Super-Oscillation Far-Field Focusing Lens Based on Ultra-Thin Width-Varied Metallic Slit Array

A super-oscillation far-field focusing micro-lens based on continuous amplitude modulation is experimentally demonstrated with 40-nm thick width-varied sub-wavelength metallic slit array. The
$228\times 200~\mu \text{m}^{\mathrm {\mathbf {2}}}$
micro-lens is designed and fabricated with numerical aperture 0.976 and focal length
$40.1\lambda $
for wavelength
$\lambda =632.8$
nm. Experimental results show that the focal length is
$\sim 26.5\pm 1~\mu \text{m}$
, and the focal line full width at half maximum is
$0.379\lambda $
, which is smaller than the corresponding diffraction limit
$0.512\lambda $
and the super-oscillation criterion
$0.389\lambda $
. A great suppression of sidelobes was observed in the measured focal plane area, and the largest sidelobe intensity was found only 10.6% of the central lobe intensity, leading to a wide field of view.