Modulation Formats And Performance Evaluation For High-speed Optical Transmission System

With the development of optical fiber communication, the desire for high-speed, large per-fiber transport capacity and long-haul transmission is increasing. In the same time, optical signal is suffering more and more transmission penalties. Being one of the newly emerging technologies, the advanced optical modulation formats not only mitigate transmission penalties hugely, but also don't require changing the transmission line completely; it is a simple and convenient technology. There have been so many optical modulation formats until now, how to find out one or more optimal modulation formats under various circumstances is one of the commonly interested problems. This paper deals with the modulation and demodulation principles of various optical modulation formats available, gives them a classification and summary, and poses some improvement methods for the above formats. Then emphasis is put on the simulation of the performances of their resilience to impairments (including optical amplifier noise, chromatic dispersion, polarization-mode, dispersion nonlinearity and so on), from the analysis and simulation, we can draw a conclusion that phase-modulated formats have the best performances and its prospect of application is also the best. Finally, the statistical characteristics of the nonlinear phase noise of phase-modulated formats are analyzed theoretically. It is pointed out that probability distribution of noise in phase-modulated formats is different from the traditional analysis. The nonlinear phase noise is the summation of many independently distributed noncentral chi-square random variables but not traditional Gaussian-distributed ones.