Porous silicon photonic crystal-based interferometric chemical sensor.

This work investigates an interferometric chemical sensor based on modulating optical bandgap parameters in a porous silicon photonic crystal. The proposed system features a fast, inexpensive setup using a single, narrow spectral response photodetector, which is advantageous for studying analyte adsorption/desorption kinetics compared to bulkier dispersive systems. Reflectance spectra were computed using the transfer matrix method, considering variations in refractive indices and bilayer numbers (Nbi). Modeling and experiments confirmed that reflectance oscillation frequency is proportional to analyte parameters like refractive index and evaporation rate. Short fast Fourier transformation (FFT) yielded analyte-specific spectrograms for ethanol and isopropanol. Sensitivity is enhanced for photonic structures designed at shorter wavelengths and remains invariant to Nbi.