Loop-Turn Optical Flows with Spectral Selectivity in Suspended Plasmonic Nanofin-Cavity Structure
Ya-Lun Ho, Minoru Abasaki, Jean-Jacques Delaunay
Metallic nanostructures sustain surface plasmons that strongly couple incident light to the surface of the metal. They have received a great amount of attention as a possible means of light manipulation. Among the various reported structures, cavities are promising for spectroscopic applications because the cavity mode, with its narrow band, large modulation, and tunability over a wide range of wavelengths, provides a means to improve the resonances in far-field measurements. This report describes a suspended plasmonic nanofin-cavity structure capable of producing tunable reflected resonances with high quality factors (Q) in the infrared (IR) region. The nanofin-cavity structure having plasmonic hot spots on the ridges supports standing-wave resonances with enhanced electric fields in the horizontal and vertical directions; strong optical flows are thus generated and light turns in a loop, resulting in high reflectance. When the nanofin cavity is further coupled to the propagating surface plasmon resonance (SPR), a strong and narrow-band reflectance resonance due to the stringent condition of SPR arises with a bandwidth having a full width at half-maximum (FWHM) of 92 nm and a Q as large as 60. Furthermore, as result of the coupled modes, the intensity of the resonance peak depends on the angle of the incident light and thus presents a potential means of angle-controlled optical switching in the IR region. Finally, high-order modes of a nanofin-cavity structure were observed in the near-infrared (NIR) region for which wavelengths are much shorter than the cavity scale, thus, demonstrating the possibility of easing the difficulty of fabrication.
FTIR - Portable, plasmonics, optical flows, nanocavities, coupling, infrared filters, nanophotonics