Abstract
Strong light-graphene interaction is essential for the integration of graphene to nanophotonic and optoelectronic devices. The plasmonic response of graphene in terahertz and mid-infrared regions enhances this interaction, and other resonance mechanisms can be adopted in near-infrared and visible ranges to achieve perfect light absorption. However, obtaining near-absolute polarization insensitivity with ultra-narrow absorption bandwidth in the visible and near-infrared regimes remains a challenge. In this regard, we numerically propose a graphene perfect absorber, utilizing the excitation of guided-modes of a dielectric slab waveguide by a novel sub-wavelength dielectric grating structure. When the guided-mode resonance is critically coupled to the graphene, we obtain perfect absorption with an ultra-narrow bandwidth (full-width at half-maximum) of 0.8 nm. The proposed design not only preserves the spectral position of the resonance, but also maintains >98% absorption at all polarization angles. The spectral position of the resonance can be tuned as much as 400 nm in visible and near-infrared regimes by tailoring geometrical parameters. The proposed device has great potential in efficient, tunable, ultra-sensitive, compact and easy-to-fabricate advanced photodetectors and color filters.
Highlights
Strong light-graphene interaction is essential for the integration of graphene to nanophotonic and optoelectronic devices
The ultra-wideband spectral response and the huge carrier mobilities make graphene a strong candidate as a backbone of novel nanophotonic and optoelectronic devices
Since graphene plasmons cannot be excited outside the THz and MIR ranges, graphene has to be coupled to other resonant mechanisms to improve the light absorption in the visible and near-infrared range (Vis-NIR) ranges
Summary
Exciting guided-mode resonances of a slab-waveguide to improve light-graphene interaction. We observed that an intermediate value of PMMA SWG width is required for the maximum possible absorption, and the resonance wavelength red-shifts as the thickness increases Both of these can be explained by considering the fill-factor of SWG that changes the effective refractive index of it[42,46,47,58,63]. The dispersion of spectrum for Device II with its optimized parameters is shown in Fig. 7a,b, under s and p-polarized light, respectively In these figures, we see a very sharp resonance at 676.8 nm (677 nm) with the absorption strength of 98% (99.2%) for s (p)-polarized light.
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