Research On Applications Of Optical Microtube Sensors Based On Whispering Gallery Modes

The Whispering gallery mode(WGM)microcavities have the advantages of extremely high-quality factor,extremely small mode volume,and can greatly enhance the interaction between the light field and the material in the cavity,so it has important application value and prospect in many fields such as low threshold laser,narrowband filter,quantum communication,and high sensitivity sensor.With the rapid development of micro-nano optical technology,WGM micro-cavities have been developing towards the direction of device,miniaturization,diversification,and other practical applications.This paper conducts theoretical and experimental research on the optical properties of WGM microcavity and problems in sensing applications,including the theoretical derivation of the transfer function of the micro-nano fiber and microcavity coupling system,WGM microcavity mode field distribution,coupling phase matching,etc.And simulation analysis,and experimental analysis of the application of WGM-based micro-lumens in the field of refractive index sensing and strain sensing.The research contents and innovation points of this paper mainly include the following:1.By establishing the coupling theoretical model of the micro-nano fiber and the micro-micro cavity,according to the electromagnetic wave theory,the field distribution characteristics of the micro-cavity WGM mode and the relation between the transmission constant of the micro-nano fiber and the micro-tube are deduced,and the phase matching problem of the micro-nano fiber and the micro-tube coupling is analyzed.In the experiment,micro-nano fiber with low loss,good repetition and high quality were successfully prepared by using the fused taper method by building the fiber pull cone system.By building the coupling system of micro-nano fiber and microtubule,the influences of micro-nano fiber diameter,coupling spacing and coupling inclination on resonance mode were analyzed,which laid a theoretical and experimental foundation for the subsequent experiments.2.The refractive index sensor based on WGM microtubule is optimized.Theoretically,by establishing the theoretical model of the refractive index sensor,systematic analysis of the main factors affecting the sensitivity of refractive index sensing,and a scheme to improve the sensitivity of the refractive index sensor is proposed.In the experiment,by building a refractive index sensing testing system and using micro-nano fiber to excite several different WGM modes in the microtubule,the sensitivity of the low-order mode in the refractive index sensing was improved,and the sensitivity of the refractive index sensing system of the third-order radial mode was measured up to 52.90nm/RIU.3.A strain sensor based on WGM microtubule is proposed,which improves the sensitivity of the strain sensor and simplifies the complexity of the device structure.The finite element software ANSYS was used to simulate the structural changes of microtubules under axial stress.The experimental results show that the WGMs resonance peak is blueshifted when the strain is applied in the axial direction of the microtubule.Due to the different sensitivity of the wall thickness to the microtube strain sensing system,by controlling the wall thickness,within the strain range of 0-1750??,the sensitivity of the strain sensing system can reach 1.18 pm/??,and the Q value is 4.4×104.