Optical detection of alcohol concentration using photonic crystal sensor

This letter proposes a novel one-dimensional photonic crystal (1D-PC) and its application in alcohol concentration sensing. It proposes a 1D-PC structure composed of four different materials alternately arranged along the axial direction, including μ-negative materials (μ-NMs) and ε-negative materials ( ε-NMs). Based on the Drude model, the relative permeability and permittivity for these materials are defined. The total equivalent transmission matrix of the 1D-PC is expressed using the transfer matrix method, which is crucial for determining the transmission spectrum of the PC structure. The study investigates how the transmittance spectra of transverse electric (TE) and transverse magnetic (TM) waves are affected by various physical parameters of the PC, such as the period number, the geometrical thickness of the dielectric layers, and the incident angle. It is found that the transmittance spectra shift towards the long-wave band with increasing period number, the geometrical thickness of the dielectric layers, or incident angle, and the peak values and half-peak width are also influenced by these parameters.The letter also proposes a PC sensor for alcohol concentration detection. When the alcoholic solution is filled into the PC structure, the central transmittance spectra of TE mode shift to the long-wave band as the concentration of the alcohol solution increases. A linear relationship is established between the central wavelength of the output beam and the alcohol-solution concentration, with good linearity confirmed by fitting results. The study suggests that this PC sensor has the potential to reliably measure the concentration of various solutions under different temperature conditions, provided the coefficients in the relevant equation are properly adjusted. The findings are expected to be significant for practical applications in fields like food safety, biomedical detection, and environmental monitoring.