Ammonia Gas Optical Sensor Based on Lossy Mode Resonances

• Published in: IEEE sensors letters 2023-08, Vol.7 (8), p.1-4
• Main Authors: Armas, Dayron, Zubiate, Pablo, Ruiz Zamarreno, Carlos, Matias, Ignacio R.
• Format: Article
• Language: English
• Subjects: Ammonia; ammonia gas sensor; Chromium oxides; Doppler effect; Humidity; lossy mode resonance (LMR); Machine learning; Optical measuring instruments; Optical properties; Planar waveguides; Predictive models; Red shift; Refractivity; Regression models; Resonance; Room temperature; Sensor materials; Sensors; Temperature measurement; Temperature sensors; Thin films; Wave attenuation; Wavelength measurement
• ISSN: 2475-1472; 2475-1472
• DOI: 10.1109/LSENS.2023.3301843

This letter presents the fabrication and characterization of an ammonia (NH 3 ) gas optical sensor based on lossy mode resonances (LMRs). A chromium (III) oxide (Cr 2 O 3 ) thin film deposited onto a planar waveguide was used as LMR supporting coating. The obtained LMR shows a maximum attenuation wavelength or resonance wavelength centered at 673 nm. The optical properties of the coating can be modified as a function of the presence and concentration of NH 3 in the external medium. Consequently, the refractive index of the Cr 2 O 3 thin film will change, producing a red-shift of the resonance wavelength. Obtained devices were tested for different concentrations of NH 3 as well as repetitive cycles. Concentrations as low as 10 ppbv of NH 3 were detected at room temperature. Machine learning regression models were used to mitigate the cross-sensitivity of the device under temperature and humidity fluctuations.