Proceedings Article | 16 November 2004
Proc. SPIE. 5579, Photonics North 2004: Photonic Applications in Telecommunications, Sensors, Software, and Lasers
KEYWORDS: Continuous wave operation, Sensors, Signal attenuation, Structured optical fibers, Single mode fibers, Fiber optics sensors, Structural health monitoring, Aluminum, Spatial resolution, Acoustics
Optical fiber sensor technology has progressed at a rapid pace over the last decade. Many different sensing techniques have been developed to monitor specific parameters. In particular, distributed Brillouin scattering-based sensor systems provide an excellent opportunity for structural health monitoring of civil structures by allowing measurements to be taken along the entire length of the fiber, rather than at discrete points, by using fiber itself as the sensing medium. One class of Brillouin-based sensors is based on the Brillouin loss technique, whereby two counter-propagating laser beams, a pulse and a CW, exchange energy through an induced acoustic field.
This type of sensing has tremendous potential for structural health monitoring since the spatial resolution can be adjusted for different applications simply by altering the pulse duration, even after the fiber is installed. Although the spatial resolution can be improved using short pulse, the loss spectrum broadens as the pulse width decreases below the phonon lifetime t. Hence, it was generally believe that sub-meter resolutions were unachievable due to rapid linewidth increases when pulse width W < t = 10 ns provided a 1 m spatial resolution limitation.
In this paper, we will report the development of distributed optical fiber sensor with centimeter spatial resolution. The sensing principle will be presented. We will also report the test results of pipeline buckling and corrosion fatigue monitoring and small damages/cracks of 1.5 cm in an optical ground wire (OPGW) cable with centimeter spatial resolution.
