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: 10.6 mum, 9.7 mum, 3.5 mum, and 3.9 mum 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.