Design and Fabrication of Micromachined Silicon Based Mid Infrared Multilenses for Gas Sensing Applications

To improve the sensitivity of a non-dispersive infrared optical gas sensor, diffractive Fresnel Lenses have been designed, fabricated and tested. The target gases determine the wavelengths for the lens design: 10.6μm, 9.7μm, 3.5μm, and 3.9μm for ethylene, ammonia, ethanol, and the reference band; respectively. Four lenses have been fabricated on the same silicon substrate using Reactive Ion Etching. In order to reduce the number of photolithographic processes, a new design based on sharing sixteen quantization steps through the four lenses is done. Finally, the test of the fabricated device is presented.