Comparing ultrastable lasers at 7 × 10−17 fractional frequency instability through a 2220 km optical fibre network

• DOI: 10.1038/s41467-021-27884-3
• Publication Date: 2022-01-11T11:02:51Z
• Authors: M. Schioppo; J. Kronjäger; A. Silva; R. Ilieva; J. W. Paterson; C. F. A. Baynham; W. Bowden; I. R. Hill; R. Hobson; A. Vianello; M. Dovale-Álvarez; R. A. Williams; G. Marra; H. S. Margolis; A. Amy-Klein; O. Lopez; E. Cantin; H. Álvarez-Martínez; R. Le Targat; P. E. Pottie; N. Quintin; T. Legero; S. Häfner; U. Sterr; R. Schwarz; S. Dörscher; C. Lisdat; S. Koke; A. Kuhl; T. Waterholter; E. Benkler; G. Grosche
• Keywords: [PHYS]Physics [physics]; Fibre optics and optical communications; Optical metrology; Science; Q; ultrastable laser, optical frequency metrology, optical fibre link, optical clock; 530; 7. Clean energy; 01 natural sciences; Article; 620; Optical sensors; 0103 physical sciences; Fluorescence spectroscopy; Seismology

Abstract Ultrastable lasers are essential tools in optical frequency metrology enabling unprecedented measurement precision that impacts on fields such as atomic timekeeping, tests of fundamental physics, and geodesy. To characterise an ultrastable laser it needs to be compared with a similar performance, but suitable system may not available locally. Here, we report comparison two geographically separated lasers, over the longest ever reported metrological fibre link network, measuring 2220 km length, at state-of-the-art fractional-frequency instability 7 × 10 −17 for averaging times between 30 s 200 s. The measurements also allow short-term complete network directly observed without using loop-back fibre. Based characterisation noise different timescales, investigate potential disseminating light improve performance remote clocks.