Low-cost fiber Bragg grating-based static and dynamic strain system for structural monitoring

A fiber Bragg grating sensor for simultaneous static and dynamic strain detection is hereby presented. The principle of operation of the interrogator is based on direct intensity detection: a fixed-wavelength laser source is filtered through the sensing element, and the output power is detected with a photodiode. Multiple sensing for matched-wavelength gratings is performed by splitting the source into multiple channels. The exploitation of cheap components for optical telecommunications results in a low-cost hardware solution that matches several budget-constrained applications. The optical sensor is complemented by signal processing techniques (adaptive filters, spectral estimation, data modeling), capable of improving performances of the system without changing the optical layout. The system has been tested both in static interrogation, as a temperature sensor, and as vibration detector in a typical structural monitoring context. The maximum interrogation range is ~200με, depending on the grating shape, with a resolution <<1 με, and a repeatability of ~1%. A 1% stability over long time has been assessed with a long-term test. The adaptive filtering improves the signal-to-noise ratio of 5.3 dB. The resolution-unlimited spectral estimator resolves resonance peak detection for a vibration of 0.1με.