Experimental verification and investigation of disks scattering slab modes in metal-dielectric heterostructures

Abstract

A thin dielectric plate can support conventional slab modes such as leaky Fabry-Perot, guided waves and radiation modes. When the plate is coated on a metallic subwavelength disk array, it can result in new confined modes, hereby named 'disks scattering slab modes' (DSSMs). By use of a terahertz time-domain spectroscopy system, we experimentally verify the existence of two types of DSSMs in terahertz range: one we refer to as highly confined disks scattering Fabry-Perot-like modes (DSFPMs) and the other as, weakly confined disks scattering radiation-like modes (DSRMs). Spectral characteristics of these confined modes are measured and numerically simulated. Particularly, based on the experimental results and a dipole-scattering model developed here, we show that the features of the DSFPMs can be tuned by changing the filling fraction of the disk array. We believe these results can make important contributions to the designs of new terahertz devices, including tunable absorbers and filters.

Observation of Disk Scattering Slab Modes Transitioning to Disk Scattering Modes on Metal–Dielectric Heterostructures in the Terahertz Waveband

“…Our samples are similar to those in [9]. If the meta-surface of a sample is illuminated by a THz beam, the measured reflectance is mainly characterized by DSSMs when the slab thickness is comparable with the THz wavelength, similar to those observed in [1]. As the slab thickness is increased, the reflection spectrum changes with the thickness.…”

“…where r a ðt a Þ is the reflection (transmission) matrix of the periodic disk array, and r s represents the reflection matrix of the substrate surface. By taking an approach similar to that in [1], we can express the reflection coefficients in r a as [1], [2], [14]…”

“…For metals in a low-frequency regime, perfect electric conductor approximation leads to a simple analytical expression of the polarizability. By taking a similar approach, but accounting for dynamic depolarization and radiation damping effects (because the disks in our samples have a relatively large diameter), can be written as [1], [6], [15] 1…”

“…It has recently been demonstrated that, in the terahertz (THz) waveband, a category of confined modes can be supported by a metal-dielectric heterostructure (MDHS) created by a subwavelength metallic disk array coated on one surface of a dielectric slab [1]. It has been shown that such confined modes originate from the interactions between scattered fields, diffracted waves, and conventional slab modes (including Fabry-Perot (FP) or radiation modes) and are therefore referred to as disk scattering slab modes (DSSMs).…”

Unexpected Strong Optical Absorption in a Free-Standing Optical Thick Transmission Metallic Grating

“…2(a)]. In order to improve the absorption in optical thick FSTMG, one can alternatively use reflection grating [2], [3] to eliminate the resonant transmission, or introduce dielectric materials to absorb lights localized by the metallic grating or couple them to the guide modes supported by the dielectric slab [11], [13], [15], [16].…”