# A compact, thermal noise limited reference cavity for ultra-low noise microwave generation

## TL;DR

This paper presents a compact, thermally noise-limited optical reference cavity designed for portable photonic microwave systems, achieving ultra-low phase noise and high frequency stability at room temperature.

## Contribution

It introduces a novel, easy-to-manufacture cavity design with improved thermal noise performance and transportability for ultra-low noise microwave generation.

## Key findings

- Laser phase noise nearly thermal noise limited from 1 Hz to 1 kHz
- Supports 10 GHz microwave generation with phase noise near -100 dBc/Hz at 1 Hz
- Achieves fractional frequency stability of 2×10⁻¹⁵ at 0.1 s

## Abstract

We demonstrate an easy to manufacture, 25 mm long ultra-stable optical reference cavity for transportable photonic microwave generation systems. Employing a rigid holding geometry that is first-order insensitive to the squeezing force and a cavity geometry that improves the thermal noise limit at room temperature, we observe a laser phase noise that is nearly thermal noise limited for three frequency decades (1 Hz to 1 kHz offset) and supports 10 GHz generation with phase noise near -100 dBc/Hz at 1 Hz offset and <-173 dBc/Hz for all offsets >600 Hz. The fractional frequency stability reaches $2\times10^{-15}$ at 0.1 s of averaging.