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 (N_bi). 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 N_bi.