Monolithic demodulator for 40-Gb/s DQPSK using a star coupler

We demonstrate a novel device that demodulates both quadratures of the optical differential quadrature phase shift keying (DQPSK) format in a single interferometer by using a 2-by-4 star coupler. We present simultaneous measurements of both DQPSK quadratures at 42.7-Gb/s.