Fast Brillouin Optical Time-domain Analysis Research Articles

High spatial resolution fast Brillouin optical time-domain analysis enabled by frequency-agility digital optical frequency comb.

A significant spatial resolution enhancement scheme for digital optical frequency comb (DOFC)-based fast Brillouin optical time-domain analysis (BOTDA) is proposed and experimentally demonstrated by using frequency-agility probes, without sacrificing the frequency resolution. The proposed system ensures high spatial resolution by using short frame duration, meanwhile enabling high frequency resolution retrieval of the Brillouin gain spectrum using frequency interleaving of multiple frequency-agility DOFC probes. Additionally, quadratic phase coding is introduced to release the influence of the high peak to average power ratio of the probes. Eventually, the proposed BOTDA sensor achieves a record 5-m spatial resolution over 10-km fiber with less than 2-MHz frequency uncertainty, and a 1-GHz dynamic measurement range. For proof of concept, 10-Hz vibration sensing is also successfully demonstrated at a 40-Hz sampling rate, showing great potential for fast measurement. It is worth mentioning that a higher spatial resolution can be achieved by using more frequency-agility DOFC probes, albeit at the expense of increasing the measurement time.

Deep Learning Enhanced Long-Range Fast BOTDA for Vibration Measurement

In this paper, we propose and experimentally demonstrate a scheme of deep learning enhanced long-range fast Brillouin optical time-domain analysis (BOTDA). The volumetric data from fast BOTDA is denoised and demodulated by using a deep video denoising network and a deep neural network, respectively. Benefitting from the advanced deep learning algorithms, the sensing range of fast BOTDA is extended to 10 km successfully. In experiment, vibration signal is measured with a sampling rate of 23 Hz, 2 m spatial resolution, and 1.19 MHz accuracy over 10 km single-mode fiber with only 4 averages. Due to the low computational complexity and GPU acceleration, the network takes less than 0.04 s to process 100 × 21800 data, which is much faster than the conventional algorithms. This method provides the potential for real-time vibration measurement in fast BOTDA with long sensing range.

Dynamic Distributed Pressure Measurement Using Frequency-Agile Fast BOTDA

A distributed pressure sensor is proposed and designed for dynamic pressure measurement by using frequency-agile fast Brillouin optical time-domain analysis (BOTDA). A double coated single-mode fiber (SMF) is used as the sensing fiber because of its 1500- $\mu \text{m}$ thickness outer coating that can significantly improve the dependence of the Brillouin frequency shift on pressure. Then, the frequency-agile technique is used to generate frequency-agile pump pulse in BOTDA system so that a fast Brillouin gain spectrum distribution measurement can be achieved. An injection locked scheme is used as both optical filter and optical amplifier to improve the measurement accuracy. As a result, the static pressure sensitivity of the double coated fiber is −3.46 MHz/MPa with the pressure ranging from 0 to 30 MPa. Subsequently, a large dynamic range pressure measurement is performed with a sampling rate of 33.3 kHz and maximum sensing distance of 25 m. Furthermore, it is proved that the uncertainty of dynamic pressure measurement system is 0.03 MPa.

Fast Brillouin optical time-domain analysis using frequency-agile and compressed sensing.

A fast Brillouin optical time-domain analysis (BOTDA) sensor has been proposed and experimentally demonstrated based on the frequency-agile and compressed-sensing technique. The proposed scheme employs a data-adaptive sparse base obtained by the principle component analysis algorithm, enabling the sparse representation of Brillouin spectrum. Then, it can be reconstructed successfully with random frequency sampling and orthogonal matching-pursuit algorithms. In the experiment, the Brillouin gain spectrum (BGS) is mapped by the conventional fast BOTDA, where the frequency step and span are 4 MHz and 500 MHz, respectively. By using compressed-sensing technology, the BGS is successfully recovered with 37 random frequency samples, the number of which is only 30% of the full data. With fewer sampling frequencies, the compressed-sensing technology is able to improve the sensing performance of the conventional fast BOTDA, including a 3.3-time increase in sampling rate and 70% reduction in data storage.

Recent Progress in Fast Distributed Brillouin Optical Fiber Sensing

Brillouin-based optical fiber sensing has been regarded as a good distributed measurement tool for the modern large geometrical structure and the industrial facilities because it can demodulate the distributed environment information (e.g., temperature and strain) along the sensing fiber. Brillouin optical time domain analysis (BOTDA), which is an excellent and attractive scheme, has been widely developed thanks to its high performance in a signal-to-noise ratio, a spatial resolution, and sensing distance. However, the sampling rate of the classical BOTDA is severely limited by several factors (especially the serially frequency-sweeping process) so that it cannot be suitable for the quickly distributed measurement. In this work, we summarize some promising breakthroughs about the fast BOTDA, which can be named as an optical frequency comb technique, an optical frequency-agile technique, a slope-assisted technique, and an optical chirp chain technique.

150 km fast BOTDA based on the optical chirp chain probe wave and Brillouin loss scheme.

Distributed long-range Brillouin optical time domain analysis (BOTDA) is an extremely time-consuming sensing scheme, which requires frequency mapping of the Brillouin spectrum and a large number of average times. Here, we propose a fast long-range BOTDA based on the optical chirp chain (OCC) probe wave and Brillouin loss scheme. The OCC-modulated probe wave is enabled by cascading fast-frequency-changing microwave chirp segments head-to-tail, which covers a large frequency range around the anti-Stokes frequency relative to the pump wave. The combination of the OCC technique and Brillouin loss scheme provides several advantages, i.e., fast measurement, a high Brillouin threshold, no additional amplification scheme, and freedom from the nonlocal effect. In the experiment, 6m spatial resolution, 3.2s measurement time, and 3MHz measurement precision were achieved over a 150km single-mode fiber.

