An Investigation On Gain Flatness Of Hybrid Raman-Erbium Doped Fiber Amplifier Based On Improved Particle Swarm Algorithm

Nowadays,the rapid development of the Internet has led to the rapid growth of communication data,which brings about the increasing demand for transmission capacity.The generation and development of wavelength division multiplexing(WDM)and dense wavelength division multiplexing(DWDM)have brought out a qualitative leap in thecapacity of optical fiber transmission systems.Correspondingly,it also makes people have a higher demand for the transmission capacity of the optical fiber amplifier in the optical fiber transmission network.Today,"extending available transmission bandwidth" method is considered as one of the most economical and effective way to expand the capacity of the system on the basis of the existing technical standards and transmission backbone.In optical fiber communication transmission system,the main communication band is of the C band(1530-1570nm)and L band(1570-1610nm).For C+L wideband it can be mainly amplified in the following two ways:1)the multi-pumped Raman fiber amplifier(RFA)(composed of several pump with different wavelengths);2)the erbium-doped fiber amplifier(EDFA)connected in series with the distributed RFA.Due to the combination of the high gain characteristics of erbium doped fiber amplifiers and the on line amplification characteristics of Raman fiber amplifiers,the latter has been widely studied and applied.In the design of broadband amplifier,the gain flatness of the amplifier is an important indicator to measure its performance,because the gain flatness is the guarantee of the transmission of the signals congruously and reposefully in the WDM system.Therefore,when designing an amplifier,it is necessary to ensure that the gain spectrum of the amplifier is relatively flat in the set of wavelengths or frequencies.The gain flatness is dependent on the pump parameters of Raman fiber amplifier and erbium-doped fiber amplifier and the characteristic parameters of the optical fiber.First of all,based on the theoretical model of the Raman fiber amplifier and Er doped fiber amplifier,the mathematical model of the Hybrid Raman erbium doped fiber amplifier is established and solved;Secondly,the influence factors of the gain spectrum flatness of the Hybrid Raman erbium doped fiber amplifier are analyzed and studied;Thirdly,based on the theoretical analysis,a reasonable Hybrid Raman erbium doped fiber amplifier is designed;Fourthly,the parameter setting problem of the Hybrid Raman fiber amplifier is transformed into a multi-objective optimization problem,and the optimization function of gain flatness is established;Then,the improved particle swarm optimization algorithm is put forward to optimize the gain flatness of the hybrid Raman-erbium doped fiber amplifier.In order to improve the convergence rate,the crossover and mutation,inspired by the genetic algorithm,and simulated annealing strategy are added to the particle swarm optimization;Finally,the fiber amplifiers with gains less than ldB and bandwidths of 1530-1580nm(50nm),1530?1600nm(70nm),1530?1635nm(105nm)are achieved by using a combination of a Raman fiber amplifier with one,two and three pumps respectively and an erbium-doped fiber amplifier with one pump.