| WGM microcavities have been favored by many research fields due to their extremely high-quality factor and small mode volume,which are widely used in lasers,sensors and nonlinear optics.With the continuous development of processing technology the types of microcavities are gradually increasing in order to better meet the needs of various fields,including microsphere,microring and micrtoroid.The quality factor of the microsphere is on the order of 10~8 for its high surface finishment.The disadvantage is the tendency to degenerate in the microsphere cavity,resulting in a messy resonance pattern.There are few resonance modes in the microring cavity,but the quality factor is limited by the preparation conditions,and can only reach 10~6 at most.The microtoroid has both a high surface finishment,capable of a quality factor of 10~8,and contains fewer resonant modes for easy control of the coupling patterns.It has become a research hotspot in recent years with the advantages of both microsphere and microring.This thesis focuses on the microtoroid with high quality factor,and the main work includes the following parts:1、Firstly,the research progress of WGM microcavity and the classification of WGM microcavity are introduced,and the applications of WGM microcavity in lasers,optical filters and nonlinear optics in recent years are summarized.Then,the theoretical model of photon confinement by microcavity and three main performance parameters are introduced.Finally,the energy transmittance of the tapered fiber coupled with the microcavity is deduced.The effects of the coupling distance,the diameter of the tapered fiber at the coupling position and the small diameter of the microtoroid on the coupling efficiency,the number of resonant modes and the FSR are obtained through simulation analysis.2、Fabrication of microtoroid cavity for high quality factors.Firstly,the silicon oxide wafer is chrome-plated,glued,photolithography,developed,de-chrome and HF buffer etching treatment,and the pattern on the reticle is transferred to the silicon oxide layer.Then,the silicon substrate is etched isotropically with HF/HNO3 solution to obtain a microdisk cavity with a diameter of 120-220μm.The carbon dioxide laser thermal reflow is performed on the microdisk cavity to obtain a microtoroid cavity with a total diameter of 160μm and a small diameter of 5μm.Finally,the quality factor Q of the microtoroid cavity is1.3×10~6,which is measured by the method of wavelength scanning in the coupling system between the microtoroid cavity and the tapered fiber.3、A single-mode narrow linewidth laser based on a microtoroid cavity is constructed.Using the Fano resonance pattern in the microtoroid cavity,the microtoroid cavity is added into the fiber ring laser as an optical narrowband filter,and the single-mode narrow linewidth output is obtained.In the case of single-mode output of the laser,the threshold power is 32.6 m W,the maximum output power is 3.075 m W,and the slope efficiency between the laser output power and the pump source power is 8.5%.Finally,the laser linewidth is measured by the time-delayed self-heterodyne method,and the linewidth curve is fitted by the Voigt line type,the laser linewidth is measured to be 1.457 k Hz. |
