Brillouin Optical Correlation Domain Analysis Research Articles

A Time-Differential BOCDA Sensor Measurement System Applied to a 1 km Long SMF Using a Semiconductor Optical Amplifier as a Pump Chopper.

A time-differential (TD) Brillouin optical correlation domain analysis (BOCDA) sensor system was applied to measure the Brillouin gain spectrum of a 1 km long sensing optical fiber. The optical delay line used in all BOCDA measurement systems was eliminated in the TD-BOCDA system by using a bit-delayed modulation relationship between the probe and pump lightwaves. These lightwaves were phase modulated using 216-1 pseudo-random binary sequence codes at 5 Gbps. A 2 cm dispersion-shifted fiber placed at the end of the 1 km optical fiber was distinctly identified by the Brillouin frequency extracted from the Brillouin gain spectrum measurement. To investigate the measurement stability of the TD-BOCDA system, experiments were conducted under two different pumping conditions. A semiconductor optical amplifier (SOA) and an intensity modulator (MOD) were compared for the pump chopper used in the TD-BOCDA system to detect the extinction ratio of the pump and the resulting noise in the Brillouin gain measurement. The stability of the Brillouin frequency measurement from the Brillouin gain spectrum in the TD-BOCDA system was investigated by increasing the average value of the measurement using either the SOA or MOD. The repeated-measurement deviation of the system with the SOA was only half of the deviation observed in the system with the MOD. The performance of TD-BOCDA is equivalent to or better than that of conventional BOCDAs in terms of measurement reliability. Moreover, TD-BOCDA is free from the drawbacks of traditional BOCDA, which uses time-delayed fibers and varies the bit rates.

High-Spatial-Resolution Dynamic Strain Measurement Based on Brillouin Optical Correlation-Domain Sensors

Brillouin-scattering-based sensors have been widely applied in distributed temperature or strain measurement in recent 20 years. Brillouin optical correlation-domain technology has extensive development and application prospects because of its millimeter-level spatial resolution, distribution measurement, and high accuracy. Traditional Brillouin-scattering-based sensors, requiring a time-consuming frequency-sweep process, struggle to achieve dynamic strain measurement. In this article, Brillouin optical correlation-domain analysis and reflectometry based on fast-sweep frequency and slope-assisted methods will be reviewed. The main merits, drawbacks, and performances of these schemes are compared, and the avenues for future research and development of these two technologies are also explored.

Recent Advances of Brillouin Optical Correlation-Domain Analysis for Enhanced Sensing Accuracy

Optical fiber sensors based on Brillouin scattering were first introduced over three decades ago, and various types of distributed sensing schemes have been developed. The Brillouin optical correlation domain analysis (BOCDA), first proposed in 2000, is a quasi-distributed Brillouin sensor which supports arbitrary access to a sensing position by the frequency modulation of a continuous-wave light source. Compared to time-domain distributed sensors, the BOCDA is more suitable for the measurement requiring a high spatial resolution or high sampling rate in a relatively short sensing distance. In this paper, we present technical reviews on recent technologies that can be applied to improve the sensing accuracy of a BOCDA system, such as differential measurement, injection-locking, and orthogonally polarized probe sidebands.

Long-range high-spatial-resolution distributed Brillouin sensing enabled by correlation-domain encoding.

A hybrid aperiodic-coded Brillouin optical correlation domain analysis (HA-coded BOCDA) fiber sensor is proposed to achieve long-range high-spatial-resolution distributed measurement. It is found that high-speed phase modulation in the BOCDA actually forms a special energy transformation mode. This mode can be exploited to suppress all detrimental effects parasitized in a pulse coding-induced cascaded stimulated Brillouin scattering (SBS) process and thereby enable the HA-coding to reach its full potential to improve the BOCDA performance. As a result, under a low system complexity and an enhanced measurement speed, a 72.65-km sensing range and a 5-cm spatial resolution are achieved with a temperature/strain measurement accuracy of 2℃/40 με.

