Application of DQPSK format based on CSRZ in PMD compensation

Abstract

The paper studied the application of Differential Quadrature Phase Shift Keying (DQPSK) in PMD compensation based on Carrier-Suppressed Return-to-Zero (CSRZ) format. Using simulation, the Differential Group Delay (DGD) and the Degree Of Polarization (DOP) value histograms based on Return-to-Zero(RZ)DQPSK and CSRZ -DQPSK signals before and after Polarization Mode Dispersion (PMD) In present, Polarization Mold Dispersion (PMD) is the primary factor to limit the 40 Gbit/s optical fiber transmission systems. There are two means to resolve this problem. One is to compensate PMD by PMD adaptive compensation system, Carrier-Suppressed Return-to-Zero (CSRZ) has been used as an important signal format in optical communication. It is more efficient than return-to-zero (RZ) format which shows a wide spectrum and is not conducive to dispersion management. However, given that both RZ and CSRZ formats are using a binary amplitude modulation (On-Off-Keying, OOK), they can only carry one bit of information. In order to improve their spectrum efficiency, multi-phase modulation technology has been developed, for example, Differential Quadrature Phase-Shift Keying (DQPSK) format, where each symbol can carry two bits of information. Without changing the optical fiber link primarily, the system capacity of DQPSK has been greatly improved. In this paper, the authors simulated PMD compensation compensation were obtained. The results showed that compared with RZ -DQPSK format, after compensation the DOP value of CSRZ -DQPSK had more values close to 1, and the residual DGD value was smaller also. Moreover, their eye diagrams showed that CSRZ-DQPSK signal could maintain satisfactory performance after PMD compensation. So CSRZ-DQPSK format has the best PMD compensation effect, which is the preferred format to achieve PMD compensation.