Research Of Optical Performance Monitoring Key Technology

As network flexibility and transmission capacity of optical communication system develops rapidly, people pay more and more attentions on optical performance monitoring (OPM) served as a guarantee of correct signal transmission. In order to reduce the operating costs, ensure optimum resources utilization and guarantee adequate operation and management of dynamic optical networks, it is essential to be able to continuously monitor various network performance parameters. Optical performance monitor plays an important role in optical communication system.In this paper, the optical performance monitoring (OPM) technology is studied. The paper analyzes the implementation methods of OPM technology from time domain, frequency domain and nonlinear direction,respectively. The mechanisms of chromatic dispersion (CD), polarization mode dispersion (PMD) and optical signal to noise ratio (OSNR) are illustrated and analyzed. Based on this study, new monitoring techniques for PMD and OSNR are proposed respectively.Firstly, we propose a Polarization Mode Dispersion (PMD)monitoring technique for phase-modulated optical signals utilizing the cross-phase modulation (XPM) effect between the input signal and the continuous-wave probe in parallel connection. The simulation shows that the technique can monitor PMD of 40Gb/s non-return-to-zero differential quadrature phase-shift keying ( NRZ-DQPSK ) from 0-20ps. The dynamic range over 3dB can be used in accurate monitoring compared to existing methods. The applicability of this monitoring technique to higher bit-rate phase-modulated signals is also investigated via simulation.Secondly, an optical signal to noise ratio monitoring method based on radio frequency power of two signals in parallel connection is proposed.The test optical signal was split equally into two signals in parallel connection. One removed out-of-band noise by optical band-pass filter, the other kept output power constant by electronic variable optical attenuators with power-locking control loop. The difference of radio frequency power of the two signals at the same place was used to monitor OSNR. The simulation results showed that the proposed technique can implement OSNR monitoring between 2dB and 30dB for 40Gb/s NRZ-DQPSK optical signal. Monitoring error was within 1dB and the proposed technique was insensitive to chromatic dispersion and polarization mode dispersion. The impacts of frequency variations, different rates and modulation formats on the proposed technique were studied.