US Patent 7389055 DQPSK receiver phase control

An optical receiver for receiving an optical differential phase shift keyed signal has an optical component sensitive to the optical phase of the signal, such as an interferometer, a device arranged to generate a control signal by non linear limiting of an output of the optical component, such as an RF amplifier arranged to operate in a region near saturation point, and a phase controller for tuning a phase response of the optical component to the received signal according to the control signal.