High-Temperature Optical Sensor

John H. Glenn Research Center, Cleveland, Ohio

A high-temperature optical sensor (see Figure 1) has been developed that can operate at temperatures up to 1,000 °C. The sensor development process consists of two parts: packaging of a fiber Bragg grating into a housing that allows a more sturdy thermally stable device, and a technological process to which the device is subjected to in order to meet environmental requirements of several hundred °C.

Figure 1. A **Probe** packaged and connectorized with a fiber Bragg grating (FBG) inside. The FBG is located at the end of the probe inside a smaller-diameter ceramic tube.

This technology uses a newly discovered phenomenon of the formation of thermally stable secondary Bragg gratings in communication-grade fibers at high temperatures to construct robust, optical, high-temperature sensors. Testing and performance evaluation (see Figure 2) of packaged sensors demonstrated operability of the devices at 1,000 °C for several hundred hours, and during numerous thermal cycling from 400 to 800 °C with different heating rates.

Figure 2. **Performance Characteristics**: (a) Wavelength stability of a sensor exposed to 1,000 °C for 500 hours and (b) wavelength readings as a function of temperature during thermal cycling from 400 to 800 °C.

The technology significantly extends applicability of optical sensors to high-temperature environments including ground testing of engines, flight propulsion control, thermal protection monitoring of launch vehicles, etc. It may also find applications in such non-aerospace arenas as monitoring of nuclear reactors, furnaces, chemical processes, and other high-temperature environments where other measurement techniques are either unreliable, dangerous, undesirable, or unavailable.

This work was done by Grigory Adamovsky, Jeffrey R. Juergens, and Donald J. Varga of Glenn Research Center and Bertram M. Floyd of Sierra Lobo, Inc. For more information, download the Technical Support Package (free white paper) at www.techbriefs.com/tsp under the Physical Sciences category.

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