Study On Properties Of Gain Flatness Of Broadband Fiber Raman Amplifier

Fiber Raman amplifier (FRA) is full communication windows amplifier based on the fiber. The importance of FRA appears gradually when long distance transmission system of DWDM adopted largely because of its excellent features of distributed amplification, high gain, high output power, quick response speed, small non-linear influence, high signal noise ratio, et al.The paper research features of gain ripple utilized theory analysis and experiment measure method. Firstly, after optimize the coupling differential equation of multi-wave pumped fiber Raman amplifier, the genetic algorithm is used to approach the flatness of signal gain and noise spectra simultaneously. The calculated results show that spectra of noise are flatter under the case of bidirectional pump than backward pump in C and L wave band. A fiber Raman amplifier pumped by 10-wavelength source is optimized and the gain ripple less than ldB in 100-channel DWDM system of 80nm gain spectra is obtained within 400s through many tests. The results of elapsed time of optimization and precision are optimized state in our country. Secondly, the nonlinear relations of gain bandwidth, gain flatness to number of pumping wave in broad-band fiber Raman amplifier are researched by using neural network technology for the first time. Utilized its peculiarity of good approaching ability to an unknown function with given input data and corresponding output data, a double layer back propagation neural network is formed. The simulation results show that under the condition of gain flatness to be determined the lowest bounds of number of pumping waves exists at different gain bandwidth.Finally, the experiment verified exactness and stability of average power analysis method and the genetic algorithm. Proved to the same group's input signal under different pump power condition, on-off gain is increased linearly with accordance to pump power increased linearly when pump power is small. Namely fiber Raman amplifier is not apt to the saturation under this situation. The saturation gain is gained highly. But as pump power increased at exceeding 200mW, on-off gain increased non-linearly. The saturation phenomenon has appeared. For two...