Study On The Structure Of Fiber Microsphere Whispering Gallery Mode Resonator

The development of the optical microcavity occupies an important position in modern science.The whispering gallery mode(WGM)resonators have attracted the attention of researchers because of their high Q factor,small mode size,easy preparation and of low cost.The WGM phenomenon depends on the size,shape,material and coupling method of the microsphere.And the WGM resonators are widely used in the measurement of temperature and pressure sensitivity,low threshold laser,narrow bandwidth filtering,nonlinear optics,etc.In this thesis,we discusse the development history and theoretical basis of the WGM mode,and propose two new WGM resonators.The details are as follows:1.The basic concepts of the WGM are introduced,and the development histories and research statuses of the WGM are reviewed.The development of theoretical researches and applications of WGM resonators are introduced,the existing WGM microcavities with several different structures are introduced,and the WGM resonators with different coupling modes are compared.Based on the above description,the research objectives of this paper are determined.2.The coupling principle of WGM is introduced from the perspective of geometric optics and mode distribution.Four parameters about the WGM microsphere cavities are introduced as important indicators for evaluating the experimental results.Finally,the Fano resonance model is introduced to explain the Fano line shape.3.We propose a WGM resonator in which a microsphere is embedded in line of an optic fiber.The femtosecond laser micro-processing technology is combined with the arc discharge technology to fabricate an air-cavity inside the optical fiber.The air-cavity bends the core of the fiber to produce Mach-Zehnder interference,and the microspheres are embedded in the air-cavity to excite the WGM.In this chapter,we describe the manufacturing principles and the actual operation process in detail.The device's quality factor Q is 1.81×10~3;the Fano linear slope is 13.88 d B/nm.At the same time,the principle of transforming the asymmetric narrow linewidth Lorentzion lineshape into the asymmetric Fano lineshape under the action of the low Q of the MZI line in the WGM is analyzed.The choice between the asymmetric Fano line type and the symmetric Lorentz line type can be made by directly changing the wavelength range.The device is stable and has strong anti-interference ability,and has the potential to be used as an optical switch in optical switching research.4.A WGM resonator with etched a fiber end is proposed.This device is fabricated by fusion splicing of a section of no-core fiber(NCF)with multi-mode fiber(MMF)and single-mode fiber at its two ends.The open end of multimode fiber is etched by hydrofluoric acid(HF)to create an arc shaped cavity,Using ultraviolet(UV)adhesive to adhere a microsphere at its bottom and the UV adhesive is cured.The device has a high Q factor of?1.21×10~4and a temperature sensitivity of 3.47 pm/°C.As a single-port WGM resonator,the device has great potential in sensing,biological detection and so on.The two optical fiber resonators which presented in this thesis are robust in structure,easy to manufacture,with compact size and in low cost.