Optical Circuit Uses Stretchable Interconnections

The first optical circuit to use stretchable, bendable interconnections could be in the pipeline, following years of difficulty with the technology. Future applications could include building networks of wearable body sensors, moving machine parts including robotic limbs, and deformable consumer electronics.

A team of Belgian researchers is developing the new interconnections with two materials, both made of the rubbery substance poly-dimethylsiloxane (PDMS): the transparent core material through which the light travels, and a surrounding transparent layer with a lower refractive index.

This configuration traps light in the guide's core, causing it to propagate along the length of the interconnection, even when stretched up to 30 percent and bent around an object the diameter of a human finger.

Belgian researchers are developing new stretchable, bendable optical circuit interconnections. Courtesy of Optics Express.

A vertical cavity surface-emitting laser (VCSEL) served as the light source, with a photodiode functioning as the detector.

Until now, a way to enable these materials to carry light while stretched had not been possible. Past efforts also included embedding waveguides made of semi-rigid glass fibers into a stretchable substance. In this new method, the stretchable substance itself is the waveguide.

Bending a waveguide beyond a certain point typically causes some of the light trapped in the core to escape. The researchers have been mindful of this as their work continues.

"We were surprised that stretching had so little influence on the waveguides and also that their mechanical performance was so good," said lead author Jeroen Missinne of Ghent University and imec, adding that the guide’s reliability was “remarkable.”

He noted that the researchers did not see degradation in the material even after mechanically stretching it to a 10 percent elongation 80,000 times.

The researchers will also develop smaller waveguides, reducing them from 50 µm to just a few µm in diameter. This could require a redesign of the parts of the waveguide where light enters and exits.

The research was published in Optics Express.

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