Ultra low frequency noise laser by locking to an optical fiber delay line

TL;DR

This paper demonstrates a fiber delay line-based stabilization method for erbium-doped fiber lasers, achieving ultra-low frequency noise comparable to cavity locking, offering a compact alternative for linewidth reduction.

Contribution

It introduces a fiber delay line locking technique for laser stabilization, providing a simple, reliable, and compact alternative to traditional cavity-based methods.

Findings

Frequency noise reduced by over 40 dB from 1 Hz to 10 kHz

Achieves noise levels below 1 Hz^2/Hz across the entire range

Comparable performance to Pound-Drever-Hall locking with a fiber delay line

Abstract

We report the frequency stabilization of an erbium-doped fiber distributed-feedback laser using an all-fiber based Michelson interferometer of large arm imbalance. The interferometer uses a 1 km SMF-28 optical fiber spool and an acousto optic modulator allowing heterodyne detection. The frequency noise power spectral density is reduced by more than 40 dB for Fourier frequencies ranging from 1 Hz to 10 kHz, corresponding to a level well below 1 Hz^2/Hz over the whole range. It reaches 10^{-2} Hz^2/Hz at 1 kHz. Between 40 Hz and 30 kHz, the frequency noise is shown to be comparable to the one obtained by Pound-Drever-Hall locking to a high finesse Fabry-Perot cavity. Locking to a fiber delay line could consequently represent a reliable, simple and compact alternative to cavity stabilization for short term linewidth reduction.