Refractive index sensing based on photonic crystal structures has emerged as a powerful platform for label-free and highly precision detection in chemical and biological applications. Here, we present a high-performance one-dimensional photonic crystal (1D PC) heterostructure tailored for ultra-sensitive refractive index sensing. The design leverages a symmetric, reverse-stacked cavity configuration to achieve an exceptionally high-quality factor ( \(\:\text{Q}-\text{f}\text{a}\text{c}\text{t}\text{o}\text{r}\text{s}\) ) and near-unity transmission in the telecom band. The structure comprises two mirror-symmetric 1D PCs arranged in reverse order to generates a localized interface state at their junction, giving rise to a sharp resonance within the photonic bandgap (PBG). Impedance-matching layers composed of silicon and air are added at both input and output interfaces to enhance light–matter interaction and transmission efficiency. We employ finite-element-method (FEM) simulations with lossless materials to realize a sharply defined resonance, yielding a \(\:\text{Q}-\text{f}\text{a}\text{c}\text{t}\text{o}\text{r}\) of 1.32 × 10⁸, sensitivity of 1197.2 nm/RIU, figure of merit ( \(\:\text{F}\text{O}\text{M}\) ) of \(\:9.04\:\times\:\:10^4\) , and detection limit ( \(\:\text{D}\text{L}\) ) of \(\:\sim1.1\:\times\:\:10^{-8}\) RIU. The structure exhibits near-unity transmission, polarization insensitivity, and operates in the telecom band ( \(\:\lambda\:\:\approx\:\:1512\:nm\) ). Despite their idealized nature, these findings lay a high-performance foundation for the design of practical 1D PCs sensors targeting trace gas or low-concentration biochemical detection.
