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Multi-level Fresnel zone lenses capable of being fabricated with only one binary mask


Fischer, R.E. ; Society of Photo-Optical Instrumentation Engineers -SPIE-, Bellingham/Wash.:
Current developments in optical design and optical engineering IV. Proceedings : 27 - 28 July 1994, San Diego, California
Bellingham/Wash.: SPIE, 1994 (SPIE Proceedings Series 2263)
ISBN: 0-8194-1587-1
Conference "Current Developments in Optical Design and Optical Engineering" <4, 1994, San Diego/Calif.>
Conference Paper
Fraunhofer HHI ()
electron beam lithography; errors; lenses; optical design techniques; optical fabrication; optical focusing; binary mask; fresnel zone lenses; reduced level numbers; outer zones; whole lens; fabrication error; diffraction efficiency; focusing efficiency; gaussian beam illumination; binary fresnel zone lens mask; modified optical stepper; scaling down factors; pattern transfer; lithographic process; e-beam written masks; binary ring zones

Multi-level approximated Fresnel zone lenses with reduced level numbers in the outer zones are investigated and compared with Fresnel zone lenses of unique level numbers over the whole lens, Calculations of the fabrication error effects on diffraction efficiency for both lens types are performed. Measurements of focusing efficiency show that, especially for Gaussian beam illumination, segmented Fresnel zone lenses can reach nearly as high focusing efficiencies as normal Fresnel zone lenses. Arrays of segmented lenses can be fabricated using only one binary Fresnel zone lens mask with the aid of a modified optical stepper with fixed scaling down factors in the ratio of 1:1/ square root 2 from one to the next step of pattern transfer in the lithographic process. The fabrication of such lenses could be advantageous because the generation of precise e-beam written masks with a large number of binary ring zones is time consuming and expensive.