Ultra sharp Fano resonances induced in a dual-cavity-waveguide integrated system and its application for temperature sensing

Optical temperature sensing is critical for on-chip photonic integration, microelectronic thermal management and other fields. This work proposes and studies a waveguide-cavity integrated temperature sensor based on ultra-sharp Fano resonances. The designed single slot-cavity structure achieves a temperature sensitivity (S) of 0.2 and a figure of merit (FOM) of 15.8 via bright-dark mode interference-induced Fano resonance. By extending to a dual-cavity configuration, cavity-cavity coupling introduces extra interference paths, suppressing radiative losses and narrowing resonance linewidths significantly. The formation and sharpening mechanisms of Fano resonances are analyzed via multimode interference coupled-mode theory(MICMT), with temperature-dependent spectral characteristics explored systematically. The designed structure exhibit an ultra narrow linewidth with FWHM (full width at half maximum) estimated to be 5 nm, and boosting an ultra high FOM to 101.3. The dual-cavity structure features excellent temperature sensitivity, superior spectral resolution and enhanced robustness against linewidth broadening, making it a promising platform for high-performance chip-scale optical temperature sensing in practical integrated photonic systems and future technologies.