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Generation of ultrastable microwaves via optical frequency division


There has been increased interest in the use and manipulation of optical fields to address the challenging problems that have traditionally been approached with microwave electronics. Some examples that benefit from the low transmission loss, agile modulation and large bandwidths accessible with coherent optical systems include signal distribution, arbitrary waveform generation and novel imaging1. We extend these advantages to demonstrate a microwave generator based on a high-quality-factor (Q) optical resonator and a frequency comb functioning as an optical-to-microwave divider. This provides a 10 GHz electrical signal with fractional frequency instability of ≤8 × 10−16 at 1 s, a value comparable to that produced by the best microwave oscillators, but without the need for cryogenic temperatures. Such a low-noise source can benefit radar systems2 and improve the bandwidth and resolution of communications and digital sampling systems3, and can also be valuable for large baseline interferometry4, precision spectroscopy and the realization of atomic time5,6,7.

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Figure 1: How the OFC from a mode-locked laser acts as an optical frequency divider and comparator.
Figure 2: Schematic of the experimental set-up used for generation and characterization of the 10 GHz low-noise microwaves.
Figure 3: Phase-noise spectrum of the photonically generated 10 GHz microwaves and contributing noise sources.
Figure 4: Time record and fractional frequency instability.
Figure 5: Approximate single-sideband phase noise for several leading microwave generation technologies in the 10 GHz range.


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The authors thank A. Hati, L. Hollberg, D. Howe, C. Nelson, N. Newbury and S. Papp for their contributions and comments on this manuscript, and A. Joshi and S. Datta of Discovery Semiconductor for providing the 10 GHz InGaAs photodiodes. This work was supported by NIST. It is a contribution of an agency of the US Government and is not subject to copyright in the USA. Mention of specific products or trade names does not constitute an endorsement by NIST.

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T.M.F., M.S.K., F.Q., J.T. and S.A.D. built, characterized and operated the femtosecond lasers and measurement systems. J.C.B., T.R., N.L., A.L., Y.J. and C.W.O. constructed and operated the stable c.w. laser sources. S.A.D., T.M.F. and F.Q. acquired and analysed the data and prepared the manuscript.

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Correspondence to T. M. Fortier or S. A. Diddams.

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Fortier, T., Kirchner, M., Quinlan, F. et al. Generation of ultrastable microwaves via optical frequency division. Nature Photon 5, 425–429 (2011).

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