| Recently, with the growth of communication services, subscribers demand for large capacity and high speed communication is increasing significantly. Presently, the commercial optical transmission systems are being upgraded from40G to100G. The research emphasis is to develop future Terabit/s and Petabit/s transmission in single fiber. The state of polarization(SOP), which should not have to be considered in low speed optical fiber communication system, have been the main limiting factors of high speed optical transmission systems. How to quickly and accurately realize endless polarization stabilization control in high-speed optical communication system becomes a very important issue. Polarization division multiplexing technology, which can double the spectral efficiency of the transmission system without increasing the system structure complexity, has attracted much attention. As the SOP of signal changes randomly with wavelength and time and cannot be maintained in a transmission link, so real-time polarization controlling has to be performed at the receiver side to eliminate crosstalk between the two polarization channels and achieve polarization division multiplexing.Polarization control can be performed in the optical domain, which equalizes SOP of signal directly in the optical domain. It also can be performed in the electronic domain to realize polarization equalization and compensation of damaged signal. This paper is concerned about these problems, on the one hand, polarization stabilization control technology based on direct tracking and detection of polarization is researched in this paper. On the other hand, relevant algorithms to realize polarization equalization based on coherent receiver is researched.Concerning the issues mentioned above, the main contents and innovations of this paper are as follows:1) Designed and implemented polarization control system based on direct tracking and detection of polarization. Firstly, theoretical analysis and simulation of this scheme are dealt with and the feasibility of achieving polarization stabilization is verified. Secondly, we designed hardware platform, including feedback signal acquisition module, polarization control module and digital signal processor module. Feedback control algorithm is very important to achieve polarization control stabilization for this scheme, and particle swarm optimization algorithm is utilized in this paper. Modified adaptive inertia weight particle swarm optimization algorithm is proposed in this paper, and it is helpful to decrease iterations and time cost in this polarization stabilization control system. The experimental platform is set up. In order to verify the scheme is independent of data rata and signal modulation format of optical signal, different kinds of signals such as10Gb/s,20Gb/s NRZ-OOK and NRZ-PSK are designed as input signals of polarization control system.2) The technology of polarization equalization based on coherent receiver is studied in this paper. Firstly, the principle of polarization division multiplexing (PDM) base on constant modulus algorithm is researched. Secondly, a novel method based on kalman filter algorithm to realize polarization division multiplexing is proposed in this paper, PDM-QPSK simulation system and the model of the various SOP is set up. The kalman filter that can estimate the SOP of signal is designed and it can achieve polarization recovery and tracking as well.3) Carrier phase recovery algorithm is studied in this paper. Firstly, the principle of4th power algorithm that achieve carrier phase recovery is researched. Secondly, kalman filter algorithm is utilized to estimate the phase noise and realize carrier phase recovery in this paper. Established the model of phase noise and set up simulation system, and verified the performance of kalman filter algorithm when dealing with phase noise estimate and carrier phase recovery. |
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