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Flexible photonic skins shape up for sensing

19 Jun 2008

optics.org speaks to the coordinator of a new EU project about the endless applications of photonic skins.

Thin and flexible polymer sheets that combine the latest fibre-optic sensing technology with optoelectronics could soon be measuring the stresses and strains placed on structures ranging from bridges and dams to helicopter blades. That's the goal of a new EU project called Phosfos, which is pioneering photonic skins for optical sensing.

"We want to show that we can integrate fibre sensors with all of the necessary driving and read-out optoelectronics in a flexible substrate," project coordinator Francis Berghmans of Vrije University in Brussels, Belgium, told optics.org. "We want to integrate photonic crystal fibres made of silica or plastic with optical sources and detectors in a polymer skin whilst keeping everything flexible."

One of the key aspects of the three year Phosfos project will be to thin down existing wafer-scale optical sources and detectors so that they are suitable for use in the photonic skin. "We are targeting a total skin thickness of 1 mm," commented Berghmans.

The team is considering LEDs and superluminescent diodes as both of these sources offer the wavelength range required to address a multiplexed array of fibre Bragg gratings (FBGs) that will act as the sensing element.

"Every FBG works in a particular wavelength region and we have to address all of these at the same time so we need a source that is relatively broadband," explained Berghmans. "A supercontinuum is another idea as then the fibre could be used as the source and sensor combined, but that is beyond the scope of the current project."

Berghmans adds that the goal is to make the photonic skins as large as possible. In the first instance, he believes that a skin the size of an A3 sheet of paper (approximately 30 x 42 cm) is feasible. The initial limiting factor is ensuring that the entire area can be polymerized with technologies such as ultraviolet lamps.

The project brings together several universities across Europe as well as two SMEs, FOS&S of Belgium and Astasense of the UK. Although the ultimate intention is to exploit the skins in as many applications as possible, the project is focusing on the strengths of its industrial partners. FOS&S specializes in structural monitoring, which could see the skins deployed on everything from dams to aircraft wings, while Astasense focuses on healthcare.

"You could imagine a skin wrapped around a patient to monitor their breathing during a scan," said Berghmans. "This is where we see the real benefit of the optical technology because it does not interact with the electromagnetic field. The polymer must also be compatible with the clinical environment so we need to make sure that these skins can be sterilized."

Once the technology has matured sufficiently, Berghmans says that the industrial partners will start to offer it as a product. Other ideas that fall out with the scope of the current project include integrating thin batteries or solar cells into the skin and transmitting the sensor data wirelessly.

Jacqueline Hewett is editor of Optics & Laser Europe magazine.

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