| Summary: | Abstract The use of annular one-dimensional (1D) photonic crystals (PCs) for salinity sensing is studied in this research. Annular 1D-PCs provide small and integrated structures that facilitate the creation of portable and miniaturized sensor equipment appropriate for field use. In order to generate annular 1D-PCs, the research explores the finite element method (FEM) simulation technique utilizing the COMSOL Multiphysics approach, highlighting the significance of exact control over layer thickness and uniformity. Furthermore, we construct a 1D annular PCs structure in the form $${(AB)}^{N}$$ ( A B ) N , where A is silicon ( $$Si$$ Si ) and B is silicon dioxide ( $${SiO}_{2}$$ SiO 2 ) of 40 nm and 70 nm, respectively, with a number of periods equal to 9. By incorporating a central defect layer of saline water (220 nm thickness), the sensor achieves optimum performance at normal incidence with a sensitivity (S) of $$782 (nm/RIU)$$ 782 ( n m / R I U ) , a quality factor (Q) of 10.22, and a figure of merit (FOM) of $$12.6 {RIU}^{-1}$$ 12.6 RIU - 1 . The design that is suggested has several advantages over past work on planners and annular 1D-PCs, including ease of implementation, performance at normal incidence, and high sensitivity.
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