  Multifocal lens, which focus incident light at multiple foci, are widely used
in imaging systems and optical communications. However, for the traditional
design strategy, it combines several lenses that have different focal points
into a planar integrated unit, resulting a low imaging quality due to the high
background noise. Here, we propose two kinds of multifocal metalens with Au
nanoslits arranged in an elliptical and a hyperbolic shape, which are able to
effectively focus incident light at all of the foci with constructive
interference, and extremely decrease the background noise and improve the lens
imaging performance at the nanoscale. We further demonstrate that, the proposed
metalens can possess a broadband operation wavelength changed from 600 nm to
900 nm, with its dual-polarity actively controlled by the incident circular
polarization lights. With great agreement between the experimental and
simulation results, our proposed conic-shaped metalens provides a significant
potential for the future integrated nanophotonic device.
