Resonance enhanced absorption in a graphene monolayer using deep metal gratings

Abstract

It has been demonstrated recently that metal gratings can significantly improve the near-infrared absorptance of graphene from 0.023 to nearly 0.70 because of the excitation of magnetic polaritons (MPs). In the present study, it is shown that the absorptance of graphene can be further enhanced to more than 0.80 by surface plasmon polaritons (SPPs) enabled by the grating. Meanwhile, graphene behaves as a sheet resistor that is able to boost the absorption when MPs or SPPs are excited without changing their resonance frequencies or dispersion relations. The effects of higher-order MPs, as well as the grating geometry on the enhanced absorptance, are also examined. Rigorous coupled-wave analysis (RCWA) is employed to calculate the radiative properties and power dissipation density in both the graphene and the metal grating. This study will facilitate the understanding of the coupling phenomena between graphene and nanostructures and may also benefit the design of next-generation graphenebased optical and optoelectronic devices.

Ultra-Wide Spectral Bandwidth and Enhanced Absorption in a Metallic Compound Grating Covered by Graphene Monolayer

“…In contrast, there were no resonance modes to be observed in the short period one with large slits (e.g., w = 0.14). The results were in agreement shown in previous work [23,24,34,48]. The structural grating was also optimized with different thicknesses to get an optimal small trench (with d = 200 nm) and to ensure for the ease of fabrication as well.…”

“…In order to validate our RCWA MATLAB codes, we repeated calculations of radiative properties for the graphene-covered deep grating in Ref. [24], and results (not shown here) have revealed that our obtained absorptance and that of this structure are well-agreed.…”

“…1, the electromagnetic field is independent to y-axis because the wavevectors of all diffracted waves lie in the x-z plane, and thus, there are no excitations in the y direction. In this study, the TM wave is used for calculations because as theoretically and experimentally demonstrated designer surface plasmons (SPPs) or Fabry-Perot modes could be excited when the TM polarization is applied in the y direction [17,23,24,34,[39][40][41][42]. The Ag base below the grating is assumed to be thick enough as an opaque.…”

“…Accordingly, absorption enhancement is necessary for the application of photon detection based on graphene designs. Many methods of the absorption enhancement have been proposed by using microcavities and nanostructures [7,[19][20][21][22][23][24][25][26][27][28][29][30][31]. A microcavity enhances absorption by allowing light to pass through the graphene layer multiple times [7].…”

“…A microcavity enhances absorption by allowing light to pass through the graphene layer multiple times [7]. Meanwhile, a deep grating structure covered by a graphene sheet could also enhance absorptance due to a strong localized electric field causing the magnetic resonances [9,23,24,32,33]. Although this grating exhibits absorptance of 81% and a spectral bandwidth of 0.3 µm, it is very sensitive to angles of incidence [23,24].…”