Study On Fabrication And Application Of Whispering-Gallery Mode Microsphere

In recent years, the whispering-gallery mode optical microcavities with high-quality factors (Q) and low-mode volume (V) has attracted attentions of many researchers. The Whispering-gallery Mode (WGM) refers to that the light is restrained inside the cavity and circulating around the equatorial plane when it is traveling inside a cavity by total reflection. When the length of the optical path is an integer multiple of the wavelength, that’s to say, when meets the phase matching requirements, the discrete resonant modes with equal intervals occur. Such electromagnetic field mode is called WGM. The WGM microcavities is very small in size as well as easily integrated, and the energy density inside the cavity is extremely high. Moreover, the manufacturing process is easy and simple with low cost. With above properties, the WGM microcavities is used as an important optical component in various fields, such as nonlinear optics, cavity quantum electrodynamics, optical filter, high-sensitivity sensor and low-threshold laser.This paper studied the whispering-gallery mode optical microcavities in theory and experiment. Detailed research contents include the following:Firstly, this paper reviewed the research background and progress of whispering gallery mode optical microcavities in recent years, and gave a brief introduction of the application situations of whispering-gallery mode optical microcavities with specific cases.Secondly, it introduced the mode theory of the whispering gallery mode optical microcavities and the tapered optical fiber. Through Maxwell’s equations and the boundary conditions of microsphere, it analyzed the modes distribution inside the microsphere, and gave a brief introduction of the basic properties of microsphere. Numerical simulations of the modes inside the microsphere were conducted by the method of finite element numerical analysis provided by COMSOL Multiphysics, a kind of commercial software, and thus the distributions of WGM at the equatorial planes inside the microsphere were obtained. The characteristics of tapered optical fiber is discussed using the method of ray optics. Furthermore, COMSOL Multiphysics was used to simulate the optical field distributions on the cross sections of optical fibers with different fiber core diameters, and thus their optical field distributions were obtained. Takeing the coupling system of tapered optical fiber and microsphere as a whole, weanalyze the coupling theoretical foundation.Then, set up an experimental system in which hydrogen flame heating method is used to prepare tapered optical fiber, and prepare a tapered optical fiber that is needed in the experiment and has a diameter on the level of micron dimension. Designing an experimental system for the preparation of microsphere with high-temperature melting technique and cooling method, we apply a carbon dioxide laser to heat and melt single-taper optical fiber, and then prepare microsphere with different diameters (about 60μm-125μm). Establishing a coupling system of tapered optical fiber and microsphere with broadband light source, opticalspectrumanalyzers and CCD monitoring device were used to measure the quality factor of microsphere. Obtain an erbium-doped fiber laser based on the coupling system of microsphere and tapered optical fiber. Erbium-doped optical fiber is used as a gain medium in the experiment, while microsphere used as a filter and reflector is coupled to tapered optical fiber, and a 980nm laser diode is used as the pumping source, to realize the laser output with a wavelength of 1563.95nm. The threshold of this laser is 42.86mW and the maximum output power is 0.1mW.Finally, use the experimental system in which hydrogen flame heating method is used to prepare tapered optical fiber, and prepare a cylindrical microcavity with a gradually-changing diameter. Test the coupling system of tapered optical fiber and cylindrical microcavity and then obtain the quality factor of the cylindrical microcavity. Apply a cylindrical microcavity with a gradually-changing diameter the diameter is about 21μm-38.7μm and achieve a tunable optical filter based on a cylindrical microcavity with a gradually-changing diameter. The displacement of the cylindrical microcavity in the experiment is 60μm; the movement amount of resonance wavelength obtained is 178.8nm, and the change relationship between resonance wavelength and the displacement is 2.98nm/μm.