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Fresnel zone lenses for an electro-optical 2x2-switch

 
: Ferstl, M.

Cindrich, I. ; Society of Photo-Optical Instrumentation Engineers -SPIE-, Bellingham/Wash.:
Diffractive and Holographic Optics Technology II, 1995. Proceedings : 9 - 10 February 1995, San Jose, California
Bellingham/Wash.: SPIE, 1995 (SPIE Proceedings Series 2404)
ISBN: 0-8194-1751-3
S.277-285
Conference "Diffractive and Holographic Optics Technology" <2, 1995, San Jose/Calif.>
Englisch
Konferenzbeitrag
Fraunhofer HHI ()
electro-optical switches; lenses; liquid crystal devices; optical design techniques; optical elements; zone plates; electro-optical 2*2-switch; fresnel zone lenses; exchange bypass module; switching element; dynamic fresnel zone lenses; static fresnel zone lenses; quartz-glass substrate; off-axis lenses; liquid crystal; transparent electrode; face down mounted cover-glass; on-axis lenses; blazed profiles; micro-structuring techniques; focal lengths; spot-sizes; diffraction limited values; diffraction efficiency; eight-level lenses; switching times; switching contrast; 1.52 mum; 0.633 mum; 1.5 mm; 0.2 to 2 mm

Abstract
An optical two by two exchange bypass module formed by a combination of static and dynamic Fresnel zone lenses is proposed. The basic concept of this switching element is to cascade pairs of dynamic Fresnel zone lenses and pairs of static Fresnel zone lenses, located on each side of a 1.5 mm thick quartz-glass substrate. Two types of elements were designed, to operate at wavelengths of 1.52 mu m and 0.633 mu m. The dynamic Fresnel zone lenses on the frontside of the substrate are off-axis lenses which are made switchable by filling them with a liquid crystal after covering the Fresnel structure with a transparent electrode. The second electrode is deposited on a face down mounted cover-glass. The static lenses on the backside of the substrate are conventional on-axis Fresnel zone lenses. The dynamic and the static Fresnel zone lenses, whose blazed profiles have been approximated by multilevels, have been fabricated by means of micro-structuring techniques. Static and dynamic, on-axis and off-axis Fresnel zone lenses with different focal lengths and of different circular diameters ranging from 0.2 mm to 2.0 mm have been realized. The measured spot-sizes of the Fresnel zone lenses were close to the diffraction limited values and the diffraction efficiency of the eight-level lenses was higher than 80%. The switching times of the dynamic lenses were in the range of several milli-seconds and the switching contrast was about 1:10.

: http://publica.fraunhofer.de/dokumente/N-13393.html