Research ArticlePLASMONICS

Asymmetric excitation of surface plasmons by dark mode coupling

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Science Advances  19 Feb 2016:
Vol. 2, no. 2, e1501142
DOI: 10.1126/sciadv.1501142
  • Fig. 1 Sample design, experimental diagram, and measured field distribution.

    (A) Schematic view of a unit cell of the metallic hole-type structure. The geometric parameters are as follows: L = 120 μm, w = 10 μm, l = 45 μm, g = 10 μm, d = −40 μm, and s = 5 μm. (B) Microscope image of a part of the fabricated metasurface. (C) Experimental schematic of the terahertz near-field mapping measurement of the metasurface. (D) Measured electric field (Ez) distribution of the excited terahertz SP amplitude at 0.75 THz under normal incidence of an x-polarized wave, where 8 × 8 unit cells were contained and arranged in a square lattice. The inset schematically shows the excitation pattern.

  • Fig. 2 Simulated SP spectra and field distributions.

    (A, C, and E) Simulated SP amplitude spectra of the 8 × 8 unit cells of BSSR, SRSR, and combination of BSSR and SRSR under the x-polarization incidences, respectively, as indicated by the insets and arrows. (B, D, and F) Corresponding (on the same row) simulated amplitude field (Ez) distributions of the excited terahertz SPs of BSSR, SRSR, and combination of BSSR and SRSR under the x-polarization incidences at 0.75 THz, respectively. The blue (3-mm distance to the center along the +x direction) and orange (3-mm distance to the center along the +y direction) circles in (B), (D), and (F) represent the positions where the spectra in (A), (C), and (E) were extracted, and the colors of the circles indicate the curves with the same colors. a.u., arbitrary unit.

  • Fig. 3 Simulated spectrum variations with different values of d and s.

    (A and B) Simulated SP amplitude spectra excited to the right and top sides (blue and orange points in Fig. 2) of the structures, with d varying from −40 to 40 μm and s = 5 μm. (C) Variations of the SP amplitude at 0.75 THz excited to the right and top sides of the structures with respect to d. (D and E) Simulated SP amplitude spectra excited to the right and top sides of the structures, with s varying from 5 to 45 μm and d = −40 μm. (F) Variations of the SP amplitude at 0.75 THz excited to the right and top sides of the structures with respect to s.

  • Fig. 4 Measured and simulated SP amplitude distributions.

    (A to D) Measured SP amplitude distributions, with d varying from −20 to 40 μm and s = 5 μm at 0.75 THz. The insets schematically show the measured structures. (E to H) Simulated SP amplitude distributions corresponding to (A) to (D), respectively. (I to L) Measured SP amplitude distributions, with s varying from 5 to 45 μm and d = −40 μm at 0.75 THz. The insets schematically show the measured structures. (M to P) Simulated SP amplitude distributions corresponding to (I) to (L), respectively.

  • Fig. 5 Schematic of the SP focusing structure and measured results.

    (A) Schematic illustrating of the unit cell arrangment of the designed structure. The brown points indicate the locations of the unit cells. The blue and red elliptical points are the designed focuses. Both the maximum and minimum radii of the blue and red circles are 400 and 4000 μm, respectively. (B to D) Measured SP amplitude distributions when the arranged unit cell was BSSR, BSSR with SRSR at its right side and left side of d = −40 μm and s = 5 μm at 0.75 THz, respectively, as indicated by the corresponding insets. The arrows indicate the pathways of the SP energy conversion.

Supplementary Materials

  • Supplementary material for this article is available at http://advances.sciencemag.org/cgi/content/full/2/2/e1501142/DC1

    Fig. S1. Simulated SP spectrum and field distribution of the BSSR array.

    Fig. S2. Simulated Ez and Hx field distributions of the BSSR and BSSR + SRSR.

    Fig. S3. Simulated spectrum variations with different values of d and s.

    Fig. S4. Schematics to describe the coupling mechanism using complementary structures.

    Fig. S5. Simulated SP spectrum and field distribution of the BSSR + 2 × SRSR array.

    Fig. S6. Simulated SP field distributions and spectra of similar metasurfaces in the infrared regime.

    Note S1. Coupled Lorentzian oscillator model.

  • Supplementary Materials

    This PDF file includes:

    • Fig. S1. Simulated SP spectrum and field distribution of the BSSR array.
    • Fig. S2. Simulated Ez and Hx field distributions of the BSSR and BSSR + SRSR.
    • Fig. S3. Simulated spectrum variations with different values of d and s.
    • Fig. S4. Schematics to describe the coupling mechanism using complementary structures.
    • Fig. S5. Simulated SP spectrum and field distribution of the BSSR + 2 × SRSR array.
    • Fig. S6. Simulated SP field distributions and spectra of similar metasurfaces in the infrared regime.
    • Note S1. Coupled Lorentzian oscillator model.

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