Research On Sensing And Tuning Application Of Whispering Gallery Optical Microcavity

Optical microcavity is a micron or sub-micron resonant cavity,which can localize photons in a very small space area,effectively reduce the size of the optical cavity,and enhance the interaction between light and matter,have been extensively used in environmental monitoring,biochemical sensing,physical sensing and medical diagnosis,etc.The commonly used optical microcavities include Fabry Perot(FP)microcavities,photonics crystal(PhC)microcavities,and whispering gallery mode(WGM)microcavities.Among them,the WGM optical microcavity is widely used in the research fields of optical sensing,tuning and nonlinear optics due to its ultra-high quality factor(Q),small mode volume and ultra-low detection limit(up to a single molecule level).So far,WGM optical microcavities with a variety of geometric structures have been extensively investigated,such as microsphere cavities,microring cavities,and microbubble cavities.In this paper,based on the whispering gallery mode optical microbubble cavity,a dual-WGM spectral self-referencing technology is proposed to study the phase transition dynamics of temperature-sensitive polymers,and a new structure of graphene-assisted tunable microbubble cavity resonator is proposed.The main content of this article is divided into the following three parts:Fabrication of WGM microbubble resonator and construction of coupling system.The fabrication of the whispering gallery mode optical microbubble cavity and the construction of the coupling test system are the basis for realizing the application research of the microbubble cavity.In this paper,a high-efficiency coupling device fiber cone and a high-quality factor microbubble cavity are prepared based on the thermal drawing method using a hydrogen flame machine and a carbon dioxide laser.In the experiment,in order to realize optical microcavity sensing application,a three-dimensional nano-translation stage was used to build a coupling test stage for fiber cone and microbubble cavity.Investigation on temperature-sensitive polymer phase transition kinetics base on WGM microbubble resonator.In the experiment,a high quality factor(>107)whispering gallery mode microbubble cavity was fabricated,and the sensing test system was built.The temperature-sensitive polymer(PNIPA)solution was injected into the microbubble cavity through a microfluidic tube,and light heating was used.To precisely control the phase transition process of PNIPA,the wavelength of heating light is 1550 nm,and the wavelength of detection light used is 780 nm.This study uses the proposed self-referencing spectrum technology to successfully decode the PNIPA refractive index and temperature information during the phase change process from the transmission spectrum of the whispering gallery mode microbubble cavity.Real-time measurement revealed the increase of intrinsic refractive index during the phase transition of PNIPA.In real-time measurements,it is found that the refractive index of PNIPA exhibits a hysteresis phenomenon in the cycles between hydrophilic and hydrophobic states for the first time.In addition,under thermal-equilibrium conditions,it is found that the refractive index of PNIPA exhibits a classical Boltzmann distribution depending on the heating power and manifests the threshold of the phase transition.This study can be further extended to other materials and provide great opportunities for exploring on-demand dynamic biochemical processes.Thermal tuning of whispering gallery mode.A novel structure of graphene-assisted tunable microbubble cavity resonator is proposed.According to the basic principle of heat transfer,a three-dimensional model of the graphene-microbubble cavity control device was established in the COMSOL software,and numerical simulation was carried out using the finite element method.The performance parameters of the graphene-microbubble cavity tuning device were studied in detail.When the current varies from 0 to 1 mA,the tuning range is?3.09 nm and the 90%rise time is?14.0 ms in the empty microbubble,and the tuning range is?3.19 nm and the 90%rise time is?14.5 ms in the microbubble filled with water.The proposed graphene-microbubble cavity hybrid integrated device provide an opportunity for tunable microcavity laser biosensing.