Microresonator Brillouin Laser Stabilization Using a Microfabricated Rubidium Cell

TL;DR

This paper demonstrates a miniature, stable laser system stabilized with a microfabricated rubidium cell, achieving high frequency stability, low drift, and potential for integration and miniaturization.

Contribution

The authors develop a microresonator Brillouin laser stabilized with a microfabricated rubidium cell, achieving unprecedented stability and robustness in a compact form.

Findings

Frequency stability at 10^{-11} level over seven decades of averaging time.

Reduction of laser frequency drift by a factor of 1000 using rubidium locking.

Generation of a 2 GHz RF signal with low phase noise.

Abstract

We frequency stabilize the output of a miniature stimulated Brillouin scattering (SBS) laser to rubidium atoms in a microfabricated cell to realize a laser system with frequency stability at the $10^{-11}$ level over seven decades in averaging time. In addition, our system has the advantages of robustness, low cost and the potential for integration that would lead to still further miniaturization. The SBS laser operating at 1560 nm exhibits a spectral linewidth of 820 Hz, but its frequency drifts over a few MHz on the 1 hour timescale. By locking the second harmonic of the SBS laser to the Rb reference, we reduce this drift by a factor of $10^3$ to the level of a few kHz over the course of an hour. For our combined SBS and Rb laser system, we measure a frequency noise of $4\times10^4$ $Hz^2/Hz$ at 10 Hz offset frequency which rapidly rolls off to a level of 0.2 $Hz^2/Hz$ at 100 kHz offset. The corresponding Allan deviation is $\leq2\times10^{-11}$ for averaging times spanning $10^{-4}$ to $10^3$ s. By optically dividing the signal of the laser down to microwave frequencies, we generate an RF signal at 2 GHz with phase noise at the level of -76 dBc/Hz and -140 dBc/Hz at offset frequencies of 10 Hz and 10 kHz, respectively.