Investigation Of Whispering Gallery Modes In A Liquid-filled Hollow Glass Microsphere

Whispering gallery mode?WGM?microcavity has attracted great attention due to the ultra-high Q value,small mode volume and unique structure.WGM microcavities are usually micron-sized dielectric structures that capture light using continuous total total internal reflections at the interface between the microcavity and the medium that surrounds it.WGM microcavity-based sensors has the unique advantages of high sensitivity,small size,low cost and real-time monitoring,which makes it attracted great attention,especially in the direction of biological and chemical sensing.WGM resonator depends on the interaction between light on the surface of the microcavity and the surrounding analytes to convert the presence of chemical or biological analytes into quantitative and measurable optical signals,thus achieving real-time monitoring.In recent decades,WGM resonators have been molded into a wide variety of geometries,ranging from the simplest ones,i.e.,the microspheres,microdisks,and microrings,to more exotic shapes,such as microbottles and microbubbles,each with their own specific advantages and disadvantages.Compared with other WGM resonators,the hollow cavity retains not only many advantages of its solid counterpart,but offers additional features that are especially beneficial in the fields of biological and chemical sensing.Because samples can be injected into the cavity,by changing the thickness of the wall,the hollow whispering gallery cavity can be used to detect nanoparticles.In addition,hollow WGM microcavities have already exhibited remarkable potential for optical component integration and cost-effective mass manufacturing.Therefore,these features make the hollow cavity more suitable for real-world applications than solid WGMs.This thesis is mainly focused on the hollow WGM microcavity.The experiment verified that the hollow glass microsphere?HGM?could be used as the WGM microcavity,explored the transfer of WGM resonance in the hollow WGM microcavity,and realized the high sensitivity temperature sensing of the WGM microcavity based on liquid-filled HGM.The detailed research work can be summarized as follows:?1?Firstly,the surface of HGM was treated by hydrofluoric acid etching,and then the liquid filled HGM were prepared by injecting liquid into the HGM with a microinjector prepared by flame heating and stretching method.The HGM was characterized by scanning electron microscopy?SEM?and microscopic photographs.Typical WGM resonance was observed in transmission spectra by coupling with tapered optical fibers.Then,based on the characteristics of WGM resonance formation,the viewpoint that WGM resonance will transfer from the wall to the core with change of the hollow WGM microcavity core refractive index from n_core<n_wall to n_core>n_wall is put forward.The simulation model of liquid filled HGM was established by COMSOL Multiphysics.The electric field distribution of cross sections of HGM with different refractive index cores was observed by changing the core refractive index.The viewpoint of the transfer of WGM resonance position from the wall to the core at the jump point(n_core=n_wall)was theoretically verified.?2?Continue to work on the liquid filled HGM cavity,mainly study the temperature sensing characteristics of liquid filled HGM and explore ways to improve the temperature sensitivity.Firstly,the principle of hollow WGM microcavity temperature sensor is analyzed,and the simulation model of HGM is established by using 3D finite difference time domain?FDTD?.The internal electric field of HGM filled with liquid of different core refractive index is explored,and the resonance characteristics of WGM are analyzed theoretically.Then,we successfully filled temperaturesensitive liquid into the HGM by the effective method.By coupling the liquid-filled HGM to a tapered fiber,the typical WGM resonance was observed.Temperature sensing was realized by changing the temperature of external environment and monitoring the shift of WGM resonance spectrum of liquid-filled HGM.Finally,two methods to improve the temperature sensitivity are explored:?1?The liquid with higher thermo-optical coefficient were injected into the HGM to investigate the influence of the thermo-optic coefficient on the temperature sensitivity.?2?Size-dependent experiments showed that the temperature sensitivity increased as HGMs diameter increased.The highest temperature sensitivity was 334.3pm/C.