| The connection between magnetic sensors and modern society has become increasingly close.Magnetic sensors have been widely used in the fields of power electronics,traffic control,biomedicine,aerospace,satellite communications,and military industry.Whispering gallery mode（WGM）optical crystalline resonator have the characteristics of small mode volume and high quality factor（Q）,which can greatly enhance the interaction between light and matter in the micro-nano scale,and have huge application potential in the field of optical sensing.The research focus of this paper is the composite structure whispering gallery mode calcium fluoride crystalline resonator magnetic sensor.This paper focuses on its historical background and research status,and carries out theoretical analysis and experimental research,aiming to provide a new perspective for further exploring the theory and sensing application of calcium fluoride crystalline resonator.（1）From the sensing mechanism,the research elucidates the theoretical basis and analytical model of crystalline cavity magnetic sensors.Based on theoretical research,a composite structure crystalline resonator is modeled and simulated by finite element analysis.The theoretical results show that the magnetic sensing mechanism of calcium fluoride mainly comes from its geometric shape change.（2）From the structural manufacturing perspective,a magnetic sensor based on calcium fluoride crystalline cavity is proposed and prepared.The magnetic sensor is composed of a high-Q value crystalline cavity based on single point diamond turning technology and ultra-precision mechanical polishing process,and a rare earth permanent magnet material neodymium iron boron.After the preparation of the magnetic sensor,the optical parameters are characterized and tested by line-width and cavity ring-down methods.The research results show that the FWHM of a single crystalline cavity is 0.075 MHz,and the optical Q factor is～2.5×109.After introducing the composite structure magnetic sensor,the FWHM is 0.14 MHz,the optical Q factor is 109,the attenuation is about twice,the photon lifetimeτis 3.8μs,and the coupling efficiency of taper optical fiber exceeds 90%.（3）Magnetic field testing research,in order to further test the performance of the magnetic sensor,a sensing test system is built to test the resonance spectrum at a wavelength of 1550 nm with the change of magnetic field size.The sensitivity of the sensor under DC magnetic field is 42.59 MHz/m T,and the reversibility of the resonance spectrum drift direction with magnetic field change is proven.Under AC magnetic field,combined with PDH lock-in technology,a magnetic field sensitivity of 794 p T Hz-1/2and a signal-to-noise ratio of 62 d B are obtained at a frequency of 42 k Hz,and the source of noise peaks on the spectrum analyzer is briefly analyzed.Finally,the thermal stability resonance wavelength variation is controlled within the range of 0.154 MHz/K by simulation analysis.Compared with the experimental result of 42.59 MHz/m T,the accuracy error is within 3.6‰,and the direction of future optimization is analyzed from the aspects of cavity size,quality factor,and material structure. |
