# Probing 10 {\mu}K stability and residual drifts in the cross-polarized dual-mode stabilization of single-crystal ultrahigh-Q optical resonators

## TL;DR

This paper demonstrates the use of cross-polarized dual-mode beat frequency metrology in a single-crystal MgF2 resonator to achieve microkelvin-level thermal stability, advancing precision in photonic applications.

## Contribution

It introduces a method for resonator temperature stabilization using dual-mode beat frequency metrology, approaching the fundamental thermal noise limit in a realistic system.

## Key findings

- Achieved 8.53 μK long-term temperature stability after stabilization.
- Identified sources limiting stability from reaching sub-μK levels.
- Validated potential for thermal noise-limited stabilization in microresonators.

## Abstract

The thermal stability of monolithic optical microresonators is essential for many mesoscopic photonic applications such as ultrastable laser oscillators, photonic microwave clocks, and precision navigation and sensing. Their fundamental performance is largely bounded by thermal instability. Sensitive thermal monitoring can be achieved by utilizing cross-polarized dual-mode beat frequency metrology, determined by the polarization-dependent thermorefractivity of a single-crystal microresonator, wherein the heterodyne radio-frequency beat pins down the optical mode volume temperature for precision stabilization. Here, we investigate the correlation between the dual-mode beat frequency and the resonator temperature with time and the associated spectral noise of the dual-mode beat frequency in a single-crystal ultrahigh-Q MgF2 resonator to illustrate that dual-mode frequency metrology can potentially be utilized for resonator temperature stabilization reaching the fundamental thermal noise limit in a realistic system. We show a resonator long-term temperature stability of 8.53 {\mu}K after stabilization and unveil various sources that hinder the stability from reaching sub-{\mu}K in the current system, an important step towards compact precision navigation, sensing and frequency reference architectures.

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Source: https://tomesphere.com/paper/1901.01463