Ultra-compact titanium dioxide micro-ring resonators with sub-10-μm radius for on-chip photonics

Microring resonators (MRRs) with ultracompact footprints are preferred for enhancing the light-matter interactions to benefit various applications. Here, ultracompact titanium dioxide (TiO2) MRRs with sub-10-μm radii are experimentally demonstrated. Thanks to the large refractive index of TiO2, the quality factors up to ∼7.9 × 104 and ∼4.4 × 104 are achieved for TiO2 MRRs with radii of 10 μm and 6 μm, respectively, which result in large nonlinear power enhancement factors (>113) and large Purcell factors (>56). The four-wave mixing (FWM) measurements indicate that, compared to the large MRR, the FWM conversion efficiency of the ultracompact TiO2 MRRs can be greatly improved (e.g., -25 dB versus -31 dB), a harbinger of significant superiorities. Demonstrations in this work provide more arguments for the TiO2 waveguides as a promising platform for various on-chip photonic devices.