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Research On Adaptively Convert Non-polarization Maintaining Fiber Laser To Polarization Maintaining One

Posted on:2016-11-20Degree:MasterType:Thesis
Country:ChinaCandidate:S H DongFull Text:PDF
GTID:2348330536967657Subject:Optical Engineering
Abstract/Summary:PDF Full Text Request
High power,high brightness,linearly polarized fiber laser are attractive for a lot of potential applications,such as nonlinear frequency conversion,detecting gravitational wave,laser communication,long distance sensing,beam combining,and so on.Up to now,linearly polarized fiber laser can be produced based on polarization maintaining(PM)fiber and polarization related devices,but Stimulated Brillouin Scattering,Stimulated Raman Scattering,mode instability threshold is lower than non-polarization maintaining(NPM)fiber laser at equal condition because of the special structure in the fiber.What’s more,the polarization related devices is costly and the process of fabricating is complicated.Also the process of cutting,splicing and heat managemeng is harder than NPM fiber.So the output power of PM fiber laser is lower than NPM fiber laser.In this paper,adaptively polarization convertion technique which can adaptively convert a completely NPM laser to PM laser with high polarization extinction ratiois presented for improving the power of linearly polarized fiber laser.polarization convertion technology based on polarization controller and polarization phase locking has been studied theoretically and experimentally.The main contents includes:Firstly,the paper begins with research status and the limiting factor of the NPM fiber laser,and illustrates the convertion of NPM fiber laser to PM laserwith high power is feasible.Then,reviewing the achievements in field of polarization control and summarizing the current state of polarization control technology in the field of sensing,communication and beam combining.Secondly,the system of polarization convertion based on the polarization convertion is designed,then introduces the basic structure and principle of the polarization convertion system.The theoretical model of adoptively polarization convertionbased on the polarization controller is built up.By large quantity of numericalsimulation,the paper comparatively analyzes some factors’ impacts on the convertion effect based on stochastic parallel gradient descent,such as gain coefficient and disturbance precision parameters of control algorithm,the precision and the step gain of the polarization controller,and the stability of the fiber laser.The results reveal that through adjusting stochastic parallel gradient descent algorithm and polarization controller parameters can further improve system stability and higher polarization extinction ratio.Based on the theoretical analysis,the adoptively polarization convertion system based on the polarization controller is set up,and the control program is compiled.Experimental study with seed at low power as well as with amplifier at high power are conducted.The experimental results reveal that,in both systems,polarization convertion system can makethe NPM laser convert to linearly one,also the system can convert the NPM laser to linearly polarization laser with any angle.Then,the system of polarization convertion based on the polarization phase lockong is designed,then introduces the basic structure and principle of the polarization convertion system.The theoretical model of adoptively polarization convertion based on the polarization phase locking is built up,different kinds of factors which impact on the convertion effect and on the out polarization extinction ration are analyzed,such as overlap error,tilt error,residual phase locking error and the difference between two combing beam power.The results show that,overlap error and tilt can effect the effect conversion efficiency by leaking light at the combing location,also the overlap effect the out polarization extinction ratio,but the tilt error dosen’t.The difference between two combining beam power can be neglect if the phase residual error is small,so the phase locking residual error is the key factor.Based on the theoretical analysis,the adoptively polarization convertion system based on the polarization phase locking is set up,and experimental study with all fiber structure as well as with space structure are conducted.The system with all fiber structure can improve the output polarization extinction ratio from 5dB to17.2dB,and the system with space structure can realize linearly polarized laser with 93.5% degree of polarization.In the last part,the scheme of convert nonpolarization maintaining fiber laser with broad spectrum based to linearly polarized laser is proposed,and the feasibility of convertion system with broad spectrum light source based on polarization locking system is analysed,then design the structure diagram with solidworks.
Keywords/Search Tags:linearly polarized laser, fiber laser, non-polarization maintaining fiber amplifier, polarization convertion, stochastic parallel gradient descent
PDF Full Text Request
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