Research On Characteristics Of Thin Micro-tube Resonator Sensors Based On Whispering Gallery Modes

Optical microcavities are important photonic devices which have the advantagesof high quality factor and small mode volume. They receive extensive attentions inthe field of basic and applied areas, such as cavity quantum electrodynamics,nonlinear optics, extremely low threshold microcavity lasers, high-sensitivity sensorsetc. Optical microcavity sensors with whispering gallery resonant modes not onlypossess small size, high sensitivity, low detection limit, but also can achieve label-freedetection of biological reagents with high detection reliability, so they have greatpractical value. In this paper, the optical microfluidic tube refractive index sensors arestudied, work completed are mainly:According to classical electromagnetic theory, based on Maxwell’s equations, inthe cylindrical coordinate system, the relationships between mode transverse andtoroidal field are derived, micro-tube electromagnetic radial distribution function isderived. According to the continuity of the boundary conditions, get the relationshipbetween the coefficients. Using of Mie scattering method, we solve the resonancewavelength of micro-tube resonators.Study the region of energy storage and radiation losses about micro-tube, getformula to calculate the value of radiation Q-factor, analyze the influence ofresonance modes on the performance of micro-tube refractive index sensors, explainthe phenomenon that sensitivity and Q-factor will increase when high refractive indexliquid is filled in micro-tube, and it is a phenomenon peculiar to small sizemicro-tubes. Find the change of high order modes sensitivity versus liquid refractiveindex is not increasing monotonically.Study the effect of wall thickness and size on micro-tube sensing properties,analysis two limiting cases of micro-tube structure, when wall thickness is zero andthe radius is relatively large. To such tube with two layers structure when wallthickness is zero, mode of the first order in radial direction has the maximumsensitivity and Q-factor.For thick wall tube with hundreds of microns radius, explain the reason forfluctuation in sensitivity with radial quantum number increasing when modes are highorder in the radial direction.