Title: Frequency-Comb-Based Optical Timing Networks
Abstract: The optical frequency comb has enabled a wide range of frequency, time and distance metrology applications due to its precise, rigid, and referenced optical output. However, the very rigidity which makes the frequency comb an excellent time-frequency ruler places limits on its applicability for comb-based sensing applications with many operating far from quantum-limited sensitivity. For instance, frequency-comb-based two-way time transfer relies on the detection of an incoming optical comb pulse train from a distant location. These incoming comb pulse trains may be weak and amplification is costly – operation close to the quantum limit would dramatically increase the scope of what is possible in terms of range, SWaP (size, weight and power), and link loss. In turn, that increased scope would enable comparison of state-of-the-art optical clocks for the future redefinition of the second, a wide range of fundamental physics tests and chronometric geodesy.
Here, I will present our development of a quantum-limited approach to optical time transfer that relies upon a time programmable frequency comb to break the inherent trade-offs which result from the rigid operation of a traditional comb. These programmable combs have a pulse time and phase which can be digitally controlled with ±2-attosecond accuracy allowing for their use as an optical tracking oscillator. Using frequency combs as optical tracking oscillators to reach the quantum limit for optical time transfer, we have been able to demonstrate sub-femtosecond time transfer across a 300-km terrestrial free-space link with greater than 100 dB of loss, a factor of 10,000 times lower received power threshold than previous frequency-comb-based approaches. I will show results from this 300-km demonstration as well as more recent work connecting optical atomic clocks across open air paths.
About the Speaker: Dr. Laura Sinclair is the Optical Time Transfer Project Lead in the Fiber Sources and Applications Group – part of the Communications Technology Laboratory at the National Institute of Standards and Technology (NIST) in Boulder, Colorado. She received a B.S. in physics from the California Institute of Technology in 2004, a Ph.D. in physics from the University of Colorado, Boulder in 2011 and was a post-doc at NIST Boulder, including as a National Research Council (NRC) post-doctoral fellow, before joining the staff. She has been awarded a Presidential Early Career Award for Scientists and Engineers (PECASE) (2019), a Department of Commerce Gold Medal for Scientific/Engineering Achievement as part of the Boulder Atomic Clock Optical Network Collaboration (2019), a NIST Excellence in Technology Transfer Award (2024), the Arthur S. Flemming Award for Basic Science (2024), and an Optica Fellow Award (2026). Her research focuses on the development of optical frequency combs and their wide-ranging applications particularly to optical time transfer and ranging. With the Optical Time Transfer Project Team, she has recently demonstrated optical time transfer at the quantum limit achieving sub-femtosecond time synchronization over 300 kilometers of air.
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