Grazing-incidence-based hollow taper for infrared laser-to-fiber coupling

Based on grazing incidence, a simple uncoated hollow glass taper as an alte rnative technique for efficient infrared laser-to-fiber coupling is present ed. Because of the mutual action of the direct parallel laser excitation, t he mode-coupling process, and mode filtering, the hollow taper serves as a mode converter that transforms the highly multimode intensity distribution of the input laser emission into a high-quality smooth profile at the taper output. When an uncoated Pyrex-glass hollow taper is used for direct launc hing, without any intermediate focusing elements, of a powerful infrared Er :YAG laser emission (lambda = 2.94 mu m), we obtain high laser-to-taper (81 %), taper-to-fiber (96%), and total laser-to-fiber (78%) coupling efficienc ies. (C) 1999 American Institute of Physics. [S0003-6951(99)05320-6].