Proposal of two tangent air hole structure for higher sensitivity gas sensor

One-dimensional photonic crystal (1D PhC) cavities are used as ultrasensitive gas sensors due to their high sensitivity to changes in the surrounding environment. One of the issues for typical 1D PhC-based sensors is that the confined optical field does not fully overlap with analytes, which therefore leads to low sensitivity. Herein, we propose and numerically investigate a photonic crystal cavity by introducing a two tangent air hole array to improve the gas refractive index sensitivity. We also investigate the spectral feature of the proposed photonic crystal cavity for varying structure parameters and methane gas concentration. In addition, the coupling efficiency of the waveguide and the influence of the temperature on the proposed structure for sensing applications are analyzed. Theoretical analysis reveals that the proposed two tangent hole structure simultaneously achieves a high sensitivity (353 nm/RIU) and figure of merit (FOM = 1.2 × 10⁴) compared to those observed in previous studies.