Research On Optical Frequency Comb Generation In Magnesium Fluoride Micro-resonator

Optical frequency comb(OFC),which behaves as a series of cascaded equivalent lines in frequency domain,has attracted much interest of researchers for its unique time-frequency properties and application potential in metrology,astronomy and op-tical communication.Recently,micro-resonator with high quality factor becomes hot in OFC generation.On one hand,the interaction intensity in microcavity between light and matter is dramatically enhanced due to the resonance,which can excite nonlinear optical effect at a low pump power threshold and generate hundreds of comb teeth with four wave mixing.On the other hand,micro-resonator is integrable and has a compact system structure,which makes it advantageous in deviceization.However,much work still need to be done on the research in microcavity OPC,including the further study on nonlinear effect,and how to excite an OFC in an efficient but simple approach and maintain its shape in a long time.Soliton is a special coherent OFC with low noise.This thesis discusses the require-ment and method of soliton generation.First the thesis introduces the bistability effect caused by Kerr nonlinearity and thermo-optic effect when scanning pump,and elabo-rates the requirement for abnormal dispersion and positive thermo-optic index to excite soliton comb.The approach through scanning from blue-detuning to red-detuning is proposed,which is detailedly illustrated in theory,and is simulated for siliton genera-ton in micro-resonator.A finite element method is established to analyze the dispersion in micro-resonator and a method is put forward to toilor the dispersion of a wedge MgF2 microcavity with three parameters which are radia,wedge angle size and angle position.Then the soliton process in micrcavity is simulated using LLE to evaluate the effect of scanning speed,quality factor and others.The analysis can be of guiding significance to the manufacture of MgF2 microcavity.MgF2 microcavities with Q close to 108 level are manufactured through ultra-precise polishing.By teating and stretching a optical fiber,a high-transmittance fiber taper is produced,and couple it with a MgF2 micro-cavity at a high efficiency,where thermo-optic effect,and mode spilt phenomenon are observed.The soliton step occurs and an OFC with hundreds of teeth is excited under a high pump power.In conclusion,the generation process of OFC and soliton is illustrated in theory and in simulation in this article.Then a method to toilor the dispersion in microcavity is proposed.MgF2 microcavity is manufactured and OFC can be excited in it.Mi-crocavity OFC studied in this article can furtherly be applied in precise measurement,astronomical spectrum and coherent optical communication,and is of importance to metrology.