Research On Gain Equalization Of Raman Fiber Amplifier

With the rapid development of communications network, the explosive growth of information will make the optical fiber communication systems that under the application of erbium doped fiber amplifier(EDFA) faced with the challenge, that is, the system capacity and bandwidth need to be improved further. In this context, Raman fiber amplifier(RFA) become a potential solution of optical fiber communication systems because of its ultra-wide gain bandwidth characteristics. Nevertheless, the gain spectrum of RFA is flat only in a very narrow wavelength range. Raman gain spectrum needs further flattening. We mainly study on gain flattening of Raman fiber amplifier in depth from two methods of multiple pumps and novel fibers. Meanwhile, we also analyze the effect of changes in pump and signal parameters on gain flatness.Firstly, according to classical electromagnetic theory, starting from Maxwell equation, we deduced theoretical model of RFA and then simplified the model in terms of the physical process of gain-flattening. This will provide a theoretical basis for follow-up numerical simulation of Raman amplifier system.Secondly, based on the above theoretical model, we researched the numerical simulation of Raman amplifier system, which focused on the effect of the number of pump sources(single-wave, 3 waves, and 6 waves), interaction between pumps, fiber parameters(fiber length, fiber effective core area) and signal bandwidth on gain flatness. We optimized the wavelength and power of three waves(C band) and six waves(C+L band) utilizing multiple pumps combined with genetic algorithm. In backward pump, we respective obtained 0.50 d B in three waves(1408nm、1439nm、1473nm) and 0.94 d B in six waves(1418nm、1437nm、1447nm、1470nm、1494nm、1509nm), which were the flatness of Raman net gain.Finally, we designed a novel photonic crystal fiber with special structure, which used a single pump achieving the target of gain flatness of less than 1d B. Meanwhile, we investigated the possibility of photonic crystal fiber applied to compensate dispersion for long distance DWDM transmission system by analyzing the dispersion properties.