Experimental Research On Tm³⁺-doped Fiber Laser

ABSTRACT: On behalf of the third generation of laser technology, fiber lasers are widely used in medical, military, optical communications, industrial processing and other fields with its advantages of good stability, high efficiency, low threshold, narrow line width, tunablity, compact and small structure, high performance-cost ratio, etc.. Thulium (Tm³⁺)-doped fiber laser can launch laser at the wavelength of 2μm, achieve 1.6-2.1μm tuning, and has the output of a number of other wavelengths through upconversion. It can also get better characters by co-doping with other elements (such as Ho). Especially for the silicon-based double-clad fiber laser, which has considerable advantages of pumping efficiency, Tm³⁺-doped fiber drawing and the compatibility of Tm³⁺-doped fiber and the ordinary SMF.Water molecules have a strong mid-infrared absorption peak at the radiate wavelength of 2μm which is in the range of eye-safe wavelength, as a result, Tm³⁺-doped fiber laser has important application prospects in eye safe, laser surgery, space optical communications, remote sensing, ultrafast optics, radar and other fields. In addition, high-power Tm³⁺-doped fiber laser operating at 2μm to be the wavelength of 2.5μm-12μm effective laser pump source in the future has got widespread concern.At present, the research of Tm³⁺-doped fiber laser at the wavelength of 2μm is focused on how to improve the slope efficiency, laser output power and beam quality. In this paper, through both theoretical and experimental studies, related performance of Tm³⁺-doped fiber and the laser is grasped, and it will lay a foundation for follow-up study of the performance optimization by the relevant parameters settings and for the future development of high-power and high-efficiency Tm³⁺-doped fiber laser. The main research work in this paper summarized as follows:1) The basic theory of the Tm³⁺-doped fiber laser is introduced. It mainly including: the basic structure and working principle, the basic characteristics and the energy level structure of Tm, the main pumping schemes of Tm³⁺-doped and Tm³⁺, Ho³⁺ co-doped fiber laser, pump-power and laser-power distribution along the fiber and the impacts of the important parameters on the output performance of Tm³⁺-doped fiber laser.2) The theoretical models of Tm³⁺-doped fiber laser corresponding to the three pumping schemes are established by the steady-state analysis method of the rate equations. According to the following experimental conditions and parameters, the ³H₆-³H₄ model is numerical simulated in Matlab simulation environment, and the pump -power and laser-power distribution along the fiber as well as the impacts of parameters of Tm³⁺-doped fiber length and doping concentration on the laser output performance are analyzed.3) The experimental research of Tm³⁺-doped fiber laser is showed. By the use of independently-developed components of Tm³⁺-doped fiber, coupler and fiber grating, also through the foundation and adjustment of experimental system, the output power, the light spectrum and the facula test of pump without or with coupling are carried on respectively, and then the fiber laser test with the Tm³⁺-doped fiber accessed is taken based on the above tests. After that, the experiment is taken again with the replaced pump source and the modified pump scheme for the difficulty of improving the overall coupling efficiency and obtaining the observable experimental phenomenon as he experimental conditions. After the experimental phenomenon observation and analysis, the issues which have not been solved or the research work which can be expanded is summarized and prospected finally.