# Thermo-refractive noise in silicon nitride microresonators

## TL;DR

This paper characterizes thermo-refractive noise in silicon nitride microresonators, demonstrating it as the dominant thermal noise source and providing quantitative bounds to inform future photonic device design.

## Contribution

It provides the first detailed measurement and theoretical validation of thermo-refractive noise in silicon nitride microresonators, highlighting its significance.

## Key findings

- Thermo-refractive noise dominates thermal noise in the platform.
- Measurements agree with theoretical models and simulations.
- Quantitative bounds on thermal noise scaling and magnitude.

## Abstract

Thermodynamic noise places a fundamental limit on the frequency stability of dielectric optical resonators. Here, we present the characterization of thermo-refractive noise in photonic-chip-based silicon nitride microresonators and show that thermo-refractive noise is the dominant thermal noise source in the platform. We employed balanced homodyne detection to measure the thermo-refractive noise spectrum of microresonators of different diameters. The measurements are in good agreement with theoretical models and finite element method simulations. Our characterization sets quantitative bounds on the scaling and absolute magnitude of thermal noise in photonic chip-based microresonators. An improved understanding of thermo-refractive noise can prove valuable in the design considerations and performance limitations of future photonic integrated devices.