Sébastien Le Floch

• Full Professor
• Professor (Full) at University of Applied Sciences, Western Switzerland

A closed-loop servo control based on balancing the gain of two probing frequencies is proposed for real-time Brillouin optical time-domain analysis (BOTDA) without post-processing. With the most basic BOTDA hardware setup, the system can perform measurement in 150 ms and track a sudden Brillouin frequency shift (BFS) change in excess of 300 MHz (co...

A closed-loop servo control based on the gain ratio of two probing frequencies is proposed for fast BOTDA, where the feedback is independent of probe and pump loss, making it robust in harsh environment.

We present a new approach for producing elastomeric optical fibers with an optical behaviour corresponding to a few-mode optical fiber. Different fibers have been produced by first fabricating thermoplastic polyurethane preforms and subsequently drawing them. The fiber attenuation has been measured by the cut-back technique and the fiber bending tr...

The temperature measurement of a drill bit during an implantology drilling process is proposed by using a fiber Bragg grating fitted inside the drill bit. Due to the rotational nature of the drilling process, a free-space fiber-optic rotary joint is used for interrogating the fiber Bragg grating. Due to mechanical clearances and interferometric noi...

We present, for the first time, a colour coded sequence running in an endless loop and dedicated to ultra-fast Brillouin distributed sensors. Measurements within the whole elastic zone of single-mode optical fibers are presented.

The authors wish to acknowledge the financial support of the Spanish Ministerio de Economia y Competitividad through the projects TEC2013-47264- C2-2-R and TEC2016-76021-C2-1-R, FEDER funds and the UPNA.

The authors wish to acknowledge the financial support of the Spanish Ministerio de Economia y Competitividad through the projects TEC2013-47264- C2-2-R and TEC2016-76021-C2-1-R, FEDER funds and the Universidad Publica de Navarra.

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 effe...

In this communication, a novel compact fibre Bragg grating-based thermometer for on-line temperature monitoring of drill bits is reported. Our proposed technique can potentially be used to optimize any drilling process, requiring the use of small drill bits, through direct temperature measurement at the drill bit instead of relying on indirect para...

This paper presents a Fabry-Perot fiber tip sensor based on an air-liquid filled cavity. The cavity is sealed off by a thin gold coated membrane of parylene C, between 300 and 350 nm, creating a particularly flexible diaphragm. In order to retrieve and track the cavity of interest from other cavities formed within the sensor tip, a signal processin...

In this communication, a novel compact fibre Bragg grating-based thermometer for on-line temperature monitoring of drill bits is reported. Our proposed technique can potentially be used to optimize any drilling process, requiring the use of small drill bits, through direct temperature measurement at the drill bit instead of relying on indirect para...

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...

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 negat...

In this paper, we propose a novel 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 first measurement over a 200 k...

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-...

A pump signal based on bipolar pulse coding and single-sideband suppressed-carried (SSB-SC) modulation is proposed for Brillouin optical time-domain analysis (BOTDA) sensors. Making a sequential use of the Brillouin gain and loss spectra, the technique is experimentally validated using bipolar complementary-correlation Golay codes along a 100 km-lo...

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 inte...

We propose and experimentally demonstrate the possibility to use a pump signal based on bipolar pulse sequences using single-sideband suppressed-carrier (SSB-SC) modulation in Brillouin optical time-domain analysis (BOTDA) sensors. The SSB-SC modulated pump makes a sequential use of the Brillouin gain and loss spectra, increasing the intensity cont...

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...

A simple technique to generate an optical frequency comb, based on a conventional dual-drive Mach-Zehnder intensity modulator, has been used as optical source for a high accuracy distance measurement in an interferometric set-up. The modulator has been driven by a direct-digital synthesizer that is able to deliver a pure ramp in frequency between 1...

A new low-cost superheterodyne configuration, without acousto-optic modulator, is applied to the two-wavelength interferometry for absolute distance measurement. The principle relies on a synchronized frequency sweep of two optical signals, but with different frequency excursions. The frequency difference between the two optical waves is highly acc...

We present a new superheterodyne technique for long-distance measurements by two-wavelength interferometry (TWI). While conventional systems use two acousto-optic modulators to generate two different heterodyne frequencies, here the two frequencies result from synchronized sweeps of optical and radio frequencies. A distributed feedback laser source...

We present a new technique applied to the variable optical synthetic wavelength generation in optical interferometry. It consists of a chain of optical injection locking among three lasers: first a distributed-feedback laser is used as a master to injection lock an intensity-modulated laser that is directly modulated around 15 GHz by a radio freque...

We propose a new approach to multiple-wavelength interferometry, targeted to high bandwidth absolute distance measurement, with nanometer accuracy over long distances. Two cw lasers are stabilized over a wide range of frequency intervals defined by an optical frequency comb, thus offering an unprecedented large choice of synthetic wavelengths. By a...

Injection locking of two DFB semiconductors opens new possibilities to generate effective signals for optical sensing, in order to reach better performances. Pure wave forms can be generated with qualities exceeding those obtained using external modulators. This is illustrated through the application to the distributed Brillouin sensing that shows...

Injection locking of two DFB semiconductors opens new possibilities to generate effective signals for optical sensing, in order to reach better performances. Pure waveforms can be generated with qualities exceeding those obtained using external modulators.

We first use the nonlocalized, fluctuating source model for the stimulated Brillouin scattering to get the exact spectrum of the Stokes wave in optical fibers with attenuation loss. A new relation for the evaluation of the critical pump power (or Brillouin threshold) depending on the fiber length is then introduced, which should be more precise tha...

A single laser pump and probe experiment demonstrating the first very low temperature Brillouin gain spectrum measurement in standard telecommunication single-mode optical fibers at is presented. A novel theoretical expression of the Brillouin gain spectrum depending on the laser sources linewidth is detailed. This makes possible measurements to ex...

A new method for chromatic dispersion mapping in optical fibers is presented. It is based on measuring the CW four-wave mixing distribution created by two beams along the fiber using a Brillouin-OTDA. Experimental results demonstrate the feasibility of the technique

The injection locking technique is successfully applied to the correlation-based technique, resulting in a simple and efficient experimental configuration. A 1-cm resolution was readily obtained and can be significantly improved.

Injection locking of two DFB semiconductors opens new possibilities to generate effective signals for fibre sensing. This is illustrated through the application to distributed Brillouin sensing that shows significant progress with respect to established techniques.

Theoretical model for the stimulated Brillouin scattering (generation and amplification). First cryogenic measurements with theoretical model. First pressure measurements.

Stimulated Brillouin scattering (SBS) is one of the effects one can observe in single-mode optical fibers and is of major interest in many applications. It results from the diffusion of laser waves through interaction with acoustical waves that are present in the medium and arises mainly threw the form of a backscattered Stokes wave, limiting the m...

We have carried out stimulated-Brillouin-scattering experiments using the pump-probe technique in a standard single-mode optical fibre for temperatures ranging from 80 to 350 K at a pump wavelength of 1.55 µm. Measurements of the internal friction and Brillouin frequency shift are given. The `tunnelling model' is used to fit our results.

Brillouin gain curves of a standard optical fibre have been measured down to 3 K. In comparison with their well-documented characteristics at room temperature, they show original and interesting features, namely non-monotonous variations of the central frequency shift and of the linewidth. These preliminary measurements indicate that Brillouin-base...

We propose a theoretical expression of the Brillouin gain linewidth ΔνB evolution with temperature. Combined with a more precise model of the Stockes power analytic expression, this should enable to decouple the effects of strain and temperature in BOTDA sensors.