Shot Noise Optimal Filters for Phase-Diversity Homodyne Receivers

Analytical expressions for the signal to shot noise power ratio (SSNR) of phase diversity homodyne (PDH) optical fiber communication systems with arbitrary waveform and receiver filter are derived. The receiver filter structures maximizing the SSNR is calculated in closed form formulas. The SSNR performance of the systems is evaluated for rectangular and Gaussian pulse shapes and receiver filter structures such as matched filtering, the ideal integrator, and the photodetector RC model. As a side outcome, we show that the SSNR is upper-bounded by twice the converted electrons of the local oscillator. Numerical results show that the proposed optimal filter outperforms the ideal integrator and the integrator plus RC receiver by a few dBs. However, matched filtering to the complex received pulse amplitude is near optimal provided that the local oscillator power is much larger than the received power.