Research Of Several Key Technologies For Digital Coherent Optical Communication System

Coherent detection enables information to be encoded in four physical quantities available on the optical signal,leading to improved spectral efficiency.The four physical quantities comprise intensity,frequency,phase and polarization.Because of the business requirements of internet game,high-definition internet television and video live broadcasting,the capacity of network grows quickly lately,which causes the fact that the existed bandwidth cannot meet the network's need.As a result,coherent detection technology arouses strong interest of researchers because of its high spectral efficiency.Meanwhile,the emergence of high-speed analog to digital converter(ADC)and the digital-signal-processing(DSP)technology empowers the digital compensation of signal impairments in the GBaud speed.DSP algorithm not only can compensate linear effects and nonlinear effects on fiber channel but also acheive carrier synchronization.For these reasons,many researchers focus their attention on the study of DSP algorithms after coherent detection.This paper first presents the basics of the DSP-based coherent optical system including transmitters and receivers,and then analyzes the factors which affect the quality of coherent communication system consisting of IQ phase imbalance,phase noise,frequency offset,and dispersion,non-linear effects caused during the transmission in the fiber.Next,this paper describes the DSP algorithms applied in the present coherent optical communication systems.The DSP algorithms discussed in this paper mainly include dispersion compensation algorithm,polarization demultiplexing algorithm,non-linear compensation algorithm,clock synchronization algorithm,and carrier recovery algorithm.This paper realizes each algorithm and then synthesize all affecting factors to analyze the joint influence.