Research On High-power High-efficiency Fiber-coupled Semiconductor Laser

In the laser processing applications, laser with some characteristics such as high electro-optical conversion efficiency and low energy consumption, can reduce processing costs. While semiconductor lasers can satisfy this requirement. Semiconductor lasers are increasingly used in industrial processes because of its high electro-optical conversion efficiency, low energy consumption and long life. Fiber-coupled semiconductor laser achieve a flexible transmission, and it also can change laser into a circular uniformly distributed field with fiber’s homogenization. However, high power diode laser arrays have drawbacks of poor beam quality and lower single emitter optical power due to its unique structures, which restrict its applications. To solve this problem, this thesis study on beam shaping techniques to improve the quality of the semiconductor laser beam. And it use space beam combiner, a polarization beam combiner and wavelength combiner to increase the power and power density. Fiber coupling technology can realize flexible transmission of the laser.The objective of this thesis is to obtain a high-power, high beam quality and high-fiber coupling efficiency fiber-coupled diode laser. Through researching on fiber-coupled diode laser domestic and international, we conclude beam shaping technology and beam combiner technology. This paper focus on cm-bar, and its main contents and the results are as follows:(1) Firstly the application of high power diode lasers and the development status were described. Then the electrical and optical characteristics of high power diode laser is analyzed.(2) The wavelength of the CW diode laser bar is 976 nm, and five bars have been collimated by fast axis collimation lens. Then the beams are transformed, and collimated by slow axis collimation optics. Then all the beams are combined in space, and focused into a multimode fiber(400 μm core diameter, the numerical aperture is 0.22). Experimental results showed that the laser output from fiber could reach to 244.6 W, and the coupling-efficiency is more than 93.6 %.(3) A 500 W high-efficiency fiber-coupled module was designed. The technologies of beam shaping, spatial multiplexing and polarization multiplexing are employed to couple 10 bars into a laser beam. The module is developed with continuous wave power of 518 W, fiber-coupled efficiency of 95%.(4) Compact spatial multiplexing module was designed, and balanced beam quality in both directions of combined beam was achieved, four spatial multiplexing modules are employed in polarization multiplexing and wavelength multiplexing, the output beam was coupled into a fiber with core diameter 400μm, NA 0.22. The maximum fiber-coupled output power of 1070 W, the coupling efficiency of 96.3%, and the electro-optical conversion efficiency of 43% was achieved.