Research On Erbium Doped Fiber Ring Laser With Narrow Line Width

Due to the relatively wide linewidths,the poor monochromatic,limited range of frequency modulationand,the poor compatibility with optical communication networks,the traditional semiconductor lasers can not increasingly adapt to the demands of modern optical communications and other fields.Therefore,fiber lasers with ultra-narrow linewidth have gradually become the research focus.Meanwhile,fiber lasers are becoming the mainstream in laser marketcomprehensively and progressivelyby replacing the semiconductor lasers.In recent years,scientific research has made remarkable achievements on ultra narrow-linewidth fiber laser.A variety of effective methods that include narrow-band filters,saturable absorbers,novel cavity structures and nonlinear effects are used to obtain the narrow-linewidth with k Hz order of magnitude,even ultra-narrow linewidth.In this paper,a method that obtains the stable single-longitudinal mode with narrow linewidth in the erbium-doped fiber ring laser is proved.Firstly,the four aspects of cavity structure,narrowband filter,saturable absorber and nonlinear effect,single-longitudinal mode output are analyzed.A comprehensive summary that the method of narrow-linewidth single longitudinal mode output of fiber lasers is given.Then,the laser output characteristics are simulated according to the theory,Moreover,the characteristics of pumping threshold power,output power,and output slope efficiency is analyzed and impacted when the doping concentration of erbium-doped fiber,the length of erbium-doped fiber,the cavity loss and the external filter reflectivity are changed.The experimental system is built based on previous work.Using three Mach-Zehnder filters and one fiber Bragg grating in the annular cavity of the laser,the comb transmission spectra of three Mach-Zehnder filters are superposed in the reflection bandwidth of the fiber Bragg grating.Accroding to the vernier principle,the single-mode oscillation output is achieved whenonly one single pulse is coincidented.And the unpumped erbium-doped fiber is used as a saturable absorber to achieve a stable single mode oscillation output by suppressing other modes oscillation.Finally,The characteristics and advantages of fiber lasers are discussed by this paper.Then the application fields and research directions of fiber lasers are put foward base on these advantages.The research status at home and abroad are introduced,The own research significance and directions are put forward.Then the factors that affect the laser linewidth and the method of measuring the linewidth of lasers are analyzed and discussed by delayed self-heterodyne experiment.The delayed self-heterodyne method is improved.The experiment platform is designed and built to measure the linewidth of erbium-doped fiber ring laser.Viogt's fitting is performed on the Keysight N9000 A spectrometer's data to obtain the Lorentz linewidth of the fiber laser.