Ultra-stable optical frequency dissemination on a multi-access fibre network

TL;DR

This paper demonstrates a method for distributing ultra-stable optical frequency signals to multiple users over a branching fibre network with active noise compensation, achieving high stability and long-term accuracy.

Contribution

It introduces a novel multi-access fibre network scheme for simultaneous ultra-stable frequency dissemination with active noise compensation at multiple points.

Findings

Fractional frequency instability of 1.4x10^-15 at 1s at the secondary link

Long-term stability of 3-5x10^-20 at 3x10^4 seconds

Effective noise rejection and testing capability at the main link input

Abstract

We report the dissemination of an ultrastable optical frequency signal to two distant users simultaneously using a branching network. The ultrastable signal is extracted along a main fibre link; it is optically tracked with a narrow-linewidth laser diode, which light is injected in a secondary link. The propagation noise of both links is actively compensated. We implement this scheme with two links of 50-km fibre spools, the extraction being setup at the mid-point of the main link. We show that the extracted signal at the end of the secondary link exhibits fractional frequency instability of 1.4x10-15 at 1-s measurement time, almost equal to the 1.3x10-15 instability of the main link output end. The long-term instabilities are also very similar, at a level of 3-5x10-20 at 3x104-s integration time. We also show that the setting up of this extraction device, or a simpler one, at the main link input, can test the proper functioning of the noise rejection on this main link. This work is a significant step towards a robust and flexible ultra-stable network for multi-users dissemination.