Solution‐Processed Barium Titanate Nonlinear Woodpile Photonic Structures with Large Surface Areas
Résumé
Three dimensional (3D) nonlinear photonic crystals are one of the potential candidates for enabling photonic circuits. Most of the current top‐down fabrication approaches for such crystals are time consuming and suffer from small surface areas and limitations to specific substrates. Herein, a bottom‐up fabrication technique (UV‐soft nanoimprint lithography) together with solution processing of barium titanate (BaTiO3) nanoparticles is used to create large‐scale 3D nonlinear woodpile photonic crystals. Opposed to other 3D photonic crystals, the woodpile structure can be fabricated layer by layer. This property makes it suitable for roll‐to‐roll fabrication, which can be easily adapted in industry. The prepared photonic crystals with up to eight layers have surface areas of 1.0 cm2. The linear and nonlinear optical behavior of these 3D woodpile structures is characterized. Their transmission stop band lies around 757 nm and a relative linear minimum transmission of 48.4% for a four‐layer sample is obtained. Images of diffraction patterns together with polarization‐dependent second harmonic generation measurements prove a cubic photonic crystal structure in the linear and nonlinear regime. In addition to second‐order nonlinearity, BaTiO3 exhibits electro‐optic, elasto‐optic, and thermo‐optic effects. Therefore, it is especially suited for future active photonic crystal applications.
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