FSK with direct detection in optical FDM networks

A novel approach for high-performance optical data networks of the future is proposed. The approach utilizes a passive star coupler for distribution, a multiplicity of frequency-shift keyed (FSK) tunable lasers to provide a frequency division multiplexed (FDM) network, and a tunable fiber Fabry-Perot filter to select the channels and convert the FSK signal to ASK (amplitude-shift keying) for direct detection. The latest results on high-speed FDM-FSK direct detection networks and the performance of critical devices, such as tunable FM lasers, tunable filters, integrated star couplers, and optical amplifiers, are reported. It is noted that FSK-FDMA offers the prospect of wide spectrum utility, and passive star distribution with tunable filter detection and demultiplexing offers the prospect of low cost. The approach requires a minimum number of electrooptic conversions and terminals with the minimum electronic bandwidth. The FSK modulation format with direct detection is especially attractive, since it takes full advantage of the intrinsic properties of semiconductor lasers under direct modulation, allows up to 1000 channels, and permits channel spacings comparable to those of coherent systems