  Tapered silica fibers are often used to rapidly probe the optical properties
of micro-resonators. However, their low refractive index precludes
phase-matching when coupling to high-index micro-resonators, reducing
efficiency. Here we demonstrate efficient optical coupling from tapered fibers
to high-index micro-resonators by loading the fibers with an ancillary
adiabatic waveguide-coupler fabricated via angled-etching. We demonstrate
greatly enhanced coupling to a silicon multimode micro-resonator when compared
to coupling via the bare fiber only. Signatures of resonator optical
bistability are observed at high powers. This scheme can be applied to
resonators of any size and material, increasing the functional scope of fiber
coupling.
