Multiplexed rectangular dielectric gratings with multiple narrow-band refractive index filtering and sensing.

We propose a low-loss compound structure consisting of a multiplexed rectangular dielectric grating and a waveguide layer, which can function as multi-band optical filters and sensors in TE and TM polarization by utilizing the resonant mode of the waveguide (WG) and the hybrid SP, respectively. By manipulating the parameters and subsequently constraining the local density of multi-resonant modes to several distinct resonant wavelengths, we propose a novel category of highly sensitive refractive index sensing platforms. Spectral shifts ranging from 110 to 131 nm/RIU with FOM of (22, 26.2)/RIU under TE polarization and 80 to 114 nm/RIU with FOM of (5.7, 8.1)/RIU under TM polarization can be accurately discerned for multiple individual analytes across a broad spectral range. The proposed structures offer enhanced flexibility in the design of structures across a wide spectral range, catering to various potential applications in multi-band optical filters, sensors, and photodetectors.