Plasmonic brewster angle: Broadband extraordinary transmission through optical gratings

TLDR: This work introduces a different mechanism to achieve total transmission through an otherwise opaque screen, based on an inherently ultra-broadband tunneling mechanism that can span from DC to the visible range.

Abstract: Extraordinary optical transmission through metallic gratings is a well established effect based on the collective resonance of corrugated screens [1]. Being based on plasmonic resonances, its bandwidth is usually narrow, in particular for thick screens and small apertures. Here we introduce a different mechanism to achieve total transmission through an otherwise opaque screen, based on an inherently ultra-broadband tunneling mechanism that can span from DC to the visible range. This phenomenon may effectively represent the equivalent of Brewster transmission for plasmonic and opaque screens. As long as only the dominant TM mode is supported inside the slit and only the zero diffraction order can propagate, i.e., w << d < λ0 = 2π/k 0 , where d is the grating period, w the slit aperture and λ0 the incident wavelength, it is possible to define a plasmonic Brewster angle as [2] : cos(ϑ B ) = (β S w)/(k 0 d), where β s is the wave-number of the fundamental TM mode guided inside each slit. In Fig. 1, we show the calculated TM power transmission spectra for a grating with thickness l=400nm and period d=192nm varying the incidence angle, frequency and the slit width, as indicated in each panel. The left column shows full-wave simulations based on the Fourier modal method [3], compared in the right to our analytical model based on a transmission line approach [2].