Harnessing optical fibers for a smarter environment

Optical fibers are well-known for their essential role in the communications revolution and in medical technology advances. Sylvain Texier, a graduate student in civil engineering, is attempting to harness the fibers for new causes – cleaner water, cleaner soil and sturdier dams.

Texier hopes to hitch polymer chains to optical fibers in order to create fiber-optic sensors that continuously monitor pressure, temperature and moisture in subsurface environments. Texier, who has a degree in geotechnical engineering from the Institute of Sciences and Technology in Grenoble, is advised by Sibel Pamukcu, associate professor of civil and environmental engineering, and Jean Toulouse, professor of physics. He also collaborates with professors of materials engineering at Drexel University.

“One of the biggest challenges in working with soil,” says Texier, “is to know where and in what quantities water is located.” Landfill operators are concerned with water location, he says, because water is vital to the bacteria that degrade waste materials. Similarly, if farmers know which portions of a field are dry, they can water only those areas instead of irrigating the entire field, thus saving water.

Hydrophilic polymers that attract water can be woven around optical fibers, Texier says. When placed in a landfill, the polymers swell when they come into contact with moisture. By sending an optical signal through the fibers, engineers can detect when the polymers are swelling and can determine, based on the degree of swelling, the amount of water that is present in a particular area of the landfill. Depending on where they are placed, the fiber-laced polymeric sensors can also alert operators when landfills are leaking. Fibers wrapped with hydrophobic polymers, which reject water, can also signal the presence of petroleum-based products and other hydrocarbons.

Fiber-optic sensors can detect the amount of water infiltrating a dam under construction, enabling engineers to determine whether it is safe to fill the dam with water, Texier says. Cost makes it prohibitive to install fiber-optic sensor systems in large areas or large structures, Texier says. To overcome this obstacle, Texier is designing a sensor that uses Stimulated Brillouin Scattering (SBS) to allow spatially distributed measurements of different parameters using only a single fiber. He is experimenting with polymers of different types and different diameters, and adjusting the gaps between the coils of the fiber.

Another graduate student in civil engineering, Necdet Tek, is also working on the project.