Sol-gel Barium Titanate Nanohole Array as a Nonlinear Metasurface and a Photonic Crystal

TL;DR

This paper presents a novel sol-gel derived barium titanate nanohole array fabricated via nanoimprint lithography, exhibiting photonic crystal and metasurface properties, with enhanced nonlinear optical responses suitable for photonic devices.

Contribution

It introduces a new fabrication method for nonlinear barium titanate nanostructures with large-area coverage and demonstrates their photonic and nonlinear optical properties.

Findings

Photonic bandgap observed in infrared range

Lattice resonant states in out-of-plane transmission

Enhanced second-harmonic generation by a factor of 18

Abstract

The quest of a nonlinear optical material that can be easily nanostructured over a large surface area is still ongoing. Here, we demonstrate a nanoimprinted nonlinear barium titanate 2D nanohole array that shows optical properties of a 2D photonic crystal and metasurface, depending on the direction of the optical axis. The challenge of nanostructuring the inert metal-oxide is resolved by direct soft nanoimprint lithography with sol-gel derived barium titanate enabling critical dimensions of 120 nm with aspect ratios of 5. The nanohole array exhibits a photonic bandgap in the infrared range when probed along the slab axis while lattice resonant states are observed in out-of-plane transmission configuration. The enhanced light-matter interaction from the resonant structure enables to increase the second-harmonic generation in the near-UV by a factor of 18 illustrating the potential in the flexible fabrication technique for barium titanate photonic devices.