Harnessing micro-Fabry–Pérot reference cavities in photonic integrated circuits

Creators: Cheng, Haotian¹; Xiang, Chao^{2, 3}; Jin, Naijun¹; Kudelin, Igor^{4, 5}; Guo, Joel²; Heyrich, Matthew⁴; Liu, Yifan^{4, 5}; Peters, Jonathan²; Ji, Qing-Xin⁶; Zhou, Yishu¹; Vahala, Kerry J.⁶; Quinlan, Franklyn^{4, 5}; Diddams, Scott A.^{4, 5}; Bowers, John E.²; Rakich, Peter T.¹

1. Yale University
2. University of California, Santa Barbara
3. University of Hong Kong
4. University of Colorado Boulder
5. National Institute of Standards and Technology
6. California Institute of Technology

Abstract

Compact photonic systems that offer high frequency stability and low noise are of increasing importance to applications in precision metrology, quantum computing, communication and advanced sensing technologies. However, on-chip resonators comprising dielectrics cannot match the frequency stability and noise characteristics of Fabry–Pérot cavities, whose electromagnetic modes live almost entirely in vacuum. Here we present a novel strategy to interface microfabricated Fabry–Pérot cavities with photonic integrated circuits to realize compact, high-performance integrated systems. Using this new integration approach, we demonstrate the self-injection locking of an on-chip laser to a millimetre-scale vacuum-gap Fabry–Pérot cavity using a circuit interface that transforms the reflected cavity response to enable efficient feedback to the laser. This system achieves a phase noise of –97 dBc Hz–1 at 10-kHz offset frequency, a fractional frequency stability of 5 × 10−13 at 10 ms, a 150-Hz 1/π integral linewidth and a 35-mHz fundamental linewidth. We also present a complementary integration strategy that utilizes a vertical-emission grating coupler and a back-reflection cancellation circuit to realize a fully co-integrated module that effectively redirects the reflected signals and isolates back-reflections with a 10-dB suppression ratio, serving as a key for on-chip Pound–Drever–Hall locking. Together, these results highlight how vacuum-gap Fabry–Pérot reference cavities can be harnessed for ultrastable, low-noise photonic systems.

Copyright and License

© 2025, The Author(s). Open Access This article is licensed under a Creative Commons Attribution-NonCommercial-NoDerivatives 4.0 International License, which permits any non-commercial use, sharing, distribution and reproduction in any medium or format, as long as you give appropriate credit to the original author(s) and the source, provide a link to the Creative Commons licence, and indicate if you modified the licensed material. You do not have permission under this licence to share adapted material derived from this article or parts of it. The images or other third party material in this article are included in the article’s Creative Commons licence, unless indicated otherwise in a credit line to the material. If material is not included in the article’s Creative Commons licence and your intended use is not permitted by statutory regulation or exceeds the permitted use, you will need to obtain permission directly from the copyright holder. To view a copy of this licence, visit http://creativecommons.org/licenses/by-nc-nd/4.0/.

Supplemental Material

Supplementary Sections I–III, Figs. 1 and 2, Table 1 and discussion: 41566_2025_1701_MOESM1_ESM.pdf

Acknowledgement

We thank C. McLemore, T. Nakamura and W. Groman for useful technical discussion and feedback. This work was supported by Defense Advanced Research Projects Agency (DARPA) under award no. HR0011-22-2-0009 (H.C., C.X., N.J., I.K., J.G., M.H., Y.L., J.P., Q.-X.J., K.J.V., F.Q., S.A.D., J.E.B. and P.T.R.) as well as the US Department of Energy (DoE) under award no. DE-SC0019406 (N.J. and P.T.R.) and the National Science Foundation (NSF) under award no. 2137740 (H.C., Y.Z. and P.T.R.). Any opinions, findings and conclusions or recommendations expressed in this publication are those of the authors and do not necessarily reflect the views of DARPA, DoE and NSF.

Data Availability

Source data are provided with this paper. Further data are available from the corresponding authors upon reasonable request.

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