Opticalwhisperinggallerymicrocavitieswithhigh-qualityfactorshaveshowngreatpotentialtowardachieveingultrahigh-sensitivitysensinguptoasinglemoleculeornanoparticle,whichraisesahugedemandonadeeptheoreticalinsightintothecrucialphenomenasuchasthemodeshift,modesplitting,andmodebroadeninginsensingexperiments.Hereweproposeanintuitivemodeltoanalyzethesephenomenafromtheviewpointofthenanoparticle-inducedmultiplescatteringoftheazimuthallypropagatingmode(APM).ThemodelunveilsexplicitrelationsbetweenthesephenomenaandthephasechangeandenergylossoftheAPMwhenscatteredatthenanoparticle;themodelalsoexplainstheobservedpolarization-dependentpreservationofoneresonanceandtheparticle-dependentredshiftorblueshift.Themodelindicatesthattheparticle-inducedcouplingbetweenthepairofunperturbeddegeneratewhisperinggallerymodes(WGMs)andthecouplingbetweentheWGMsandthefree-spaceradiationmodes,whicharewidelyadoptedincurrenttheoreticalformalisms,arerealizedviathereflectionandscattering-inducedfree-spaceradiationoftheAPM,respectively,andadditionallyexhibitsthecontributionofcrosscouplingbetweentheunperturbedWGMsandotherdifferentWGMstoformingthesplittingresonantmodes,especiallyforlargeparticles.
