Highly Compact Linear Variable Filter in the Mid Infrared Region for Acetone Level Monitoring

Due to the recent rapid industrialization and urbanization across the world, chemicals are released into the environment at an unprecedented rate. Gas sensors, in particular, interferometric based devices represent an important toolkit for air quality monitoring. Amongst different interferometers, linear variable filter (LVF) holds the promise of a fixed optical component that can be operated under various conditions. In this work, oxide pillars were deposited on a [Si-SiO2] mirror coated wafers. Thick oxide deposition was performed using a low temperature high density chemical vapor process with photoresist as mask to form pillars. By sandwiching two such substrates together, a milli-degree taper angle was formed by a difference in pillar height. The mated normal incidence LVF was demonstrated with an operating range of 0.7 μm, full width half maximum of 230 nm at 3,500 nm and was tested for the presence of acetone vapor. The relationship between transmission intensity and acetone concentration was plotted with a correlation R2of 0.972.