| Because of the importance of light-matter interaction,people are very interested in looking at how to enhance the interaction.As we know,optical cavity can improve the light-matter interaction by increasing the optical energy density of light.Optical cavity is also widely used in many areas,such as the generation of laser,high-sensitivity optical sensing,quantum information,and so on.Photonic crystal cavity not only possesses the quality of usual optical cavity,but also is capable to realize the light control at micro/nanoscale using photonic bandgap.For example,two dimensional photonic crystal cavity based on silicon has extremely small cavity mode volume and ultrahigh cavity quality factor.In recent years,people start to pay more attention on the cavity based on the micro/nanofiber because the cavity exhibits strong evanescent field which is useful for enhancing the interaction between cavity and the surrounding matter.But until now,due to reasons of material processing and nanofabrication fabrication difficulties,silica fiber cavity Bragg reflector only has low refractive index contrast,thus it usually needs several hundreds periods to confine light efficiently within the cavity.At the same time,micro/nanocavity based on silica fiber is more likely to produce radiation loss for the reason of low refractive index,although the can be useful for the generation of strong evanescent field.In this thesis,we investigate and explore these issues related with fiber based micro/nanocavity.The main contents are as follows.Firstly,we fabricate a one dimensional photonic crystal cavity based on microfiber with a broadband and realize suppression of the radiation loss theoretically and experimentally.Each reflector of the cavity,which is suspended in the air with a 150 nm bandgap,has only 11 through-holes etched by focused ion beam etching technique in a fiber taper with diameter of 1.7 microns.The rule of hole size design is to produce a high refractive index contrast as possible and ensure sufficiently large mechanical strength of the micro device at the same time.Then we use the method of radiation coherence,which is realized by changing the two inside holes of cavity reflector in experiment to reduce the losses.Secondly,we theoretically design and experimentally realize a broadband ultrasmall microcavity in a freely suspended microfiber for sensing different numbers of polystyrene microparticles whose diameter is 2 ?m.The performance of the microcavity is predicted by the theory of one-dimensional photonic crystal and verified by the numerical simulation using the finite difference time domain(FDTD)method and the experimental characterization of reflection and transmission spectra.The penetrating length into the reflectors as small as about four periods is demonstrated in the numerical simulation,giving rise to the ultrasmall effective mode volume that can increase the sensitivity and spatial resolution of sensing.Moreover,the reflection band as large as 150 nm of the reflectors of the microcavity has been realized in silica optical microfiber in experiment,which highly expands the wavelength range of sensing.Our proposed microcavity integrated in a freely suspended optical fiber offers a convenient and stable method for long-distance sensing of microparticles without the need of complicated coupling systems and free from the influence of substrates.Finally,we realize the elongation of plasmon lifetime through the interaction between the mentioned photonic crystal cavity and the Au nanorod.The localized surface plasmon resonance(LSPR)of the Au nanorod is excited by a vertically incident broadband light source.The LSPR bandwidth is suppressed to about 7 nm from 70 nm for a bare Au nanorod.To conveniently study the coupling with the change of cavity length,we have utilized cavities with micron cavity length. |
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