Brillouin Time Domain Analysis Research Articles

Link Insertion Loss Measurement of Deployed PON

We propose and demonstrate a novel scheme for measuring the in-service, centralized link insertion loss (LIL) of a deployed passive optical network. The proposed technology can measure the LIL with a single-end measurement using a quasi-bidirectional method specially designed for end-reflection assisted Brillouin time domain analysis. We describe the performance of our proposed LIL measurement system. In the experiments, the LIL value obtained with the proposed measurement scheme agree well with that obtained with the standard light source power meter method.

Enhanced Coherent BOTDA System Without Trace Averaging

We propose and experimentally demonstrate a scheme of a coherent Brillouin time domain analysis (BOTDA) system without any trace averaging. Assisted by a commercial integrated coherent receiver with a local oscillator generated through single sideband modulation from the same laser source, the Brillouin signals carried on a stable intermediate frequency (IF) are extracted by electrical/digital filters and then recovered to baseband by digital signal processing. This increases the signal-to-noise ratio and avoids the need of trace averaging and enables real-time signal acquisition. To eliminate the Brillouin gain fluctuation, two adjacent Brillouin time-domain traces stimulated by two sequential orthogonal pump pulses are recovered after the IF signals are detected in a real-time manner. Based on this configuration, a spatial resolution of 4 m and Brillouin frequency shift uncertainty of 1.473 MHz are realized in distributed temperature sensing over 40.63 km range. With the nonlocal means algorithm and distributed Raman amplification integrated into the system, the BFS uncertainty is enhanced to 0.843 MHz and better spatial resolution of 2 m over the same sensing fiber is achieved.

Dynamic Strain Measurement of 10-km Fiber With Frequency-Swept Pulsed BOTDA

We propose a high-speed, dynamic strain measurement with random access based on real-time Brillouin time-domain analysis of correlated gain measured with an oscilloscope. A frequency-swept probe obtains the Lorentzian-shaped correlated gain in a time domain. We simply monitor the peak time change, which relates to the Brillouin frequency shift. We achieved the theoretical sampling rate limit of 10 kilo-points/s in 10-km fiber. To the best of our knowledge, this is the first report to achieve the theoretical sampling rate and a measurement range of over 10 km with a Brillouin-based dynamic strain measurement.

Full scale strain monitoring of a suspension bridge using high performance distributed fiber optic sensors

This paper investigated field monitoring of a 1108 m suspension bridge during an assessment load test, using integrated distributed fibre-optic sensors (DFOSs). In addition to the conventional Brillouin time domain analysis system, a high spatial resolution Brillouin system using the differential pulse-width pair (DPP) technique was adopted. Temperature compensation was achieved using a Raman distributed temperature sensing system. This is the first full scale field application of DFOSs using the Brillouin time domain analysis technique in a thousand-meter-scale suspension bridge. Measured strain distributions along the whole length of the bridge were presented. The interaction between the main cables and the steel-box-girder was highlighted. The Brillouin fibre-optic monitoring systems exhibited great facility for the purposes of long distance distributed strain monitoring, with up to 0.05 m spatial resolution, and 0.01 m/point sampling interval. The performance of the Brillouin system using DPP technique was discussed. The measured data was also employed for assessing bridge design and for the assessment of structural condition. The results show that the symmetrical design assumptions were consistent with the actual bridge, and that the strain values along the whole bridge were within the safety range. This trial field study serves as an example, demonstrating the feasibility of highly dense strain and temperature measurement for large scale civil infrastructures using integrated DFOSs.

Robust and High-Sensitivity Brillouin Time-Domain Sensing With Branched-Fiber Configuration

We describe branched-fiber sensing with a novel Brillouin time-domain analysis configuration for temperature or strain sensing within a 2-D expanded area. By using a branch configuration with an appropriate number of branches and the newly proposed multiprobe pulse arrangement, the system dynamic range may surpass that of the conventional Brillouin time-domain analyzer, which employs a unicursal fiber configuration. The proposed Brillouin sensing would be useful particularly when the sensed area is 2-D, rather than when the area expands 1-D.

Pump-Power-Independent Double Slope-Assisted Distributed and Fast Brillouin Fiber-Optic Sensor

A small modification of the fast and distributed slope-assisted Brillouin time domain analysis (SA-BOTDA) method allows it to easily implement pump-power independent measurements of strain and/or temperature, using the ratio between readings taken on both slopes of the Brillouin gain spectrum. Employing this new double SA-BOTDA measurement technique, fast ( <formula formulatype="inline" xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex Notation="TeX">${\sim}{\rm 100}~{\rm Hz}$</tex></formula> at <formula formulatype="inline" xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex Notation="TeX">${\sim}{\rm 1}\hbox{-}{\rm kHz}$</tex></formula> effective sampling rate) strain measurements are shown to be immune to pump pulse power variations as large as 6 dB. At the expense of halving the sampling rate, this technique still maintains all the benefits of its SA-BOTDA predecessor. In particular, its ability to handle (Brillouin) longitudinally inhomogeneous fibers is demonstrated.

Dark-Pulse Brillouin Optical Time-Domain Sensor With 20-mm Spatial Resolution

Brillouin scattering-based distributed fiber-optic sensing is a powerful measurement tool that uses the inelastic scattering of incident light by an acoustic wave (phonon) to determine strain and/or temperature conditions of the fiber. Since the original Brillouin-time-domain-analysis (BOTDA) technique was proposed, several other analysis methods have been introduced to improve sensing performance in four key areas: spatial resolution; measurement accuracy; total sensing length; and measurement-acquisition time. The four factors are generally interrelated and improvements to one factor often come at the cost of one or more of the others. For example, one system might sacrifice spatial resolution for total sensing length, while another might sacrifice accuracy to gain acquisition speed. We present a BOTDA system based on dark-pulse scattering that provides improved resolution, accuracy, and acquisition time over conventional BOTDA systems, without the severe limitations on sensing length often imposed by other high-resolution techniques. Theoretical validation of the method is given, and experimental results are presented that demonstrate 20-mm resolution strain measurements with an accuracy of plusmn20 muepsiv, which is the highest spatial resolution yet reported for a BOTDA system