新型相位调制格式技术能够有效地减少光传输损伤，是光传输系统中的重要技术。从理论上分析了光MDPSK(M进制差分相移键控)的调制解调原理，构建了通用的调制解调结构，并首次推导出MDPSK的通式和解调公式，最后以基于CSRZ(载波抑制归零，占空比为67%)码的DQPSK(差分正交相移键控)、8DPSK(3阶差分相移键控)和16DPSK(4阶差分相移键控)为例，用MATLAB软件仿真得到了其调制后的频谱图和解调后的眼图。仿真结果表明，随着级数的增加，MDPSK调制格式的频谱宽度会逐渐变窄，且解调后的眼图也令人满意。

The novel phase modulation format technology is important to optical transmission systems as it can effectively reduce the damages in optical transmissions. This paper theoretically analyzes the principles of modulation and demodulation of optical M-ary Differential Phase Shift Keying (MDPSK), establishes its common modem structure and derives for the first time its general and demodulation formulas. Finally, it obtains by using MATLAB software the spectrum after modulation and eye diagram after demodulation, taking DQPSK, 8DPSK and 16DPSK that are based on Carrier-Suppressed Return-to-Zero (CSRZ with duty cycle of 67%) as the examples. The simulation results show that the spectral width of MDPSK modulation format gradually becomes narrower with the increase of M, and the eye diagrams is also satisfactory.