Experimental Studies Of Whispering-gallery Modes On The Microsphere Resonator Coupled By Tapered Fiber

The Whispering Gallery Modes(WGMs) microcavities had attracted great interest because of its ultrahigh-Q, and become a new direction for studies in optoelectronics. In this paper, the microsphere and tapered fiber coupling system, as a whole, is regarded as the object of study. In the experiment, the discrete structural resonance in the quartz microsphere and glass microsphere doped by Er³⁺ is observed. This part contains the following contents:Firstly, we introduce the developments of microsphere cavity and the applications in detail. According to the Mie scattering theory, the optical field in the microsphere cavity had been obtained. And the characteristics of microsphere cavity had been analyzed.Secondly, the rig proposed by E. D. Timothy had been changed in structure and control method. The physical parameters which affect the fabrication process of the tapered fibers were analyzed. According to the self-regulating effect of the CO2 laser in the process of melt-drawn fiber, the relation between the required CO2 laser power and the moving distance of the motorized stage in the fabrication process of fiber taper is found. The dependence of the required laser power and the moving distance of one motorized stage running is of approximately linear increment, which largely simplifies the computer control. The tapered fibers fabricated by our system have the good shapes. Using the fabricating system, the quartz microsphere and the glass microsphere doped by Er³⁺ had been made, and the microspheres have the good shapes.What's more, the coupling system between microsphere and tapered fiber had been analyzed theoretically. Using the weakly guided mode, the propagation constants of basic mode for tapered fiber with different waist radius had been calculated precisely. The correspondence relationship for radius had been given when the tapered fiber as pump method to phase-matched excite the WGM laser in the microsphere. Furthermore, the relation between the air gap and the coupling efficiency was discussed.The spherical microcavity coupling system had been constructed with taper fiber and the quartz microsphere. In the experiment, a coupling system was made of fiber taper with the diameter of 3.1μm and a quartz microsphere with 143.1μm diameter. The discrete structural resonance in the absorption spectra of quartz microsphere was observed. According to the spherical microcavity theory, the above structural resonance was analyzed, and the Mie scattering theory was used to calculate the position of the first order TE modes and their spacing distance. The calculated result was in accordance with the observed resonance, with an error of only 0.03%.Lastly the characterizes of Er³⁺ doped phosphate glass was measured, such as the absorption spectra, fluorescence spectra and fluorescence lifetime, and the experimental results were accordance with the given date of Er³⁺ doped phosphate glass. Using the Er³⁺ doped phosphate glass, the Er³⁺ doped phosphate glass microsphere is fabricated. A coupling system was made of fiber taper with the diameter of 2μm and a Er³⁺ doped phosphate glass microsphere with 80.4μm diameter. The discrete structural resonance in the absorption spectra of Er³⁺ doped phosphate glass microsphere was observed. The result is found at the first time in china.