A novel approach to salinity monitoring using two dimensional hexagonal photonic crystals

We developed a novel structure by constructing a hexagonal cylindrical configuration within a dielectric host, which showcases a substantial band gap. This was achieved using two-dimensional photonic crystals that possess triangular lattice periodicity. The design and analysis of this structure were conducted using the COMSOL multiphysics approach along with the finite element method (FEM). Our enhancements to the two-dimensional hexagonal photonic crystals are aimed at targeting the infrared frequency spectrum and concentrating the area of the photonic band gap. The structure under consideration consists of a 2D hexagonal photonic crystal (PC) with dimensions r = 500 nm, a₂ = 250 nm, and N = 5, all cylinders within this structure are filled with air, resulting in a photonic band gap (PBG) that spans approximately from 2550 to 4700 nm, with a width of 2150 nm. Introducing a defect by injecting saline water into the central hexagonal cylinder generates a defect peak within this PBG range. Consequently, the sensitivity of the system is measured at 670 nm/RIU, with a quality factor (Q) of 905, and a figure of merit (FOM) of 253 RIU^-1. This proposed technology is simple and practical for integration in thermal desalination processes, offering a potential alternative to traditional salinity sensors in photonic sensing applications.