Research On Optical OFDM System With High Fiber Nonlinear Effect Tolerance

With the rapid development and popularization of mobile data services and applications with high speed and high quality such as digital high-definition video service,cloud storage computation and big data Internet of things technology,people's demand for data transmission rate shows explosive growth.The increasing growth of data communication demands in the different networks will cause the explosive growth of bandwidth demand of physical layer in entire optical communication system.High speed optical communication system is limitated by receiving optical signal-to-noise ratio and fiber nonlinear effect.In recent years,advanced high-order quadrature amplitude modulation format has drawn more and more attention for improvements of channel capacity and signal the tolerance to fiber nonlinear effects under the condition of limited optical signal-to-noise ratio.In this dissertation,key technologies to overcome nonlinear effect of optical fiber are mainly studied,whose main contents and innovations are as follows.1.Concerning the peak-to-average power ratio problem in the current optical transmission system employing orthogonal frequency division multiplexing,a discrete Fourier Transform-spread spectrum(DFT-spread)technology similar to the singlecarrier modulation technology is studied,whose basic principle and system framework are expounded in the paper,and whose computational complexity is analyzed.Compared with the traditional optical transmission system applying OFDM,only a few multiplication operations are introduced.The additional computational complexity of the system is negligible compared with the saved transmitting optical power.2.The transmission performance of fiber-optic communication system is limited by nonlinear effect of optical fiber caused by high PAPR.In this paper,a probabilistic shaping technology based on the Maxwell-Boltzmann distribution is proposed,and the PS influence on optical-fiber transmission system is explored with respects to basic principle,algorithm and experiments.In this scheme,the QAM signal with a uniform distribution can be shaped into one with a near-Gaussian distribution,which improves the spectral efficiency and reduces the PAPR of the signal.The 150Gbit/s bit error ratio performance of DFT-spread PS-optical OFDM system over 20 km transmission is experimentally verified.3.Most research results of high-speed optical communication system based on PS technology derive from the classical Bernoulli distribution matching algorithm.In addition to the PS overheads introduced by the algorithm itself,the LDPC coding integrated with forward error correction and the algorithm(after PS mapping)also introduces additional channel coding overheads,resulting in a sharp increase in system overheads and the consumption of available bandwidth.Last but not the least,for this scientific problem,the technology with a ‘many-to-one' mapping rule based on LDPC coding is studied,which makes the channel capacity of the system more approximate to the Shannon limit without changing the coding structure of the transceiver in the traditional optical communication system.