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Work Package

Objetives

Dispersive Bragg Spectrometry is emerging as a powerful monitoring approach to overcome these limitations. The underlying principle is to use a high repetition rate (40 MHz to 100 MHz) ps/fs, pulsed laser associated with a highly dispersive optical media providing a Bragg-to-time delay conversion and High Bandwidth Oscilloscope (HBO, 30-40 GHz). Data are sampled at the repetition rate of the laser (i.e. every 10 ns at 100 MHz, or an equivalent space resolution of 50 μm for a 5,000 m/s wave velocity). The objective is to design and qualify in both the laboratory and the field the metrological performances of a DBS for high speed/high capacity tomography. Several challenges are identified with the OTS technique such as generation of giant dispersion with the aim to improve resolution in Bragg wavelength (compatible with acoustic detection), management of TDM trade-off between delay time (distance between sensors and span range) and time range (Bragg-to-time conversion), etc. OTS will be preliminary applied to the monitoring of spaced-apart FBGs. Another field of investigation might be to use OTS with Chirped FBGs (CFBGs) to generate a time-domain interferogram resulting from the interference between light reflected back by a sensing CFBG and a reference one and to apply Fourier-Transform based inverse calculation to retrieve the strain distribution.

Planned intersectoral, interdisciplinary and international secondments

• BAM, Franziska Baensch, 2 months, M13-M14: The DBS set-up investigated by CEA tested on a prototype concrete structure.
• Faber, Alberto Agnoletti, 2 months, M20-M21: DBS prototype implementation on a H2-reservoir.
• ENI, Guiseppe Giunta, 2 months, M26-M27: DBS prototype tested on a metal pipeline bench-top used for gas transport.