Team Taps Chalcogenide For Flexible Devices

A method for making photonic devices that can bend and stretch without damage could find uses in cables to connect computer devices, or in diagnostic and monitoring systems that could be attached to the skin.

A new material produced by Juejun Hu and his team can be repeatedly stretched without losing its optical properties. Courtesy of MIT.

A research team from MIT, the University of Texas, Xiamen University and Chongqing University in China, Universite Paris-Sud in France, the University of Southampton in the UK, and the University of Central Florida used a specialized kind of glass called chalcogenide for their device.

“Most current photonics devices are fabricated from rigid materials on rigid substrates, and thus have an inherent mismatch for applications that should be soft like human skin,” said Juejun Hu, an associate professor at MIT. “But most soft materials, including most polymers, have a low refractive index, which leads to a poor ability to confine a light beam.”

Instead of using such flexible materials, Hu and his team formed a thin layer of the chalcogenide into a spring-like coil. Just as steel can be made to stretch and bend when formed into a spring, the architecture of this glass coil allowed it to stretch and bend freely while maintaining its desirable optical properties.

"You end up with something as flexible as rubber, that can bend and stretch, and still has a high refractive index and is very transparent," said Hu.

Tests have shown that such spring-like configurations, made directly on a polymer substrate, can undergo thousands of stretching cycles with no detectable degradation in their optical performance. The team produced a variety of photonic components, interconnected by the flexible, spring-like waveguides, all in an epoxy resin matrix, which was made stiffer near the optical components and more flexible around the waveguides.

This research is still in the early stages as Hu's team has demonstrated only single devices.

"For it to be useful, we have to demonstrate all the components integrated on a single device," said Hu. Work is ongoing to develop the technology to that point so that it could be commercially applied, which Hu says could take another two to three years.

Such flexible, stretchable photonic circuits could be useful for applications where the devices need to conform to the uneven surfaces of some other material, such as in strain gauges. Optics technology is very sensitive to strain, according to Hu, and could detect deformations of less than 1/100th of 1 percent.

The research has been published in the journal Nature Photonics (doi:10.1038/s41566-017-0033-z), and is supported by the National Science Foundation.