Identification of Gases by Porous Optical Sensors Using Reflectivity Difference and Wavelength Shift

We propose a novel method for identification of various gases using combined measurements of wavelength shift (Δλ₀) and reflectivity difference (ΔR). The method relies on plotting the measurement data on the ΔR-Δλ₀ space and exploits in the identification process the effect of significant loss behavior of bulk silicon near or within the visible range (for lossless gas vapors). It has been validated by reflectivity measurements on a Fabry-Perot cavity resonating around 745 nm for four different gas vapors whose reflective indices are close to each other and by two metrics for separability/identification analysis by the scattering matrix method. It is noted that the combined measurements of Δλ₀ and ΔR result in better identification than that obtained by the measurement of Δλ₀ (or ΔR) itself.