Hybrid nano-PER: Scalable metasurfaces to accelerate mass production for high-performance optics

Metasurfaces, with their ability to manipulate light at the nanoscale, offer immense potential to replace bulky conventional optics with compact, lightweight devices. However, the path to commercialization has been blocked by fabrication challenges: scalable methods like NIL often use low-index resins, which require tall, high-aspect-ratio meta-atoms that are difficult and costly to produce without defects.The proposed solution is a hybrid meta-atom based on TiO₂ nanoparticle-embedded resin (nano-PER). This composite material enhances the refractive index (~ 2.0 in the visible spectrum) of standard imprint resins (~ 1.5) while retaining printability. The core innovation is the deposition of a thin TiO₂ film (refractive index ~2.5) using Atomic Layer Deposition (ALD) onto the nano-PER structure. This "hybrid" approach achieves a sufficiently high effective refractive index contrast between two axes of dominant modes. Through this design, the team achieved a significant reduction in structural dimensions: the meta-atom height was minimized to 650 nm (down from 900 nm in previous polymer-only hybrids). This reduction ensures greater stability and robustness in the fabrication process. Using Particle Swarm Optimization (PSO), the meta-atom parameters were fine-tuned for broadband performance across RGB wavelengths (450, 532, and 635 nm). The optimized structure (coated with an 18 nm TiO₂ film) achieved an impressive average conversion efficiency of 76%. A hyperbolic metalens was successfully fabricated using the combined NIL and ALD process, which is compatible with semiconductor fabrication and supports high-throughput, low-cost mass production. Experimental results confirmed its effectiveness, achieving an average focusing efficiency of 51.23% across the RGB wavelengths and demonstrating diffraction-limited performance with an average Strehl ratio of 0.86. These findings mark a crucial step in simplifying nanofabrication and advancing the commercial viability of high-performance metasurfaces.