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21 April 2006 Fresnel lenses: study and fabrication in silicon technology for medium-IR applications
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Diffractive Fresnel Lenses (FL) were designed, fabricated and tested. The lens aims for increasing the sensitivity of a Non-Dispersive InfraRed (NDIR) silicon based optical gas system, focusing as much radiation as possible onto the detector. The studied wavelengths are 10.6μm and 3.4μm, which are the main absorption lines for ethylene and ethanol respectively. The lens diameter (5mm) and the focal length (4mm) are fixed by the detector package. Those diffractive lenses are compatible with the planar nature of silicon microtechnology. A theoretical study about the global lens efficiency as a function of the technological constrains and the process complexity has been carried out. Using only three photolithographic masks, eight quantization steps can be etched and a theoretical lens efficiency of 95% can be achieved. Once the devices were fabricated, the focal length and the spot size have been measured.
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Jordi Fonollosa, Rafael Rubio, Jürgen Hildenbrand, Mauricio Moreno, Santiago Marco, Joaquín Santander, Luis Fonseca, Susanne Hartwig, and Jürgen Wöllenstein "Fresnel lenses: study and fabrication in silicon technology for medium-IR applications", Proc. SPIE 6186, MEMS, MOEMS, and Micromachining II, 61860R (21 April 2006);

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