MICROLENSES FOR COUPLING OPTICAL FIBERS TO ELLIPTICAL LIGHT BEAMS

An asymmetric hyperbolic microlens on the end of a single-mode optical fiber enhances the fiber's coupling to elliptical laser beams. The lense s, with controlled eccentricity ratios, are made by micromachining the end of the fiber with a pulsed CO2 laser as the fiber is directed, preferably by computer control, abo ut the focused laser beam. Coupling effiencies of 90 percent (-0.75 dB) have been realized with single transverse mode transverse mode lasers at a wavelength of 0 .98 .mu.m having an approximately 3 to 1 beam ellipticity. With multimode lasers at 1,48 .mu.m havin g similar elliptical beams, the asymmetric lenses demonstrate an almost 2 dB incre ase in coupling efficiency over symmetric hyperbolic microlenses. Such lasers are useful to pump erbium-doped fiber amplifiers. About 120 mw was coupled from such a laser into single-mode fiber.