Focus‐Tunable Planar Lenses by Controlled Carriers over Exciton

While recent studies on nanoscale diffractive lenses demonstrate their potential as possible candidates for thin-film display applications, their narrow focal ranges limit their application. Graphene, however, may realize focal controllability for its unique optoelectric property; due to its unique band structure among 2D materials, its carriers can be controlled by adjusting the Fermi level. Furthermore, due to the bandgap property of graphene, the intraband excitation of carriers is dominant over the interband excitation of carriers, which results in enhanced photonic transmission and reduced absorbance. Utilizing this property, graphene-based ultrathin focusing device is fabricated that alters its optical characteristics when direct-current voltage is applied producing vertical fringe-specific electric field. The proposed device demonstrates 8.6% change in focal length and 48.85% focusing efficiency at wavelength of 405 nm. Overall, this study on electrically tunable ultrathin microlens introduces potential for holographic displays and expands the research scope in future display technologies.