Ultrastable optical frequency dissemination on a multi-access fibre network

We report a laboratory demonstration of 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 by 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 set up at the mid-point of the main link. We show that the extracted signal at the end of the secondary link exhibits a fractional frequency instability of 1.4 × 10−15 at 1-s measurement time, almost equal to the 1.3 × 10−15 instability of the main link output end. The long-term instabilities are also very similar, at a level of 3–5 × 10−20 at 3 × 104-s integration time. We also show that the setting up of this extraction device, or of 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 ultrastable network for multi-users dissemination.

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