Reference transmission schemes for phase noise immunity

We consider an optical communication system where a reference signal is transmitted along with a phase modulated information carrying signal. This system has the potential of alleviating the effect of phase noise considerably. We perform a joint optimization of the receiver bandwidth and the powers of the two signals. The scheme achieves a performance that is close to that of ideal phase modulation systems when the ratio of bit rate to laser linewidth is large, and a performance that is identical to that of frequency modulation when the ratio is small. We also introduce a centered filter structure which achieves a far better performance than traditional filters due to increased the phase coherence.<>