Capacity of QAM SCM systems utilising opticallylinearised Mach-Zehnder modulator as transmitter

The limitation imposed by nonlinear distortion and Gaussian noise on the capacity of a subcarrier multiplexed system with quadrature amplitude modulated channels and an optically linearised Mach-Zehnder externally modulated laser transmitter is calculated. A typical system can support 140 6 MHz quadrature phaseshift keying channels (an aggregate bit rate of 1.4 Gbit/s) at 10–9 bit error rate with a received power of –25 dBm or 300 64-QAM channels (8.9 Gbit/s) with a received power of –15 dBm.