A team from the University of Pittsburgh has developed a high-temperature fiber sensor for gas flow measurements. The researchers said they were able to operate the sensor at up to 850 °C, about 200 °C hotter than has been achieved in previous experiments using MEMS-based sensors. The new approach integrates optical heating elements, optical sensors, energy delivery cables and a signal cable inside a single optical fiber. The optical power produced by the fiber supplies energy to the heating element, the researchers said. The optical sensor within that same fiber measures the heat transfer from the element. Hundreds of fiber optic flow sensors (in red) can be packed into a single fiber. Courtesy of Kevin Chen/University of Pittsburgh. “We call it a ‘smart optical fiber sensor powered by in-fiber light,’” said Dr. Kevin P. Chen, an associate professor in Pitt’s Department of Electrical and Computer Engineering. The researchers used optical fiber sensors because they have strong multiplexing capabilities and are immune to electromagnetic interference. They were able to pack many of these sensors into a single fiber, reducing or even eliminating wiring problems associated with having numerous leads. “Tapping into the energy carried by the optical fiber enables fiber sensors capable of performing much more sophisticated and multifunctional types of measurements that previously were only achievable using electronic sensors,” Chen said. In addition, the researchers discovered how to achieve active measurements in the optical fibers, as they are able to deliver both signal and optical power. This has demonstrated improvement in “the sensitivity, functionality and agility of fiber sensors without compromising the intrinsic advantages of fiber optic sensors,” Chen said. The new technology could be used in industrial sensing applications in harsh environments, ranging from deep geothermal drill cores and the interiors of nuclear reactors, to the vacuum of space. The researchers said it could also extend into other similar applications, such as highly sensitive chemical sensors for cryogenic environments. “In-fiber optical power can also be converted into ultrasonic energy, microwave or other interesting applications because tens or hundreds of smart sensors can be multiplexed within a single fiber,” Chen said. “It just requires placing one fiber in the gas flow stream — even in locations with strong magnetic interference.” The research was published in Optics Letters (doi: 10.1364/OL.39.003966). For more information, visit www.pitt.edu.