A research team led by Wenjie Wan at Shanghai Jiao Tong University Global College (SJTUGC, abbreviated as GC hereafter), in collaboration with Xianfeng Chen’s team at the School of Physics and Astronomy of Shanghai Jiao Tong University (SJTU), has published a paper titled “Stopped-light-enhanced gravitational force sensing” in Nature Nanotechnology. The study uses a stopped-light effect in an optical microcavity to detect the gravitational force of a millimeter-scale mass source with high sensitivity on a chip-scale platform. The findings offer a new approach to weak-force sensing and may support further investigations of gravity at small scales.
Gravity is the weakest of the four fundamental interactions, making the gravitational effects of small masses difficult to detect. Although traditional torsion-balance experiments can measure weak gravitational forces, integrating such measurements with micro- and nanophotonic sensing systems remains challenging.
Schematic illustration of stopped-light-enhanced gravitational acceleration sensing
To address this challenge, the team used stimulated Brillouin scattering-induced absorption (BSIA) in an optical microcavity to create a stopped-light point, where light propagation slows significantly and optical phase dispersion becomes extremely steep. In a silica microsphere cavity with a radius of 150 micrometers, the researchers achieved a group delay of approximately 420 microseconds by controlling forward stimulated Brillouin scattering.
The steep phase dispersion enables tiny changes in the coupling distance between the microcavity and a tapered optical fiber to be converted into measurable optical signals. This allows the system to detect nanoscale distance changes induced by gravitational disturbances.
In the experiment, a 1.2-gram source mass, 6 millimeters in diameter, was placed approximately 4.2 centimeters from the test mass. A piezoelectric platform modulated the gravitational field, while changes in the coupling between the microcavity and the tapered fiber were used to measure the resulting acceleration. The sensor achieved a displacement sensitivity of 7.85 pm/√Hz and an acceleration sensitivity of 3.06×10⁻¹⁶ g. The smallest detectable change in gravitational force under time-modulated measurement was 3.02×10⁻¹⁶ N.
The sensor operates at room temperature and atmospheric pressure, without requiring a vacuum environment or cryogenic cooling. The approach may also offer opportunities for sensing other weak forces, including Casimir and van der Waals forces, and for developing compact accelerometers, gravimeters and inertial sensors.
Yicheng Zhu, a postdoctoral researcher at GC, is the first author of the paper, and Wenjie Wan is the corresponding author.
Personal Introduction
Yicheng Zhu received his PhD from GC under the supervision of Associate Professor Wenjie Wan. His research focuses on nonlinear optics in optical microcavities. He was nominated for SJTU’s 10th Graduate Academic Star award and has published first-author papers in Nature Nanotechnology, Nature Communications and Proceedings of the National Academy of Sciences (PNAS).
