Compensation Algorithm In High-speed Coherent Optical Communication System

With the rapid development of internet technology, the data transmission volume has been showing the geometric growth. Faster information transmission speed and longer information transmission distance are required. Because the traditional way of Amplitude Modulation cannot keep up with these requirements, new technology of coherent optical communication is being rapidly developed nowadays. It is able to transfer information with higher rate in single channel and to restore system distortion combined with the Digital Signal Processing. Also, the coherent optical communication can be used in core network and will be a hot research topic in the future.This paper focus on discussing the research of frequency offset algorithm and carrier phase offset algorithm in coherent optical communication. First, a simulation of the entire DQPSK coherent optical transmission system was built and various losses of the system during transmission were analyzed. Then, it a signal model after dispersion compensation algorithm and equalization was obtained. A symbol time separation-based frequency offset estimation algorithm was proposed.The simulation results show that when the deviation is less than 2GHz, the frequency offset estimation error is close to 0.5MHz, which is better than the maximum spectrum periodic frequency offset algorithm. A carrier phase recovery algorithm was proposed to reduce the phase noise in the analysis of carrier phase compensation algorithm. The carrier phase recovery algorithm uses wavelet decomposition and wavelet reconstruction method and the phase recovery property was analyzed with different base wavelet. The simulation results show that the initial phase can effectively be recovered by the wavelet transform algorithm. When the SNR is 16 dB, the wavelet db8.4 can tolerate laser line-width of 5MHz, which is better than the fourth power carrier phase offset algorithm.