title: Focusing subwavelength light by using nanoholes in a transparent thin film.
abstract: A circle of planar nanoholes in a dielectric thin film can focus light into a sub-half-wavelength spot. The nanostructure with higher rotational symmetry shows better focusing properties. From finite-difference time-domain calculations, we verified such a focusing spot coming from the constructive interference of diffraction beams near the nanoholes. For a 1 microm size lens with eight 200 nm diameter holes, we achieved an optical spot smaller than 250 nm measured at 650 nm wavelength. This nanostructure provides a simple way to massively fabricate a planar lens array with a scale down to the submicrometer level.
authors.affiliation: Research Center for Applied Sciences, Academia Sinica, 128, Section 2, Academia Road, Nankang, Taipei 11529, Taiwan. pkwei@gate.sinica.edu.tw
authors.forename: Pei-Kuen
authors.initials: PK
authors.lastname: Wei
authors.forename: Wei-Lun
authors.initials: WL
authors.lastname: Chang
authors.forename: Kunag-Li
authors.initials: KL
authors.lastname: Lee
authors.forename: En-Hong
authors.initials: EH
authors.lastname: Lin