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Computer generated microlenses with high efficiency

: Pawlowski, E.; Ferstl, M.; Kuhlow, B.

Benton, S.A. ; Society of Photo-Optical Instrumentation Engineers -SPIE-, Bellingham/Wash.:
Practical holography VII. Imaging and materials 1993. Proceedings : 1 - 2 February 1993, San Jose, California
Bellingham/Wash.: SPIE, 1993 (SPIE Proceedings Series 1914)
ISBN: 0-8194-1147-7
Conference "Practical Holography, Imaging and Materials" <7, 1993, San Jose/Calif.>
Conference Paper
Fraunhofer HHI ()
antireflection coatings; computer-generated holography; holographic optical elements; integrated optics; lenses; optical films; photolithography; blazed fresnel zone microlens arrays; ir; computer-generated microlenses; circular apertures; high efficiency; ion-beam-sputter deposition technique; substrate materials; square apertures; kinoform profile; stepped profiles; masks; electron-beam; photolithographic technology; fabrication errors; level heights; alignment; linewidths errors; diffraction efficiency; antireflection coating; angular spectrum approach; minimum reflectivity; in situ controlled multilayers; spot-sizes; diffraction limited values; sixteen level structure; 0.2 mm; 1.52 micron; 0.63 micron; 96 percent; tio2; sio2

Blazed Fresnel zone microlens arrays were fabricated by ion-beam-sputter deposition technique on different substrate materials. The lenses have circular and square apertures with the smallest width of 0.2 mm and different focal lengths for the wavelengths of 1.52 mu m and 0.63 mu m respectively. The kinoform profile in each zone of the Fresnel zone lenses was approximated by a sixteen level profile. Such stepped profiles were realized with several masks, written with electron-beam and with photolithographic technology. The effects of fabrication errors, such as level heights, alignment and linewidths errors, on the diffraction efficiency were discussed. The microlenses were coated with an antireflection coating. The reflection of these lenses was analyzed on the basis of an angular spectrum approach. A minimum reflectivity as low as 2*10-4 was realized using in situ controlled multilayers of TiO2 and SiO2. Our measurements reveal, that the spot-sizes of the fabricated microlenses are close to the diffraction limited values. The highest measured diffraction efficiency for the sixteen level structure is 96%.