Addressing fiber Bragg grating sensors using all-fiber low coherence interferometry

In this paper we propose an interrogating system for the quasi-distributed measurement of strain or temperature. The system basically consists of an all-fiber low coherent interferometer that includes the cascaded fiber Bragg gratings used in its test arm. The variable optical delay line with movable mirror traditionally used as the reference arm is here replaced by a set of fibers with different optical lengths all connected to an optical switch. This switch makes it possible to set the desired length for the reference arm. Second proposed solution is to replace variable delay line by fiber with multiple reflection points placed at positions close to those used at reference arm. Temperature and strain resolutions are 0.8 °C and 10 μm/m, respectively. The advantages of the system are the possibility to interrogate identical FBGs and to interrogate sensors placed far apart. The system does not use tunable laser source or movable elements.