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
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