In recent years, high-power erbium-doped fiber lasers have been widely used in industrial, medical, scientific research, and military fields due to their high power, high reliability, and high beam quality. However, with the gradual increase of output power, nonlinear effects and thermal damage have become important factors restricting the development of fiber lasers. They reduced the beam quality of fiber lasers and it was difficult to further increase the output power, which hindered the further development of fiber lasers. Therefore, research on large-mode-field, high-doped, high-beam-quality optical fibers is an urgent problem in the development of fiber lasers.
Under the guidance of Yang Luyun, Li Jinyan, Dai Nengli, PhD student Ph.D. students from Wuhan Optoelectronics National Laboratory's Fiber Laser Technology Team (FLTG) and others, Yb3 + quartz glass core rods were prepared using borosilicate glass phase separation technology. , And further prepare a large core diameter double-clad fiber. The refractive index distribution, Yb3 + absorption, and background loss of this fiber were experimentally tested and its laser performance was demonstrated. Studies have shown that the core diameter of this fiber is 30 microns and the cladding is 400 microns; the refractive index distribution of the core is uniform and the numerical aperture is about 0.09; the absorption of Yb3 + at 976 nm is 5.5 dB / m, and the background loss is 0.02 dB / m; Through the water removal process, the hydroxyl content in the fiber was reduced to 1.06 ppm; the fiber achieved a laser output of 1071 nm under the pump of a 976 nm semiconductor laser, the slope efficiency reached 72.8%, and the fiber length was 2.3 m. The research results show that this method has great potential for preparing active fibers with large core diameter and high doping and complex core structure.
Successful development of new double-clad active fiber
With the development of fiber lasers toward higher power, shorter pulses, and higher beam quality, the mode field area of traditional active double-clad fibers has become a bottleneck in their development. Active fiber based on microstructured fiber technology provides effective ideas for increasing the mode field area.
Professor Li Jinyan and PhD student Wei Huifeng from Wuhan Optoelectronics National Laboratory's fiber laser technology team developed a new all-solid double-clad active optical fiber. This fiber design uses PDC (passively doped) that can precisely control the effective refractive index of the cladding. (cladding) technology, which greatly meets the requirements of ultra-large mode field fiber for precise control of refractive index. In this study, it has been confirmed that the refractive index change as low as 1 × 10-5 can be achieved by adjusting the filling rate of the cladding doped lattice and the cladding doping concentration. In the experiment, the same preform was used to draw optical fibers with diameters of 50um and 127um, respectively. Tests show that 50um fiber can achieve stable single-mode operation at 1064nm, and 127um fiber can also achieve single-mode output with mode optimization technology. This optical fiber is an all-solid optical fiber and does not contain any air holes. Therefore, its drawing process is simple, and it brings great convenience in practical use, such as splicing, end-face polishing, and coupler manufacturing. Therefore, this type of fiber is very suitable for practical applications of high-power, high-energy fiber lasers.