US Patent 7734196 Optical receiver device

A DQPSK receiver extracts first and second phase modulation components from an input optical signal, and respectively converts the extracted components into the first and second data signals. The DQPSK receiver extracts a clock signal from one of the data signals, and produces an inverted clock signal by inverting the extracted clock signal. Then, the DQPSK receiver latches the first data signal by using the extracted clock signal or the inverted clock signal, and latches the second data signal by using the extracted clock signal.