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

Dual-pump sweep-free stimulated Brillouin optical distributed sensing method and device

The present invention concerns a Brillouin optical distributed sensing method, comprising steps of: (i) providing a first and a second optical pulsed pump wave (20, 23) and an optical probe wave comprising at least one probe spectral component (26), (ii) detecting a stimulated Brillouin scattering signal resulting from the interactions in a sensing optical fiber of the optical probe wave with the first and the second optical pulsed pump waves (20, 23), (iii) spectrally arranging the first and the second optical pulsed pump waves (20, 23) and the optical probe wave so that the optical probe wave comprises a probe spectral component (26) located within the Stokes Brillouin spectrum (21) of the first optical pulsed pump wave (20) and a probe spectral component (26) located within the anti-Stokes Brillouin spectrum (24) of the second optical pulsed pump wave (23), (iv) deducing the Brillouin frequency (22, 25) of the Brillouin spectra (21, 24) from the stimulated Brillouin scattering signal. The present invention concerns also a device for implementing the method

Differential chirped-pulse pair for sub-meter spatial resolution Brillouin distributed fiber sensing

A distributed fiber sensor based on a differential chirped-pulse pair Brillouin optical time domain analysis (DCPBOTDA) is proposed for sub-meter spatial resolution sensing. The technique is based on the subtraction of two measurements made with the same pump pulse widths, but differing in the final short section of the pulse by a positive or negative frequency chirp, respectively. Experimental results are compared with a precise theoretical modeling, validating the sub-meter sensing capabilities of the technique

Optical Sensor for the Detection of OH- Contamination during Optical Fibre Manufacturing

Sub-ppm (HCl) and (H2O) monitoring using photoacoustic spectroscopy is reported in optical fibre manufacturing for the production of low-water-peak fibres. Contamination sources of the carrier gas used for fibre preforms manufacturing were identified and discussed

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

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 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