Tunable Opto Thermal Sensor Based on HfO2 for Ultra-High Temperature Sensing

This paper is proposed a tunable opto-thermal sensor for ultra -high temperature-sensing by developing a one-dimensional (1-D) photonic crystal (PC) structure of alternating layers of Silicon-Dioxide (SiO₂), Titanium-Dioxide (TiO₂) and integrated with a single defect layer of Hafnium-Dioxide (HfO₂) based on the thermo-optic response. The sensor is analysed under high-temperature variations, where the RI changes induced by heating directly. The HfO₂ defect layer enables a sharp resonance peak within the photonic bandgap, significantly improving the detection capability. The optical behaviour of the proposed 1-D PC is modelled using the Transfer Matrix Method. Transmission and reflection spectra are computed numerically and the significance performance of the sensor are plotted such as defect layer thickness variation (−3% to +3%), Quality Factor (Q-factor), sensitivity and evaluated the numerical value. To enhance the sensing accuracy, the defect-layer thickness is optimized and the calculated Q-Factor is increased from 15.6 to 15.85. The PC demonstrates a high temperature sensitivity of approximately 0.145 nm/°C, indicating a substantial shift in resonance wavelength with the variation temperature. The results confirm that the SiO₂–TiO₂ periodic structure, combined with an optimized HfO₂ defect layer, provides a robust, thermally stable, and highly responsive platform for high-temperature PC sensing applications.