Light: Science & Applications (Sep 2024)

Picotesla-sensitivity microcavity optomechanical magnetometry

  • Zhi-Gang Hu,
  • Yi-Meng Gao,
  • Jian-Fei Liu,
  • Hao Yang,
  • Min Wang,
  • Yuechen Lei,
  • Xin Zhou,
  • Jincheng Li,
  • Xuening Cao,
  • Jinjing Liang,
  • Chao-Qun Hu,
  • Zhilin Li,
  • Yong-Chang Lau,
  • Jian-Wang Cai,
  • Bei-Bei Li

DOI
https://doi.org/10.1038/s41377-024-01643-7
Journal volume & issue
Vol. 13, no. 1
pp. 1 – 12

Abstract

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Abstract Cavity optomechanical systems have enabled precision sensing of magnetic fields, by leveraging the optical resonance-enhanced readout and mechanical resonance-enhanced response. Previous studies have successfully achieved mass-produced and reproducible microcavity optomechanical magnetometry (MCOM) by incorporating Terfenol-D thin films into high-quality (Q) factor whispering gallery mode (WGM) microcavities. However, the sensitivity was limited to 585 pT Hz−1/2, over 20 times inferior to those using Terfenol-D particles. In this work, we propose and demonstrate a high-sensitivity and mass-produced MCOM approach by sputtering a FeGaB thin film onto a high-Q SiO2 WGM microdisk. Theoretical studies are conducted to explore the magnetic actuation constant and noise-limited sensitivity by varying the parameters of the FeGaB film and SiO2 microdisk. Multiple magnetometers with different radii are fabricated and characterized. By utilizing a microdisk with a radius of 355 μm and a thickness of 1 μm, along with a FeGaB film with a radius of 330 μm and a thickness of 1.3 μm, we have achieved a remarkable peak sensitivity of 1.68 pT Hz−1/2 at 9.52 MHz. This represents a significant improvement of over two orders of magnitude compared with previous studies employing sputtered Terfenol-D film. Notably, the magnetometer operates without a bias magnetic field, thanks to the remarkable soft magnetic properties of the FeGaB film. Furthermore, as a proof of concept, we have demonstrated the real-time measurement of a pulsed magnetic field simulating the corona current in a high-voltage transmission line using our developed magnetometer. These high-sensitivity magnetometers hold great potential for various applications, such as magnetic induction tomography and corona current monitoring.