Florian Sauser

Leakage detection using fiber optics distributed temperature monitoring

The monitoring of temperature profiles over long distance by means of optical fibers represents a highly efficient way to perform leakage detection along pipelines, in dams, dykes, or tanks... Different techniques have been developed taking advantages of the fiber geometry and of optical time domain analysis for the localization of the information. Among fiber optics distributed temperature sensing techniques, Brillouin-based systems have demonstrated to have the best potential for applications over distances up to several tens of kilometers. The key features and performances are reviewed in the present article and a 55km pipeline equipped with a fiber optics leakage detection system is presented as a case study.

Colour simplex coding for brillouin distributed sensors

The possibility to customize Simplex coding for long range Brillouin Optical Time Domain Analysis is demonstrated by “colouring” the sequences in the frequency domain. The coding gain is identical to the traditional intensity-modulated Simplex code, though with much simplified series of sequences. The frequency-hopping pulses in return-to-zero intensity-modulated format are generated with a Direct-Digital Synthesizer. The proof-of-concept is experimentally demonstrated with measurements over a 50 km range (100 km fibre-loop) and a 2 meter spatial resolution.

Time/frequency coding for Brillouin distributed sensors

In this paper, we propose a novel coding for long range Brillouin Optical Time Analysis (BOTDA) distributed sensors based on a combination of time and frequency pulses, resulting in an additional coding gain of √2 with respect to traditional intensity-modulated codes. The generation of frequency-chirped pseudo-arbitrary pulses in return-to-zero (RZ) format with a Direct-Digital Synthesizer (DDS) is presented and the coding gain is experimentally verified, perfectly matching its theoretical value.

Novel Brillouin Optical Time-Domain Analyzer for Extreme Sensing Range Using High-Power Flat Frequency-Coded Pump Pulses

In this paper, we propose a novel Brillouin optical time-domain analysis setup that combines simultaneous Brillouin gain/loss measurements with colour coding. This technique gives the advantage that the pump power can greatly be increased, compared to other coding schemes; thus, increasing the sensing range. A first measurement over a 200-km fiber loop is performed, with a 3-m spatial resolution and an accuracy of ±3 MHz (2σ) at the end of the sensing fiber. In a second setup, high-power flat pump pulses are generated by applying an arbitrary waveform signal on a frequency shifter; thus, further increasing the performance of the novel Brillouin sensor. To the best of our knowledge, these are the best results obtained with a Brillouin sensor without Raman amplification.

Cyclic coding for Brillouin optical time-domain analyzers using probe dithering

We study the performance limits of mono-color cyclic coding applied to Brillouin optical time-domain analysis (BOTDA) sensors that use probe wave dithering. BOTDA analyzers with dithering of the probe use a dual-probe-sideband setup in which an optical frequency modulation of the probe waves along the fiber is introduced. This avoids non-local effects while keeping the Brillouin threshold at its highest level, thus preventing the spontaneous Brillouin scattering from generating noise in the deployed sensing fiber. In these conditions, it is possible to introduce an unprecedented high probe power into the sensing fiber, which leads to an enhancement of the signal-to-noise ratio (SNR) and consequently to a performance improvement of the analyzer. The addition of cyclic coding in these set-ups can further increase the SNR and accordingly enhance the performance. However, this unprecedented probe power levels that can be employed result in the appearance of detrimental effects in the measurement that had not previously been observed in other BOTDA set-ups. In this work, we analyze the distortion in the decoding process and the errors in the measurement that this distortion causes, due to three factors: the power difference of the successive pulses of a code sequence, the appearance of first-order non-local effects and the non-linear amplification of the probe wave that results when using mono-color cyclic coding of the pump pulses. We apply the results of this study to demonstrate the performance enhancement that can be achieved in a long-range dithered dual-probe BOTDA. A 164-km fiber-loop is measured with 1-m spatial resolution, obtaining 3-MHz Brillouin frequency shift measurement precision at the worst contrast location. To the best of our knowledge, this is the longest sensing distance achieved with a BOTDA sensor using mono-color cyclic coding.

Brillouin distributed sensor over a 200km fiber-loop using a dual-pump configuration and colour coding

In this paper, we propose a new Brillouin Optical Time Domain Analysis (BOTDA) set-up that combines simultaneous Brillouin gain/loss measurements with colour coding. This technique gives the advantage that the pump power can greatly be increased, compared to other coding schemes, thus increasing the sensing range. A measurement over a 200 km fiber-loop is performed, with a 3 meter spatial resolution and an accuracy of ± 3 MHz (2σ) at the end of the sensing fiber. To the best of our knowledge, this is the best result obtained with a Brillouin sensor without Raman amplification.

Brillouin optical time-domain analyzer for extended sensing range using probe dithering and cyclic coding

We present an enhanced performance Brillouin optical time-domain analysis sensor that uses dual probes waves with optical frequency modulation and cyclic coding. The frequency modulation serves to increase the probe power that can be injected in the fiber before the onset of non-local effects and noise generated by spontaneous Brillouin scattering. This leads to higher detected signal-to-noise ratio (SNR), which is further increased by the coding gain. The enhanced SNR translates to extended range for the sensor, with experiments demonstrating 1-m spatial resolution over a 164 km fiber loop with a 3-MHz Brillouin frequency shift measurement precision at the worst contrast position. In addition, we introduce a study of the power limits that can be injected in the fiber with cyclic coding before the appearance of distortions in the decoded signal.

Enhancement of signal-to-noise ratio in Brillouin optical time domain analyzers by dual-probe detection

We demonstrate a simple technique to enhance the signal-to-noise ratio (SNR) in Brillouin optical time-domain analysis sensors by the addition of gain and loss processes. The technique is based on the shift of the pump pulse optical frequency in a double-sideband probe system, so that the gain and loss processes take place at different frequencies. In this manner, the loss and the gain do not cancel each other out, and it makes possible to take advantage of both informations at the same time, obtaining an improvement of 3 dB on the SNR. Furthermore, the technique does not need an optical filtering, so that larger improvement on SNR and a simplification of the setup are obtained. The method is experimentally demonstrated in a 101 km fiber spool, obtaining a measurement uncertainty of 2.6 MHz (2σ) at the worst-contrast position for 2 m spatial resolution. This leads, to the best of our knowledge, to the highest figure-of-merit in a BOTDA without using coding or raman amplification.

New improvements for Brillouin optical time-domain reflectometry

This paper presents new techniques designed to improve the performances of a BOTDR. The first one introduces a second pump to the sensor, thus doubling the Brillouin signal on the receiver. The second one uses image processing with a two-dimensional Gaussian filter whose parameters are defined. The last technique explores the possibilities offered by colour codes. The benefits of each, in terms of signal-to-noise ratio, is presented by comparing measurements over a distance range of 50km with a spatial resolution of 5m. These techniques can easily be combined and the global improvement is estimated at 10dB, compared to conventional sensors.

Colour cyclic code for Brillouin distributed sensors

For the first time, a colour cyclic coding (CCC) is theoretically and experimentally demonstrated for Brillouin optical time-domain analysis (BOTDA) distributed sensors. Compared to traditional intensity-modulated cyclic codes, the code presents an additional gain of √2 while keeping the same number of sequences as for a colour coding. A comparison with a standard BOTDA sensor is realized and validates the theoretical coding gain.