Dual-band refractive index sensor with cascaded asymmetric resonant compound grating based on bound states in the continuum

We propose a cascaded asymmetric resonant compound grating (ARCG) for high-performance dual-band refractive index sensing. The physical mechanism of the sensor is investigated using a combination of temporal coupled-mode theory (TCMT) and ARCG eigenfrequency information, which is verified by rigorous coupled-wave analysis (RCWA). The reflection spectra can be tailored by changing the key structural parameters. And by altering the grating strip spacing, a dual-band quasi-bound state in the continuum can be achieved. The simulation results show that the highest sensitivity of the dual-band sensor is 480.1 nm/RIU, and its figure of merit is 4.01 × 105. The proposed ARCG has potential application prospects for high-performance integrated sensors.