Coherent optical detector and coherent communication system and method

An monolithically integrated optical device for receiving and demodulating of an incoming quadrature modulated optical signal having one polarization and transmitted via optical path;

• the device having a first and a second inputs, comprising:
• a first adjustable coupler connected to the first input and producing at least a first and second output;
• a second adjustable coupler connected to the second input and producing at least a first and second output;
• a third adjustable coupler connected to the first output of the first coupler and to the first output of the second coupler;
• a fourth adjustable coupler connected to the second output of the first coupler and to the second output of the second coupler;
• electrodes providing said tuning of the first, second, third, and fourth couplers;
• first and second crossing waveguides with an angle selected to minimize crosstalk and losses between the first and second cross waveguides,
• the first crossing waveguide connecting one of the first or second outputs from the first coupler with an input of the fourth coupler,
• the second crossing waveguide connecting one of the first or second outputs from the second coupler with an input of the third coupler;
• a first phase shifter coupled to the first and second waveguides,
• the first and second waveguides connecting one of the outputs of the first or second coupler and one of the inputs of the third or fourth couplers,
• a first, a second, a third and a fourth photodiodes converting optical signal into a first, a second, a third and a fourth electrical signals;
• the first, second, third and fourth electrical signals being processed to obtain an in-phase and an in-quadrature signals and to recover quadrature modulated data embedded in the incoming quadrature modulated optical signal having one polarization;
• wherein the first, second, third and fourth couplers, the two crossing waveguides and the phase shifter are each formed as part of a single planar chip made of an electro-optical material.