Invention of silica based optical fiber not only led to revolution in communication but also provided fundamental basis for many research areas. One example area is distributed optical fiber sensing, which has been attracting research interests for decades. Optical fiber sensors are immune to electromagnetic interference, and resistant to corrosion and can endure harsh environment so they have found applications such as structural health monitoring, intrusion detection and oil downhole measurement.
Significant research efforts have been paid to fiber sensing area, many techniques have been developed and some of them have been successfully demonstrated, however achieving both high-speed and long-range is still under intensive research.
This dissertation proposes and demonstrates a technique with the capability of simultaneous long-range and high-speed sensing by employing serial ultra-weak fiber Bragg gratings (UW-FBGs) and dispersive components. Various factors which have influence on the system performance, including wavelength resolution, spatial resolution and sensing rate, are analyzed. Different types of light sources and dispersive units were designed and a sensing system was built. With this system, both static and dynamic response were measured, and a sensing link consisting of more than 2000 UW-FBGs was successfully measured at the speed of 20kHz. The noise sources of the system were also theoretically analyzed and experimentally measured. This demonstrated sensing technique can be applied to long range temperature and strain sensing. / Ph. D. / Optical fiber is a thin glass rod with normally two layers of slightly different silica. Because of its low loss, optical fiber can guide light for a long distance without causing significant signal fading. Modifications can be made to a small section of an optical fiber to form a fiber Bragg grating, whose optical characteristics are dependent on its temperature or the strain applied to it.
This dissertation proposes a technique with the ability of measuring the temperature or strain of a long length of optical fiber which has large quantity of fiber Bragg gratings fabricated in it. Along with the capability of long range sensing, this technique also has high sensing speed. It has been demonstrated that the sensing system could perform measurement in every 50µs when the optical fiber has about 2000 fiber Bragg gratings in it. The resolution, if converted to temperature, is about 1.5°C and the accuracy is 2°C.
With the ability of monitoring temperature or strain of a large span at high speed, this technique could be used in areas such as civil structure and air craft health monitoring, instruction detection and high speed temperature monitoring.
| Identifer | oai:union.ndltd.org:VTETD/oai:vtechworks.lib.vt.edu:10919/74429 |
| Date | 25 January 2017 |
| Creators | Ma, Lingmei |
| Contributors | Electrical and Computer Engineering, Wang, Anbo, Beex, Aloysius A., Zhu, Yizheng, Pickrell, Gary R., Xu, Yong |
| Publisher | Virginia Tech |
| Source Sets | Virginia Tech Theses and Dissertation |
| Detected Language | English |
| Type | Dissertation |
| Format | ETD, application/pdf |
| Rights | In Copyright, http://rightsstatements.org/vocab/InC/1.0/ |
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