Research On The Performance Improvement Method Of Fiber Raman Amplifier

With the rapid development of the Internet and the increase in the number of users,bandwidth and capacity are the key issues that need to be solved for optical fiber communication systems.Fiber Raman amplifiers can be effectively applied to fiber optic communication systems to expand bandwidth and increase cap acity.The broadband flatness and high gain of fiber Raman amplifiers are important indicators of amplification performance.Therefore,this disseration studies the performance improvement method of fiber Raman amplifier in these two aspects,the main contents are as follows:(1)The principle of spontaneous Raman scattering and stimulated Raman scattering in optical fiber is studied,and the mathematical model of fiber Raman amplifier is established.The model is solved by the fourth-order Runge-Kutta method,and the effects of pump light parameters and fiber length on the Raman gain performance are analyzed.The results show that the pump power enhancement within a reasonable range will increase the gain value,the pump wavelength will hardly affect the shape of the gain curve,and the use of multi-wavelength pump light can better optimize the flatness of the amplifier.In order to avoid gain saturation due to too long fiber length,the fiber length should be selected reasonably.(2)Particle swarm optimization(PSO)was used to optimize the pump wavelength and power of the three-wavelength pumped fiber Raman amplifier,and a flat gain spectrum with an average gain of more than 18 d B and a flatness of less than1 d B in the 100 nm bandwidth range is obtained.The pump power versus fiber transmission length for using unoptimized and optimized pump light parameters are analyzed.The results show that the short-wavelength pump will transfer energy to the long-wavelength pump,and the power decays faster,and a larger power configuration for the short-wavelength pump is required.(3)The structure of the photonic crystal fiber is studied,and a photonic crystal fiber whose cladding is arranged with octagonal air holes is designed,and the fiber is numerically simulated by the full vector finite element method,the mode electric field distributions of undoped and germanium-doped photonic crystal fibers are obtained,the influence of air hole structure parameters on the effective mode field area and Raman gain coefficient is analyzed.The research shows that increasing the diameter of air holes,reducing the spacing of air holes and doping germanium to the core can improve the Raman gain coefficient of photonic crystal fibers.Finally,the pump wavelength and power of the designed photonic crystal fiber Raman amplifier are optimized by PSO,and the average gain is more than 25 d B and the flatness of less than 1.2 d B in the wavelength range of 100 nm signal light,the performance improvement of high gain and broadband flatness of fiber Raman amplifier is realized.