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Publication Citation: Optical two-way time and frequency transfer over free space

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Author(s): Fabrizio R. Giorgetta; William C. Swann; Laura C. Sinclair; Esther Baumann; Ian R. Coddington; Nathan R. Newbury;
Title: Optical two-way time and frequency transfer over free space
Published: April 28, 2013
Abstract: The transfer of high-quality time-frequency signals between remote locations underpins many applications, including precision navigation and timing, clock-based geodesy, long-baseline interferometry, coherent radar arrays, tests of general relativity and fundamental constants, and future redefinition of the second. However, present microwave-based time-frequency transfer is inadequate for state-of-the-art optical clocks and oscillators that have femtosecond-level timing jitter and accuracies below 1 × 10−17. Commensurate optically based transfer methods are therefore needed. Here we demonstrate optical time-frequency transfer over free space via two-way exchange between coherent frequency combs, each phase-locked to the local optical oscillator. We achieve 1 fs timing deviation, residual instability below 1 × 10−18 at 1,000 s and systematic offsets below 4 × 10−19, despite frequent signal fading due to atmospheric turbulence or obstructions across the 2 km link. This free-space transfer can enable terrestrial links to support clock-based geodesy. Combined with satellite-based optical communications, it provides a path towards global-scale geodesy, high-accuracy time-frequency distribution and satellite-based relativity experiments.
Citation: Nature Photonics
Volume: 7
Issue: 6
Pages: pp. 434 - 438
Keywords: frequency combs; frequency transfer; time transfer
Research Areas: Calibrations (Time and Frequency), Time and Frequency, SI (Time & Frequency)
DOI: http://dx.doi.org/10.1038/nphoton.2013.69  (Note: May link to a non-U.S. Government webpage)
PDF version: PDF Document Click here to retrieve PDF version of paper (5MB)