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5 February 1990 Optical Time Domain Reflectometry For Local Strain Measurements
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In recent years Optical Time Domain Reflectometry (OTDR) and, more generally, optical time delay methods, have been applied to measure optical fiber strain and elongation. These techniques have been recognized as having significant potential in the area of non-destructive testing and analysis of structures. However, limitations such as the lack of local strain monitoring capabilities and poor spatial resolution have kept OTDR based fiber optic sensors from becoming more popular in the Non-Destructive Evaluation (NDE) industry. Significant advances and improvements regarding these two main limitations have been achieved. Extremely fast OTDR systems which are capable of launching optical pulses with Full Width Half Maxima (FWHM) on the order of 100 ps and temporal stabilities of less than 2 ps have recently made spatial resolutions in the sub-millimeter range possible. Furthermore, techniques have been developed which allow quasi-distributed local strain sensing using a single optical fiber. Such systems rely on the physical segmentation of the fiber through the use of partially reflective air-gap splices which provide marker reflections. The positions in time of these reflections are individually monitored to obtain local strain measurements. In this report we present an analysis of such systems, and discuss experimental results obtained using a picosecond resolution OTDR. It is shown that it is possible to measure strain locally with a resolution on the order of 0.0001 m/m with a gage length as small as a few centimeters. A discussion on how to further improve upon the performance by taking advantage of reentrant fiber loop technology is also given.
© (1990) COPYRIGHT Society of Photo-Optical Instrumentation Engineers (SPIE). Downloading of the abstract is permitted for personal use only.
B. Zimmermann, R. Claus, D. Kapp, and K. Murphy "Optical Time Domain Reflectometry For Local Strain Measurements", Proc. SPIE 1170, Fiber Optic Smart Structures and Skins II, (5 February 1990);

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