Metasurface Modeled as Chebyshev Impedance Transformer for Super-Broadband Anti-Reflection of Visible and near Infrared Light

Facilitating anti-reflection has been of great scientific and practical interest due to its diverse applications in optical devices including solar cells and photodetectors. Various anti-reflection schemes are exploited and elaborated to realize effective broadband suppression of reflected light. In this work, we present and analyze a metasurface coating on silicon for efficient anti-reflection by leveraging the design rules of the Chebyshev transformer in the field of transmission line theory in the microwave regime. We explore the underlying physics of the metasurface by comparing the two representative types of constituent nanostructures and evaluating their optical properties using effective index retrieval methods. In particular, by designing nanostructures with subtle vertical etching in the pyramid valley, a broadband anti-reflection coating ranging from 400 to 1100 nm is achieved with reflection of less than 3%. We believe that the proposed design rule and analysis for this Chebyshev metasurface could pave an important way to realize systematic and effective anti-reflection schemes for diverse optical devices.