High-Q miniaturized bound state in the continuum microcavities on thin-film lithium niobate towards efficient spatial...

We report the design, fabrication, and experimental characterization of high-quality factor (Q) photonic crystal microcavities on a thin-film lithium niobate (TFLN) that could potentially be utilized for spatial light modulation applications. Specifically, our design features inverted trapezoidal structures to address the realistic shapes in the fabrication and employs the transverse magnetic mode to incorporate the electro-optic effect of lithium niobate via its large r₃₃ coefficient. By leveraging the high-order topological charge of q = -2 carried by bound states in the continuum (BICs), the proposed microcavity reaches an ultra-high Q up to 1.2 × 10⁵, showing as a milestone record for the BIC cavities on the TFLN platform, thus paving the way to efficient spatial light EO modulation upon light radiation.