US Patent 9755759 Polarisation-independent coherent optical receiver

In a coherent optical receiver, a received signal and an oscillator-generated signal, having frequency difference such that the receiver operates under intradyne conditions, are made to beat in a 3×3 optical coupler. A polarizing beam-splitter splits one of the signals into components with orthogonal polarization which are applied to inputs of the coupler, which receives the other of the received or oscillator-generated signal. After photoelectric conversion, the signals are fed to analog processing devices generating an electrical signal representing the received signal that is fed to a low pass filter before being demodulated. The frequency difference between the signals and the passband of the filter are such that a component of the electrical signal, oscillating at a frequency depending on the frequency difference and having amplitude and phase depending on the instant state of polarization of the received signal, is suppressed. A method is also provided.