An asymmetric grating refractive index sensor generating quasi-bound states in the continuum with high figure of merit and temperature self-compensation

A subwavelength asymmetric grating refractive index (RI) sensor based on quasi-bound states in the continuum (q-BIC) with temperature self-compensation was proposed. The sensor structure consisted of a prism/asymmetric grating/analytes, where the grating layers were periodically arranged asymmetric silicon (Si) and polydimethylsiloxane. The asymmetry of the structure led to the fact that the tangential field component and the radiative field component in the grating layer were no longer in a fully decoupled state at the resonance position, creating two extremely narrow q-BIC resonance peaks, which gave the sensor a high figure of merit (FOM) and a low detection limit (DL). In addition, the thermo-optical coefficient of the materials made one of the resonance peaks more sensitive to temperature changes, realizing the temperature self-compensation of RI detection and thus improving the detection accuracy. From the results, reducing the asymmetry of the structure by modifying the parameters could theoretically make FOM > 5.1 × 10 6 RIU −1 and DL < 9.8 × 10 −9 RIU. For the RI sensor with temperature self-compensation, FOM = 3057.85 RIU −1 and DL = 1.64 × 10 −5 RIU for the RI, FOM = 0.88 °C −1 and DL = 0.057 °C for the temperature. These findings could effectively improve the temperature interference resistance of the sensor and thus the accuracy of trace substance detection.