Densely-spaced FDM coherent star network with optical signals frequency-locked to comb of equally-spaced frequencies

Results obtained using a fiber optical star network using densely-spaced frequency-division multiplexing (FDM) and heterodyne detection techniques are presented. The system consists of three optical sources frequency-shift keyed at 45 Mb/s and spaced by 300 MHz. Frequency selection of the desired channel is done by a heterodyne FM receiver at a bit-error rate of 10/sup -9/ is -61 dBm or 113 photons/b, which is 4.5 dB from the shot-noise limit. Cochannel interference is found negligible for this channel spacing and modulation rate. Frequency stabilization of the FDM signals to a comb of equally-spaced frequencies, imperative in such a densely-spaced FDM system, is also demonstrated. The results indicate that this system can provide a throughput of 4500 Gb/s.<>