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Terahertz-Rate Kerr-Microresonator Optical Clockwork



Tara E. Drake, Travis Briles, Daryl T. Spencer II, Jordan R. Stone, David R. Carlson, Daniel D. Hickstein, Qing Li, Daron A. Westly, Kartik A. Srinivasan, Scott A. Diddams, Scott B. Papp


Kerr microresonators generate interesting and useful fundamental states of electromagnetic radiation through nonlinear interactions of continuous-wave (CW) laser light. When implemented with photonic-integration techniques, functional devices with low noise, small size, low power consumption, scalable fabrication, and heterogeneous combinations of photonics and electronics are realized. Kerr solitons, which can stably circulate in a Kerr microresonator, have emerged as a source of coherent, ultrafast pulse trains and ultra-broadband optical frequency combs. Using the f-2f technique, Kerr combs support carrier-envelope-offset phase stabilization for optical synthesis and metrology. In this paper, we introduce a Kerr-microresonator optical clockwork based on optical-frequency division (OFD), which is a powerful technique to transfer the fractional frequency stability of an optical clock to a lower frequency clock signal. The clockwork presented here is based on a silicon-nitride (Si$_3$N$_4$) photonic circuit that produces a microresonator comb composed of soliton pulses at 1 THz repetition rate. By electro- optic phase modulation of the entire Si$_3$N$_4$ comb, we arbitrarily generate additional continuous-wave modes between the Si$_3$N$_4$ comb modes; operationally, this reduces the pulse train repetition frequency and can be used to implement OFD to the microwave domain. Our experiments characterize the intrinsic frequency noise of this Kerr-microresonator clockwork to one part in $10^{17}$, which introduces the possibility of using Kerr combs with the highest performance optical clocks. In contrast, the photonic integration and 1 THz resolution of the Si$_3$N$_4$ frequency comb makes it simultaneously appealing for broadband liquid-phase absorption spectroscopy, which we demonstration with short-wave IR measurements of water, soybean oil, ethanol, and dichloromethane.
Physical Review X


Kerr-microresonator, NIR spectroscopy, optical frequency division
Created August 12, 2019, Updated May 28, 2020