Flexible control of absorption enhancement ofcircularly polarized light via square graphene disks

A narrowband absorber consisting of periodically patterned square graphene disks (SGDs) is proposed to achieve flexible control of the absorption enhancement of circularly polarized light (CPL) in the far-infrared region. It is shown that absorption of CPL can be enhanced by utilizing the double-cavity enhancement of edge graphene plasmons (EGPs) of the SGDs in both x and y directions. Perfect light absorption can be achieved by minimizing the reflectance through perfect impedance matching and simultaneously eliminating the transmittance by the metallic substrate. By using the Fabry-Perot (F-P) cavity model with a linear fitting method, the location of the absorption peak of CPL can be well estimated. The location of the absorption peak can be modulated by changing the Fermi level of graphene, while it can be kept almost the same even though the structural parameters such as period and the thickness of the dielectric spacer are significantly altered. Furthermore, by integrating multi-sized SGDs into the unit cell of the structure, multiple absorption channels of CPL with good absorption performances can be realized. As examples, two and three absorption channels with high peak absorptivity are demonstrated via double and triple SGDs, respectively.