A PGC-DCDM demodulation scheme insensitive to phase modulation depth and carrier phase delay in an EOM-based SPM interferometer

Abstract

Phase modulation depth (C) and carrier phase delay (θ) are two critical factors for the phase generated carrier (PGC) demodulation scheme. Traditional PGC demodulation schemes require θ be mπ (m=0, ±1, …) and C be specified values, otherwise, the demodulated signal will be distorted. In this paper, a PGC-DCDM demodulation scheme insensitive to C and θ is proposed. By performing the differential-cross-dividing-and-multiplying (DCDM) operation on the quadrature components in PGC demodulation, the influences of C and θ are eliminated simultaneously, and the linear and nonlinear distortions in traditional PGC schemes can be suppressed effectively. As expected by the theoretical analysis, simulation and experimental results have confirmed that the PGC-DCDM scheme is insensitive to C and θ and has low distortion and large dynamic range. Experimental results showed that, as C varies from 1.5 rad to 3.5 rad or θ changes from -180°to 180°, the amplitude of the demodulated signal maintains at the true value, and a stable low THD below 0.6% as well as a high SINAD greater than 44 dB were achieved by PGC-DCDM scheme.