 channels, at 100 Mb/s per channel