为提高光纤通信系统的频谱利用率,搭建了八进制幅度差分相移键控(8APSK)和八进制差分相移键控(D8PSK)密集波分复用(DWDM)系统。仿真结果表明：当探测信道为8APSK,最佳入射平均光功率随其幅 度调制指数的增大而明显变大。不管是8APSK还是D8PSK调制,入射平均光功率取最佳值时,四波混频噪声对系统性能的影响并不大。然而当其超过最佳值,四波混频噪声随入射平均光功率的增加对系统性能的影响快速增加。对于 所讨论的DWDM系统,幅度调制指数优化的8APSK信号传输性能明显优于D8PSK,因为前者对总的非线性效应有更好的容忍度。

In order to improve the spectrum utilization of fiber communication system, the dense wavelength division multiplexing (DWDM) system of 8-level amplitude and differential phase-shift keying (8APSK) and differential 8-level phase-shift keying (D8PSK) are set up. Simulation results show that when the probe channel is 8APSK, the optimal incident average optical power increases with increasing of 8APSK amplitude modulation index. Whether it is 8APSK or D8PSK modulation, four-wave mixing noise has little influence on the system performance when the incident average optical power is optimal. While it exceeds the optimal value, the influence increases rapidly. For the discussed DWDM system, the transmission performance of 8APSK signal with amplitude modulation index optimization is obviously better than that of D8PSK, which is mainly attributed to the better tolerance of total nonlinearities for the former.