Research On The Structure And Properties Of The High Q Optical Microresonator

With the continuous improvement of microprocessing technology,the whispering gallery mode(WGM)microcavity has been widely concerned and applied in recent years owing to the advantages of high quality factor and small mode volume.In the field of linear optics,because of the high energy density of the light field,WGM microcavity can be used as an ideal carrier for basic physics research including cavity quantum electrodynamics and cavity optomechanics,as well as for photoelectronic devices such as high sensitivity sensor,filter modulator and narrow linewidth laser.In the field of nonlinear optics,because photons are bound to the boundary of WGM microcavity,internal reflection constantly occurs,thus forming a strong light field,which can greatly reduce the threshold of nonlinear effect.WGM microcavity has important applications in optical frequency comb,Raman effect,parametric oscillation and other aspects.However,there are few commercial products based on WGM microcavities at present,and there are many factors restricting the practicality of microcavities,mainly including noise interference,coupling robustness and stability.The WGM microcavity is susceptible to environmental temperature and its own temperature changes in the resonance state,which causes the resonance wavelength to drift.In the experiment,the perturbation caused by the environment will also destroy the coupling state of the fiber and the microcavity.Therefore,in many cases,in order to improve the robustness of the coupling,the fiber and the microcavity are usually in direct contact,which will also reduce coupling efficiency and quality factor.In order to solve the above problems,we put forward the corresponding solutions.This thesis mainly includes two parts:coupling experiment and theoretical simulation of optical microcavity.In the experiment,the microsphere,quasi-cylindrical microcavity,microbottle and micro-capillary were prepared,and their coupling characteristics were analyzed.In theory,for the problem of eliminating thermal noise,we proposed a three-layer-coated microsphere;for the problem of coupling robustness,we proposed the concept of a graded index microcavity.Specific research contents are as follows:1.In experiments,a high-efficiency coupler fiber was prepared,and then a common microsphere was prepared.The Q value of the microsphere can reach 108.The quasi-cylindrical microcavity is processed by the arc discharge modification scheme.Unlike other microcavities,the quasi-cylindrical microcavity has a clean and nearly equidistant transmission spectrum.The microbottle is prepared by melting and docking two microsphere cavities in the welding machine,and the selective excitation of the mode can be achieved by changing the coupling position.Finally,the micro-capillary was prepared,which has a good application prospect in the fields of liquid sensing and microfluidic.2.A design scheme of a three-layer-coated structure microcavity is proposed.The refractive index of the three-layer film is high,low,and high.The two high refractive index layers of the inner layer and the outer layer can support the whispering gallery mode,which is called the inner mode(IM)and outer mode(OM).There is a huge difference in the detection sensitivity of the two modes to temperature and external refractive index.Therefore,it is possible to modify the thickness of the intermediate film to monitor the difference between the resonant wavelengths of the internal and external modes for refractive index sensing,which not only has high sensitivity,but also thermal noise has been greatly reduced.Similarly,the dual-parameter measurement of temperature and solution concentration can also be carried out with the help of the three-layer-coated structure microsphere.3.The concept of a graded index microcavity is proposed.The refractive index of this kind of microcavity presents a gradient state at the edge.The characteristics of the graded index microcavity under waveguide coupling are analyzed.It can be seen that when the coupling distance between the waveguide and the microcavity decreases,the coupling efficiency and quality factor of the microcavity with gradient refractive index are less affected than those of the common microcavity with constant refractive index.Moreover,the graded index microcavity does not support high-order radial modes,and has a relatively clean transmission spectrum.