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Hybrid fiber links for accurate optical frequency comparison
Lee, Won-Kyu,Stefani, Fabio,Bercy, Anthony,Lopez, Olivier,Amy-Klein, Anne,Pottie, Paul-Eric Springer-Verlag 2017 Applied physics. B, Lasers and optics Vol.123 No.4
<P>We present the experimental demonstration of a local two-way optical frequency comparison over a 43-km-long urban fiber network without any requirement for measurement synchronization. We combined the local two-way scheme with a regular active noise compensation scheme that was implemented on another parallel fiber leading to a highly reliable and robust frequency transfer. This hybrid scheme allowed us to investigate the major limiting factors of the local two-way comparison. We analyzed the contributions of the interferometers at both local and remote locations to the phase noise of the local two-way signal. Using the ability of this setup to be injected by either a single laser or two independent lasers, we measured the contributions of the demodulated laser instabilities to the long-term instability. We show that a fractional frequency instability level of 10(-20) at 10,000 s can be obtained using this simple setup after propagation over a distance of 43 km in an urban area.</P>
Test of Special Relativity Using a Fiber Network of Optical Clocks
Delva, P.,Lodewyck, J.,Bilicki, S.,Bookjans, E.,Vallet, G.,Le Targat, R.,Pottie, P.-E.,Guerlin, C.,Meynadier, F.,Le Poncin-Lafitte, C.,Lopez, O.,Amy-Klein, A.,Lee, W.-K.,Quintin, N.,Lisdat, C.,Al-Maso American Physical Society 2017 Physical Review Letters Vol.118 No.22
<P>Phase compensated optical fiber links enable high accuracy atomic clocks separated by thousands of kilometers to be compared with unprecedented statistical resolution. By searching for a daily variation of the frequency difference between four strontium optical lattice clocks in different locations throughout Europe connected by such links, we improve upon previous tests of time dilation predicted by special relativity. We obtain a constraint on the Robertson-Mansouri-Sexl parameter |alpha| <= 1.1 x 10(-8), quantifying a violation of time dilation, thus improving by a factor of around 2 the best known constraint obtained with Ives-Stilwell type experiments, and by 2 orders of magnitude the best constraint obtained by comparing atomic clocks. This work is the first of a new generation of tests of fundamental physics using optical clocks and fiber links. As clocks improve, and as fiber links are routinely operated, we expect that the tests initiated in this Letter will improve by orders of magnitude in the near future.</P>