Research On Thermal Oscillation Effect Of Composite Whispering Gallery Optical Microcavity

With high quality factor and low mode volume,whispering-gallery-mode(WGM)optical microcavity becomes the focus of scientific research increasingly and has been applied in various applications.Multilayer composite microcavity has unique phenomenon that can not be observed in single-material resonators.However,current researches on thermal oscillation phenomenon of microcavity is limited to the material with double or single layers.This paper focuses on three-layer composite WGM microsphere.Two different models are proposed.The first is a three-layer microcavity composed of silicon dioxide,polydimethylsilane(PDMS),and silicon dioxide.Their optothermal effect are positive,negative and positive respectively.The second type is a three-layer microcavity composed of silica,PDMS,and filamentous protein,whose optothermal effect are positive,negative and negative respectively.Both thermal expansion effect and two heat dissipation processes are considered.Based on coupled-mode theory and optothermal dynamics model,we use Runge-Kutta method to perform theoretical simulations.Then we give physical explanations for their thermal oscillation processes and analyze their reasons.According to the analysis of theoretical simulation,we find that:In the first model,the greater thickness ratio of silica to PDMS,the greater the number of self-excited oscillation periods and oscillation frequency of composite WGM microcavity.The composite microcavity with three-layer structure has a narrower resonance spectrum and more oscillation periods than double-layer microcavity.In the second model,we observe the unique oscillation waveform of the composite WGM microcavity.The waveform is composed of two oscillation periods with different speeds.The slow oscillation period contains several fast oscillation periods,and the fast oscillation only occurs in the temperature rise interval of filamentous protein and silica.We construct a thermodynamic equation based on the coupled-mode theory to explain this phenomenon.The simultaneous phenomenon of oscillation may have potential applications in sensitive detection.