Sensing features of Lorentzian and Fano resonances in waveguide–cavities couplers

In this paper, we present a numerical study of an efficient refractive index sensor composed of side-coupled microcavities in a two-dimensional photonic crystal (2DPC). The crystal is created by arranging infinite zinc selenide (ZnSe) rods in a 2D triangular lattice with an air background. The transmission features of the structure are studied using the finite element method when the microcavities are loaded with different organic chemical compounds. The simulation results demonstrate a symmetric Lorentzian resonance and an ultrasharp, asymmetrical Fano resonance. The Lorentzian resonance wavelength shifts to higher values as the analyte refractive index (RI) increases, while the Fano resonance wavelength remains unchanged at 1117.52 nm. Therefore, the Lorentzian resonance is used in this study to detect various organic chemical compounds. The sensitivity (S) of the structure shows a remarkable average value of 149 nm/RIU while the quality factor (Q) and detection limit (DL) yield moderate average values of 85, and 8.2 × 10 -3 RIU, respectively. These results indicate that the proposed structure can serve as an efficient refractive index sensor. Additionally, the sensors compact footprint of approximately 126 µm 2 allows for easy integration into electronic circuits.