In-line fiber etalon (ILFE) for internal strain measurement

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Abstract
This paper describes an optical fiber interferometer that uses a short segment of silica hollow- core fiber spliced between two sections of single-mode fiber to form a mechanically robust in- line optical cavity. The hollow-core fiber is specifically manufactured to have an outer diameter that is equal to the outer diameter of the single mode lead fibers, thereby combining the best qualities of existing intrinsic and extrinsic Fabry-Perot sensors. Uniaxial tension and pure bending strength tests are used to show that the new configuration does not diminish the axial strength of bare fiber and reduces the bending strength by 17% at most. Similar tests confirm that the fiber sensor has 1.96% strain to failure. Axisymmetric finite element analysis is used to investigate the reliability of the in-line etalon during typical thermoset composite cure conditions, and parametric studies are performed to determine the mechanically optimal cavity length. The sensor strain response tests demonstrate a dynamic strain resolution of 21 n(epsilon) /(root)Hz at frequencies > 5 Hz with a sensor gauge length of 137 micrometers .© (1994) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.

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