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(a) Analytical dispersion curve of the lowest-order TM mode of waveguide for . The open (closed) circles indicate the resonances of the open (closed) cavities for a certain value. The coordinate system, the cavity structures, and the electric field of each resonance are schematically illustrated. An -polarized plane wave incident in the direction excites the TM modes. (b) Electric field enhancement at the center of the core entrance for and . The solid and dotted curves are for the closed and open cavities, respectively. The peaks correspond to the resonances in (a). The upper axis denotes the ratio of to obtained from (a).
Fabrication process of a closed cavity. (a) Deposition of multilayer on a fused silica substrate. The Cr layer prevents the damage to the structures during the FIB observation. (b) FIB milling of the surroundings. (c) Oblique evaporation of Au (thickness: ). (d) Finishing the entrance surface by FIB. (e) Fabricated closed nanosheet plasmon cavity of , , and . The direction and the electric fields of the incident light for TM and TE (transverse electric) polarizations are depicted. (f) Magnification of the box in (e) to show the details.
(Color online) (a) Measured and (b) calculated reflectance for various values. and TM polarization. The individual spectra are offset for better viewing. The arrows indicate the dips assigned as the resonance. (c) Dispersion relations plotted from reflection dips. The closed and open symbols were obtained from the experimental and calculated reflectances, respectively. Solid curves: analytical dispersions of MIM waveguides. Dashed lines: propagation in the media with refractive indices of drawn for reference.
(a) Energy density distribution at resonance. Energy is higher in brighter area. A TM-polarized plane wave is incident from the left. (b) Electric and magnetic fields at . These are the snapshots at the maximum amplitude. (a) The first and (b) the second resonances for and . The fields are normalized by those of the incident wave.
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