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Single Crystal Optical Fiber
NETL Pursues Innovative Distributed Sensing System for Harsh Energy Environments

Turbines, nuclear power plants and chemical reactors operate at increasingly higher temperatures to boost efficiency and reduce expenses. However, these extreme temperatures also create harsh environments that contribute to corrosion, oxidation and other materials challenges in monitoring advanced energy systems.

NETL’s novel laser-heated pedestal growth system enables researchers to fabricate custom single-crystal optical fibers from bulk materials, such as sapphire or yttrium aluminum garnet (YAG), that can withstand ultra-high temperatures. Now, researchers are building upon that work to incorporate these specially made fibers into fully distributed sensing systems that effectively monitor temperatures, strains or other important parameters up to 1,500 degrees Celsius, or more than 2,700 degrees Fahrenheit.

Target industrial applications for the refined sensing technology include power generation, transportation and chemical production. NETL’s work to develop improved sensors and controls ultimately offers the potential to cut costs for industry and consumers alike by increasing efficiency, limiting outages and reducing CO2 emissions to meet America’s growing needs.

Optical fibers are flexible, transparent light guides slightly thicker than a human hair that are usually made of glass or plastic. They offer unique advantages in monitoring harsh energy environments, including resistance to electromagnetic interference, corrosion resistance, compact size and the ability to measure multiple parameters at once. Single-crystal optical fibers provide added benefits including greater mechanical strength, a higher laser damage threshold, power-delivering capabilities and better corrosion resistance.

NETL’s new distributed temperature sensing system transmits light from a high-powered laser through a single-crystal optical fiber, which directs backscattered light through a series of mirrors, filters and other spectroscopy equipment to provide temperature information for the entire length of fiber. The data is derived based on the analysis of Raman scattering, which reflects changes in the vibrational or rotational states of the matter being observed and can be used to determine temperature. 

NETL researchers recently demonstrated the system’s operational capabilities using a single-crystal optical fiber made of sapphire to accurately measure temperatures from 30 to 1,500 degrees Celsius. Multiple tests with sapphire fiber provided insight into how the rudimentary system might be improved to develop a more robust high-temperature distributed sensing system ready for industrial use. For instance, researchers recommend adding a complementary substance to the sapphire or replacing it with similar materials that offer opportunities to amplify the optical signal, producing enhanced Raman scattering data for analysis. They are also actively investigating possibilities for high-temperature cladding, or an exterior layer, that would better protect the optical fiber and improve long-term performance.

“We’re really encouraged by the experiment results, which demonstrate an innovative new way to monitor extreme temperatures in harsh energy-system environments,” said Michael Buric, Ph.D., who oversaw the experiment as part of NETL’s Functional Materials Team. “Our goal is to produce a commercially viable, state-of-the-art system capable of addressing critical high-temperature measurement needs to aid in the control of industrial processes.”

To learn more about NETL’s sensors and controls work, click here.