Recent developments in stabilized lasers have resulted in ultrastable optical oscillators with spectral purities below 1 Hz refs 1–6. These oscillators are not transportable at present and operate at a single frequency. To realize their full potential, a highly coherent, frequency-diverse fibre-optic network is needed to faithfully transfer the optical signals to remote sites and to different optical frequencies. Here we demonstrate such a coherent network composed of erbium fibre and Ti:sapphire laser-based, optical-frequency combs7,8,9, stabilized optical-fibre links4,10 and cavity-stabilized lasers4,5,6. We coherently transmit an optical carrier over 750 m of optical fibre with conversions to wavelengths of 657, 767, 1,126 and 1,535 nm, an overall timing jitter of 590 attoseconds, and a frequency instability of 12 mHz for the 195 THz carrier in 1 s and 250 µHz in 1,000 s. This first remote synchronization of two frequency combs also demonstrates a factor of 30 improvement in the relative stability of fibre frequency combs11,12.
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We acknowledge assistance from J. Stalnaker and T. Fortier with the Ti:sapphire frequency comb and useful discussions with L. Hollberg and T. Rosenband. We acknowledge funding from the National Institute of Standards and Technology and from the DARPA PHOR-FRONT program.
The authors declare no competing financial interests.
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Coddington, I., Swann, W., Lorini, L. et al. Coherent optical link over hundreds of metres and hundreds of terahertz with subfemtosecond timing jitter. Nature Photon 1, 283–287 (2007). https://doi.org/10.1038/nphoton.2007.71
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