Fiber Raman amplifier is one of the most important optical devices in modern long distance optical fiber communication systems. Compared with the rare earth ion optical amplifiers, such as erbium-doped fiber amplifier, the fiber Raman amplifier has advantages of low noise index, flexible wavelength configuration and gain range, distributed amplification, and weaker fiber nonlinear effects. The accurate modeling of various optical effects and their interactions in fiber Raman amplification optical fiber communication systems is the key and very difficult point of the analysis of ultra-long span optical fiber communication systems. Among these optical effects, the stimulated Raman scattering effect brings gain to the signal. The spontaneous Raman scattering and double Rayleigh backscattering effects introduce noise to the signal. The nonlinear Kerr effect causes the phase noises, the coupling between the signal and the noises, and the transforming between the signal phase noises and the intensity noises. Moreover, since the transmission distance of ultra-long span system is very long (upper to 700km) and the optical power is very high, Brillouin scattering is also a system limiting factor that cannot be ignored. The noise introduced by a variety of optical effects degrades the communication quality, and these optical effects interact with each other. Suppressing a single noise separately may lead to the deterioration of other noises and degrade the overall performance of the system. Therefore, it is necessary to consider a variety of optical effects and noise mechanisms to coordinate the intensity of each type of noise so as to optimize the overall performance of the systems.
Professor Wei Li of Wuhan National Laboratory for Optoelectronics has focused on the in-depth study of ultra-long span unrepeatered optical fiber communication system based on bidirectional Raman amplification for many years. Her team paid attention to the basic theory of Raman amplification as well as the innovation of practical technology, found and analyzed the variation of Rayleigh scattering spectrum with the distance of transmission fiber, and put forward the power coupling theory of Rayleigh scattering and Brillouin scattering. The transmission models of double Rayleigh backscattering and spontaneous Raman scattering noise in optical fiber has been established. The numerical model of pump light transmission and amplification process in the erbium-doped fiber of the remote pump EDFA was improved. And a nonlinear compensation algorithm suitable for bidirectional Raman amplification system had been proposed.
Based on the above theoretical research and innovation works, Professor Wei Li with her team has established a set of simulation platform suitable for bidirectional Raman amplification optical fiber communication system, which can synthetically and quantitatively analyze the influence of all kinds of noise, dispersion, nonlinear Kerr effect, stimulated Brillouin scattering and other factors on the performance of the system, and optimize the configuration of the system to improve the transmission performance. The above research results has been published in the journals of IEEE Journal of Lightwave Technology, Optics Express, IEEE Photonics Journal, IEEE Photonics Technology Letters, etc., and had reported in the Asia Communications and Photonics Conference.
In the cooperation projects with Accelink Technology Co. Ltd., China Southern Power Grid, etc., the research results had been applied to the design and optimization of the power communication system. After optimization, the noise and nonlinear effects in the power communication system had been effectively suppressed, and the nonlinear effect was compensated by the algorithm, which could improve the performance and reliability of the system. A low-cost and high-efficiency power communication system solution had been realized. Based on the above works Professor Wei Li had won the first class prize of Hubei Province Science and Technology Progress Award and the second class prize of China Institute of Communications Science and Technology Award from 2018 to 2019.
With the guidance of Professor Wei Li, the doctoral candidates Qiguang Feng, Qiang Zheng, You Wang and Muyang Mei participate in the research of bidirectional Raman amplification optical fiber communication system, and Qiguang Feng had won the Student Award of Wuhan National Laboratory for Optoelectronics in January 2019.
