Characterizations And Applications Of Surface Plasmon Polaritons In Metallic Micro/nanowires

Surface plasmon polaritons (SPPs) in the metallic micro/nanostructures are the collective oscillations of the free electrons on the interface of metal and dielectric. Owing to its unique properties of tight confinement and field enhancement on the surface, SPP waveguides can break the diffraction limit of light and carry optical and electrical signals simultaneously. Plasmonic components and devices based on the metallic micro/nanostructures have become one of the main research topics for the next-generation high-density photonic circuits. For this purpose, field distribution and waveguiding properties of plasmonic strucutres are among the basic and hot topics in the current micro/nanophotonics research. In this work, we focus on the characterizations and applications of SPPs in one-dimensional Au and Ag micro/nanowires which are among the typical plasmonic micro/nanostructures.In the first part of this work, we introduce the fabrication of metallic micro/nanowires and glass microfibers. We synthesized Au and Ag nanowires by chemical method, and fabricated silica microfibers by flame-heated taper drawing of optical fibers. We investigated the field distribution of waveguiding microfibers and metallic nanowires using a scanning near-field optical microscopy (SNOM), which was proved helpful for the following studies.In the second part of this work, we introduce the fabrication and characterization of single-nanowire plasmonic Bragg gratings. We fabricated the single-nanowire Bragg gratings by focused-ion-beam (FIB) milling of single Au nanowires, and collected singals out of the nanowire using nanofiber evanescent coupling. We observed evident grating features in the single-nanowire gratings. The Bragg wavelength can be adjusted by changing the grating periodicity. The grating effect is also sensitive to the grating parameters, such as grating depth, width and length. Our results suggest a novel approach to one-dimensional plasmonic grating with high compactness and flexibilities, which may find applications in low-dimensional wavelength-selective plasmonic circuits and nanoscale optical sensing. In the third part of this work, we demonstrated the whispering gallery (WG) resonances of SPPs in Au microwires. On the surface of a30-μm-diameter Au microwire, SPP WG resonances were observed by using a fiber-taper-coupling technique. Although SPPs leaked out along the axis direction, the SPP WG resonance could be supported in the circumference plane of the Au microwire by SPP self-interference. The quality factors of WG resonator went up to375. The coupling-angle-dependence of the WG resonance was also investigated. The obvious WG resonance could be found under the condition of vertical coupling. The SPP WG resonator we proposed opens opportunities to realize easy-fabrication, flexible, high-quality and compact SPP cavities and can be extended to diverse metallic structures such as metallic nanowires. The simple SPP resonator we demonstrated has potential applications in a variety of areas including plasmonic sensing.In the last part of our work, we used electron beam to excite SPPs in single-crystalline Au nanowires, and characterizied the SPPs using electron energy loss (EEL) spectroscopy. The preliminary results of the EEL spetra revealed different SPP modes in coupled nanowires. The spectral shape was more complex than that of a single Au nanowire. The peak shift was attributed to the multiple SPP modes in the coupling structure. Further understanding of the formation of the peak-shift is important to the study of SPP in metallic micro/nanostructures.Overall, in this work, for the first time, we demonstrated the Bragg grating in single metallic nanowire and realized the plasmonic WG resonantor with two-dimensional confinement in metallic microwires. Our results may helpful for the excitation, propagation and application of SPPs in one-dimensional metallic micro/nanostructures.