Achieving perfect absorption of graphene in the near-infrared and visible wavelength ranges by critical coupling with a photonic crystal slab

Abstract

Critical coupling phenomena is a structure absorbs nearly 100% of incident electromagnetic energy, leading to null scattering. This strong light-matter interactions can lead to extremely compact and high performance photonic devices based on graphene and other two-dimensional materials. The graphene's surface conductivity is governed by the Kubo formula, Graphene cannot support plasmonic effects in the near-infrared and visible wavelength ranges due to a low Fermi level by a limited electrostatically doping. Consequently, depositing a graphene layer onto a resonant photonic crystal slab is an effective way to enhance the absorption of graphene. Here, we study the critical coupling condition to achieve the perfect absorption of graphene. The ratio of the hole radius to the lattice constant of the slab is the critical factor to achieve the critical coupling. In order to control the critical coupling frequency, the thickness and lattice constant of the slab are investigated also. Our results demonstrate that as the thickness or lattice constant increases, the critical coupling frequency decreases. Then we investigate the modifications of the absorption peak as the incident angle of plane wave changes with both TE and TM polarizations. This structure proposed is easy to fabricate and has excellent performance. The work can lead to a wide range of ultra-compact and high performance photonic and optoelectronic devices, such as high responsivity and high speed graphene (or other two-dimensional materials) detectors, modulators, and light sources.