DPSK modulation and demodulation system based on a novel Mach-Zehnder interference structure

Abstract

As the conventional fiber Mach-Zehnder (M−Z) interference structure being sensitive to temperature variation and mismatching of arm length in Differential Phase Shift Keying (DPSK) system, we proposed a modulation and demodulation system of DPSK based on novel M−Z interference structure. This novel M−Z interference structure has some advantages of higher temperature stability, better robustness and lower restriction of laser linewidth. A detailed discussion of the working principle is presented and demonstrated, the influences of the delay induced by arm mismatching and temperature variation on the Q factor of DPSK system are analyzed. Experimental results as well as simulations show that the delay length mismatching corresponding to descent point of 3dB increases from [0.925,1.124] to [0.536,1.31], which reduces the requirement for the length accuracy of the interference arm, and the demodulation effect of the novel structure is better under the same deviation. The Q factor of the system keeps fluctuation within a narrow range when the temperature variation in the range of 20°C–120°C, and the demodulation effect of the system is almost unaffected by the variation of ambient temperature.