Simple phase offset monitoring technique for 43 Gbit/s optical DQPSK receiver

Proposed is a simple phase offset monitoring technique that uses a simple electric limiter amplifier circuit for the optical differential quadrature phase shift keying (DQPSK) receiver. Phase offset can be monitored even if the eye pattern of the waveform of the demodulated 43 Gbit/s DQPSK signal is completely closed due to chromatic dispersion exceeding 250 ps/nm.