Extraordinary optical transmission induced by strong plasmon-phonon coupling: Shape resonance versus non-shape resonance

摘要

The study of the localized surface plasmons induced by a rectangular hole has been a basic building block for understanding the shape dependence of extraordinary optical transmission (EOT). A recent discovery has shown that the substrate significantly affects the aperture resonance position. However, the substrate effect on aperture resonance has been limited to the non-dispersive case, in which the refractive index of the substrate is assumed to be constant. Here, by employing strong plasmon-phonon interactions, we study the EOT of a rectangular hole with a dispersive medium. By changing the slot antenna length, various plasmon modes are generated, and they then interact with the phonon of the SiO_2 film in the mid-infrared range. We report that the transmission resonance changes from shape resonance to non-shape resonance as the length of the slot increases. The origin of the shape resonance is the destructive interference of the evanescent modes; in contrast, the propagation modes and the material property of the substrate determine the non-shape resonance. Because of the effect of evanescent coupling, shape resonance is much more sensitive than non-shape resonance to the dielectric environment.