Confined Whispering-Gallery Mode In Silica Double Toroid Microcavities For Application

In recent years,optical microcavities become more and more important in the fundamental research and corresponding applications.Especially whispering gallery mode in optical microcavities with high quality factor,small mode volume and easy to integrate in the chip,plays important role in nonlinear optics,optical sensors and tweezer.In the thesis,I give an introduction of optical microcavities and describe the theory of optical sensing and optical trapping.Also,I have proposed the whispering gallery modes in silica double-toroid microcavities and studied their mode distributions,influence factors,the characters of optical sensing application and gradient optical force.Based on the demonstrations mentioned above,this double-toroid structure is good for optical sensing and optical trapping.The main content of the thesis is listed as follows:1.I summarized the research background of optical microcavities and principle of whispering gallery mode optical microcavities.Then,I introduced the types of microcavity,the technology of optical sensing and optical trapping.The applications of optical microcavities in optical sensing and several types of optical trapping are described in details.2.Based on the theory of the optical microcavity,I described the COMSOL Multiphysics software which can be used to simulate and calculate the optical microcavity.The finite element method is used to introduce the simulation process of the optical ring resonator.A series of operations such as geometric modeling and boundary condition setting are described in details.3.In this part,I presented a promising approach and a good reference to obtain the confined WGM in the silica double-toroid microcavity.The structure of silicon double-toroid microcavities and the schematic diagram are described.The structure is consisted of a pair of microtoroid cavities and a gap region with the low refractive index.Through the simulation calculation of the designed optical microcavity and then the analysis the mode of microcavity,it can be found that TM mode could be used to realize the maximal field enhancement.Due to the extremely local field enhancement and confinement,the minimum mode volume is only 4.8 ?m3,which is much smaller than that of the cavity with only single microtoroid.Furthermore,the resonant wavelength,energy ratio and mode volume of the double-toroid microcavity in symmetric TM mode are studied.4.The performances of double-toroid microcavity in optical sensing and optical trapping are analyzed.Through the simulation,the sensitivity of the double-toroid microcavity is about 245 nm/RIU and the sensitivity of double-disk microcavity is about 150 nm/RIU.I can find that the sensitivity of the double-toroid microcavity is obviously larger than that of the double disk microcavity.This is a conclusion that the higher the energy ratio of the microcavity,the higher the sensitivity of the microcavity.The refractive index sensitivity can up to 468 nm/RIU.In addition,the gradient optical force of a single nanoparticle(r=5 nm)could be as high as 22 pN/W because of the local field enhancement,which makes it possible to achieve optical trapping.