Performance of a coherent optical PSK receiver employing optical amplification

Presents an optical homodyne PSK receiver with theoretical performance which is asymptotically super-quantum-limited. The receiver uses a small portion of the incoming wave to provide a coherent reference for homodyne detection. The modulation is removed from the reference using the past decisions so that the reference signal is narrowband (relative to the bandwidth of the modulated signal). This signal is then amplified using a narrow-bandwidth optical amplifier. By using this technique, a coherent reference is generated which matches the modulated wave in both phase and amplitude thus providing performance potentially 3 dB better than the quantum limit. The main advantage of this system is its improved performance in the presence of phase noise relative to previously reported optical PSK systems, while a practical limitation is the need for a narrowband optical amplifier