High-quality photonic crystals with a nearly complete band gap obtained by direct inversion of woodpile templates with titanium dioxide

TL;DR

This paper demonstrates a novel method combining multiphoton lithography and atomic layer deposition to create high-quality titanium dioxide photonic crystals with nearly complete band gaps, exhibiting excellent optical properties in the near-infrared.

Contribution

It introduces a new fabrication technique for direct inversion of polymer templates into TiO₂ photonic crystals with superior optical performance.

Findings

Achieved near-perfect specular reflectance.

Observed a transmission dip close to detection limit.

Bragg length comparable to lattice constant.

Abstract

Photonic crystal materials are based on a periodic modulation of the dielectric constant on length scales comparable to the wavelength of light. These materials can exhibit photonic band gaps; frequency regions for which the propagation of electromagnetic radiation is forbidden due to the depletion of the density of states. In order to exhibit a full band gap, 3D PCs must present a threshold refractive index contrast that depends on the crystal structure. In the case of the so-called woodpile photonic crystals this threshold is comparably low, approximately 1.9 for the direct structure. Therefore direct or inverted woodpiles made of high refractive index materials like silicon, germanium or titanium dioxide are sought after. Here we show that, by combining multiphoton lithography and atomic layer deposition, we can achieve a direct inversion of polymer templates into TiO$_{2}$ based photonic crystals. The obtained structures show remarkable optical properties in the near-infrared region with almost perfect specular reflectance, a transmission dip close to the detection limit and a Bragg length comparable to the lattice constant.