Optical Time Domain Analysis Fiber Research Articles

Generalized linear model for enhancing the temperature measurement performance in Brillouin optical time domain analysis fiber sensor

This study describes the deployment of machine learning algorithm called generalized linear model (GLM) to improve the temperature prediction performance in Brillouin optical time domain analysis (BOTDA) fiber sensor for distributed temperature sensing application. In GLM, the temperature prediction is made from the Brillouin gain spectrum (BGS) and the link function, without the need to determine the Brillouin frequency shift (BFS). In this proof-of-concept experiment, the performance of GLM was investigated by collecting the BGS and comparing it to the conventional Lorentzian curve fitting (LCF) method. From the experimental results, we have found that the GLM method produced a more consistent temperature prediction than the conventional LCF method. Furthermore, the proposed GLM method could still retain an accurate temperature measurement regardless of low signal-to-noise ratio (SNR) and large frequency scanning step while collecting BGS, which is difficult to be achieved by the conventional LCF method at certain level. In addition to that, the prediction obtained is 655 times faster than the conventional LCF method. The small and negligible deterioration to the temperature resolution confirmed the robustness of GLM in performing fast and accurate temperature measurement for BOTDA.

Temperature and Strain Discrimination in BOTDA Fiber Sensor by Utilizing Dispersion Compensating Fiber

Standard single mode fiber that normally used in Brillouin optical time domain analysis fiber sensors typically has only one Brilllouin gain peak (BGP), and its central frequency [i.e., Brillouin frequency shift (BFS)] can be affected by both temperature and strain, which gives rise to temperature and strain cross sensitivity. In this paper, we propose a new method to realize temperature and strain discrimination, for the first time to the best of our knowledge, by using commercial single mode dispersion compensating fiber (DCF) that has two BGPs located around 9.536 and 10.052 GHz, respectively. The two peaks have different temperature coefficients but nearly the same strain coefficients, which permits simultaneous temperature and strain sensing by combing the BFSs obtained from the two BGPs. The biggest advantage of the DCF is that the frequency space between its two BGPs is >100 MHz wider than some other fibers, ensuring much wider temperature and strain sensing range. In a proof of concept experiment, temperature and strain are fully discriminated with a temperature resolution of ~2.6 °C and a strain resolution of $\sim 64.6~\mu \varepsilon $ at the end of a 1-km sensing fiber with 2-m spatial resolution.

Damage evaluation of concrete based on Brillouin corrosion expansion sensor

To evaluate the damage degree of reinforced concrete due to steel bar corrosion, a damage factor is proposed to quantitatively evaluate the damage degree of concrete before initial cracking and during the development of cracks. Brillouin optical fiber time domain analysis (BOTDA) sensors are fabricated to monitor the expansion strain of steel corrosion. Two concrete specimens embedded with corrosion sensors are cast. An accelerated corrosion experimental program is used to accelerate the process of steel corrosion. The experimental results show that the corrosion sensor can be used to monitor the expansion strain of steel corrosion in real-time. At last, to map the monitoring results with the damage factor, finite element analysis is used to simulate the process of steel corrosion to determine the cracking strain of the interfacial concrete and concrete cover.

Reconstruction technique for stimulated Brillouin scattering distributed fiber-optic sensors

A novel numerical technique for temperature/strain profiles reconstruction based on Brillouin optical-fiber time-domain analysis (BOTDA) sensors is proposed. In this approach, we search directly for the temperature/strain profile along the fiber that matches the measured data. The algorithm is based on a harmonic expansion of the unknown profile, whose coefficients are determined by a multidimensional minimization. Several numerical simulations, even in presence of noise, prove the capability of the proposed algorithm to compensate for some systematic errors suffered by classical approaches based on the direct reading of Brillouin power spectra.

Measurement of distributed strain due to laying and recovery of submarine optical fiber cable

Strain distribution due to cable laying and recovery is measured, using Brillouin optical fiber time domain analysis in a 3.7-km long submarine optical fiber cable. We believe this is the first time that the residual strain distribution in the recovered submarine cable has been measured. The residual strains measured in some cable sections due to the cable laying and recovery are found to be as small as 0.02 and 0.04%, respectively.

A technique to measure distributed strain in optical fibers

The technique is based on Brillouin optical-fiber time-domain analysis (BOTDA), which uses Brillouin interaction between counterpropagating pump and probe light waves. Experimental results for fibers wound on drums at various tensions are presented. A strain measurement accuracy of better than 2*10/sup -5/ and a spatial resolution of 100 m are achieved.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

Distributed-temperature sensing using stimulated Brillouin scattering in optical silica fibers

Temperature distribution in silica single-mode optical fibers, from -30 to +60 degrees C, is successfully measured by using Brillouin optical-fiber time-domain analysis. A temperature measurement accuracy of 3 degrees C with a spatial resolution of 100 m is attained over a fiber length of 1.2 km.

First measurement of strain distribution along field-installed optical fibers using Brillouin spectroscopy

Strain distributions along optical fibers in a 1.3-km-long cable before and after installation are measured using Brillouin optical-fiber time domain analysis. The residual strains in the installed optical fibers were found to vary from zero to 0.07%, depending on the conduit configuration and installation procedure. Strain distribution measurements were carried out on a 24-fiber slotted-core type single-mode optical fiber cable for 1.55- mu m-wavelength transmission, whose length, outer diameter, and weight were 1.3 km, 14 mm, and 0.18 kg/m, respectively. No clear relation between strain distributions and the fiber configuration in the test cable are found.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

BOTDA-nondestructive measurement of single-mode optical fiber attenuation characteristics using Brillouin interaction: theory

A theoretical investigation of Brillouin optical-fiber time-domain analysis (BOTDA) is described. BOTDA uses Brillouin interaction in optical fibers to analyze the attenuation characteristics of the optical fibers nondestructively. The dynamic range performance of BOTDA is approximately 10-dB greater than that of conventional optical time-domain reflectometry. >