Broadband Fiber Raman Amplifiers Optimized Design

All-optical amplifiers with large gain-bandwidth are required extensively because of the increasing of the capacity of optical fiber communication systems and the development of Wavelength Division Multiplexing (WDM) technologies. Fibre Raman Amplifiers (FRAs), which use the intrinsic nonlinear properties of transmission fibers to obtain signal amplification, are the most promising in broadband optical amplifiers owning its unique performances. Flat gain bandwidth is an important requirement in designing the amplifiers. This dissertation studies the optimization of the gain spectrum of FRAs in order to obtain the FRAs with optimal gain-flattened and larger gain-bandwidth performances.The fundamentals and developments of FRAs are firstly introduced in the first chapter. In the second chapter, a theoretical model of FRAs is presented and the main characteristics of FRA are discussed. In the third chapter, the optical gains and noise figures are numerically calculated by making use of the 4-step Adams_Bashforth method. The analysis includes all the interactions among pumps, signals and noise without any approximation. Comparing the calculation results with reported data shows that a good agreement is given. The optimal design of broadband FRAs is the main target in this dissertation. A novel optimal design method for FRAs is presented. The propagation equations of FRAs pumped backward at multiple wavelengths are solved with two steps. First, the simulated annealing algorithm and the genetic algorithm are used to obtain required pump frequencies; Then, by making use of average power analysis method, the 4-step Adams_Bashforth method is adopted to design optimal gain-flatness and gain-bandwidth performances. Two fiber Raman amplifiers are designed with two pumps and four pumps,respectively. The relative gain flatnesses for the two-pump FRA and the four-pump FRA are all less than 1dB within the bandwidths of more than 50nm and 80nm,respectively. The calculational results verify that the proposed method is practicable and useful for designing FRAs with flat gain in broad bandwidth.