  Microresonator devices which posses ultra-high quality factors are essential
for fundamental investigations and applications. Microsphere and microtoroid
resonators support remarkably high Q's at optical frequencies, while planarity
constrains preclude their integration into functional lightwave circuits.
Conventional semiconductor processing can also be used to realize
ultra-high-Q's with planar wedge-resonators. Still, their full integration with
side-coupled dielectric waveguides remains an issue. Here we show the full
monolithic integration of a wedge-resonator/waveguide vertically-coupled system
on a silicon chip. In this approach the cavity and the waveguide lay in
different planes. This permits to realize the shallow-angle wedge while the
waveguide remains intact, allowing therefore to engineer a coupling of
arbitrary strength between these two. The precise size-control and the
robustness against post-processing operation due to its monolithic integration
makes this system a prominent platform for industrial-scale integration of
ultra-high-Q devices into planar lightwave chips.
