A high-Q lithium niobate microresonator integrated with a silicon nitride waveguide in vertical configuration for evanescent light coupling

We demonstrate hybrid integration of a lithium niobate microring resonator with a silicon nitride waveguide in vertical configuration to achieve efficient light coupling. The microring resonator is fabricated on a lithium niobate on insulator (LNOI) substrate using photolithography assisted chemo-mechanical etching (PLACE). A fused silica cladding layer is added on the LNOI ring resonator. The silicon nitride waveguide embedded in the fused silica layer is fabricated by producing a trench in the fused silica using focused ion beam (FIB) etching followed by deposition of silicon nitride into the trench to form the embedded waveguide. The FIB etching ensures the positioning accuracy between the waveguide and the ring resonator. We achieve Q-factors as high as 1.4´107 can in the integrated device.