Long-range chaotic Brillouin optical correlation domain analysis with more than one million resolving points

We propose and experimentally demonstrate a long-range chaotic Brillouin optical correlation domain analysis by employing an optimized time-gated scheme and differential denoising configuration, where the number of effective resolving points largely increases to more than one million. The deterioration of the chaotic Brillouin gain spectrum (BGS) and limitation of sensing range owing to the intrinsic noise structure, resulting from the time delay signature (TDS) and nonzero background of chaotic laser, is theoretically analyzed. The optimized time-gated scheme with a higher extinction ratio is used to eliminate the TDS-induced impact. The signal-to-background ratio of the measured BGS is enhanced by the differential denoising scheme to furthest remove the accumulated nonzero noise floor along the fiber, and the pure chaotic BGS is ulteriorly obtained by the Lorentz fit. Ultimately, distributed strain sensing along a 27.54-km fiber with a 2.69-cm spatial resolution is experimentally demonstrated, and the number of effective resolving points is more than 1,020,000.

Enlargement of Dynamic Strain Range in Chaotic Brillouin Optical Correlation Domain Analysis by Cross-Arranged Multislope Assistance

We propose and experimentally demonstrate a cross-arranged multislope-assisted chaotic Brillouin optical correlation domain analysis (MSA-CBOCDA) to achieve a large-range dynamic strain measurement. Based on the broadband chaotic Brillouin gain spectrum (BGS), the cross-arranged MSA model is first constructed, whose high measurement accuracy and slope utilization rate (SUR) are further verified in simulation. The dynamic strain with a range of <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$4780~\mu \varepsilon $ </tex-math></inline-formula> is finally realized in the experiment, where the standard deviation is around <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$23.8~\mu \varepsilon $ </tex-math></inline-formula> . The range of dynamic strain is enlarged fourfold than the previous slope-assisted (SA) CBOCDA with a virtually identical accuracy.

Brillouin Optical Correlation Domain Analysis With Over 2.5 Million Resolution Points Based on Raman Amplification and Injection Locking

We propose and experimentally demonstrate a long-range Brillouin optical correlation domain analysis (BOCDA) system based on distributed Raman amplification and injection-locking to reach over 2.6 million resolving points. The optimization of key parameters in the Raman amplification, time domain data processing, differential measurement scheme, and injection-locking are applied to achieve a spatial resolution of 2 cm over a 50 km sensing fiber. Our result corresponds to at least twice improvement compared to former records, and the best one among distributed Brillouin sensors in terms of the number of resolving points.

Brillouin optical correlation domain analysis at MHz sampling rates using lock-in-free orthogonally polarized probe sidebands

Brillouin optical correlation domain analysis at MHz sampling rates using lock-in-free orthogonally polarized probe sidebands

Recent Progress in Long-Range Brillouin Optical Correlation Domain Analysis.

Distributed optical fiber sensing technology has been widely applied in the areas of infrastructure health monitoring, national defense security, etc. The long-range high-spatial-resolution Brillouin optical correlation domain analysis (BOCDA) has extensive development and application prospects. In this paper, long-range BOCDAs are introduced and summarized. Several creative methods underpinning measurement range enlargement, including the interval enhancement of the adjacent correlation peak (CP), improvements in the signal-to-noise ratio, and the concurrent interrogation of multiple CPs, are discussed and experimentally verified, respectively. The main drawbacks in the present BOCDA schemes and avenues for future research and development have also been prospected.

Distributed Ultraviolet Sensor Based on Brillouin Optical Correlation-Domain Analysis Using An Azobenzene Polymer-Coated Optical Fiber

Distributed Ultraviolet Sensor Based on Brillouin Optical Correlation-Domain Analysis Using An Azobenzene Polymer-Coated Optical Fiber

Brillouin Optical Correlation Domain Analysis Using Orthogonally Polarized Probe Sidebands

A single-mode fiber-based polarization-independent Brillouin optical correlation domain analysis system is experimentally demonstrated by applying orthogonally polarized probe sidebands. The Brillouin gain and loss on orthogonally polarized Stokes and anti-Stokesprobe waves are simultaneously measured by balanced detection. The output is processed by a differential measurement scheme for suppressing the polarization dependency of the Brillouin gain spectrum. Compared to a polarization diversity scheme using a polarization switch, the measurement speed is doubled, and the error is reduced by more than 50&#x0025;.

Computed tomography for distributed Brillouin sensing.

A method to reconstruct the spatial distribution of Brillouin gain spectrum from its Radon transform is proposed, which is a type of optical computed tomography. To verify the concept, an experiment was performed on distributed Brillouin fiber sensing, which succeeded in detecting a 55-cm strain section along a 10-m fiber. The experimental system to obtain the Radon transform of the Brillouin gain spectrum is based on a Brillouin optical correlation-domain analysis with a linear frequency-modulated continuous-wave laser. Combining distributed fiber sensing with computed tomography, this method can realize a high signal-to-noise ratio Brillouin sensing.

