Q-enhanced racetrack micro-resonators

TL;DR

This paper introduces a geometry modification strategy for racetrack microresonators that significantly enhances their quality factor by reducing radiation losses, without compromising their coupling versatility, especially for silicon nitride integrated photonics.

Contribution

The paper presents a novel Q-enhancement method for racetrack microresonators through geometric modifications that reduce radiation losses while maintaining coupling capabilities.

Findings

Over 100% improvement in Q factor for Si3N4/SiO2 resonators.

Effective reduction of radiation losses at junctions and curved sections.

Designs compatible with large-scale photonic integration.

Abstract

A $Q$-enhancement strategy for racetrack microresonators is put forward. The design is based on the modification of the resonator geometry in order to mitigate the two main sources of radiation loss in the presence of curved waveguides: the discontinuities at the junctions between straight waveguides and the bent sections, and the continuous loss at the curved waveguide sectors. At the same time, the modifications of the geometry do not affect the versatility of coupling of racetrack resonators in integrated optical circuits, which is their main advantage over ring microresonators. The proposal is applied to the design of high-$Q$ racetrack resonators for the silicon nitride CMOS-compatible platform having bent radii amenable for large-scale photonic integration. Numerical calculations show over $100\%$ improvement of the $Q$ factor in $\text{Si}_3\text{N}_4/\text{SiO}_2$ resonators.