Effects of Building Blocks and Defects on the Performance of Two-Dimensional Photonic Crystal Sensors for Black Liquor Detection

In this study, to achieve convenient and sensitive detection of the concentration of the black liquor solution, we constructed two-dimensional photonic crystal sensors with a periodic arrangement of elliptical and circular pores in a hexagonal lattice. The photonic bandgap in transverse magnetic (TM) mode was analyzed using the plane wave expansion method. This was followed by simulations to obtain absorption spectra at different concentrations of black liquor, with subsequent processing and computation. The simulation results revealed a linear correlation between the concentration of black liquor and the position of the trough in the absorption spectrum under consistent temperature conditions. Notably, as the concentration of black liquor solution increased, the position of absorption spectra trough shifted towards the low-frequency region. Through parameters optimization, we achieved a relationship equation with a linear fitting coefficient R² of 1.000. The sensitivity of the two-dimensional photonic crystal sensor composed of circular scatters with line defects in the hexagonal lattice can be as high as 508.3 nm/RIU when the mass fraction of black liquor solution ranges from 10 to 20%. These results provide an essential theoretical basis for applying photonic crystal sensors to detect black liquor concentrations. This study holds promise for the design and fabrication of high-performance photonic crystal sensors for practical applications.