Phase diversity receivers for homodyne detection of optical DQPSK signals

Phase diversity (PD) receivers are an elegant option to handle the phase noise at homodyne detection and are especially interesting when used as wideband tunable wavelength-division multiplexing receivers. In the late 1980s and early 1990s, they were proposed and investigated for binary modulation formats (amplitude-shift keying, differential phase-shift keying, and frequency-shift keying). In this paper, a homodyne PD receiver for differential quadrature phase shift keying (DQPSK) modulation is analyzed, which provides a promising alternative to presently investigated DQPSK-direct-detection receivers and homodyne receivers with digital phase estimation.