| Summary: | The optics and photonics development is currently driven towards nanometer scales.
However, diffraction imposes challenges for this development because it prevents confinement of light below a physical limit, commonly known as the diffraction limit. Several implications of the diffraction limit include that conventional optical microscopes are unable to resolve objects smaller than 250nm, and photonic circuits have a physical
dimension on the order of the wavelength. Metals at optical frequencies display collective electron oscillations when excited by photon energy, giving rise to the surface
plasmon modes with subdiffractional modal profile at metal-dielectric interfaces. Therefore, metallo-dielectric structures are promising candidates for alleviating the obstacles due to diffraction. This thesis investigates a particular branch of plasmonic structures, namely plasmonic antennas, for the purpose of optical imaging and sensing applications. Plasmonic antennas are known for their ability of dramatic near-field enhancement, as well as effective coupling of free-space radiation with localized energy. Such properties are demonstrated in this thesis through two particular applications. The first one is to utilize the interference
of evanescent waves from an array of antennas to achieve near-field subdiffraction focusing, also known as superfocusing, in both one and two dimensions. Such designs
could alleviate the tradeoffs in the current near-field scanning optical microscopy by improving the signal throughput and extending the imaging distance. The second application
is to achieve more efficient radiation from single-emitters through coupling to a highly directive leaky-wave antenna. In this case, the leaky-wave antenna demonstrates the ability of enhancing the directivity over a very wide spectrum.
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