Research On High-Q Whispering Gallery Mode Microcavity Sensor

Whispering gallery mode(WGM)optical microcavity is a kind of ring resonator with a size on the order of micrometers.WGM optical microcavity has many different optical characteristics from ordinary resonators because of its special structure and resonance principle.Due to its strong light field confinement ability,WGM optical microcavity can enhance the interaction between light and matter,so that there are broad application prospects in many fields such as optical sensing,lasers,precision measurement and nonlinear optics.With the development of micro-nano fabrication technology and material growth technology,it is possible to combine WGM optical microcavity with special materials,which further expands the application scene of WGM optical microcavity and it also is developing towards miniaturization,diversification,and integration.In this paper,the coupling state,the line shape of the transmission spectrum and the non-Hermitian degeneration of WGM optical microcavity and tapered fiber coupling system are theoretically deduced and numerically simulated.The application of microcapillaries in electric field sensing and DNA molecular detection,and the tunable characteristics of the microspheres are studied.The detailed contents of this paper are as follows:1.The coupling system of WGM optical microcavity and tapered fiber is studied by using the theory of waveguide coupling and electromagnetic wave.The resonant spectrum and transmission spectrum of WGM microcavity are theoretically deduced and its change under different coupling conditions is analyzed.The WGM resonance is related to the Fano resonanceband the Fano resonance in the microcavity is simulated and analyzed.The phenomenon of non-Hermitian degeneration near the exceptional point of the double microcavity coupling system is simulated and analyzed.2.The relationship between the sensitivity of the bulk refractive index and the radius,the wall thickness,and the resonant wavelength of the microcapillary is analyzed by using the wave optics theory.The high Q-factor microcapillaries are prepared by the method of melt inflation and pressure.A contactless mechanical packaging structure is designed and implemented,which can keep the Q-factor of microcapillary at the same level before and after the package.The electric field sensing is realized by introducing protein solution into microcapillary based on the electrophoresis effect.3.The relationship between the molecular density and the sensitivity of the bulk refractive index of the microcapillary is analyzed by using the first-order perturbation to a single-photon resonant state.Then,Poly-L-Lysine solution and DNA probe are ued to functionalize the inner surface of microcapillary and the labe-free specific DNA molecules detection is realized.4.Firstly,the tuning principle of the microsphere is theoretically analyzed according to mode coupling theory and optical waveguide theory.Secondly,the influence of the optical distribution of WGM under different Ti O₂ film thickness is simulated by using of finite element method.Then,a high-power CO₂ laser processing system is designed and built to fabricate a high Q-factor microsphere microcavity,and then the Ti O₂ films are deposited on the surface of the microsphere by atomic layer deposition technology to enhance the tuning characteristics of WGM.The experimental results show that the thermal tuning sensitivity of the coated microsphere is up to 0.43 nm/m W.Finally,a double-ring fiber laser is realized by putting the coated microspheres into the sub-ring severing as a tunable filter and mode selection device with a tunable rang of 0.22 nm.