Optical frequency transfer via 146 km fiber link with 10^−19 relative accuracy

Abstract

We demonstrate the long-distance transmission of an ultrastable optical frequency derived directly from a state-of-the-art optical frequency standard. Using an active stabilization system we deliver the frequency via a 146-km-long underground fiber link with a fractional instability of 3 x 10(-15) at 1 s, which is close to the theoretical limit for our transfer experiment. After 30,000 s, the relative uncertainty for the transfer is at the level of 1 x 10(-19). Tests with a very short fiber show that noise in our stabilization system contributes fluctuations that are 2 orders of magnitude lower, namely, 3 x 10(-17) at 1 s, reaching 10(-20) after 4,000 s.

How to make the propagation time through an optical fiber fully insensitive to temperature variations

“…However, due to their many unique properties, optical fibers continue to penetrate into new research areas and keep attracting interest from novel and diverse fields of science and engineering. Examples include fiber lasers and more recently also precise time [1] and frequency transfer and dissemination [2] over optical fibers and optical networks.…”

“…A specific example of where precise frequency transfer is needed concerns comparison of optical clocks in various national metrology laboratories (e.g., between Germany and France [4]) at a required precision (fractional stability) at/below the 5x10 -17 level, and which can currently only be achieved using optical fiber networks. However, such a level of precision is easily compromised by thermally-induced changes in optical path length (temperature drift) with time that unavoidably result in a Doppler frequency shift [2,4]. In these systems, active stabilization of the optical path length is required and achieved using bi-directional propagation of the same signal in the same fiber.…”

Hybrid fiber links for accurate optical frequency comparison

“…The technique of phase-compensated optical fiber link [1][2][3][4][5] has developed rapidly over the last decade and has enabled the transfer and comparison of optical frequencies over continental-scale distances of more than 1000 km [6][7][8][9]. Optical fiber-based clock frequency comparison is not only useful for time-frequency metrology, but can also provide a powerful experimental tool in many applications, such as test of variation of fundamental constants [10], relativistic geodesy [6], and dark matter search [11].…”

Frequency and time transfer for metrology and beyond using telecommunication network fibres

“…2) and demonstrated a 172-km link using recirculation in the same fibres [23]. Following these pioneering results, several groups worldwide have initiated experiments on optical links [24,27,28,[30][31][32][46][47][48].…”

“…The high sensitivity detection of the optical phase using heterodyne methods in conjunction with spectrally very pure lasers, are the basic tools to achieve low-noise optical frequency transfer. In the last decade, several experiments in Europe, USA and Japan have explored the limits of this method, paving the way for a new generation of ultra-stable optical networks [18,[21][22][23][24][25][26][27][28][29][30][31]. A groundbreaking frequency transfer has been demonstrated on a record distance of 920 km and even 1840 km on a dedicated fibre network [27,32].…”