Brillouin optical correlation domain analysis based on intensity modulation

We present a signal formula for correlation domain Brillouin analysis that uses short pulse trains arranged at different power intervals. The proposed signal can be realized by using only an intensity modulator, and the signal period (the measurement range) and the signal length can be independently realized without using an additional modulator for time gating. In the numerical analysis, we show that the proposed scheme obtains a gain advantage over the conventional scheme for fibers under test of approximately a few hundred meters when the available pump average power is limited. In the experiment, it was demonstrated that Brillouin frequency shifts can be discriminated with a spatial resolution of 5 cm over a 95-m-long fiber.

Dynamic strain measurement based on ultrafast Brillouin collision in the correlation domain.

The Brillouin collision rate in a Brillouin optical correlation domain analysis fiber sensor is ultimately limited by the sensing fiber length, which restricts the single point sampling rate in dynamic strain measurement. Here, a time-gated long-phase-sequence-coded pump method is proposed to overcome this limitation. The Brillouin collision rate is limited only by the phonon lifetime, since it governs the building and decaying time of the acoustic wave. For a sensing fiber length of ∼1km, a Brillouin collision rate as high as 1 MHz is experimentally realized. This further results in a single-point sampling rate of 1 kHz for dynamic strain sensing with a spatial resolution of ∼2cm and a measurement uncertainty of <33.5µε.

Improvement of Strain Measurement Accuracy and Resolution by Dual-Slope-Assisted Chaotic Brillouin Optical Correlation Domain Analysis

A dual-slope-assisted chaotic Brillouin optical correlation domain analysis (DSA-CBOCDA) technique is proposed to improve the measurement accuracy and resolution for static and dynamic strain sensing. By using the gain ratio obtained from two slopes of the Brillouin gain spectrum (BGS), the influence of random fluctuation in chaotic pump power on the measurement result is alleviated. Compared with the previous single-slope-assisted CBOCDA, the measurement accuracy of the DSA-CBOCDA is improved from 25.0 μϵ to 3.9 μϵ for the static strain, and from 28.5 μϵ to 6.2 μϵ for the dynamic strain. Meanwhile, the static strain resolution of 10 μϵ and dynamic strain resolution of 15 μϵ are verified in the experiment. Moreover, the dynamic strain measurement range of 800 μϵ for the proposed DSA-CBOCDA system is also experimentally confirmed, which is approximately fivefold larger than the current DSA-based Brillouin sensing system.

Effects of Differential Measurement Scheme on Brillouin Optical Correlation-Domain Analysis

Differential measurement (DM) is a modified lock-in detection technique that was introduced to the Brillouin optical correlation domain analysis (BOCDA) for improving the spatial resolution and dynamic range of distributed measurement. In the first report of the DM-based BOCDA the improvement of spatial resolution by 5-fold as well as the extension of dynamic range have been experimentally confirmed, however the maximum achievable improvement and the validity of DM in various measurement conditions have not been theoretically analyzed so far. In this paper we present an in-depth analysis on the effects of DM applied to the BOCDA by numerical simulations and test experiments. Our results show that the DM can bring up to 6-fold improvement in the spatial resolution of the BOCDA system, and the frequency of the phase modulation in the DM should be optimized according to the target spatial resolution, as a key factor determining its performance. In the experimental confirmation a 5 cm strain-applied section is measured by a DM-based BOCDA system with a nominal spatial resolution of 30 cm. The applicability to the long-range BOCDA system using double modulation and the practical limitation coming from the reduction of signal amplitude are also discussed.

High-accuracy dual-slope-assisted chaotic Brillouin fiber dynamic strain measurement

