# All-polarization-maintaining, single-port Er:fiber comb for high-stability comparison of optical lattice clocks

## TL;DR

This paper presents the development of all-polarization-maintaining, single-port Er:fiber combs that provide highly stable, long-term operation for precise optical clock comparisons, achieving unprecedented measurement stability.

## Contribution

The authors built and evaluated two all-polarization-maintaining Er:fiber combs capable of linking optical clocks with extremely low noise, enabling highly stable clock ratio measurements.

## Key findings

- Achieved fractional frequency-noise spectral density of (1-2)×10^{-17} Hz^{-1/2} at 1 Hz.
- Enabled clock ratio measurements with 10^{-17} instability at 1 second.
- Demonstrated long-term robust operation of the fiber combs.

## Abstract

All-polarization-maintaining, single-port Er:fiber combs offer long-term robust operation as well as high stability. We have built two such combs and evaluated the transfer noise for linking optical clocks. A uniformly broadened spectrum over 135-285 THz with a high signal-to-noise ratio enables the optical frequency measurement of the subharmonics of strontium, ytterbium, and mercury optical lattice clocks with the fractional frequency-noise power spectral density of $(1-2)\times 10^{-17}$ Hz$^{-1/2}$ at 1 Hz. By applying a synchronous clock comparison, the comb enables clock ratio measurements with $10^{-17}$ instability at 1 s, which is one order of magnitude smaller than the best instability of the frequency ratio of optical lattice clocks.

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Source: https://tomesphere.com/paper/1706.00174