Fabrication And Characteristics Of Chalcogenide Glass-based Microsphere Resonators

In recent years,whispering-gallery mode optical microspheres with high-quality factors?Q-factors?,small mode volume?Vm?,and narrow spectral linewidths have attracted attentions from many researchers.The volumes of optical microsphere resonators are small,the energy density is very large,and the fabrication methods are relatively convenient.Due to excellent properties mentioned above,microsphere resonators have found important applications in various fields such as low threshold microlasers,non-line optics,cavity quantum electrodynamics,superhigh sensitivity sensors,and narrow-band spectral filters.Current microsphere resonators are mostly operative in the visible or near infrared spectra.In this thesis,we research on utilizing the novel infrared material of chalcogenide glasses in building microsphere resonators.Chalcogenide glasses have excellent optical properties in the infrared spectrum,such as wide transmission windows?0.5-25 ?m?,high refractive indices?2.0-3.5?,and low phonon energies?low 350 cm-1?.Therefore,chalcogenide glass based microsphere resonators can potentially be used in mid-or long-wavelength infrared optical/photonic application fields.We report the fabrication and characterization of two different types of chalcogenide glass based microsphere resonators,including a Ge₂₈Sb₁₂Se₆₀ based passive microsphere resonator and a Tm³⁺ doped Ge-Ga-S based active microsphere resonators.The content of this thesis is organized as follows:In chapter one,we first introduce the current research status of whispering-gallery mode optical microsphere resonators.We then propose the research topics of this thesis and provide a general research plan.The last part of this chapter explains the importance of this work.In chapter two,the thesis introduces background theories of microsphere resonators.By using the Maxwell equations,we numerically analyze the whispering-gallery mode in microsphere resonators and obtain the characteristic equation of microsphere resonators,analytical expression of whispering gallery modes,and four characteristic quantities describing a specific mode.Also,inthe last part of this chapter,we explain the coupling theory between a fiber taper and the microsphere cavity.Chapter three provides important experimental details of this work.We introduce the general fabrication methods of chalcogenide glass and chalcogenide glass microsphere resonators.We also explain the experimental process of fabricating silica fiber tapers and coupling the pump light into microsphere resonators via a fiber taper.In chapter four,we discuss the fabrication and characterization of a specific type of chalcogenide glass: Ge₂₈Sb₁₂Se₆₀(Ge₂₈)and explain why this glass is suitable for building microsphere resonators.We then introduce the fabrication process of microsphere resonators using the Ge₂₈ glass.Finally,we provide characterization results of Ge₂₈ microsphere resonators and demonstrate that Q values of Ge₂₈ microspheres can reach Q?1.717×104.In chapter five,we introduce the utilization of Tm³⁺doped Ge-Ga-S glass to build active microsphere resonators.We introduce the fabrication and characterization of Tm³⁺ doped Ge-Ga-S glass samples and provide detailed procedures about building Tm³⁺doped Ge-Ga-S glass microsphere resonators.We also provide fluorescent whispering-gallery mode patterns obtained with the microsphere resonator and explain why these mode patterns fit with theoretical calculations.The last chapter concludes the work.We summarize experimental results and point out problems that are still existent in the current work.We also discuss research topics that might be interesting to carry out in the future work.