Optical transmitting and receiving system having polarization diversity in each hybrid circuit

An optical transmitting and receiving system for connection to an optical bidirectional transmission path and comprising a transmitter, a receiving circuit and a hybrid circuit, said hybrid circuit having a bidirectional port connected to the transmission path, an outgoing input connected to the transmitter and at least one uni-directional incoming output connected to the receiving circuit, wherein the hybrid circuit is constituted by a fine polarisation splitter, (PBS1), a nonreciprocal polarisation rotator (R) and a second polarisation splitter (PBS2), a first incoming output (u11) of the first polarisation splitter (PBS1) serving as the transmitting input of the hybrid circuit and the second polarisation splitter (PBS2) having a bidirectional port (2) serving as the bidirectional port of the hybrid circuit and the outgoing input and output of the nonreciprocal polarisation rotator (R) being respectively connected to an incoming input (i1) of the first polarisation splitter (PBS1) and to a first incoming output (u21) of the second polarisation splitter (PBS2), and wherein the receiving circuit comprises two coherent receivers (O1, O2) connected to a local oscillator (LO) and the inputs of the coherent receivers are respectively connected to second outputs of the first and second polarisation splitters (PBS1, PBS2), the outputs of the coherent receivers being connected to a summing circuit (S) for obtaining a received signal.