HfO₂-based platform for high-index-contrast visible and UV integrated photonics

Ultraviolet and visible integrated photonics enable applications in quantum information, sensing, and spectroscopy, among others. Few materials support low-loss photonics into the UV, and the relatively low refractive index of known depositable materials limits the achievable functionality. Here, we present a high-index integrated photonics platform based on HfO 2 and Al 2 O 3 composites deposited via atomic layer deposition (ALD) with low loss in the visible and near UV. We show that Al 2 O 3 incorporation dramatically decreases bulk loss compared to pure HfO 2 , consistent with inhibited crystallization due to the admixture of Al 2 O 3 . Composites exhibit refractive index n following the average of that of HfO 2 and Al 2 O 3 , weighted by the HfO 2 fractional composition x . At λ = 375 nm, composites with x = 0.67 exhibit n = 2.01, preserving most of HfO 2 ’s significantly higher index, and 3.8(7) dB/cm material loss. We further present fully etched and cladded waveguides, grating couplers, and ring resonators, realizing a single-mode waveguide loss of 0.25(2) dB/cm inferred from resonators of 2.6 million intrinsic quality factor at λ = 729 nm, 2.6(2) dB/cm at λ = 405 nm, and 7.7(6) dB/cm at λ = 375 nm. We measure the composite’s thermo-optic coefficient (TOC) to be 2.44(3) × 10 −5 RIU/°C near λ = 397 nm. This work establishes (HfO 2 ) x (Al 2 O 3 ) 1− x composites as a platform amenable to integration for low-loss, high-index photonics spanning the UV to NIR.