The key component of any monitoring system is the sensor technology, which needs to provide reliable and accurate measurement results, ensuring the in-situ self-calibration, durability, and high spatial resolution. The Stimulated Brillouin Scattering (SBS) measuring technique addresses all of these issues, however, requires further progress in the area of the spatial resolution, as well as measurements accuracy. The currently available (on the market) optical fiber strain measurement devices allow one to achieve the spatial resolution of 1 m, only, and the strain measurement accuracy of ± 0.01%, thus unable to meet requirements of both resolution and accuracy in majority of real-life applications.

Neubrex Co., Ltd. developed in 2004 an innovative method, the Pulse-Pre-Pump Optical Time Domain Analysis (PPP-BOTDA*1), which ensures simultaneously 10 cm spatial resolution and ± 0.0025% strain measurement accuracy (see Figure 1). The traditional BOTDA technique for measuring strains along the fiber, detects changes in stimulated Brillouin scattering (SBS) light frequency distribution if the pulse pump and probe set at both ends of the optical fiber. In general, decreasing the pump pulse width should result in higher spatial resolution. Unfortunately, as it takes approximately up to 28 ns to stimulate the phonon waves in the fiber, the consequence of small pulse width of the pump is a decrease and distortion in SBS gain.

In the new PPP-BOTDA technique, the pulse shape in the pump laser is modified to step function. Moreover, an additional pre-pump pulse is used to stimulate phonon waves prior to the arrival of the measuring pump pulse. As a result, the 10 cm spatial resolution with ± 0.0025% strain measurement accuracy can be achieved (see Figure 2). The NEUBRESCOPE NBX-6000 offers 10 cm resolution over the distance of more than 1 km. The developed technique is thus expected to meet all requirements of wide range of engineering applications, including energy industry (pipelines, pressure vessels, technological systems), transport (railroads, ships, airplanes) and civil infrastructure (bridges, tunnels, dams).

For detailed specifications of NEUBRESCOPE NBX-6000 series, click here.

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*1 PPP-BOTDA: Pulse-PrePump Brillouin Optical Time Domain Analysis

When insert stepwise Pulse light and Probe light from each end of the optical fiber, Brillouin backscattering will be stimulated from the Probe light. PPP-BOTDA is to measure and analyze the frequency distribution of backscattering for calculating the longitudinal strain and/or temperature with high resolution and high accuracy.