Abstract

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.
tunable performance.

https://iopscience.iop.org/article/10.1088/2058-8585/ae57bc

Figure 1. (a) Schematic of the DSG fabrication process showing tailorable parameters: (i) grating line width (w), pitch (p), and waveguide thickness (d), shown in cross-section, (ii) relative rotation (θ) of the BSG and TSG, shown top down, and (iii) an additional intermediate spacer layer(s) of thickness (s), shown in cross-section. (b) Cross-section scanning electron micrographs of DSG structures with (i) varying waveguide thickness, (ii) rotation where the TSG and BSG are orientated with θ = 90°, and (iii) a PDMS − chitosan spacer layer between the BSG and TSG.