Tunable optical source for the interrogation of Bragg gratings via spectral scanning

This paper describes the implementation of an interrogation system with a tunable Erbium doped fiber ring-laser (EDFL). The EDFL is used to illuminate optical devices like Bragg gratings, so that it can also be used as an interrogation system to determine the spectral characteristics of the devices. An intra-cavity Fabry-Perot filter, driven by a dedicated voltage ramp generator, tunes the EDF laser. The resulting optical signal is captured by a photodetector and analyzed in a personal computer. The apparatus can be used as an optical spectrum analyzer for passive components and as an interrogation system for multiplexed fiber Bragg grating based sensors. As an application example, the temperature inside a concrete beam submitted to systematic heating and vibrations has been remotely measured with the system.