Graphene has recently emerged as a promising candidate for a wide range of photonic and optoelectronic applications, with a high application potential in devices using infrared radiation. The optical absorption of 2D materials and graphene can be uniquely enhanced when they are embedded in optical resonant cavities, since optically-thin atomic-thickness absorbers do not perturb the cavity itself. Despite the many theoretical studies, experimental validation is still lagging behind. Here, large near infrared (NIR) absorption of unpatterned chemical vapor deposition graphene is experimentally demonstrated for the first time in a large area (1 inch) passive optical device by exploiting the enhancement of the electric field at the center of a Fabry-Perot cavity. Test devices were fabricated with single layer, double layer and five layers graphene, sandwiched between two almost symmetric Bragg mirrors deposited by radio frequency sputtering and consisting of alternate layers of Si and SiO 2 . A thin evaporated MgF 2 overlayer was used to reduce sputtering induced damage on graphene layers. Measured absorption values, in the range of 37%-45%, were found in very good accordance with simulated ones. A maximum absorption of 45% was measured at 2345 nm for the double-layer graphene.

There is a growing interest toward graphene and 2D materials for their exceptional geometrical, optical, and electronic features, which make them unique for photonic and optoelectronic applications. Achieving extraordinarily high absorption by the electric field enhancement on a single atomic plane is a challenging goal for physics and for many of the abovementioned uses. We demonstrate here experimentally for the first time a great enhancement absorption on a large (1 in.) optical device based on single-layer chemical vapor deposition graphene (SLG) by exploiting the electric field inside an asymmetric Fabry−Perot resonator fabricated by radio frequency sputtering. In such a filter, graphene absorption of 84% peaked at 3150 nm is obtained, in very good agreement with COMSOL Multiphysics calculations. Absorption intensity and bandwidth are modeled as a function of the incident angle of the electromagnetic radiation, and the optical constants of SLG are obtained as a function of Fermi energy. The Raman spectrum measured on the SLG in the Fabry−Perot cavity proves the effectiveness of the fabrication method in preserving graphene's physical properties. Our results disclose exciting potentialities for building visible and infrared optical light-absorbing devices based on 2D materials.

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 S i O 2 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%.

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