Low-noise microwave generation with an air-gap optical reference cavity

Published

January 30, 2024

Author(s)

Yifan Liu, Dahyeon Lee, Takuma Nakamura, Naijun Jin, Haotian Cheng, Megan Kelleher, Charles McLemore, Igor Kudelin, William Groman, Scott Diddams, Peter Rakich, Franklyn Quinlan

Abstract

We demonstrate a high finesse, microfabricated mirror-based, air-gap cavity with volume less than 1 ml, constructed in an array, that can support low-noise microwave generation through optical frequency division. We use the air-gap cavity in conjunction with a 10 nm bandwidth mode-locked laser to generate low phase noise 10 GHz microwaves, exhibiting a phase noise of −95 and −142 dBc/Hz at 100 Hz and 10 kHz offset frequencies, respectively. This is accomplished using the 2-point lock optical frequency division method, where we exploit 40 dB common-mode rejection of two lasers separated by 1.29 THz and locked to the same air-gap cavity. If used with an octave spanning comb, the air-gap cavity is capable of supporting 10 GHz phase noise below −160 dBc/Hz at 10 kHz offset, a level significantly lower than electronic synthesizers. These results show how extremely small optical reference cavities, operated without the benefit of vacuum enclosures or thermal insulation, can, nonetheless, support state-of-the-art microwave phase noise in compact and portable systems.

Citation

APL Photonics

Pub Type

Journals

Download Paper

https://doi.org/10.1063/5.0174544

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Citation

Liu, Y. , Lee, D. , Nakamura, T. , Jin, N. , Cheng, H. , Kelleher, M. , McLemore, C. , Kudelin, I. , Groman, W. , Diddams, S. , Rakich, P. and Quinlan, F. (2024), Low-noise microwave generation with an air-gap optical reference cavity, APL Photonics, [online], https://doi.org/10.1063/5.0174544, https://tsapps.nist.gov/publication/get_pdf.cfm?pub_id=956580 (Accessed October 28, 2025)