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

Abstract

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 × 200 μm <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> micro-lens is designed and fabricated with numerical aperture 0.976 and focal length 40.1λ for wavelength λ = 632.8 nm. Experimental results show that the focal length is ~26.5 ± 1 μm, and the focal line full width at half maximum is 0.379λ, which is smaller than the corresponding diffraction limit 0.512λ and the super-oscillation criterion 0.389λ. 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.