Thermally tunable dual-channel ultra-high-Q absorber in a hybrid grating-photonic crystal.

We propose and theoretically investigate a thermally tunable, dual-channel near-infrared absorber based on an amorphous silicon (a-Si)-integrated hybrid grating-photonic crystal. Utilizing rigorous coupled-wave analysis and coupled-mode theory, we demonstrate that the device achieves polarization-selective, near-perfect absorption (>98%) governed by mode-selective critical coupling. Due to distinct spatial confinement, the structure exhibits a completely decoupled thermal response. One resonant mode achieves critical coupling with a high linear thermal sensitivity of 118.3 pm/°C, while the other acts as an ultra-high-Q reference (Q≈13147) that remains spectrally locked with a negligible sensitivity of 4.4 pm/°C. Furthermore, the absorber features high fabrication tolerance and angular mode anti-crossing. This integration of an actively tunable channel and a temperature-insensitive reference within a single monolithic platform provides a robust paradigm for self-calibrating optical sensors and dynamic narrowband filters.