Optical microsphere resonators: optimal coupling to high-Q whispering-gallery modes

A general model is presented for coupling of high-Q whispering-gallery mode s in optical microsphere resonators with coupler devices that possess a dis crete and continuous spectrum of propagating modes. By contrast to conventi onal high-Q optical cavities, in microspheres the independence of high intr insic quality-factor and controllable parameters of coupling via an evanesc ent field offer a variety of regimes similar to those that are already avai lable in rf devices. The theory is applied to data reported earlier on diff erent types of couplers to microsphere resonators and is complemented by th e experimental demonstration of enhanced coupling efficiency (similar to 80 %) and variable loading regimes with Q > 10(8) fused-silica microspheres. ( C) 1998 Optical Society of America [S0740-3224(98)01412-X] OCIS codes: 270. 0270, 290.4020, 250.5300, 060.1660.