Research Of EDFA Gain Flattening Based On Two-stage Pump Structure

Erbium-doped fiber Amplifier with the characteristics of low noise, high gain and low loss has been widely used in optical fiber communication. But with the DWDM (Dense Wavelength Division Multiplexing) technology continues to mature, optical communication towards to more transmission capacity and longer transmission distance, erbium-doped fiber amplifier has also exposed some shortcomings. Based on the characteristics of erbium ion energy levels structure, EDFA(Erbium-doped fiber Amplifier) gain is different between the gain bandwidth. The same power of input signal is amplified by EDFA, the output power will have deviation. The bias will be accumulated through the cascade amplification, resulting in the optical signal distortion and increasing system error rate. At present, making specialty optical fiber or using gain flatting filters is the most method to achieve gain flatness.In this paper, a novel technique is proposed based on researching of EDFA working principle and gain characteristic for gain flatting. According to EDFA's gain saturation characteristics, structure of two-stage is taken to realize the whole C-band gain flatness without gain flatting filters. The main work is as follow:1. EDFA basic structure, erbium ions transition process, traveling wave rate equations and gain characteristics were introduced, analyzing EDFA structure and principle based on the two-stage pump structure;2. Based on the traveling-wave equation, using the numerical methods to obtain the numerical solution in time domain;3. In the steady state case, using Matlab to simulate the two-stage pump structure EDFA, in the two different structural parameters obtained and analyzed the changes of upper level number density, signal power, pump power and gain characteristics;4. Genetic algorithm basic principles and processes were introduced. By improving the algorithm, writing the objective function and.using Matlab GADS (Genetic Algorithm and Direct Search) toolbox to optimize erbium fiber length and pump power in two-stage structure, obtain and analyze the optimal flat spectrum;...