Study On The Fano Resonance And Its Application Based On Cylindrical Microcavity

Whispering gallery mode microcavity has the advantages of high Q factor and small mode volume.It has wide applications in low threshold lasers,nonlinear optics and biochemical sensing.In recent years,researchers dedicated to explore the design of optical devices and high sensitivity sensors based on WGM microcavity,promoting the integration and innovation of WGM microcavity with surface plasmon and Fano resonance technology.In this paper,firstly,the mode characteristics of a metal-coated cylindrical microcavity are studied theoretically.Starting from the Maxwell equations,electromagnetic eigenequation is derived in the three layer cylindrical coordinate.By drawing the mode dispersion curves in metal-coated microcavity,we found coupling phenomenon between WGM and surface plasmon polariton(SPP).Through the analysis of the hybrid WGM-SPP modes generated from strong coupling,we found that they have high Q factor,high refractive index sensitivity,low detection limit and high FoM,which has potential application in sensing areas.The other core of this paper is the excitation of the Fano resonance and the exploration of its related applications in cylindrical microcavity.Ultrathin fiber taper can excite localized mode and delocalized mode simultaneously in the cylindrical microcavity.In the vicinity of coupling point,the discrete WGM and continuous background light will interference with each other,producing asymmetric Fano resonance spectrum.By adjusting the coupling strength or the diameter of the fiber taper,we can adjust the intensity of the continuous background light,change the ratio of the discrete resonance mode to the continuous background light intensity(that is defined as the Fano parameter),and adjust the phase and intensity of the Fano resonance eventually.When the fiber taper with diameter 1?m contacts microcavity,EIT-like(electromagnetically induced transparency)Fano resonance will be generated,which has lOdB extinction ratio,15%transmittance.Thus,based on Fano resonance,we can design a narrow-band optical filter and apply it in ring fiber laser as mode selection device.The threshold of the laser is 27.9mW and the wavelength of the laser can be tunable by adjust the polarization of pump light.In addition,combined with Optofluidics technology,different concentrations of water and alcohol solution as the sample are injected into microcapillary.By observing the wavelength shift of Fano resoannce in the oscilloscope,we can realize the 800nm/RIU refraction sensitivity,4192 FoM(Figure of merit),which has great applications in biochemical sensing.