Densely spaced FDM coherent optical system with random access digitally tuned receiver

The authors report the results obtained with a densely spaced FDM (frequency division multiplexing) coherent optical fiber star network utilizing monolithic frequency-tunable lasers to generate optical signals frequency-shift-keyed at 200 Mb/s, which provides an optical receiver sensitivity of 74 photons/b at a bit error rate of 10^-9 and random access channel selection by a computer-controlled digitally tuned receiver. The demonstration system consists of six optical channels spaced by 2.2 GHz, the minimum frequency interval possible without adjacent channel interference. The channels are generated by multiple-quantum-well distributed-Bragg-reflector lasers operating at a wavelength of 1.53 μm. These lasers provide a narrow linewidth (2-4 MHz) that is small enough for coherent detection application.