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We have performed finite-difference time-domain (FDTD) analysis of optical transmission through a nanoslit array structure formed on a metal layer with tapered film thickness. The analysis result shows refractive transmission of light through the nanoslit array, opening up the possibility of creating metallic lenses that resemble glass lenses in their shape. Metallic lenses with curved surfaces are designed such that each nanoslit element transmits light with phase retardation controlled by the metal thickness in the aperture region. The FDTD analysis result demonstrates a focusing or collimating function of convex-shaped metal lenses.
Sun et al. (2004) studied this question.