Ultra-Sensitive Magnetic Sensor Based on Resonator With Asymmetric Wedge Structure

Whispering-gallery mode (WGM) optical resonators with ultrahigh optical quality factor ( <tex-math notation="LaTeX">Q) </tex-math> and small mode volume ( <tex-math notation="LaTeX">V) </tex-math> are one of the most promising platforms for magnetic sensing. However, the low conversion efficiency between the magnetic signal and the optical resonator makes it difficult to break through the pico-Tesla (pT) level of sensitivity, limiting its performance in applications. Here, we propose an ultrahigh <tex-math notation="LaTeX">Q </tex-math> calcium fluoride (CaF <tex-math notation="LaTeX">_2) </tex-math> WGM resonator with an asymmetric wedge structure for magnetic sensing. Theoretically, the structural parameters of the asymmetric wedge significantly regulate the deformation of the resonator under magnetic induction. Interestingly, certain structural parameters correspond to zero deformation. Based on this phenomenon, an optimized sensitivity of 0.93 pT/Hz <tex-math notation="LaTeX">^ 1/2 </tex-math> at 654.2 kHz is obtained utilizing the resonator with <tex-math notation="LaTeX">Q </tex-math> of <tex-math notation="LaTeX">8.6× 10^8 </tex-math> . Moreover, the system demonstrated a highly sensitive response from 10 kHz to 1 MHz. The CaF2 resonator magnetic sensor based on asymmetric wedge structure will play an important role in areas such as magnetic anomaly detection and mineral exploration.