Research On Optical Performance Monitoring Of High Speed Coherent Optical Communication System

With the rapid development of the Communication network,high speed,large capacity and long distance have been considered as the main trend for the next generation optical communication system.At the same time the optical network is developing towards the direction of dynamic and transparent.As the key technology to ensure the reliable and stable operation of optical communication network,optical performance monitoring(OPM)technique becomes more and more important.Optical signal to noise ratio(OSNR)and chromatic dispersion(CD)are important parameters of OPM,and are also the main indicators to measure the quality of optical networks.Therefore,it is very important to realize the accurate and effective monitoring of OSNR and CD in optical signal for the configuration and optimization of optical network.In this paper,we conduct theoretical investigation on OSNR and CD monitoring of the high-speed optical coherent communication systems based on Quadrature Phase Shift Keying(QPSK)modulation format,combined with digital signal processing technology.The main research work is as follows:(1)This paper expounds the recent achievements and the future of OPM technology and makes a detailed analysis of the modulation format,coherent detection technology,DSP technology and network damage parameters of coherent optical communication system in theory.(2)The typical OSNR monitoring technology is analyzed from the aspects of advantages and disadvantages.Then we employ a method based on high order statistical moments for OSNR monitoring of high speed coherent optical communication system.Firstly,we successfully derive the relationship between higher order statistical moments and OSNR and carry on a correction method for data processing.Secondly,in order to validate this method,we set up a 112Gb/s PM-QPSK fiber transmission simulation system and process received signal using DSP.The results show that the OSNR monitoring method is feasible.It shows a good monitoring effect within the scope 10?25dB OSNR in the back-to-back system,and the monitoring error is below 0.1dB after correction.We analyze the effect of residual CD on OSNR monitoring using this method.The result shows that this method is not sensitive to residual CD when the value of OSNR is small.However,the larger value of residual CD,the greater monitoring error of OSNR.(3)Based on the autocorrelation function of the signal power waveform,we realize CD monitoring of high speed coherent optical communication system by simulation.Then the proposed method is analyzed and verified on coherent optical systems of 56Gb/s single polarization QPSK and 112Gb/s PM-QPSK.The simulation results show that the proposed method is suitable for different codes,insensitive to amplifier spontaneous emission(ASE)noise while having good tolerance for first order polarization mode dispersion in the range of 0?60ps.