Thermal Nonlinear Behavior Analysis And Modulation Of Refraction Index In Optical Microcavity

The unique ultrahigh quality factor(Q) and ultrasmall mode volume of a whispering gallery mode(WGM) resonator make it a common device for studying light-matter interaction. In this paper, detailed investigation about the mode theory of microspherical resonator and microdisk manufactory technique are presented. Thermal dynamical model describing thermal nonlinear effect in the microresonator is introduced, based on which thermal oscillation and refractive index modulation characteristics are analyzed experimentally and theoretically. The research contains:(1) The WGMs in microspherical and microdisk resonator are calculated with combined analytical method and finite element method. Parameters concerning the microresonator such as resonant frequency, mode volume as well as the influence of kinds of loss mechanisms on quality factor are estimated analytically. Model describing the coupling of tapered fiber and microsphere is built. Detailed analysis about the phase matching condition during near field coupling and the influences of under coupling critical coupling and over coupling on quality factory and the transmission spectrum are introduced.(2) Low loss biconical optical fiber(<0.3d B) and high-Q microspherical resonator(107~108) are made, using the homemade tapered fiber pulling system. The fiber microsphere coupling system is built to test the microsphere. The processing crafts of silica microdisk investigated, methods to reduce the surface roughness are introduced. A silica microdisk on Silicon substrate with roughness about 1.7nm is made.(3) By considering the two thermal relaxation processes simultaneously, the thermal nonlinear effect was analyzed. Based on the improved model, the influence of the sweeping pump under different velocities on the temperature change and the fluctuation of a resonance were investigated. The universally exacting thermal oscillation phenomenon as well as the method to reduce oscillation was illustrated; it is a combined interaction between the fluctuation of the pump and the two thermal relaxation processes that leads oscillation on the transmission spectrum.(4)The frequency response characteristic of refractive index modulation based on thermo-optic effect was investigated theoretically. Experimentally, the refractive index modulations in the mode volume and microsphere structure were achieved. The modulation in the mode volume is small range but high frequency, and that of the microsphere structure is large but low frequency.(5) Super resolution image of 100 nm is experimentally achieved under white light illumination with silica microsphere. The experimental super resolution image was illustrated based on the whispering gallery mode theory.To summarize, we improve the thermal dynamical model and reveal the mechanism of thermal oscillation as well as method to reduce oscillation. And refractive index modulation in the microspherical resonator based on thermal relaxation processes is attained.