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].