Microsphere whispering gallery mode coupler based on a S-bend waveguide structure

Resonant cavities are key components in photonic circuits which provide feedback, wavelength selectivity and energy storage. Microspheres^[1], in particular, support ultrahigh-Q whispering gallery modes (WGMs) that may lead to large delays and enhanced optical nonlinearity within several tens of microns length scale. Most of the demonstrated devices to date utilize a tapered fiber to excite the WGMs, however this coupling architecture not only lacks of rigid stability but inhibits dense integration to form more sophisticated planar lightwave circuits (PLCs). Here we report an alternative approach based on evanescent coupling between the microsphere and a S-bend waveguide structure. This approach provides better mechanical stability and is capable for on-chip integration.