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20 April 1995 Fresnel zone lenses for an electro-optical 2 x 2 switch
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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 micrometers and 0.633 micrometers . 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 multi-levels, 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 eighth 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.
© (1995) COPYRIGHT Society of Photo-Optical Instrumentation Engineers (SPIE). Downloading of the abstract is permitted for personal use only.
Margit Ferstl "Fresnel zone lenses for an electro-optical 2 x 2 switch", Proc. SPIE 2404, Diffractive and Holographic Optics Technology II, (20 April 1995);

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