Thermal and driven noise in Brillouin Lasers

TL;DR

This paper develops a coupled mode theory to analyze and understand the dominant noise sources in Brillouin lasers, including thermal fluctuations, to improve their frequency stability for advanced applications.

Contribution

It introduces a comprehensive noise model for Brillouin lasers that includes thermo-optic drift, enabling better prediction and mitigation of frequency and intensity noise.

Findings

The model accurately captures frequency and intensity noise characteristics.

Thermal fluctuations significantly impact laser frequency stability.

Strategies for noise reduction can enhance laser coherence and performance.

Abstract

Owing to their highly coherent emission and compact form factor, Brillouin lasers have been identified as a valuable asset for applications including portable atomic clocks, precision sensors, coherent microwave synthesis and energy-efficient approaches to coherent communications. While the fundamental emission linewidth of these lasers can be very narrow, noise within dielectric materials leads to drift in the carrier frequency, posing vexing challenges for applications requiring ultra-stable emission. A unified understanding of Brillouin laser performance may provide critical insights to reach new levels of frequency stability, however existing noise models focus on only one or a few key noise sources, and do not capture the thermo-optic drift in the laser frequency produced by thermal fluctuations or absorbed power. Here, we develop a coupled mode theory of Brillouin laser dynamics that accounts for dominant forms of noise in non-crystalline systems, capturing the salient features of the frequency and intensity noise for a variety of systems. As a result, theory and experiment can be directly compared to identify key sources of noise and the frequency bands they impact, revealing strategies to improve the performance of Brillouin lasers and pave the way for highly-coherent sources of light on a chip.