Research On Laser Based On Ytterbium Doped Multimode Fiber

The gain medium of fiber lasers can be divided into single-mode fiber and multimode fiber.The pulse fiber lasers with single-mode fiber as the gain medium have been studied deeply.The monopulse energy and peak power output of this fiber laser is mainly limited by the narrow core diameter of the single-mode fiber,which requires additional amplifiers in many applications.In order to obtain higher monopulse energy and peak power,the most direct method is to enlarge the core area and use large mode field fiber.In this paper,Ytterbium-doped multimode fiber is used as the gain fiber,and the Ytterbium-doped multimode fiber laser is studied from both theoretical and experimental dimensions.The main research contents are as follows:1.The research progress of multimode gain fiber lasers at home and abroad in recent years is analyzed,and the current problems faced by multimode gain fiber lasers and the latest research hotspots based on multimode gain fiber lasers are proposed.2.The basic characteristics of multimode fiber are studied theoretically,including the theoretical analysis of the mode in the fiber,the difference between single-mode fiber and multimode fiber,as well as the nonlinear effects in multimode fiber,such as multimode interference effect and beam self-purification effect;Finally,the linear and nonlinear propagation of pulses in a multimode fiber are analyzed respectively according to the generalized multimode nonlinear Schrodinger equation.3.The energy level structure and spectral characteristics of ytterbium ion are analyzed;The different pump coupling modes and different cavity structures of fiber lasers are compared and analyzed;By establishing the rate equation of a ytterbium-doped double-clad fiber laser,the effect of the length,doping concentration and pump wavelength of the gain fiber on the output characteristics of the laser was simulated;Through theoretical analysis,the continuous wave laser output characteristics of ytterbium-doped multimode fiber laser are experimentally studied.4.A new saturable absorber with multimode-single mode fiber structure is proposed,and a ytterbium-doped multimode fiber laser based on all-fiber structure is built.By using two kinds of single mode fibers,the Q-switched operation of 1um band laser is realized respectively.In this paper,the experimental study on the output of continuous wave laser and Q-switched pulse laser of ytterbium doped multimode fiber laser provides a good reference value and promotes the further research on the realization of all-optical thinning of multimode gain fiber pulse laser.