Aluminum Plasmonic Metasurface Enabling a Wavelength-Insensitive Phase Gradient for Linearly Polarized Visible Light

For conventional phase-gradient metasurfaces, the phase tuning is mostly fulfilled by the exploitation of a nanoantenna- or a Pancharatnam–Berry-phase-based nanoresonator. The former scheme typically suffers from a dispersive phase gradient, while the latter is dispersionless yet functions only for circularly polarized light. The precise reproduction of such sophisticated nanoscale structures, which is essential for applications in color printing, color displays, and image sensing, is especially challenging in the visible band. In this work, an Al plasmonic metasurface, which enables a wavelength-insensitive phase gradient for linearly polarized light throughout the visible spectral band, is proposed and embodied. The unit cells constituting the metasurface capitalize on a trapezoidal Al nanoantenna that supports a gap-surface plasmon. The incident light, of which the spectrum ranges from 400 to 700 nm, is highly angle resolved via an anomalous reflection, providing a splitting angle as large as 42° in view of the corresponding captured color images. It is presumed that the demonstrated wavelength-insensitive phase gradient will lead to a well-defined planar wavefront, thereby substantially suppressing the crosstalk between the different wavelengths at a given angle. Last, the proposed trapezoidal Al nanoantenna has been meticulously inspected in terms of its phase variations that are associated with the plasmonic resonance mode.