| Whispering Gallery modes(WGMs)are specific electromagnetic modes confined in circular resonators,where light beams are guided along the circumferences of the resonators with very small losses by total internal reflections.The ultra-high quality factors(Q-factors)of WGMs,to-gether with their extremely small mode volumes,allow for a wide variety of potential applications in microwave photonics,nonlinear optics and quantum optics.Ultra-high Q WGM resonators are investigated systematically in this thesis.Starting from the field distributions of WGM,WGM fea-tures and behaviors are fully characterized.The optical and electrical properties of ultra-high Q WGM resonators are analyzed thoroughly by a wide range of theocratical calculations and experi-mental researches.A method to calculate WGM using conformal transformation and transmission line theory is proposed.With this simple and efficient method,the field distributions and resonant frequencies of WGM in different resonators are studied in detail,including small resonators with micrometer diameters,and large resonators with millimeter diameters.A second harmonic generation model of WGM resonator is built.Starting from the Maxwell's equations and nonlinear optical effects of WGM resonator,the second harmonic generation model is realized and simulated.The mechanism of the second harmonic generation in WGM resonator is studied deeply,and the self-pulsing effects of fundamental and second harmonic waves are also ful?ly investigated.Besides,the power threshold of self-pulsing effect in WGM resonator is calculated from the theocratical model.The design and manufacture of ultra-high Q WGM resonators are realized,and the method to fabricate WGM resonators is demonstrated.Different kinds of WGM disk resonators are fabricated successfully,including z-cut lithium niobate(LiNb03)resonator,x-cut LiNbO3 resonator,and magnesium fluoride(MgF2)resonator.The Q factors of the fabricated WGM resonators are measured successfully using our experi-mental setup,and the features of Q factors are also studied in detail.Q factors of different kinds of optical WGM resonators are measured based on the linewidth method and cavity ring down(CRD)method.The measurement results show that,the Q factors of z-cut and x-cut LiNbO3 WGM disk resonators are respectively Q=1.2×107 and Q=2.7×107.These ultra-high Q factors,suggest the excellent optical properties of LiNbO3.In addition,Q factors in different WGM resonators and their measurement methods are discussed and compared.The loss mechanism of the Q factors are also investigated in detail.The optical properties of WGM resonators are studied.Numerous WGM coupling issues are investigated,including the incident angle of the laser light,the coupling gap between the prism and the resonator,the polarization state of the incident light,and the thermal effect in WGM resonators.The mechanism and effect on the WGM resonances of these coupling issues are also discussed and analyzed.The electrical properties of WGM resonator are also investigated.The electro-optic effect in LiNbO3 WGM resonators are studied experimentally and theoretically,and the results show excellent electro-optic effects of LiNb03.In addition,the radiation effect of WGM is analyzed in detail,and an orbital angular momentum(OAM)antenna based on the radiation effect of WGM is demonstrated.The coupling mechanism between WGM and OAM is explained,and the OAM radiation effect is demonstrated based on the simulation and experimental results. |
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