Miniaturized Fourier transform spectrometer for gas detection in the MIR region

Selective multi-gas detection is often based on spectroscopic methods in the infrared region. The resulting setup consists of a spectrometer and the probing setup where often the spectrometer makes the sensing device large and heavy and does not allow easy on the field integration. We report on the application of a silicon micromachined lamellar grating interferometer in a Fourier transform infrared spectrometer for the detection of gases in the mid infrared region. The spectrometer heart was miniaturized consequently to fit in a box of 30 mm × 30 mm × 55 mm. The Fourier transform infrared spectrometer was equipped with mid infrared optical fibers for light coupling. Gas measurements in the mid infrared region were focused on specific gases (CO2 and CH4) in order to determine the limit of detection and the selectivity that could be obtained using such a micro-spectrometer. Using two different spectral regions we were able to detect concentrations of carbon dioxide over a span from 100 to 9000 ppm with a theoretical detection limit evaluated less than 10 ppm. The performed gas measurements showed the proof of principle of a miniaturized Fourier transform infrared gas analyzer based on a micromachined spectrometer and fiber optics.