Patent ID: 8145072

Claim:
A Differential Quadrature Phase Shift Keying (DQPSK) optical receiver, comprising: a first interferometer associated with a first arm; a second interferometer associated with a second arm; first optical-electrical converter to convert an optical signal output from the first interferometer to an electrical signal; second optical-electrical converter to convert an optical signal output from the second interferometer to an electrical signal; a first low pass filter coupled to a line branching off from between the first optical-electrical converter and a first clock and data recovery circuit; a second low pass filter coupled to a line branching off from between the second optical-electrical converter and a second clock and data recovery circuit; a first limit amplifier to amplify a signal output from the first low pass filter and to limit an amplitude of an output signal thereof; a second limit amplifier to amplify a signal output from the second low pass filter and to limit an amplitude of an output signal thereof; a first mixer for to multiply the output signal from the first limit amplifier by a signal output from the second low pass filter; and a second mixer to multiply the output signal from the second limit amplifier by a signal output from the first low pass filter.