Brillouin optical time-domain analysis at a high sampling rate (invited)

In the modern industry, a distributed ultra-fast measurement for obtaining environment information (e.g. strain and temperature) is required. Brillouin optical time-domain analysis (BOTDA), one of widely used optical fiber sensing, is usually employed to measure the distributed Brillouin frequency shift over fiber under test via a time-consuming frequency-sweeping process which limits the sampling rate of BOTDA. Several fast BOTDA schemes proposed by our team are summarised and are classified into three categories: frequency-agile technique, slope-assisted methods and optical chirp chain technique.

Polarization independent fast BOTDA based on pump frequency modulation and cyclic coding

We propose and experimentally demonstrate a scheme of polarization independent fast Brillouin optical time domain analysis (F-BOTDA) based on pump frequency modulation and cyclic coding. The Brillouin gain spectrum (BGS) is reconstructed by fast scanning frequency of the pump using an arbitrary waveform generator (AWG). To realize long range distributed dynamic strain sensing, polarization diversity technique and cyclic coding are employed to eliminate polarization fading and enhance the signal-to-noise ratio (SNR). Based on this configuration, the need of trace averaging is avoided, sensing speed of 440 Hz is achieved over ~2 km single mode fiber with 50 scanning frequencies and a spatial resolution of 1.5 m. Vibration events up to 40 Hz are successfully identified.

Distributed measurement of dynamic strain based on multi-slope assisted fast BOTDA.

We propose and demonstrate a dynamic Brillouin optical fiber sensing based on the multi-slope assisted fast Brillouin optical time-domain analysis (F-BOTDA), which enables the measurement of a large strain with real-time data processing. The multi-slope assisted F-BOTDA is realized based on the double-slope demodulation and frequency-agile modulation, which significantly increases the measurement range compared with the single- or double- slope assisted F-BOTDA, while maintaining the advantage of fast data processing and being suitable for real-time on-line monitoring. A maximum strain variation up to 5000με is measured in a 32-m fiber with a spatial resolution of ~1m and a sampling rate of 1kHz. The frequency of the strain is 12.8Hz, which is limited by the rotation rate of the motor used to load the force on the fiber. Furthermore, the influence of the frequency difference between two adjacent probe tones on the measurement error is studied theoretically and experimentally for optimization. For a Brillouin gain spectrum with a 78-MHz width, the optimum frequency difference is ~40MHz. The measurement error of Brillouin frequency shift is less than 3MHz over the whole measurement range (241MHz).

Retraction Note to: Fast Brillouin Optical Fiber Sensor for Distributed Dynamic Measurement Based on Differential Double-Pulse

We demonstrate a high-spatial-resolution fast Brillouin optical time-domain analysis scheme based on frequency agility and differential double-pulse for distributed dynamic measurement. The frequency-agility probe wave is obtained from the second-order sideband of modulated light by using frequency-agility microwave signal from a wideband arbitrary waveform generator. The differential double-pulse technique is proposed to improve the spatial resolution while keeping the capability of dynamic measurement. In experiment, a spatial resolution of 20 cm is achieved by using a 52/50 ns differential double-pulse, and the distributed vibration measurement is demonstrated over a 50-m Panda fiber with a maximum vibration frequency of up to 50 Hz. With only five averages, the standard deviation of the strain accuracy is of 14 μV.

RETRACTED ARTICLE: Fast Brillouin Optical Fiber Sensor for Distributed Dynamic Measurement Based on Differential Double-Pulse

We demonstrate a high-spatial-resolution fast Brillouin optical time-domain analysis scheme based on frequency agility and differential double-pulse for distributed dynamic measurement. The frequency-agility probe wave is obtained from the second-order sideband of modulated light by using frequency-agility microwave signal from a wideband arbitrary waveform generator. The differential double-pulse technique is proposed to improve the spatial resolution while keeping the capability of dynamic measurement. In experiment, a spatial resolution of 20 cm is achieved by using a 52/50 ns differential double-pulse, and the distributed vibration measurement is demonstrated over a 50-m Panda fiber with a maximum vibration frequency of up to 50 Hz. With only five averages, the standard deviation of the strain accuracy is of 14 μV.

Cyclic pulse coding for fast BOTDA fiber sensors

A cyclic pulse coding technique is proposed and experimentally demonstrated for fast implementation of long-range Brillouin optical time-domain analysis (BOTDA). The proposed technique allows for accurate temperature and strain measurements with meter-scale spatial resolution over kilometers of standard single-mode fiber, with subsecond measurement times.

High-Spatial-Resolution Fast BOTDA for Dynamic Strain Measurement Based on Differential Double-Pulse and Second-Order Sideband of Modulation

We demonstrate a high-spatial-resolution fast Brillouin optical time-domain analysis (BOTDA) for distributed dynamic strain measurement based on differential double-pulse and second-order sideband of modulation. The frequency-agility probe wave is obtained from the second-order sideband of the modulated light by using the microwave signal from a wideband arbitrary waveform generator (AWG), which reduces the bandwidth requirement of the AWG by half to <formula formulatype="inline" xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex Notation="TeX">$\sim$</tex></formula> 5.5 GHz. The differential double-pulse scheme is proposed to improve the spatial resolution while keeping the capability of dynamic measurement. In experiment, a spatial resolution of 20 cm is achieved by using a 52/50 ns differential double-pulse, and the distributed vibration measurement is demonstrated over a 50-m Panda polarization-maintaining fiber observing the vibration frequency of up to 50 Hz. With only five averages, the standard deviation of the strain accuracy is measured to be 14 <formula formulatype="inline" xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex Notation="TeX">$\mu\varepsilon$</tex></formula> .