Abstract

Subwavelength dielectric gratings based on guided mode resonances (GMRs) provide a compact, low-cost, and readily fabricable platform for narrowband spectral filters applied in numerous fields, such as sensors, spectrometers, and hyperspectral imaging. We numerically designed two long-wave infrared transmission bandpass filters based on Ge–ZnS–Ge thin film stacks and 2D zero-contrast gratings. The first filter is attributed to double GMR mode coupling, exhibiting a broadband high reflectance between 8 and 12 µm and a narrow transmission peak with a spectral linewidth of 53 nm and transmittance efficiency of 98% at the resonance. The other filter adopts a low-refractive-index material ${{\rm BaF}_2}$ as the substrate, which displays a lower-transmittance sideband from 8.6 to 9.4 µm, and a higher transmission efficiency up to 100% at the resonance. The physical mechanisms of two spectral responses are all relevant to guided mode coupling and Fabry–Perot resonance.

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