Design Of The Real-time Optical Field Reconstruction And Dispersion Compensation Module For Simplified Optical Coherent Receivers

With the development of information technology,modern society has increasingly higher requirements for communication speed and capacity.Coherent optical communication technology has the advantages of high spectral efficiency and high sensitivity,which can be combined with digital signal processing technology to compensate for various signal distortions.so it is one of the key technologies to improve the performance of optical fiber communication and free space optical communication(FSOC)systems.However,the traditional coherent optical receiver has a complex structure,high cost,and high power consumption,which is not suitable for access network or space platform.The recently proposed simplified digital coherent optical receiver(SCR)can realize coherent reception of one polarization signal by a single optical detector,which retains the advantages of high sensitivity of traditional coherent optical receiver,and reduces its hardware complexity and power consumption.This article is focused on the pseudo-single-sideband signal based simplified coherent optical receiver(P-SCR)and the design of its optical field reconstruction and dispersion compensation algorithm modules for the needs of free space optical communication and optical fiber communication systems.This paper mainly introduces the system structure,working principle and main DSP algorithm flow of SCR are introduced.Then,the SCR optical field reconstruction algorithm and dispersion compensation algorithm are optimized.The optical field is reconstructed by frequency domain overlap preserving algorithm(OFDE)and Hilbert transform(HT).A real-valued FFT-based implementation of Hilbert is proposed.The special method can reduce the computation complexity by a half compared with the traditional HT algorithm.To satisfy the requirement of dispersion compensation in optical fiber communication systems,an optical field reconstruction and dispersion compensation merged algorithm is proposed,which reduces the computation complexity by 61% compared with the traditional algorithm when the HT size is 256.On this basis,we built a joint simulation platform based Matlab and VPI Transmission Maker to verify the signal demodulation algorithm offline,and then developed a 256-channel fully parallel optical field reconstruction and dispersion compensation module based on Xilinx's Ultra Scale+ XVCU9 P FPGA chip.Real-time optical field reconstruction of 40 Gbps polarization multiplexed quadrature phase shift keying(PM-QPSK)signal is implemented.The sensitivity of the receiver meets the expected requirements.