Near-field Optical Characterizations And Applications Of One-dimension Micro/nanostructures

One-dimension micro/nano material has become one of the focuses in micro/nanotechnology due to its novel physical, chemical and biological properties. Recently, micro/nanofibers (MNFs), semiconductor nanowires and metal nanowires have been fabricated or synthesized with uniform diameters, smooth surfaces and good mechanical properties. Using these micro/nano materials, light can be highly confined on subwavelength scale with strong evanescent fields propagating in vicinity of the wire surfaces, making them suitable for subwavelength optical waveguiding in photonic applications. In micro/nanophotonic devices, the optical interactions among micro/nanostructures usually occur in subwavelength area (so called "near-field" region). Therefore, near-field optics is proven to be one of the key points in studying optical properties of micro/nanostructures. In this article, the near-field properties of one-dimension micro/nanostructures are experimentally investigated.Normally, the as-synthesized one-dimension micro/nano materials do not directly functionalize as photonic devices. Thus, the manipulation of the as-synthesized micro/nano material has become one of the most important processes in device fabrication. In this article, we introduce a simple and effective approach for micromanipulation of MNFs and nanowires.As strong evanescent waves existed in vicinity of the micro/nanostructures directly reflect the waveguiding properties and optical interaction, evanescent wave detection became a direct method for investigating optical properties of micro/nanostructures. However, evanescent waves can not be detected by far-field optical microscope. In this case, near-field scanning optical microscope (NSOM), using a fiber probe in vicinity of the micro/nanostructure to detect evanescent waves, became an important tool. In chapter 3, using a commercial NSOM, we investigate the near-field characteristics of MNFs. Single-mode and multimode outputs of MNFs in the presence of a substrate are studied. Spatial modulation of the longitudinal field intensity near the output end of a silica MNF is well resolved. Energy exchange through evanescent coupling between two parallel MNFs is also investigated.To improve the signal-to-noise ratio of the NSOM measurement, uncoated probes are introduced. The uncoated probes used here are fabricated by etching commercially available aluminum-coated probes. Compared with those obtained using coated probes, except the "edge effect", the main features read from the NSOM images with uncoated probes, including the spatial modulation period and the coupling length, are in accordance with each other.Conventional approaches for surface plasmon (SP) excitation in silver nanowires including Kretschmann geometry and objective-focusing require bulk optical components (e.g., prism or objective), which may limit the compactness of the launching system. In Chapter 4, we demonstrate SP excitation in silver nanowires directly deposited on the emission facet of a laser diode (LD) chip. The main advantage of this approach is the realization of on-chip integration of optical sources (LDs) and plasmonic waveguides (silver nanowires), and therefore greatly miniaturization of the scale of SP excitation system for compact plasmonic and photonic applications. The nanowire output is found to be dependent on the polarization and the nanowire orientation. Simultaneous SP excitations in multiple silver nanowires and SP excitation at the central part of a nanowire are also investigated. On-chip SP excitation proposed here may open opportunities for realizing plasmonic and photonic circuits or components with high compactness.