A Scalable Large-Area Fabrication Strategy for Transparent Polymeric Encapsulated Metagratings

In this work, we present the design, fabrication, and experimental demonstration of fully polymeric and transparent guided-mode resonant (GMR) metagratings for visible-light operation and integration into augmented reality (AR) systems. The proposed metastructure employs an encapsulated grating architecture in which the periodic pattern is embedded at the substrate-waveguide interface, intrinsically protecting the grating from environmental exposure while preserving the optical functionality. The negative pattern is first transferred by thermal nanoimprint lithography (T-NIL) into a CYTOP substrate and subsequently backfilled with a high-index maN resist, providing the refractive-index contrast required for guided-mode resonance excitation. Structural characterization by SEM and AFM confirms the successful transfer of the designed geometry, high pattern fidelity and structural uniformity, and excellent reproducibility across independently fabricated samples. Spectroscopic ellipsometry reveals three well-defined resonances positioned close to the target RGB wavelengths, in good agreement with RCWA simulations, whereas preliminary angle-dependent reflectance measurements further validate the predicted angular evolution of the guided-mode resonances. The proposed fabrication strategy demonstrates that thermal nanoimprint lithography provides a robust, scalable, and cost-effective route for fabricating transparent polymeric GMR metagratings, enabling their implementation in large-area transparent optical combiners for augmented reality.