Ammonia Gas Optical Sensor Based on Lossy Mode Resonances

This letter presents the fabrication and characterization of an ammonia (NH3) gas optical sensor based on lossy mode resonances (LMRs). A chromium (III) oxide (Cr2O3) 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 NH3 in the external medium. Consequently, the refractive index of the Cr2O3 thin film will change, producing a red-shift of the resonance wavelength. Obtained devices were tested for different concentrations of NH3 as well as repetitive cycles. Concentrations as low as 10 ppbv of NH3 were detected at room temperature. Machine learning regression models were used to mitigate the cross-sensitivity of the device under temperature and humidity fluctuations.