Optical Anisotropy of Multilayer Graphene Probed by Coupled Plasmon-Waveguide Resonators

The characterization of the optical constants of single-layer graphene has been the subject of deep investigation in the last 2 decades, and the optical anisotropy has been discovered to be an important parameter linked to the structural defects of the plane of the carbon atoms. Using graphene-loaded coupled plasmon-waveguide resonator, which offers pure transverse electric or transverse magnetic electromagnetic modes, we demonstrate the possibility to characterize the optical anisotropy using evanescent electromagnetic fields in the visible and middle-infrared range of a single, double, and triple layer of graphene. On the assumption that a universal opacity of graphene holds for both in-plane and out-plane electronic displacement, we extract the anisotropic coefficient of the graphene layers with an accuracy of about 20%. The results are coherent with the literature and indicate that coupled plasmon-waveguide resonator spectroscopy is a valid, low-cost, and simple technique for the alternative optical characterization of uniaxial anisotropic bidimensional materials.