Enhanced phase noise reduction in localized two-way optical frequency comparison

TL;DR

This paper introduces a timed-delayed local two-way scheme for optical frequency comparison that significantly reduces phase noise, enhancing stability over 50 km fiber links, with experimental validation and modeling of inhomogeneous noise effects.

Contribution

The paper presents a novel timed-delayed local two-way method that improves optical frequency comparison stability and models the impact of inhomogeneous phase noise along fiber links.

Findings

Fractional instability reduced from 1.30×10⁻¹⁵ to 5.25×10⁻¹⁶ at 1 s

Improvement factor of 2.48 in comparison stability

First experimental verification of inhomogeneous phase noise effects

Abstract

High-stability optical frequency comparison over fiber link enables the establishment of ultrastable optical clock networks, having the potential to promote a series of applications, including metrology, geodesy, and astronomy. In this article, we theoretically analyze and experimentally demonstrate a timedelayed local two-way (TD-LTW) optical frequency comparison scheme with improved comparison stability, showing that the fractional instability of optical frequency comparison over a 50- km transfer link can be reduced from $1.30\times10^{-15}$ to $5.25\times10^{-16}$ at the 1 s integration time with an improvement factor of 2.48. Additionally, we also for the first time model and experimentally verify the effect of the inhomogeneous phase noise along the fiber link on the system performance. We believe that the theory and technique proposed here will be helpful in developing the high-stability optical clock networks over large-area fiber links.