# Laser-based underwater transfer of radio-frequency clock signal with electronic phase compensation

## TL;DR

This paper demonstrates a laser-based method for transferring radio-frequency clock signals underwater over 5 meters with phase compensation, achieving high stability and low timing fluctuations, suitable for atomic clock dissemination.

## Contribution

It introduces a novel laser-based underwater RF frequency transfer scheme with phase compensation, improving stability over previous methods.

## Key findings

- RMS timing fluctuations of 2.1 ps with phase compensation
- Frequency stability of 5E-13 at 1 s for phase-compensated link
- Transfer distance of 5 meters with high stability

## Abstract

We demonstrate a laser-based underwater transfer of radio frequency clock signal with a phase compensation technique. With this frequency transfer scheme, a 100 MHz signal has been transferred over 5 m underwater link. Timing jitter power spectral density, timing fluctuations and instabilities were all measured to evaluate the quality of the transferred frequency signal. The experimental results show the root-mean-square (RMS) timing fluctuations of the transferred frequency signal over 5 m underwater link with and without phase compensation are 2.1 ps and 9.6 ps within 5000 s, respectively. The relative fractional frequency instabilities are on the order of 5E-13 at 1 s and 7E-16 at 1000 s for phase-compensated link, and 2E-12 at 1 s and 7E-15 at 1000 sfor uncompensated link, respectively. The proposed frequency transfer scheme has a potential application that disseminating Cs and H-master clocks signal over the underwater transmission link since the stability of the transmission link is superior to these atomic clocks.

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Source: https://tomesphere.com/paper/1901.06927