Polarisation-Diversity Receiver for Coherent FSK Communications

A polarisation-insensitive optical heterodyne receiver, in which two signals with orthogonal polarisations are independently detected and demodulated, and subsequently combined, has been demonstrated for FSK-modulated signals at 50 Mbit/s with a sensitivity of -55.5 dBm (P sub e=10 sup -9). The receiver uses the entire received signal and local oscillator signal with only one photodiode in each branch. Differences between the two PINFET detectors result in a +-1 dBm sensitivity variation for all polarisation states of the received signal.