Study On Multiwavelength Erbium-doped Fiber Laser Based On Nonlinear Effects

Dense wavelength division multiplexing can improve the rate and the capacity of fiber-optic communication effectively, in which the key technique is to generate the multiwavelength signals. Tranditionally, the semiconductor lasers array can generate multiwavelength signals, but this lasers array is considerably large, complicated and expensive. Compared with the lasers array, the erbium-doped fiber laser has a simple constructure, small volume, light weight and low cost to generate the multiwavelength signals, and is considered as the most potential laser source of multiwavelength in the system of fiber-optic communication. However, there is a severe mode competition in the erbium-doped fiber laser, which limits the multiwavlegth output of fiber laser. To solve this problem, the dissertation centres on nonlinear effects which can mitigate the mode competition, and then studies the multiwavelength erbium-doped fiber lasers which are based on the stimulated Brillouin scattering, four-wave mixing, the combination of stimulated Brillouin scattering and nonlinear optical loop mirror, and the combination of stimulated Brillouin scattering and four-wave mixing, respectively.The dissertation firstly builds up a theoretical model of a multiwavelength erbium-doped fiber laser which is based on the stimulated Brillouin scattering by combining the rate equations of erbium-doped fiber with the analytical solutions of coupled equations of stimulated Brillouin scattering. Using this model, the impacts of the erbium-doped fiber pump power, Brillouin pump power and wavelength on the number of output wavelength from the multiwavelength erbium-doped fiber laser have been studied numerically. In addition, the output characteristics of the multiwavelength erbium-doped fiber laser have been verified experimentally. The numerical results are in well agreement with the experimental results.Secondly, by utilizing two seeding signals, a method to freely adjust the wavelength spacing of a multiwavelength erbium-doped fiber laser based on fourwave mixing has been proposed. The dependences of the number of output wavelength on the wavelengths, powers, wavelength spacing of the two seeding signals, and erbium-doped fiber pump power have been observed experimentally and studied numerically. The experimental observations are firmly supported by the numerical results.Thirdly, the dissertation has proposed a multiwavelength erbium-doped fiber laser which is based on the combination of stimulated Brillouin scattering and nonlinear optical loop mirror to improve the amplitude flatness. And then, a- III- theoretical model of this multiwavelength erbium-doped fiber laser has been built up. By using the model, the influences of the erbium-doped fiber pump power, the angle of quarter-wave plate and the input polarization state on the number of output wavelength and amplitude flatness of such fiber laser have been studied numerically. The experimental studies have been taken to verify the numerical results. The numerical results are favorably compared with the experimental results.Lastly, a multiwavelength erbium-doped fiber laser which is based on the combination of stimulated Brillouin scattering and four-wave mixing has been proposed. The coupled equations describing the power and phase evolutions caused by these two nonlinear effects have been derived by utilizing the nonlinear polarization equation which takes into account the effects of stimulated Brillouin scattering and four-wave mixing. With these equations, a theoretical model of this multiwavelength erbium-doped fiber laser has been built up. The impacts of erbium-doped fiber pump power and Brillouin pump power on the output number of this fiber laser have been studied experimentally and numerically.The results of this work are instructive to improve the theoretical model of the multiwavelength erbium-doped fiber laser based on these nonlinear effects, optimize the design of such a laser, and promote its pratical applications in the optical communication system.