Nowadays, distributed dynamic sensing technology based on stimulated Brillouin scattering has been widely employed in civil structure health monitoring, disaster warning, national defense, etc. In this paper, we propose and experimentally demonstrate a novel Brillouin optical correlation-domain analysis based-on gain-switch modulation and dual-slope assisted method for achieving high-accuracy large-range dynamic strain measurement. In single-slope assisted chaotic Brillouin sensing, the measurement accuracy of dynamic strain is deteriorated by the inherent characteristics of time delay signature and power stochastic fluctuations. First, the mechanism behind the acoustic field deterioration and principle of background noise suppression are analyzed theoretically. Then, the chaotic continuous pump light is modulated into pulsed light with a higher extinct ratio of 48.6 dB, where the electro-optical modulator is replaced by a gain switch. And thus, the noise peaks, induced by the secondary peaks and irregular basal oscillations of chaotic auto-correlation curve, are greatly restrained. Comparing with the electro-optical modulator-based system, the signal-to-noise ratio of stimulated Brillouin acoustic field is increased by 3.31 dB in simulation and the signal-to-background ratio of Brillouin gain spectrum is doubled in experiment. Consequently, the measurement accuracy of dynamic strain is improved from ± 40.2 με to ± 23.1 με and the relative error decreases from ± 5.0% to ± 2.9% in single-slope assisted system based-on gain switch modulation. In addition, a dual-slope assisted method is inspired to eliminate the detrimental effect caused by the intrinsic power fluctuations of chaotic laser. A verification experiment is pre-conducted that the dynamic strain could be correctly interrogated although a wide range pump power variation has been manually applied. The measurement accuracy is ultimately enhanced to ± 8.1 με and the relative error is ± 1% correspondingly, implying a higher stability. The dynamic range of this proposed system is retained at 800 με, which is approximately 5 times as large as the dynamic range of the traditional dual-slope assisted configurations. The 4-cm spatial resolution along 30-m FUT is also investigated and consistent with the result obtained previously. A larger measurement range and a higher vibration frequency would be further explored by using the multi-slope assisted method and piezoelectric ceramic oscillator respectively. The superior slope-assisted chaotic Brillouin optical correlation-domain analysis will provide a new solution for the accurate positioning and real-time monitoring of dynamic parameters in modern industry.

Simultaneous Strain and Temperature Measurement Based on Chaotic Brillouin Optical Correlation-Domain Analysis in Large-Effective-Area Fibers

Chaotic Brillouin optical correlation domain analysis (BOCDA) has been proposed and experimentally demonstrated with the advantage of high spatial resolution. However, it faces the same issue of the temperature and strain cross-sensitivity. In this paper, the simultaneous measurement of temperature and strain can be preliminarily achieved by analyzing the two Brillouin frequencies of the chaotic laser in a large-effective-area fiber (LEAF). A temperature resolution of 1 °C and a strain resolution of 20 µε can be obtained with a spatial resolution of 3.9 cm. The actual temperature and strain measurement errors are 0.37 °C and 10 µε, respectively, which are within the maximum measurement errors.

High-Accuracy Distributed Bend Sensor Eligible for High-Curvature Structures Based on Brillouin Optical Correlation Domain Analysis

We present a high-accuracy distributed bend sensor suitable for high-curvature structures based on Brillouin frequency measurement using a multi-fiber probe. Brillouin optical correlation domain analysis (BOCDA) with differential measurement is adopted for distributed strain sensing with a cm-order spatial resolution (minimum 1 cm), and a specially designed sensing probe embedding three optical fibers is used to enhance the minimum measurable bending radius and accuracy of bend sensing. Analysis on the reconstruction accuracy is performed for various spatial resolutions (10, 20, 30, 40 mm) and steps (1, 5, 10, 15, 20 mm) of the BOCDA system. Our results show that the maximum measurable curvature of three-dimensional bending is 143 m <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">-1</sup> , which is the highest curvature so far measured by Brillouin sensors in three-dimensional space, with about 0.7% of tip position error. Additionally, both pseudo-discrete sensing and fully distributed sensing are performed together to analyze the relation between the methods of sensing (discrete or distributed) and the accuracy of probing multi-bend curvatures according to the measurement step.

50 km-Range Brillouin Optical Correlation Domain Analysis With First-Order Backward Distributed Raman Amplification

We demonstrate the enlargement of sensing range of Brillouin optical correlation domain analysis (BOCDA) system by introducing the first-order distributed Raman amplification. The time-domain data processing is adopted for the BOCDA system utilizing a gated Brillouin pump, and the Raman amplification is applied to compensate for the depletion of Brillouin pump induced by Rayleigh scattering and Brillouin interaction. The Raman pump is injected in the opposite direction to the propagation of Brillouin pump, where the pumping scheme is optimized by simulations. A differential measurement scheme is additionally introduced for improving spatial resolution and dynamic range. In experiments, we measure the strain distribution along a 52.1 km sensing fiber with 7 cm spatial resolution, where the number of resolving points of measurement is more than 744 000.