Study On High Power Dual-cavity Multi-wavelength Fiber Laser

Stimulated Raman scattering is one of the dominant limitations of power scaling in continuous-wave fiber lasers.It is expected to increase the SRS threshold by utilizing multi-wavelength laser as seed in lasers and amplifiers,which can boost the output power.The hybrid-gain scheme,based on dual-cavity or multi-cavity structure,is a feasible solution to realize multi-wavelength laser output.In order to analyze the characteristics of multi-wavelength laser output in dual-cavity hybrid-gain scheme based on Yb gain and Raman gain,theoretical and experimental study have been carried on in this paper.Firstly,the developments and limitations of power enhancing in Ytterbium-doped fiber lasers at 1 μm waveband is reviewed.The feasibility of suppressing SRS by using multi-wavelength seed is analyzed.Several kinds of Yb-Raman hybrid-gain fiber lasers using multi-wavelength seed are introduced with their benefits and drawbacks being summarized.Secondly,the steady-state model of hybrid-gain fiber laser is established based on Yb gain and Raman gain.Main factors which influence the characteristics of output power are analyzed,including fiber length,reflectivity of fiber Bragg gratings,the ratio of diameters of core and inner-cladding and pump directions.Results show that fiber length influences the output power ratio at different wavelengths.The reflectivity of output coupler FBGs has little influence on output power.The laser power increases by improving the ratio of diameters of core and inner-cladding and forward pumping the fiber laser.Thirdly,the dual-cavity hybrid-gain fiber laser based on Yb gain and Raman gain is designed,which realizes 110.8W output power at 1150 nm.Study on the output characteristics of this fiber laser is carried on by changing the reflectivity of FBGs and fiber length.Hybrid-gain Yb-doped fiber laser emitting at 1080 nm and 1120 nm is demonstrated.The difference between its output characteristics and that of the 1150 nm fiber laser is discussed by comparing factors such as wavelengths,ratio of diameters of core and inner-cladding and fiber length.Hybrid-gain pulsed 1150 nm fiber lasers based on half cavity and laser cavity structure are also demonstrated.Fourthly,the numerical simulation and experimental study of amplification of single-wavelength seed and multi-wavelength seed are carried on to analysis the ability of power scaling in amplifiers.By adding a small quantity of Raman light,the SRS threshold has an obvious increase,which indicates more potential in power scaling.