A comprehensive research study, leading to the development of a novel sapphire-fiberoptic sensor, for high temperature testing of composite turbine engines in "real" environments, is proposed. The sensor will operate on the principle of modal power distribution (MPD) modulation in multimode sapphire fibers caused by thermal and mechanical stresses in the smart materials. The strategy for the proposed research is to use the mpd in a special coated sapphire multimode optical fiber as a sensitive tool, in high temperature environment, for measurements of smart structural response of various modes of perturbation. This technique will be applied for sensing these perturbations by comparative measurements of modal power distribution and subsequent redistribution at the output end of the fiber. A preliminary investigation was carried out successfully in the last year, through the SBIR Phase I of the Army contract # DAAl04-91-C-0011, using a silica fiber embedded in low temperature composite. The results indicate that this developed technique is highly sensitive and well suited for smart structure applications. To optimize the sensor configuration for high temperature composites, an extensive study of coated sapphire fiber will be investigated, using special coated multimode sapphire fibers. The Phase I work will include the design and fabrication of protectively-coated sapphire optical waveguide that can withstand high temperature without cracking or chemical degradation. The optical fiber will be embedded the material and tested to prove the concept of using the mpd technique with embedded sapphire fiber.
