Research On Polarization-dependent Impairment Equalization In High Spectrum Efficiency Optical Fiber Communication Systems

With the gradual deployment of the fifth generation mobile communication system(5G),the booming development of the Internet of things,virtual reality,mobile Internet and cloud computing has brought the explosive growth of global information traffic.Facing massive data transmission requirements,both the coherent system for long-distance transmission of the core backbone network or a direct detection system for short-distance interconnection between data centers are facing great challenges.The establishment of high speed,large capacity and high spectral efficiency optical fiber communication system has become the common goal of communication transmission.The advancement of advanced modulation formats,such as QPSK,16QAM or higher-order modulation formats,effectively increases the spectrum efficiency of the system;The development of various multiplexing technologies,such as PDM,WDM and even SDM,has greatly improved the transmission capacity of optical communication systems.Therefore,with the explosive demand of global data traffic and a series of major technological breakthroughs,optical fiber communication system is developing with vigorous vitality.However,in the optical fiber,optical signal will inevitably suffer from such as CD,RSOP,PMD and PDL,which will cause optical signal distortion and seriously affect the transmission performance of communication system.With the development of DSP technology,many impairments mentioned above can be equalized in the electric domain in receiver.However,with the continuous improvement of the transmission rate and modulation format of optical fiber communication system,the combined effect of single channel impairment and multiple impairment enhance,and the original equalization algorithm for low rate and single impairment become stretched;Secondly,in some extreme polarization impairments scenarios(such as the violent vibration when the train passes by and the lightning strike in rainy days),the performance of the equalization algorithm will decline sharply or even fail,resulting in the communication interruption;In addition,with the increase of system transmission rate,the research on the theoretical model of channel impairment also faces challenges.Therefore,the breakthrough of equalization algorithm and the perfection of impairment model are of great significance to ensure the stable operation of communication system.In view of the above problems,this thesis focuses on the topic of polarization dependent impairments equalization in high spectral efficiency optical fiber communication system,analyze the physical mechanism of polarization dependent impairments,establish a three-parameter RSOP model,and propose an efficient signal impairments equalization scheme based on Kalman filter.In order to ensure the normal and stable operation of the communication system,and provide core technical support for telecommunications operators and equipment manufacturers.The innovative and research work of this thesis is as follows:(1)Research on RSOP modeling and fast RSOP equalization in fiber channelIn this thesis,a three-parameter model of RSOP is proposed,which can accurately and completely describe the polarization state changes in the optical links.Based on the three-parameter RSOP model,an equalization scheme based on Kalman filter is designed.The tracking speed of RSOP can reach 100 megabit radians per second for QPSK signals and 10 megabit radians per second for 16QAM signals.(2)Research on jointly copy with fast RSOP and PDLIn this thesis,a scheme to true equalization of PDL with the presence of fast RSOP by using polarization-time code and Kalman filter is proposed.First,the polarization model is simplified,and based on the simplified model,a scheme that can true equalization of the combined effect of PDL and ultra-fast RSOP is designed.This scheme enables the power balance in Stokes space,RSOP tracking by Kalman filter and BER recovery caused by OSNR asymmetry.The proposed approach was proved to be very effective and provided a significant performance.With 1.2 dB OSNR penalty,it can jointly cope with large PDL of 7 dB and fast RSOP of up to 1 Mrad/s.(3)Research on joint equalization of CD and RSOP in SVDD systemIn this thesis,a new Kalman filter structure is proposed,and based on it,a joint blind equalization for CD and RSOP in SV-DD system is designed.At first,we perform a simple analysis of the nonlinear form of the combined effect of CD and RSOP in the SV-DD system.Secondly,the equalization method based on the Kalman filter both in the time and frequency domain is proposed.The tracking of RSOP is performed in the time domain and the compensation for CD is conducted in the frequency domain.The simulation results confirm that the method is very effective and has strong tolerance to CD(more than 2550 ps/nm,equivalent to a 150 km G.652 fiber)combined with ultra-fast RSOP(up to 2 Mrad/s).The difficulty problem of joint equalization of CD and RSOP in SVDD system is solved.