High power 976 nm fiber coupled module based on diode laser short bars

By taking twelve 976 nm diode laser short bars as emitting units, a high power fiber coupled diode laser module with several hundred watts was developed. Firstly, the laser beam emitting from each diode laser short bar was shaped by a Beam Transform System (BTS) and a cylindrical lens, by which fast and slow axis beam parameter products could be symmetrized and the divergence was similar in the two directions. Then, every six diode laser short bars made up a laser stack by spatial multiplexing technology in the perpendicular direction and the laser beams from the two laser stacks were combined by polarization multiplexing. Finally, optimized triplet lens focused laser beams into a single multimode fiber. Experimental results indicate that the continues wave optical power of the coupled diode laser module can reach to 418 W from the multimode fiber with a core diameter of 400 μm and numerical aperture of 0.22, and its brightness is 2.19 MW/(cm²·sr). Matlab software was also applied to research of the near field intensity distribution of the laser spot output from the fiber and the result shows that the intensity distribution is a top hat, which proves that the module can be used in numerous applications like the welding and hardening of metal. The optical spectrum was also measured to determine the heat dissipation of the device and the result shows that the center wavelength of the device has shifted 6.8 nm with the driving current increasing from 20 A to 50 A, and the spectral width is just 4.12 nm (Full Width at Half Maximum, FWHM) for the diode laser short bar at the current of 50 A, which indicates that the device is favorable to the heat dissipation and could reliably work for long time. As compared with other candidates, the designed module has higher conversion efficiency and fiber output powers, and is suitable for the fields of material process and laser pumping.