Optical Metasurfaces with Double-Sided Guided Mode Resonances for Dual-Band Sensing

We report vertically stacked, double-side gratings fabricated by large-area nanoimprint lithography of colloidal TiO₂ nanocrystal inks to achieve dual-band dielectric metasurfaces with high quality factor, guided-mode resonances (GMRs). The periodicity of the top and backside gratings can be independently tailored to realize spectrally distinct GMRs. The gratings can be coupled through a shared waveguide or isolated by incorporating a spacer layer. We demonstrate differential humidity sensors by incorporating a polydimethylsiloxane blocking layer in the spacer stack to allow the backside grating to serve as an in situ optical reference and the topside grating to be sensitive to water. This work establishes a scalable and versatile strategy for fabricating monolithic, multifunctional optical devices with high accuracy and tunable performance.