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Sketch of a planoconcave grating lens. The lens is made of a medium with . The horizontal step size is smaller than the free space wavelength with .
(a) Bird’s eye view of the tapered waveguide and the binary-staircase lens. (b) Close-up view of the binary-staircase lens.
Optical images, from an optical scanning microscope, obtained at around the focal point of (a) the binary-staircase lens (b) and the analogous structure with no zones/steps (semicircle with smooth walls). Note that focusing is observed only with the binary-staircase lens.
(a) 3D FDTD simulation of the planoconcave binary-staircase lens and (b) 3D FDTD simulation of the lens having the same geometrical dimensions as the binary-staircase one, but bearing no steps (or zones).
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