Analysis of the dual-parallel Mach–Zehnder modulator-based equivalent phase modulation

In a dual polarization quadrature phase shift keyed (DP-QPSK) modulator, it is desired that one dual-parallel Mach–Zehnder (MZ) modulator in it is operated as a phase modulator (PM) to achieve some functions in conjunction with the other dual-parallel MZ modulator. Equivalent phase modulation is realized by controlling the bias points of a dual-parallel MZ modulator. If the parameters are accurately set, it functions as a true PM. However, the amplitude imbalance and the different arrival time of the two RF signals applied to the dual-parallel MZ modulator, and the deviations of the three bias points in the dual-parallel MZ modulator influence the performance of the equivalent phase modulator (e-PM). In this paper, we study the influences of these non-ideal factors on the performance of the e-PM. The results show important guidelines for significance for the further use of the dual-parallel MZ modulator-based equivalent phase modulation in a DP-QPSK modulator.