Mode Properties Of Hybrid Plasmonic Whispering-Gallery Mode Microcavities

In recent years, the whispering-gallery mode optical microcavities with high quality factor and low mode volume have drawn attentions of many researchers. They are suitable for a wide range of applications including nonlinear optics, Cavity Quantum Electrodynamics, optical filters, high-sensitivity sensors and low threshold lasers, this is because that the whispering-gallery mode optical microcavities posses small size, high energy density inside the cavity, convenient manufacture, low costs and ease integration. However, due to the diffraction limit, the optical mode size and physical device dimension of those optical microcavities are restricted to being larger than half the wavelength of the optical field, which is undesirable in micro/nano applications. On the other hand, surface plasmon polarition (SPP) is an electromagnetic excitation existing on the interface between the dielectric and metallic media. The electromagnetic energy of a surface plasmon mode is highly confined at the metal-dielectric interface. Moreover, it has the ability to concentrate and channel electromagnetic energy below the so called diffraction limit. Therefore, plasmonic structures have attracted a lot of attentions in various applications. Thus plasmonic microcavities are proposed. But the problem is that the metal absorption loss is high, which prevent the plasmonic microcavities in applications.Recently hybrid plasmonic whispering-gallery mode microcavities which are a combined of whispering-gallery mode optical microcavity and plasmonic microcavity have been proposed as a good option to realize relatively high O factor as well as nano-scale light confinement. The hybrid microcavities provides the potential applications at deep sub-wavelength scale.In this thesis, we mainly studied the hybrid plasmonic whispering-gallery mode microcavities in theory. Specially, the content of this research is as follows:Firstly, the study of whispering gallery mode optical microcavities and plasmonic microcavities is briefly reviewed, furthermore, we introduce the research background and progress of hybrid plasmonic whispering-gallery mode microcavities.Secondly, research method id investigated. The thesis applied the finite element method which is introduced in detail. The characteristics of the whispering gallery mode optical microsphere are studied, the result obtained by the COMSOL Multiphysics is in agreement with the experimental values in the previous literature.Then, the characteristics of the hybrid plasmonic whispering-gallery mode microcavities are discussed. Section one studies the hybrid plasmonic whispering-gallery mode microdisk, which possess relatively high quality factor and small effective mode volume. The second section theoretically studies the hybrid plasmonic whispering-gallery mode microring, it can be engineered to be applicable for ultra-compact sensing applications with a high sensitivity of 497 nm/RIU at deep sub-wavelength scale.Finally, we theoretically propose novel hybrid plasmonic whispering-gallery mode microcavities which have hybrid gaps but not homogeneous gaps. Section one studies a hybrid plasmonic microdisk with air-filled regions in the low-permittivity dielectric gap. the modified plasmonic microresonator demonstrates higher O factor than the traditional hybrid plasmonic microcavity due to the existence of the air-filled regions. But when we talk able the effective mode volume V curves, the conventional hybrid microresonator can be superior to the modified structure. However, reductions in the loss could be achieved when the effect mode volume V is only slightly increased. Moreover, in sensing application, calculations show that the modified hybrid plasmonic microresonator with air-filled gap regions can offer possibilities for both high Q factor and high sensitivity. The second section studies a hybrid plasmonic microring with double gaps. Our simulations show that a high quality factor of 1181 and a small mode volume of 0.154 μm3 have been achieved. On the other hand, due to the double gaps between metallic and high-index semiconductor structures, the modified structure simultaneously allows a large refractive index sensitivity and a high quality factor.