Amorphous metal oxide mixtures for high-Q integrated nonlinear photonics

TL;DR

This paper demonstrates how mixing titania and tantala in amorphous metal oxide films enhances integrated nonlinear photonics by reducing defects and optical losses, enabling high-Q microresonators for frequency combs.

Contribution

It introduces a novel amorphous titania-tantala mixture as a customizable material for integrated photonics with improved optical properties.

Findings

Achieved microresonator Q factor up to 10^7.

Reduced optical absorption by a factor of 1.7.

Demonstrated low-loss, high-index amorphous metal oxide films.

Abstract

Choice of material is ubiquitous in integrated photonics to design device properties, whereas changing material composition is much less common. With phase matching as an additional objective, constraints in depositing and patterning thin films limit the use of integrated nonlinear photonics to only select materials. Here, we explore an amorphous metal oxide mixture of titania (TiO2) and tantala (Ta2O5) in which material composition is a tool to enhance and customize photonics properties. In particular, the inclusion of titania reduces the oxygen-defect density in a tantala film, while maintaining a comparable Kerr nonlinear index. With ion-beam sputtering at room temperature, we deposit a thick, ultralow-loss titania-tantala film, and we nanopattern it to create microresonator frequency combs. Titania-tantala microresonators offer lower loss, higher index of refraction, and reduced optical absorption and photorefractive effects. Specifically, the titania-tantala mixture enables microresonator quality factor up to $10^7$ and a direct factor of 1.7 reduction in optical absorption. Our work demonstrates that composition in metal-oxide mixtures is a design parameter alongside the nanofabrication process and photonics design for integrated nonlinear photonics.