ABSTRACT
Fiber-optic sensing of deformation and temperature has characteristics that make it a promising, emerging technology for applications in underground rock engineering. In general, there are two main types of fiber-optic sensors, discrete and distributed. Discrete sensors respond to strain and temperature, by changes in spacing of a diffraction grating in the fiber or in a cavity between two ends of fiber that are micrometer-scale. In distributed sensing, the fiber optic cable itself is the strain and temperature sensor. Distributed sensors are based on Rayleigh, Raman, and Brillouin scattering of light from the fiber-optic cable itself. The backscattered light can be analyzed for strain and/or temperature with a spatial resolution of one meter. In this chapter, the physics underlying Fiber Bragg Gratings (FBG), SOFO, Distributed Temperature Sensing (DTS), Distributed Strain and Temperature (DST), and Distributed Acoustic Sensing (DAS) are described. Several prototype case studies of fiber-optic monitoring in underground mines, recent developments in fiber-optic extensometers, and fiber-optic sensing in boreholes in the oil and gas industry are reviewed.
