High Power Random Fiber Laser And Its Spectral Manipulation Property

Random fiber lasers operate through the passive gain induced by stimulated Raman scattering,and the random distributed feedback provided by Rayleigh scattering in the long-distance passive fiber.Unlike the traditional fiber oscillators,random fiber lasers do not need the cavity structure to provide point feedback,and thanks to the advantages of simple structure,high temporal stability and high conversion efficiency,random fiber lasers have been applied to a variety of fields such as communication,sensing and optical imaging.In this thesis,based on the reported average power balance model,the numerical simulation on the main factors that affect the power scaling of random fiber lasers is carried out.The longitudinal power distribution and the output power characteristics of a half-opened random fiber laser are simulated.And the feasibility of employing low power handling devices to realize the high power spectral manipulation is predicted in theory.In order to improve the output power of random fiber lasers,new method such as controlling the time-domain characteristics of pumping,or manipulating the polarization dependent Raman gain,has been proposed.By adjusting the polarization dependent Raman gain,the output power of a linearly polarized random fiber laser has been increased by ～49.7%.Pumped by the superfluorescent fiber source with high temporal stability,a random fiber laser with output power of more than 102 W and spectral purity of close to 100% is obtained.The simulation results show that high power output over 400 W can be achieved by shortening the length of the passive fiber.In order to meet the needs of spectral manipulation,the tunability and wavelength expansion of high power random fiber lasers are studied experimentally.By adjusting the reflection spectrum of the point feedback,a tunable random fiber laser with a wavelength tuning range of 1095-1115 nm and a linewidth tuning range of 0.6-2 nm is realized for the first time.Furthermore,the wavelength and linewidth of a 100-watt-level random fiber laser can be tuned simultaneously by using a watt-level device for spectral control.Finally,based on the special fiber with distinctive Raman gain spectrum,the advantages of high-order cascaded random fiber laser in wavelength extension are studied.A random fiber laser at 1308 nm with output power of 32.2 W and spectral purity of ～98% is demonstrated.