Fiber-coupled high brightness, high power diode laser for solid-state laser pumping and material processing

The theoretical modeling, design and prototype set-up of a fiber-coupled high brightness, high power diode laser system is presented in this paper. Based on the radiation characteristics from an individual diode laser bar, a system is created to maximize the coupling efficiency of the laser light into multimode fibers. Two diode laser stacks with six bars each, delivering 370 watts of initial laser power are polarization-multiplexed to achieve higher brightness. Each stack incorporates a beam transformation optic that transforms the oblong mode distribution of the diode laser stacks into symmetric beams. The multiplexed beam is passed through a common optical set-up to adapt the square mode distribution to the rotationally symmetric transmitted modes of the fiber. Fibers of different core diameter and numerical aperture with a silica core and a lower index doped silica cladding are used to transmit the laser beam. Based on experimental results, transfer efficiencies of up to 82% are reached for the laser system set-up including all optical elements.