Scalable Lithium Niobate Nanoimprinting for Nonlinear Metalenses

TL;DR

This paper introduces a scalable, low-cost nanoimprint lithography method to create polycrystalline lithium niobate nanostructures, enabling efficient nonlinear metalenses with enhanced second-harmonic generation for integrated photonics.

Contribution

It presents a novel bottom-up fabrication technique for lithium niobate nanostructures, expanding nonlinear metasurface applications with high aspect ratios and improved nonlinear efficiency.

Findings

Achieved near-vertical features with aspect ratios up to 6.

Demonstrated second-harmonic focusing across UV to IR spectrum.

Increased nonlinear signal intensity by up to 34 times.

Abstract

Miniaturizing nonlinear optical components is essential for integrating advanced light manipulation into compact photonic devices, enabling scalable and cost-effective applications. While monocrystalline lithium niobate thin films advance nonlinear nanophotonics, their high inertness limits the design of top-down fabricated nanostructures. Here we present a versatile bottom-up fabrication method based on nanoimprint lithography for achieving polycrystalline lithium niobate nanostructures, and demonstrate its significant potential for nonlinear metasurfaces. The fabrication enables nearly vertical features and aspect ratios of up to 6, which we combine with a novel solution-derived material with high effective second-order nonlinearity of d_{eff}=5 pm/V. On this platform, we demonstrate second-harmonic focusing over a broad spectral range from near-UV to near-IR, increasing the nonlinear signal intensity by up to 34 times. Our method enables the first lithium niobate metalens and expands the field of nonlinear metasurfaces by providing a low-cost, highly scalable fabrication method for engineered nonlinear nanostructures