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28 August 2008 Nanoplasmonics in near-field optics and active coupling
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Surface plasmons enable the transmission of optical information in confined geometries, inaccessible for diffraction-limited far-field light, while having high signal bandwidth and propagation speed like conventional optics. These advantages have resulted in novel applications for surface plasmons, such as offset-apertured near-field scanning optical microscope (NSOM) probes. A subwavelength aperture couples surface plasmons that illuminate the tip apex of an adjacent metal-coated tip, which results in a single-lobed probing optical spot having a full-width half maximum (FWHM) similar to the apex diameter. Since the surface plasmons converge at the apex, an offset-apertured probe promises stronger localized electric fields than an apertured NSOM having comparable FWHM. Additionally, the subwavelength aperture does not permit the passage of far-field light, reducing the background signal in comparison to apertureless NSOM probes. For other applications, the ability to selectively switch a waveguide "on" or "off" is desired. Optical-optical switching for selective surface plasmon coupling would ideally permit high-speed switching on a small scale. Two nodes are presented as means to perform switching of four planar thin surface plasmon waveguides by interfering TEM10, TEM01, and TEM00 light beams normally-incident upon a node. One node uses a flat-apexed pyramidal reflector to reflect the incident light toward the waveguides' ends. An alternative node is a simple square aperture, which couples surface plasmons through light diffraction at the aperture's edges. Individually turned-off waveguides are shown to have their coupled power attenuated by at least -10 dB.
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Michael C. Quong and Abdulhakem Y. Elezzabi "Nanoplasmonics in near-field optics and active coupling", Proc. SPIE 7033, Plasmonics: Nanoimaging, Nanofabrication, and Their Applications IV, 70330R (28 August 2008);

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