Highly efficient optical power transfer to whispering-gallery modes by useof a symmetrical dual-coupling configuration

We report that greater than 99.8% optical power transfer to whispering-gall ery modes was achieved in fused-silica microspheres by use of a dual-tapere d-fiber coupling method. The intrinsic cavity loss and the taper-to-sphere coupling coefficient are inferred from the experimental data. It is shown t hat the low intrinsic loss and the symmetrical dual-coupling structure are crucial for obtaining the high coupling efficiency. (C) 2000 Optical Societ y of America OCIS codes: 230.5750, 230.3990, 060.1810, 230.1150.