# Sensitivity enhancement of distributed Brillouin fiber optic sensing using two-frequency pump and probe

08 Nov 2020-Vol. 11525, pp 1152505

TL;DR: In this paper, a two-frequency pump and probe light was used to enlarge the Brillouin gain spectrum to 2 MHz/℃ or 0.1 MHz/μe.

Abstract: Brillouin fiber optic sensing has been attracting much attention as one of the best ways of monitoring the temperature and/or strain distribution of large structures, such as bridges or pipelines. To detect abnormal sections of such structures at an earlier stage, improvement of measurement sensitivity is required. In the standard Brillouin fiber optic sensing, sensitivity given by the temperature or strain coefficient of Brillouin frequency shift (BFS) is about 1 MHz/℃ or 0.05 MHz/μe, respectively. In this study, we introduce a new method utilizing two-frequency pump and probe light to enlarge these coefficients without using special fibers. In this method, Brillouin gain spectrum is measured by sweeping the two frequencies of probe light in the opposite directions, where the measured spectrum has two peaks. The separation between the two peaks linearly changes with BFS, and so it has a linear relation to temperature and strain of an optical fiber. Since the changing rate of the separation between the two peaks is twice as large as that of BFS, the temperature or strain sensitivity is doubled to 2 MHz/℃ or 0.1 MHz/μe. The enhanced sensitivity was experimentally confirmed in the proof-of-concept experiment.

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09 May 2021TL;DR: In this article, a slope assisted Brillouin optical time domain analysis using dual frequency probe light amplified by the gain and attenuated by the loss of BrillouIN loss is presented.

Abstract: We demonstrate a slope assisted Brillouin optical time domain analysis using dual frequency probe light amplified by Brillouin gain and attenuated by Brillouin loss, which generates linear output against temperature change.

1 citations

##### References

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TL;DR: In this article, a distributed strain and temperature sensing technique that uses Brillouin scattering in single-mode optical fibers is presented, which is based on strain- and temperature-induced changes in the frequency shift.

Abstract: This paper reviews the developments of a distributed strain and temperature sensing technique that uses Brillouin scattering in single-mode optical fibers. This technique is based on strain- and temperature-induced changes in the Brillouin frequency shift. Several approaches for measuring the weak Brillouin line are compared. >

685 citations

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TL;DR: A novel method, based on stimulated Brillouin scattering (SBS), is presented, for the simultaneous distributed measurement of fast strain variations along the entire length of the sensing fiber.

Abstract: We present a novel method, based on stimulated Brillouin scattering (SBS), for the simultaneous distributed measurement of fast strain variations along the entire length of the sensing fiber. A specially synthesized and adaptable probe wave is used to place the Brillouin interaction always on the slope of the local Brillouin gain spectrum, allowing a single pump pulse to sample fast strain variations along the full length of a fiber with an arbitrary distribution of the Brillouin frequency shift. In this early demonstration of the method, strain vibrations of a few hundred Hz are demonstrated, simultaneously measured on two different sections of an 85m long fiber, having different static Brillouin shifts and with a spatial resolution of 1.5m.

173 citations

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TL;DR: In this paper, a new configuration of Brillouin optical correlation-domain reflectometry was developed, which can measure strain, temperature, and optical loss distributions simultaneously with a high sampling rate.

Abstract: Exploiting the slope of the Brillouin gain spectrum, we develop a new configuration of Brillouin optical correlation-domain reflectometry, which can measure strain (or temperature) and optical loss distributions simultaneously with a high sampling rate. The strain, temperature, and loss dependence coefficients of the output signal are measured to be $1.95\times 10^{-4}\ \text{dB}/\mu\varepsilon$ , $4.42\times 10^{-3}\ \text{dB/K}$ , and 0.191, respectively, which are consistent with the theoretical predictions. We also verify the basic operation of simultaneous measurement of the three parameters.

47 citations

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TL;DR: In this paper, a multipoint fiber Bragg grating (FBG) sensing system was proposed to measure both spectral change of FBGs and precise distance to them by using intensity-modulated light and two-photon absorption process in a silicon avalanche photodiode.

Abstract: We propose a multipoint fiber Bragg grating (FBG) sensing system that measures both spectral change of FBGs and precise distance to them by using intensity-modulated light and two-photon absorption process in a silicon avalanche photodiode. We experimentally confirm the principle using five cascaded FBGs with almost the same Bragg wavelength. The optical path length difference and the reflection spectrum for each FBG are successfully measured at the same time. The relative uncertainty of path length measurement is in the order of 10−4.

22 citations

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TL;DR: In this article, a simple and precise measurement method for high-frequency dynamic displacement is proposed, which uses a fiber optic interferometer with a LiNbO3 phase modulator in the reference path.

Abstract: We propose a simple and precise measurement method for high-frequency dynamic displacement It uses a fiber optic interferometer with a LiNbO3 phase modulator in the reference path The phase of the reference light is modulated with high-frequency triangle wave By monitoring the interference signal waveform, the change in the phase difference of the fiber interferometer and the displacement are measured without either complex calculation or complicated feedback system The proof-of-concept experiments show that displacement waveforms with relatively large amplitudes of several tens of nanometers are measured without distortion even when the vibration frequency is 1 MHz

21 citations

### Additional excerpts

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