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Diffractive microlenses with antireflection coatings fabricated by thin film deposition

: Pawlowski, E.; Engel, H.; Ferstl, M.; Furst, W.; Kuhlow, B.


Optical engineering 33 (1994), No.2, pp.647-52
ISSN: 0091-3286
ISSN: 0036-1860
Journal Article
Fraunhofer HHI ()
antireflection coatings; computer-generated holography; electron beam lithography; holographic optical elements; lenses; masks; optical workshop techniques; photolithography; reflectivity; sputter deposition; computer-generated holograms; diffractive microlenses; 2d arrays; electron beam writing; thin film deposition; fresnel zone microlenses; ion beam sputter deposition; angular spectrum approach; minimum reflectivity; in situ controlled multilayers; kinoform profile; eight-level profile; stepped profiles; photolithographic technology; diffraction-limited values; 1.52 micron; 0.63 micron; tio2-sio2 multilayers

Two-dimensional arrays of Fresnel zone microlenses were fabricated and coated with antireflection layers by an ion beam sputter deposition technique. The reflection of these lenses was analyzed on the basis of an angular spectrum approach for different substrate materials. A minimum reflectivity as low as 2*10-4 was realized by means of in situ controlled multilayers of TiO2 and SiO2. The lenses have a circular aperture of 2 mm and different focal lengths for the wavelengths of 1.52 and 0.63 mu m, respectively. The kinoform profile in each zone of the Fresnel zone lenses was approximated by an eight-level profile. Such stepped profiles were realized with several masks written with an electron beam and transferred by photolithographic technology. The measurements reveal that the spot sizes of the fabricated microlenses are close to the diffraction-limited values.