Kinzo Kishida

Pulse pre-pump method for cm-order spatial resolution of BOTDA

The distributed Brillouin scattering technique, using pulse width of 1ns, that is, one order of magnitude smaller than currently available in commercial applications of BOTDA, was successfully implemented and examined in laboratory environment by Bao et al. However, the two main problems prohibits its commercial use, namely, the measurement setting must be modified each time the measurements object is changed, and, furthermore, long-range measurements cannot be effectively carried out due to substantial increase in signal noise level with the measurement distance. This paper presents a new technique, which overcomes both of these problems, by introducing the pre-pump pulse in front of standard laser pulse. Theoretical analysis clearly demonstrates that the cm-order distributed sensing, independent of the fiber length, can be realized. Moreover, a quantitative analysis of strain measurement accuracy is also presented.

Hybrid Brillouin-Rayleigh distributed sensing system

The paper deals with the design and principles of the hybrid Brillouin-Rayleigh sensing system. The system is capable of separating strain and temperature values in single SM fiber and offers spatial resolution as high as 2 cm. Furthermore, the paper introduces a method to determine required separation coefficients for optical fiber cables. Finally, it presents several validation examples and results of industrial applications.

Synthetic Spectrum Approach for Brillouin Optical Time-Domain Reflectometry

We propose a novel method to improve the spatial resolution of Brillouin optical time-domain reflectometry (BOTDR), referred to as synthetic BOTDR (S-BOTDR), and experimentally verify the resolution improvements. Due to the uncertainty relation between position and frequency, the spatial resolution of a conventional BOTDR system has been limited to about one meter. In S-BOTDR, a synthetic spectrum is obtained by combining four Brillouin spectrums measured with different composite pump lights and different composite low-pass filters. We mathematically show that the resolution limit, in principle, for conventional BOTDR can be surpassed by S-BOTDR and experimentally prove that S-BOTDR attained a 10-cm spatial resolution. To the best of our knowledge, this has never been achieved or reported.

Validation of TW-COTDR method for 25km distributed optical fiber sensing

The paper reports results of the long distance (25 km range) distributed optical fiber sensing by means of Tunable Wavelength Coherent Optical Time Domain Reflectometry (TW-COTDR) method. The tests were designed to verify the accuracy and repeatability of the method in long distance measurements, as well as compatibility with various optical fiber types. Results demonstrate the capability of the method to detect strain or temperature changes over long distances. This proposed method is compared to Brillouin sensing techniques, into the same fibers. Unlike the Brillouin-based methods, measurement uncertainty does not increase with increasing distance. We demonstrated 0.16°C uncertainty at 21km.

Monitoring of the ground settlement during a tunnel excavation using 4D optical fiber sensing system

In this paper we present an engineering application of optical fiber distributed sensing for monitoring of the ground settlement during a tunnel excavation. The design, installation methods, and implementation of 4D (space plus time) warning system are outlined. The ground settlement was closely monitored for entire 6 months of tunnel construction process, revealing a wide range of geomechanical phenomena. Obtained on-line vertical displacements allowed engineers to control the excavation speed and monitor ground settlement, contributing substantially to the overall reliability and safety.

Optical fiber sensor cable for pipe thinning detection in high temperature environment conditions

The paper presents a newly developed, heat-resistant optical fiber sensor cable, exhibiting excellent sensitivity to local strain variations. The strain measurements acquired by means of the cable was used in 3D structural analysis, allowing us to detect pipeline wall thinning with high accuracy.