Wavelength-modulated optical gas sensors

Abstract

An experimental investigation of optical gas sensors based on wavelength-modulated absorption-band detection with simple optical components is reported. Attention is focused on factors that influence the overall performance of wavelength-modulated optical gas detection. These include spectral properties of the gases as well as design and operational parameters of both optics and signal detection. The wavelength selection and modulation are performed by a vibrating diffraction grating, batch-fabricated on a thin silicon chip with microelectronic fabrication technology. A prototype of a hand-held multicompound mid-IR gas analyser built with few low-cost optical components and simple electronics shows minimum detectable CO 2 and hydrocarbon concentrations of 10 and 20 ppm, respectively, at 20 cm optical path length. A laboratory set-up of a NIR gas analyser, tuned at 0.95 μm and with the same pathlength, can be used as a humidity sensor with high accuracy and short response time.