Foam offers way to manipulate light

Applications and Research

An analysis by Princeton researchers has shown that a type of foam, long studied by scientists, is able to block particular wavelengths of light. This is acknowledged as a highly desirable property for next-generation information technology that uses light instead of electricity.

The researchers, integrating expertise from materials science, chemistry and physics, conducted exhaustive computational simulations of a structure known as a Weaire-Phelan foam. They found that this foam would allow some frequencies of light to pass through, while completely reflecting others. The selective blocking, known as a photonic band gap, is similar to the behaviour of a semiconductor.

“This has the property we want: an omnidirectional mirror for a certain range of frequencies,” said Salvatore Torquato, Professor of Chemistry and the Princeton Institute for the Science and Technology of Materials. Torquato, the Lewis Bernard Professor of Natural Sciences, published the results this month in the Proceedings of the National Academy of Science, with co-authors Michael Klatt, a Postdoctoral Researcher, and Physicist Paul Steinhardt, who is Princeton’s Albert Einstein Professor in Science.

While numerous examples of photonic band gaps have been shown previously in various types of crystals, the researchers believe that their new finding is the first example in a foam, similar to the froth of soap bubbles or a draft beer.

Torquato, Klatt and Steinhardt became interested in the Weaire-Phelan foam as a tangent of another project in which they were investigating “hyperuniform” disordered materials as an innovative way to control light. Although not their original focus, the three realised that this precisely structured foam had intriguing properties.

“Little by little, it became apparent that there was something interesting here,” observed Torquato. “And eventually we said, ‘Ok, let’s put the main project to the side for a while to pursue this.'”

To show that the Weaire-Phelan foam exhibited the light-controlling properties they were seeking, Klatt developed a meticulous set of calculations that he executed on the supercomputing facilities of the Princeton Institute for Computational Science and Engineering.

“The programs he had to run are really computationally intensive,” Torquato said.

The work opens numerous possibilities for further invention, suggested the researchers, who dubbed the new area of work as “phoamtonics” (a mashup of “foam” and “photonics”). Because foams occur naturally and are relatively easy to make, one possible goal would be to coax raw materials to self-organise into the precise arrangement of the Weaire-Phelan foam.

With further development, the foam could transport and manipulate light used in telecommunications. Currently much of the data traversing the Internet is carried by glass fibres. However, at its destination, the light is converted back to electricity. Photonic band gap materials could guide the light much more precisely than conventional fibre optic cables and might serve as optical transistors that perform computations using light. “Who knows?” asked Torquato. “Once you have this as a result, then it provides experimental challenges for the future.”

For more information, visit https://engineering.princeton.edu