Monolithic integration of high-Q wedge resonators with vertically coupled waveguides

Typical UHQ resonators, microspheres and microtoroids, lack the possibility of integration into lightwave circuits due to their planarity constrains. In this context, CMOS-compatible alternatives in the form of wedge resonators have been proposed. However, the mode retraction from the wedge cavity inhibits the possibility to side couple with integrated waveguides and therefore, halts the full integration within a planar lightwave circuit. In this work, we propose and demonstrate experimentally the complete integration of wedge resonators with vertically coupled dielectric bus waveguides. This coupling scheme permits to use arbitrary gaps, geometries and materials, enables simplified and precise control of the light injection into the cavity and opens the door to an industrial mass-fabrication of UHQ resonators.