50 W passively cooled, fiber coupled diode laser at 976 nm for pumping fiber lasers using 100 μm fiber bundles

Abstract

Pumping fiber lasers is the driving force for the development of high brightness, mid power, passively cooled, fiber coupled diode lasers. We compare concepts for providing 50 W in a 100 micron fiber at the optimum fiber laser pump wavelength of 976 nm. The set up is experimentally demonstrated and compared to the optical analysis. Three basic diode laser concepts are included into this comparison: single emitters, high density emitter arrays and low density emitter arrays on bars. Low density stacking in the horizontal direction with increasing the filling factor by a microlens array is the first concept. For this concept two diode bars with low filling factor are fast and slow axis collimated. Beam transformation, shaping and focusing are similar to the second concept. In the second concept a diode laser array with high filling factor is regarded. An 800 μm diode laser bar consists of an array of four or five emitters. Two bars are polarization coupled and collimated with single lenses. Beam symmetrization is performed by the well known step mirror. A simple anamorphotic optic enables beam shaping and fiber coupling. The third one, single emitters, represents optical beam combining of laser diodes that are high density stacked in the vertical direction. Five emitters are placed in an optical stack, each one collimated with its own lens. Two optical stacks are polarization coupled and focused on the fiber end. The three concepts are compared in terms of power efficiency and complexity, and the results of prototype systems are presented.