# Unveiling delay-time-resolved phase noise dynamics of narrow-linewidth laser via coherent optical time domain reflectometry

## TL;DR

This paper introduces a novel method using coherent optical time domain reflectometry to accurately characterize the phase noise dynamics and intrinsic linewidth of highly coherent, narrow-linewidth lasers, which are vital for high-precision optical applications.

## Contribution

The paper presents a new approach to measure delay-time-resolved phase noise dynamics of narrow-linewidth lasers using COTDR, enabling precise linewidth determination.

## Key findings

- Successfully reveals delay-time-resolved phase noise dynamics.
- Enables precise measurement of ultra-narrow laser linewidth.
- Validated by analytical modeling and numerical simulations.

## Abstract

Laser with high spectral purity plays a crucial role in high-precision optical metrology and coherent communication. Thanks to the rapid development of laser frequency stabilization, the laser phase noise can be remarkably compensated, allowing its ultra-narrow linewidth subject to mostly quantum limit. Nevertheless, the accurate characterization of phase noise dynamics and its intrinsic linewidth of a highly coherent laser remains ambiguous and challenging. Here, we present an approach capable of revealing delay-time-resolved phase noise dynamics of a coherent laser based on coherent optical time domain reflectometry (COTDR), in which distributed Rayleigh scattering along a delay fibre essentially allows a time-of-flight mapping of a heterodyne beating signal associated with delay-time-dependent phase information from a single laser source. Ultimately, this novel technique facilitates a precise measurement of ultra-narrow laser linewidth by exploiting its delay-time-resolved phase jitter statistics, confirmed with the analytical modelling and numerical simulations.

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Source: https://tomesphere.com/paper/1906.02676