Stretchable optical circuit enables wearable body sensor networks

February 20, 2014 // By Paul Buckley
Stretchable optical circuit enables wearable body sensor networks
A team of researchers from Ghent University are claiming the first optical circuit that uses interconnections which are not only bendable, but also stretchable and may be ideal for developing wearable body sensors and robotic skin.

The interconnections, made of a transparent poly-dimethylsiloxane (PDMS) material, are capable of guiding light along their path even when stretched up to 30% and when bent around an object the diameter of a human finger.
By integrating the stretchy interconnections into a circuit – with a light source on one end and a detector on the other – the researchers have created a miniature stretchable, bendable 'link' that could be incorporated into optical communications systems.
“To our knowledge, this is indeed the first truly bendable, stretchable optical link with these miniature dimensions,” said lead author Jeroen Missinne of Ghent University and imec, a micro- and nano-electronics research center, in Belgium.
Previously, researchers had created optical interconnections – also called lightguides or waveguides – from various rubbery materials. But until now, the researchers say, no one had discovered a way to enable these materials to carry light while stretched. Past efforts also included embedding waveguides made of semi-rigid glass fibers into a stretchable substance. In the new method, the stretchable substance itself is the waveguide.
The new connector consists of two materials, both made of PDMS: a transparent core through which the light travels, surrounded by another transparent layer of PDMS with a lower refractive index, a characteristic of the material that describes how light moves through it. The configuration traps light in the guide’s core, causing it to propagate along its length.
The Belgian team have tested how far they could bend and stretch their new optical connector before too much light escaped.
“We were surprised that stretching had so little influence on the waveguides and also that their mechanical performance was so good,” Missinne said. The guide’s reliability was also 'remarkable',” explained Missinne. The researchers did not see a degradation in the material even after mechanically stretching it to a 10 percent elongation 80,000 times.
"waveguides are useless if you cannot launch

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