Performance analysis of synchronous coherent optical systems in the presence of multiple in-line amplifiers

The performance of synchronous binary and M-ary coherent optical systems with cascaded optical amplifiers are analysed. From the relative performance of the various demodulation techniques that are compared in terms of power penalties due to amplifier input power, noise accumulation and bit rate, it is predicted that binary homodyne PSK and M-ary FSK schemes not only accommodate more noise accumulation due to multiple amplifiers but also facilitate improvement in dynamic range. The results on the performance of systems in the 1-10 Gb/s range show that total system lengths of the order of 5000 km can be achieved at 10 Gb/s for 16-FSK and homodyne PSK for a bit error rate of 10-9 and 1 dB power penalty, whereas it is reduced by a factor of about two for DPSK which was the best of the direct detection and asynchronous coherent schemes that have been previously analysed.