Dual quasi-bound states in the continuum of photonic crystal slab for simultaneous measurement of refractive index and temperature with low demodulation deviation

In this paper, a silicon photonic crystal slab driven by dual symmetry breaking-induced quasi-bound states in the continuum (quasi-BICs) is theoretically proposed for high-performance refractive index and temperature sensing. The suspended photonic crystal slab structure and the small inclination angle α of trapezoidal nanoholes enhance the sensitivities and Q-factors of quasi-BICs, respectively. The effects of geometric parameters and polarization angle of light source on quasi-BICs are analyzed. Numerical results show the Q-factors of dual quasi-BICs (QBIC1 and QBIC2), which are dominated by electric quadrupole (EQ) and magnetic dipole (MD), are close to 106 and 105, respectively. The refractive index sensitivities of QBIC1 and QBIC2 exceed 700 nm/refractive index unit (RIU). In addition, the demodulation deviation caused by the resolution of the sensor is calculated by analyzing the two-dimensional sensing matrix. The simultaneous enhancement of Q-factor and sensitivity creates favorable conditions for reducing the demodulation deviation. The maximum demodulation deviations of refractive index and temperature of the designed sensor are 3.1 × 10−6 RIU and 0.1 K, respectively. Our work shows the potential of quasi-BICs for developing high-performance dual-parameter and multi-parameter detection.