Abstract: An apparatus includes an optical splitter, an optical combiner, first and second optical paths, and a digital signal generator. The optical splitter has an input port and first and second output ports. The optical combiner has first and second input ports and an output port. The first optical path couples the first output port of the splitter to the first input port of the combiner. The second optical path couples the second output port of the splitter to the second input port of the combiner. Each optical path includes an electro-optical phase shifter, and one of the optical paths includes an electro-optical attenuator. The digital signal generator is configured to apply binary-valued voltage signals to control inputs of the phase shifters and the attenuator.

Abstract: A receiver for coherent detection of a PSK modulated optical carrier includes an optical detector, digital-to-analog converters, and a digital module. The optical detector is configured to mix the modulated optical carrier with two phase components of a reference optical carrier and to produce analog output signals representative of optical signals produced by said mixing. The digital-to-analog converters are connected to receive the analog output signals and to produce digital signals from the received analog output signals. The digital module is connected to receive the digital signals and to perform one of compensating the received digital signals for a conjugate phase misalignment between the mixed components, extracting phase of the received digital signals, and estimating a frequency offset between the two carriers from the received digital signals.