Near‐Infrared Dielectric Microcavity Temperature Sensor Based on SiO ₂ /TiO ₂ Distributed Bragg Reflectors With a Silicon Cavity

Lithium‐ion battery packs develop spatial temperature gradients that accelerate nonuniform aging and can trigger localized hotspots, motivating electrically isolated and EMI‐immune thermal monitoring. We present a numerical design and analysis of a short‐wave infrared (SWIR) wavelength‐encoded temperature sensor based on a 1D dielectric Bragg microcavity formed by symmetric SiO ₂ /TiO ₂ multilayer mirrors and a central silicon defect cavity. Transfer‐matrix modelling predicts that five‐period SiO ₂ /TiO ₂ distributed Bragg reflectors produce a broad high‐reflectance stopband ≈1.3–1.9 µm with a narrow defect‐mode resonance near 1.55 µm, compatible with mature SWIR/telecom‐band interrogation components. Temperature is obtained by tracking the resonance wavelength shift dominated by the silicon thermo‐optic response. Over −20 to 100 °C, the cavity dip shifts monotonically from 1546.898 to 1556.253 nm (Δ λ = 9.355 nm), giving an average sensitivity of 0.0778 nm/°C with near‐linear behavior suitable for straightforward calibration. Spectral sharpness remains stable (FWHM ≈ 5.503–6.053 nm; Q ≈ 256–283), supporting low‐jitter resonance fitting. Angular analysis indicates that near‐normal incidence is preferred for temperature‐only readout, with behavior consistent with the BK7‐air critical‐angle regime at larger angles. The proposed SWIR dielectric microcavity provides compact, wavelength‐encoded temperature sensing suitable for distributed battery‐module thermal mapping and early hotspot detection.