Improving the sensitivity of refractive index sensors with integrated double-layer resonant meta-grating structure

A refractive index (RI) sensor with a high sensitivity based on an integrated double-layer resonant meta-grating (DRMG) is theoretically demonstrated. The presented DRMG consists of two top/ bottom grating layers with meta-grooves, and a slab waveguide layer. The physical mechanism of the device is elucidated by combining a theoretical model with the eigenmode information of the grating structures. The reflection spectra of DRMG-based sensor are then investigated by the theoretical model, which is simultaneously verified by rigorous coupled-wave analysis (RCWA). It is found that the sensitivity is improved by controlling the key structural parameters of the DRMG for enhancing the interaction between its leaky mode and analyte. Meanwhile, the optical field is trapped around the region of DRMG. Consequently, the sensitivity of the RI sensor is further increased without decreasing its quality factor (Q-factor). The simulation results show that the sensitivity of the sensor is achieved up to 930 nm/RIU with its Q-factor as high as 11575. Such an all-dielectric meta-grating sensor is expected to hold great promise for realizing high-performance sensor.