Study On The Output Power Characteristics Of Raman Fiber Lasers

Raman fiber lasers (RFLs), based on the stimulated Raman scattering (SRS) effect, have been extensively studied as the signal sources and pump sources of DWDM systems due to their characteristics of simple structure, high output beam quality, powerful wavelength conversion ability and stable performance at room temperature. In order to optimize the design process of RFLs, it's very important to find a detailed method to solve the optical coupling equations effectively.Firstly, the theory of Raman scattering and the gain characteristics of SRS are described in this dissertation, the basic structure of RFLs and the popular applications of RFLs are also presented. Secondly, from the analysis of the theoretical model of RFLs and the optical coupling equations, it can be concluded that the numerical solving of Raman equations could be transformed to the problem of optimization complex functions. According to the actual situation of fitness function which derived from the Raman equations, focused on the two pervious optimization algorithms: Particle Swarm Optimization (PSO) and Quantum Genetic Algorithm (QGA), both an improved PSO algorithm and an improved QGAs algorithm are proposed. In the improved PSO algorithm, with the absorption of the advantages of GA algorithm, the symmetrical mutation operator of genetic arithmetic and hybrid arithmetic are used to increase the multiformity of the particles, and enhance the convergence speed as well as to reduce the probability of getting into local optimization. The improved QGAs algorithm are put forward in integrating the thought of former improved QGA, GA cross-factor and the characteristics of quantum gate, which enhance the optimization capability of the algorithm. The simulation results demonstrate that comparing with other algorithms, the new algorithms fit to solve optimization problem of complex functions and have a better comprehensive performance. Other applications of the optimization algorithms proposed such as in numerical fitting of mode-field radius and the complex Raman gain profile are also given in this dissertation.Finally, based on the analysis of RFLs's optical power coupling equations and optimization algorithms, a new method in using the optimized numerical algorithm to solve the cascade RFLs is proposed. Improved Runge-Kutta algorithm are used to solve the equations and optimized algorithms were used to screen the initial values at the sensitive points, aiming at ameliorating the drawbacks of easy undershoot and too much calculation time in the numerical simulation process of RFLs of the normal Newton-Raphson shooting algorithm. The key parameters that impact the output power of second-order P-doped RFLs are numerically analyzed, the results indicate that the new algorithm not only effectively reduce the calculating time but also enhance the stability of the shooting method, it's an effective method for getting numerical results.