High-Precision Optical Time and Frequency Transfer

Published

May 2, 2025

Author(s)

Emily Caldwell, Theodora Triano, Laura Sinclair

Abstract

High-precision optical time and frequency transfer is accomplished by a collection of laser-based techniques that achieve time dissemination with sub-picosecond instabilities and frequency dissemination with instabilities below one part in 1016. The ability to distribute and compare time and frequency at these precisions enables current optical timing networks such as interconnected optical atomic clocks for the redefinition of the second, relativistic geodesy, and fundamental physics tests as well as time and frequency dissemination systems for large-scale scientific instruments. Future optical timing networks promise to expand these applications and enable new advances in distributed coherent sensing, precise navigation, and more. The field of high-precision optical time and frequency transfer has made significant advances over the last 20 years and has begun to transition from technique development to deployment in applications. Here, we present a review of approaches to high-precision optical time and frequency transfer. We first present a brief overview of the metrics used to assess time and frequency transfer. We then provide a discussion of the difference between time transfer and frequency transfer and review the various technical noise sources. We also provide a background on the optical frequency comb and its role in optical time and frequency transfer for additional context. The next sections of the paper cover specific time-frequency transfer techniques and demonstrations beginning with time and frequency transfer over fiber-optic links including continuous wave (CW) laser-based frequency transfer, CW-laser-based time transfer, and frequency-comb-based time transfer. We then discuss approaches for time and frequency transfer over free-space including pulsed-source time transfer, CW-laser-based frequency transfer, and frequency-comb-based time transfer. Since no existing review article covers frequency-comb time transfer over free-space, we provide additional details on the technique. Finally, we provide an outlook that outlines outstanding challenges in the field as well as possible future applications.

Citation

Advances in Optics and Photonics

Volume

17

Issue

2

Pub Type

Journals

Download Paper

https://doi.org/10.1364/AOP.545290

Local Download

Keywords

optical time transfer, optical frequency transfer, precise time transfer, precise frequency transfer

Citation

Caldwell, E. , Triano, T. and Sinclair, L. (2025), High-Precision Optical Time and Frequency Transfer, Advances in Optics and Photonics, [online], https://doi.org/10.1364/AOP.545290, https://tsapps.nist.gov/publication/get_pdf.cfm?pub_id=958405 (Accessed December 13, 2025)