  We design plano-concave silicon lenses with coupled gradient-index plasmonic
metacoatings for ultrawide apertured focusing utilizing a reduced region of
$\sim 20 \lambda^2$. The anomalous refraction induced in the planar input side
of the lens and in the boundary of the wavelength-scale focal region boosts the
curvature of the emerging wavefront, thus significantly enhancing the
resolution of the tightly-focused optical wave. The formation of a light tongue
with dimensions approaching those of the concave opening is here evidenced.
This scheme is expected to have potential applications in optical trapping and
detection.
