【摘 要】 Internet的迅速发展使得光通信的速率和带宽需求成为了亟待解决的问题。目前大多数的光纤通信系统采用的是IM/DD调制解调方式，也即ASK调制解调方式。最近差分相位调制方式（DPSK）日益引起人们的注意，仿真和实验表明DPSK具有很强的抗色散性能。多级的调制格式如DQPSK和ASK/DPSK等，正日益受到人们的关注。本文在ASK、DPSK、DQPSK等调制格式的基础上，研究了ASK与DPSK以及ASK与DQPSK相结合的调制格式。提出了光纤非线性自相位调制对ASK/DPSK以及ASK/DQPS... 更多 >> Internet的迅速发展使得光通信的速率和带宽需求成为了亟待解决的问题。目前大多数的光纤通信系统采用的是IM/DD调制解调方式，也即ASK调制解调方式。最近差分相位调制方式（DPSK）日益引起人们的注意，仿真和实验表明DPSK具有很强的抗色散性能。多级的调制格式如DQPSK和ASK/DPSK等，正日益受到人们的关注。本文在ASK、DPSK、DQPSK等调制格式的基础上，研究了ASK与DPSK以及ASK与DQPSK相结合的调制格式。提出了光纤非线性自相位调制对ASK/DPSK以及ASK/DQPSK系统相位通道接收性能有不可忽略的影响。本文对ASK/DPSK和ASK/DQPSK系统的性能进行了仿真。从仿真结果可以看出，过大的功率会导致非线性自相位调制的影响增大，引起了码元反转的现象。相关的文献提到了ASK/DPSK以及ASK/DQPSK的最佳消光比，本文通过仿真发现，最佳消光比并不是定值，随着功率的增加会变化。本文采用最佳幅度比来表示最佳消光比。仿真的结果显示，功率的增加会导致最佳幅度比增大，ASK/DQPSK的增加趋势比ASK/DPSK更为明显。对ASK/DPSK以及ASK/DQPSK色散和非线性仿真表明，ASK/DPSK和ASK/DQPSK在相同的码速率条件下，具有更强的抑制色散的能力。ASK/DPSK具有较好的抑制非线性影响的能力，而ASK/DQPSK抑制非线性的能力较弱。关键词：ASK/DPSK、ASK/DQPSK、调制格式、自相位调制With the development of Internet, the speed and the bandwidth of optical communication system become a key problem. So far, the modulation format in most fiber communication system is binary intensity modulation with direct detection (IM/DD), which also can be called ASK. Recently, differentially phase shift keying format (DPSK) has been noticed and researched for its high robustness against fiber nonlinearty. Multilevel modulation formats such as DQPSK and ASK/DPSK also have attracted much attention in the past few years.In this thesis, modulation formats of combined ASK/DPSK and ASK/DQPSK has been investigated on the basis of ASK, DPSK and DQPSK.With theoretical analysis, it is indicated that the impact of SPM on the the receiver performance in phase path of ASK/DPSK and ASK/DQPSK can not be ignored. With simulated result revealed that SPM may cause additional phase difference between adjacent symbols of ASK/DPSK and ASK/DQPSK, resulting in higher decision error at the receiver. In this thesis, we use optimal amplitude ratio instead of optimal extinct ratio which has been mentioned by some references. We find that the optimal amplitude ratio is not permanent, but varies when peak-power changes. The optimal amplitude ratio of ASK/DQPSK changes more dramatically than that of ASK/DPSK. The chromatic dispersion and non-linearity in ASK/DPSK and ASK/DQPSK is also discussed. It suggests that both ASK/DPSK and ASK/DQPSK has high robustness against dispersion, and ASK/DPSK has relatively higher robustness against fiber non-linearity than ASK/DQPSK.Keywords: ASK/DPSK, ASK/DQPSK, modulation format, Self-Phase-Modulation (SPM) << 收起
