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Thin film deposition: An alternative technique for the fabrication of binary optics with high efficiency

: Pawlowski, E.

Institution of Electrical Engineers -IEE-, London:
Fourth International Conference on Holographic Systems, Components and Applications : 13 - 15 September 1993; venue: Neuchatel, Switzerland
London: IEE, 1993 (IEE conference publication 379)
ISBN: 0-85296-578-8
International Conference on Holographic Systems, Components and Applications <4, 1993, Neuchâtel>
Fraunhofer HHI ()
computer-generated holography; electron beam lithography; holographic gratings; holographic optical elements; lenses; optical workshop techniques; optical zone plates; photolithography; sputter deposition; ion beam sputter deposition; thin film deposition; electron beam writing; alignment errors; fabrication; binary optics; high efficiency; blazed profile; thin film dielectric gratings; kinoform profile; fresnel zone lenses; stepped profiles; photolithographic technology; anti-reflection coating; angular spectrum approach; minimum reflectivity; in situ controlled multilayers; spot-sizes; fabrication errors; level heights; linewidths errors; 1.52 micron; 0.63 micron; tio2-sio2 multilayers

Binary optics were fabricated by an ion-beam sputter deposition technique on different substrate materials for the wavelengths of 1.52 mu m and 0.63 mu m respectively. The blazed profile of thin film dielectric gratings was approximated by a 2 and 4 phase level profile and the kinoform profile in each zone of the Fresnel zone lenses was approximated by a 2,4,8,16 and a 32 level profile. Such stepped profiles were realized with several masks, written with electron-beam and with photolithographic technology. The microlenses were coated with an anti-reflection coating. The reflection of these lenses was optimized on the basis of an angular spectrum approach. A minimum reflectivity as low as 1*10-4 was realized using in situ controlled multilayers of TiO2 and SiO2. The measurements reveal, that the spot-sizes of the fabricated microlenses are close to the diffraction limited values. The highest measured diffraction efficiencies for the 32 level structures are 97%. The effects of fabrication errors, such as level heights, alignment and linewidths errors, on the diffraction efficiency of Fresnel zone lenses were discussed.