Research On The Gain Spectrum Flattening Of Multi-Wavelength Hybrid Optical Amplifier

With the development of long-distance unrepeatered optical fiber communication systems, the requirements on the performance of optical fiber amplifier are increasing. Thus, hybrid optical amplifier has begun to get more and more attention. Hybrid optical fiber amplifier in this paper combine a fiber Raman amplifier (FRA) with an Erbium-doped fiber amplifier (EDFA) or a fiber optical parametric amplifier (FOPA) in order to achieve a flat gain spectrum with ultra-bandwidth. In long-distance optical fiber communication system, in order to achieve the transmission of multiple signals, we need to guarantee the flatness of the gain spectrum of the optical amplifier. In this paper, the gain-flattening of hybrid multi-wavelength optical amplifiers has been studied by way of modeling and simulation. The gain spectrum flatness has been optimized by differential evolution (DE) algorithm. The main work and achievements of this paper are as follows:(1) The FRA’s, EDFA’s and FOPA’s theories, structures and classifications are described. And the main factors are explored by modeling and simulation, which influence the gain spectrum of these three kinds of fiber amplifier. All the work above provides a theoretical basis for the research on the gain spectrum optimizing.(2) The theory of DE algorithm is introduced, which is used to optimize the gain spectrum. The way to optimize the gain spectrum by DE is studied and the flowchart is drawn. In this way, we optimize the gain spectrum of FRA with two pumps. The bandwidth of the optimized gain spectrum is28nm and the fluctuation of it is1.6dB. By changing the parameters, DE can be used to optimize the gain spectrum of hybrid optical amplifier with more pumps.(3) The simulation model of second-order FRA is set up. Different collocations of first and second order pumps’power are studied by observing power distribution of the first-order pump, second-order pump and signal. The optimal collocation is finally obtained, laying a theoretical foundation for optimizing the gain spectrum of the second order pumped FRA/FOPA hybrid optical amplifier.(4) The simulation models of multi-pumped FRA/EDFA hybrid optical amplifier and second order pumped FRA/FOPA hybrid optical amplifier are set up. Based on DE algorithm, the gain spectrums of these two hybrid optical amplifier are optimized. The gain bandwidth of the spectrum is93nm. The gain fluctuations of these two spectrums are1.4dB and1.2dB respectively. The feasibility of this optimization for hybrid optical amplifier’s gain spectrum is demonstrated.