IMEC paves the way toward optical sensing foils

IMEC said with this technique, it will be possible to create foils that sense changes in pressure, and such sensing, skin-like foils could be used for monitoring irregular or moving surfaces, like in robots, pliable machinery, or as an artificial skin.

By Ann Steffora Mutschler, Senior Editor -- Electronic News, 10/7/2008

Moving one step closer to artificial skin with sensing properties, Leuven, Belgium-based nanoelectronics and nanotechnology research center IMEC vzw reported today that its associated laboratory at the Ghent University – INTEC -- has made the first functional optical links embedded in a flexible substrate including optical waveguides, light sources, and detectors.

IMEC explained that with this technique, it will be possible to create foils that sense changes in pressure, and such sensing, skin-like foils could be used for monitoring irregular or moving surfaces, like in robots, pliable machinery, or as an artificial skin.

What makes this possible are integrated optical interconnections that are insensitive to electromagnetic interference, applicable in harsh environments, and highly sensitive, IMEC said.

Last year, IMEC said it reported that it had achieved embedded optical links on rigid surfaces, and this current research takes optoelectronics one step further.

In this work, standard, commercially available GaAs photo-detectors and GaAs vertical-cavity surface-emitting lasers (VCSELs) are thinned down to 30-microns and are then embedded into a flexible foil of optical transparent material and optically coupled with embedded waveguides and out-of-plane micromirrors with the resulting structure showing good adhesion and flexible behavior, IMEC noted.

Also, IMEC said it is working on two types of sensors: array waveguide sensors and optical fiber sensors, both of which can be used for sensor foils.

More specifically, array waveguide sensors rely on the change in coupling between arrays of crossing waveguides with two layers of polymer waveguides separated by a thin layer of soft silicone. When no pressure is applied, no crosstalk is detected but when pressure is applied to the foil, the distance between the waveguides in the separated layers decreases, and light is transmitted from one layer to the other, which makes this approach suited for high-density pressure sensors on small areas.

On the other hand, optical sensing foils combine two technologies that have lately seen a growing interest: integrated optical interconnections, and flexible, stretchable electronics with the ambition of researchers to create a flexible and stretchable skin-like foil sensitive to touch, pressure, or deformation. Such artificial skin could be used in medical and industrial environments, and to this aim, a group of European research institutes, including IMEC, are collaborating in the 7th Framework project Photonic Skins For Optical Sensing (PHOSFOS).

IMEC noted that PHOSFOS will develop photonic foils based on optical fiber sensors t targeted at applications in civil engineering and medicine that will, for example, continuously monitor the integrity and the behavior of buildings, dams, bridges, roads, or tunnels with other uses including monitoring aircraft wings, helicopter blades, or windmill blades to allow early warning of failure or anomaly.

Also, skin-like PHOSFOS membranes are set to be used in long-term monitoring of respiration and cardiac activity, and the detection of pressure points under bed-ridden patients, IMEC added.