Research On Polarization Demultiplexing Technology Based On DSP

In today's rapidly evolving Internet era,the demand for bandwidth has grown exponentially.At the same time,with the advancement of science and technology and the advancement of optical fiber processing technology,the transmission bandwidth of the backbone network is also growing rapidly.With the modulation format,With the development and application of wavelength division multiplexing,polarization multiplexing technology and digital coherence technology,the capacity of optical fiber transmission systems has been greatly improved,and the transmission rate of 400Gb/s and even 1Tb/s has been gradually advanced.Among the technologies of these applications,some need to upgrade the optical fiber medium,and some can realize the system capacity increase on the original transmission link,but greatly increase the cost of the transmission system upgrade.Among them,the implementation of Polarization Multiplexing(PM)technology is the simplest.Since the polarization state of the optical signal transmitted in the fiber link changes randomly,the RSOP effect is generated.After the demultiplexing at the receiving end,the two optical paths with stable state cannot be obtained,and the polarization state needs to be controlled at the receiving end to realize the solution.In the optical communication system realized by polarization multiplexing,the demultiplexing method adopted by the receiving end is divided into an optical domain implementation based on direct detection and an electrical domain implementation based on digital coherent detection.Coherent detection can suppress PMD,polarization-dependent loss,nonlinear polarization rotation,etc.Compared with direct detection,it has many advantages,but direct detection is still widely used due to its simple structure,simple operation and low cost.This paper will separately study the demultiplexing system realized by the two methods.The main work and achievements of the thesis are as follows:(1)Research and design a polarization demultiplexing system based on direct detection.Firstly,the detailed analysis of the demultiplexing process based on this scheme is given.The theoretical basis of the implementation is given and the feedback variables are derived by the formula.The relationship between the feedback variable and the azimuth and ellipticity of the input optical signal is given.The demultiplexing system implemented based on the scheme is transparent to the modulation format and rate of the transmitted optical signal.Then the feedback control algorithm based on particle swarm optimization is studied.Based on the improvement,the weight adaptive adjustment PSO is proposed.The particle search step size is adjusted according to the interval of the feedback value.Then based on the scheme,the hardware is designed and the experimental platform is built,which mainly includes AD,DA conversion module,feedback variable acquisition part,polarization controller module and power management module.The above verification experiment was completed under the experimental platform.Finally,the performance of PSO and weight adaptively adjusted PSO in polarization stabilization and demultiplexing is compared by experiments.The latter has a great improvement in both convergence success rate and convergence rate.(2)Research on digital coherent demultiplexing system based on Kalman filter.Firstly,the coherent optical communication system is discussed.The structure of the system is studied.The principle of polarization-multiplexed light in the high-order modulation format is generated at the transmitting end.The principle of polarization diversity coherent reception adopted by the receiving end is analyzed.Then the extended Kalman filter is studied from shallow to deep,and an adaptive Kalman filter is proposed for its application.The Q value is dynamically changed,and the relevant theoretical analysis and formula derivation are given.Finally,a coherent optical communication simulation system based on PM-16QAM is designed and constructed.Firstly,the demultiplexing performance of EKF under different Q values is simulated,and the parameter setting when the performance is optimal is taken.Then,the tolerance of the AKF to the polarization rotation frequency is studied,and the limit of 105 rad/s is obtained,which is higher than the current commercial requirement of 103 rad/s.Finally,the performance of polarization demultiplexing of EKF and AKF is compared under different transmission distances and OSNR.The convergence speed of AKF is nearly three times faster than that of EKF,which verifies the dynamic change of Q value for system convergence and solution.The importance of using.