ABSTRACT
Propagation of signals through optical fibers is said to be immune from external perturbations, and this is true, at first approximation. However, at a closer scrutiny, fibers reveal small sensitivity to a variety of physical quantities, like stress, pressure, temperature, magnetic/electric fields, and chemicals, just to cite a few. Reading the effects of such measurands on an optical quantity of the field propagated in the fiber, for example intensity, polarization state, and optical phase-shift, we can then build an optical fiber sensor. The chapter starts with a classification of the effects and of the readouts to sense the optical quantity, and exemplifies cases for the three methods, describing in particular low and high range temperature measurement, magnetic field and current sensors, geothermal temperature probe, and hydrophones. The chapter ends with an appraisal of multiplexed and distributed fiber sensors, and a short account to Raman and Brillouin optical time domain reflectometry.
