3D printing of photonic crystals that completely block light

Photonic crystals are materials with periodic structures that interact uniquely with light. They can block light at certain wavelengths, which is known as a ‘photonic bandgap’. This property allows light to be precisely controlled, opening up applications in telecommunications and quantum technology. Researchers have now developed a method to 3D print photonic crystals that completely block visible light and therefore hold great potential for technological innovation.

“For decades, researchers have been trying to produce photonic crystals that completely block light in the visible range. These crystals will have potential use in the elaborate 3D control of light flow, the behavior of single-photon emitters, and quantum information processing,” explained Dr. Zhang Wang, SUTD research fellow and first author of the paper.

In a recent study published in Nature Nanotechnology, researchers from Singapore and China, led by Professor Joel Yang from the Singapore University of Technology and Design (SUTD), have now developed a ground-breaking method to produce 3D photonic crystals with a full bandgap in the visible range. The researchers used a customised titanium resin and printed the crystals using two-photon polymerisation lithography (TPL), an additive manufacturing technique.

“It is used for its whitening properties due to light scattering from titania particles, and is found in common consumer items such as toothpaste and sunscreen and in self-cleaning surfaces,” said Prof Yang.

While conventional resins used in TPL are mostly organic in nature and of low refractive index, the use of titanium dioxide, an inorganic material with a high refractive index, allows for more precise control of light manipulation. A special heating process shrinks the printed structures down to one sixth of their original size, resulting in a lattice spacing of only 180 nm. This enables unprecedented resolution and the appearance of a complete photonic bandgap in the visible spectrum.

“The structure of the crystals shrinks by approximately six times during the heating process, and its pitch can become as small as 180 nm after shrinkage,” said Dr. Zhang. The pitch refers to the distance between different layers within the printed crystal; the smaller the pitch, the more enhanced the resolution.

This development could have far-reaching implications for applications such as light control, quantum information processing and waveguides. Furthermore, due to the flexibility of the printing process, the method offers the possibility to customise structures for specific applications, for example by introducing defects into the crystals.

“This collaborative study pushed the boundaries of material science and nanofabrication process design and technologies,” added Prof Yang. “It also reflects SUTD’s mission to draw on multiple disciplines to make a positive impact on society.”