Research On ~2.1 μm All-Fiber Laser Based On Holmium-doped Fluorotellurite Glass Fiber

The 2.1μm wavelength band laser is located in the high-transmission atmospheric window and gas characteristic absorption frequency band,thus having important and clear application prospects in fields such as remote sensing,laser medical treatment,material processing,and military confrontation.Compared with other laser generation methods such as solid-state and gas lasers,all-fiber lasers have the advantages of high integration,simple structure,high conversion efficiency,and good beam quality,and have become one of the mainstream laser generation technologies.Silica fiber has achieved great success in near-infrared wavelength laser output due to its excellent mechanical properties and ultra-low transmission loss.However,its narrow infrared transmission window and low rare earth doping concentration limit its application in the mid-infrared wavelength fiber laser field.This thesis aims to develop an all-fiber,high-efficiency 2.1μm wavelength laser using fluorotellurite glass fiber with a wide infrared transmission window and low phonon energy and to solve key technical problems such as fluorotellurite glass fiber grating writing and heterogeneous fiber fusion between silica and fluorotellurite glass fibers,ultimately achieving an all-fiber,high-efficiency,and stable 2.1μm wavelength laser output.High-reflectivity fiber Bragg gratings were written using femtosecond laser direct writing,and asymmetric fiber fusion technology was used to fusion splice fluorotellurite glass fiber and single-mode silica fiber,and finally,the silica fiber was connected to the pump source to construct an all-fiber laser.The main contents of this thesis are as follows:1.Ho³⁺-doped fluorotellurite glass fibers were fabricated by the rod-in-tube method with a loss of 0.8 d B/m.A femtosecond laser with a central wavelength of 800 nm was used to inscribe fiber Bragg gratings in the home-made fluorotellurite glass fibers using a line-by-line direct writing technique.The effects of femtosecond laser pulse energy,grating order,and grating length on the spectral characteristics of the fiber Bragg gratings were investigated.The experimental results showed that a three-order fiber Bragg grating with a length of 10 mm and a high reflectivity of 98%at a central wavelength of 2075 nm was fabricated using a single pulse energy of 0.30μJ.2.Low-loss and high-strength fusion splicing between the home-made fluorotellurite glass fibers and single-mode silica fibers was achieved using an asymmetric fiber fusion splicing technique.The quality of the fusion splice was optimized by adjusting the fusion splicing power and offset.The fusion splicing loss was measured by an all-fiber testing system,and the lowest loss was 0.08 d B,with a tension monitoring value of 269 g.3.A fiber Bragg grating with a reflectivity of 98%was used as a laser cavity mirror,and a28 cm home-made Ho³⁺-doped fluorotellurite glass fiber was used as the laser medium.The gain fiber and pump source were connected by heterogeneous fiber fusion splicing technology,and a 1976 nm thulium-doped silica fiber laser was used as the pump source for in-band pumping.A maximum unsaturated output power of 7.33 W was achieved with a slope efficiency of 93.4%.The all-fiber laser based on Ho³⁺-doped fluorotellurite glass fibers at～2.1μm has the advantages of a compact structure and high laser output efficiency,which lays a theoretical and technical foundation for the development of highly integrated all-fiber mid-infrared lasers.