Large-Scale Bottom-Up Fabricated 3D Nonlinear Photonic Crystals

TL;DR

This paper reports the first successful bottom-up fabrication of 3D nonlinear photonic crystals using sol-gel derived barium titanate, achieving larger surface areas and finer periodicities than previous top-down methods, enabling enhanced nonlinear optical applications.

Contribution

It introduces a novel bottom-up fabrication method for 3D nonlinear photonic crystals with larger areas and smaller periodicities than existing techniques.

Findings

First bottom-up fabrication of 3D NPhC in barium titanate.

Surface areas exceed 5.3×10^4 μm^2, surpassing previous methods.

Periodicities of 1 μm (xy) and 300 nm (z) achieved.

Abstract

Nonlinear optical effects are used to generate coherent light at wavelengths difficult to reach with lasers. Materials periodically poled or nanostructured in the nonlinear susceptibility in three spatial directions are called 3D nonlinear photonic crystals (NPhCs). They enable enhanced nonlinear optical conversion efficiencies, emission control, and simultaneous generation of nonlinear wavelengths. The chemical inertness of efficient second-order nonlinear materials ($\chi^{(2)}$) prohibited their nanofabrication until 2018. The current method is restricted to top-down laser-based techniques limiting the periodicity along z-axis to 10 um. We demonstrate the first bottom-up fabricated 3D NPhC in sol-gel derived barium titanate by soft-nanoimprint lithography: a woodpile with eight layers and periodicities of 1 um (xy-plane) and 300 nm (z-plane). The surface areas exceed $5.3\cdot 10^4$ um^2, which is two orders of magnitude larger than the state-of-the-art. This study is expected to initiate bottom-up fabrication of 3D NPhCs with a supremely strong and versatile nonlinear response.