| The Whispering Gallery Mode(WGM)optical resonator has attracted the attention of researchers at home and abroad due to its advantages of small size,high optical quality factor,immunity to electromagnetic interference,compatibility with optical fiber communication systems,and lightweight.Sensors based on WGM optical resonators can measure multiple physical quantities such as temperature,humidity,refractive index,and magnetic field.Based on the existing research on ultrasonic and magnetic field sensing in WGM optical resonators,this thesis aims to improve the sensitivity by changing the optical resonator’s structure.Furthermore,we realize dual parameter sensing of acoustic and magnetic fields based on the designed resonators.The main contents of this thesis are as follows:Firstly,three optical resonator structures have been fabricated.The first resonator is obtained by burning two nodes on a cylindrical resonator using an optical fiber fusion splicer,and this resonator has fewer radial modes and increased sensitivity.The second resonator is a solid fiber microsphere that is fabricated by arc-melting optical fibers.The fabrication process can reduce high-order radial modes while changing the geometry of the cavity,thereby changing its detection performance.The third resonator is the peanut-shaped hollow microsphere resonator.Based on the preparation of an optical fiber microsphere resonator,we use hollow capillaries to obtain hollow microsphere resonators that can reduce the wall thickness and mass of the resonator,and therefore are able to improve the ultrasonic detection performance;The fabrication method of dual microspheres resonator is used to prepare two hollow microsphere resonators into peanut-shaped hollow microsphere resonator.The mechanical mode of the peanut-shaped hollow microsphere resonator is changed to the detection frequency band,and that helps improve the magnetic field detection sensitivity.Secondly,in order to realize ultrasonic and magnetic field sensing,piezoelectric ceramic sheets and magnetostrictive materials are integrated into WGM optical resonators,and their sensing performance is tested.The magnetic field and ultrasonic sensing performance of the three resonators were tested respectively.Experimental results show that the ultrasonic sensitivities of the cylindrical resonator,the solid microsphere resonator,and the peanut-shaped hollow microsphere resonator are 0.62 m Pa/√Hz,52.77 m Pa/√Hz,and 12.59 m Pa/√Hz,respectively.The sensitivity of the proposed cylindrical resonator is 66 times higher than the sensitivity of the cylindrical resonator without two-nodes heating processing.The corresponding magnetic field sensitivities are 31.2n T/√Hz,27.9n T/√Hz,and 5.16 n T/√Hz,respectively.The sensitivity of the peanut-shaped hollow microsphere resonator is improved by9 times compared to the cylindrical resonator filled with magnetostrictive materials.Also,the sensitivities of the microsphere resonators are higher than that of the cylindrical resonators of a similar size.Finally,three resonators are all used to conduct dual parameter sensing of magnetic and ultrasonic fields,and we investigate that whether the two parameters will affect each other.The experimental results show that the two parameters do not affect each other at different frequencies,and the two detected signals are superimposed on each other if they have the same frequency and phase.The proposed optical sensors based on three WGM resonators in this paper can achieve100 k Hz to 2MHz magnetic and ultrasonic dual parameter sensing,providing a new idea and experimental basis for the design of WGM-based optical resonator sensors. |
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