Experimental demonstration of mid-IR absorption enhancement in single layer CVD graphene

Mid-IR absorption of single layer graphene (SLG) was simulated and experimentally demonstrated by embedding a SLG grown by chemical vapor deposition (CVD) inside a Fabry-Perot (FP) filter made by alternating quarter wave Si and SiO₂ layers fabricated by radiofrequency sputtering. The absorption from the graphene layer was modeled by using COMSOL Multiphysics in four different configurations, depending on its position inside the filter, an asymmetric FP made of two different dielectric mirrors separated by a cavity. In the first three configurations, graphene was inserted at the center of the optical cavity and inside the top or bottom dielectric mirror forming the FP. The fourth configuration involves two layers of graphene, each positioned inside one of the dielectric mirrors. The calculated electric field distribution inside the FP shows two symmetric maxima just above and below the cavity, i.e., inside the mirrors, while the electric field at the center of the cavity is negligible. For the experimental demonstration, the graphene geometry corresponding to the maximum electric field intensity was chosen, and, between two equivalent alternatives, the one with the easiest fabrication procedure was selected. Results demonstrate a maximum experimental absorption of 50% at 4342 nm for SLG when inserted in the top mirror of the FP, in excellent agreement with the simulated value of 53%.