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Here we propose a simulation model based on a previously reported analytical description of the Brillouin gain, that takes into account pump depletion, which allows us to make very accurate calculations for Brillouin fiber lasers (BFLs) working both in a single and cascaded multi-wavelength configurations. Output powers and conversion efficiencies are analyzed and compared with experimental results for various lasers setups using 25 km of a non-zero dispersion-shifted fiber (NZDSF) as the Brillouin gain media. In our experimental investigations, we used a pump laser at 1565 nm, with a bandwidth of 1 kHz, and output powers varying from 0 to its maximum value of 14 mW. We analyzed the laser behavior under various conditions using output couplers with output ratios varying from 10% to 90%, and to generate the cascaded Brillouin laser we have used a 10 m Erbium-doped optical fiber amplifier as a gain block in a separated cavity. Additionally, a spectral reconstruction is made based on power predictions of our model for the cascaded BFL with excellent agreement with experimental data.

This study describes the deployment of machine learning algorithm called generalized linear model (GLM) to improve the temperature prediction performance in Brillouin optical time domain analysis (BOTDA) fiber sensor for distributed temperature sensing application. In GLM, the temperature prediction is made from the Brillouin gain spectrum (BGS) and the link function, without the need to determine the Brillouin frequency shift (BFS). In this proof-of-concept experiment, the performance of GLM was investigated by collecting the BGS and comparing it to the conventional Lorentzian curve fitting (LCF) method. From the experimental results, we have found that the GLM method produced a more consistent temperature prediction than the conventional LCF method. Furthermore, the proposed GLM method could still retain an accurate temperature measurement regardless of low signal-to-noise ratio (SNR) and large frequency scanning step while collecting BGS, which is difficult to be achieved by the conventional LCF method at certain level. In addition to that, the prediction obtained is 655 times faster than the conventional LCF method. The small and negligible deterioration to the temperature resolution confirmed the robustness of GLM in performing fast and accurate temperature measurement for BOTDA.

A novel double-clad As2Se3 chalcogenide photonic crystal fiber is proposed and the slow light via stimulated Brillouin scattering is theoretically investigated. The Brillouin gain spectrum by taking into account the high-order acoustic modes is analyzed. The simulated results indicate that the slow light can be tuned by varying the air filling fraction in the inner cladding. The time delay upto 1120ns can be achieved with 1-m-long fiber when pumped with 10mW. But these features of slow light are less affected with the change of the air filling fraction in the outer cladding.

A scheme based on hybrid polarization pulling and pushing effects is utilized for eliminating Brillouin gain fluctuation in Golay-coded BOTDA sensor. Maximum Brillouin gain fluctuation is reduced from ∼ 0.31% to ∼ 0.04%.

Single mode (SM) optical fiber with multiple Brillouin scattering peaks can be used for simultaneous strain and temperature measurement based on Brillouin frequency shift (BFS), but the measurement uncertainties are high due to the low Brillouin gains of higher-order acoustic modes. A new SM fiber is designed and fabricated with enhanced Brillouin gain of higher-order acoustic modes so that the gains of the multiple Brillouin peaks are at a similar level. The temperature coefficients of the BFSs of the peaks are also made significantly different to improve the accuracy of the measured strain and temperature.

An optimized fitting function is studied to restore the BFS in BOTDA system when double-peak Brillouin gain spectrum appears. Based on this technique, the frequency accuracy and spatial position accuracy is improved greatly around hotspot.

The optical forces of forward stimulated Brillouin scattering (FSBS) in nanofibers are investigated through numerical methods. Only the transverse-distributed boundary pressure of FSBS contributes significantly to the Brillouin gain in nanofibers.

Specialty optical fibers employed in Brillouin-based distributed sensors are briefly reviewed. The optical and acoustic waveguide properties of silicate glass optical fiber first are examined with the goal of constructing a designer Brillouin gain spectrum. Next, materials and their effects on the relevant Brillouin scattering properties are discussed. Finally, optical fiber configurations are reviewed, with attention paid to fibers for discriminative or other enhanced sensing configurations. The goal of this brief review is to reinforce the importance of fiber design to distributed sensor systems, generally, and to inspire new thinking in the use of fibers for this sensing application.

We propose and demonstrate a novel modal attenuation measurement that can provide splice loss of purely LP 11 mode group dependent on a state of mode excitation in spliced GI-FMF based on inter-modal Brillouin gain analysis.

Brillouin optical time domain analysis (BOTDA) system is a very popular system for distributed optical sensing. In order to achieve its full performance quality, every system element and setting has to be carefully set. This paper specifically performs optimization analysis on the polarization and probe power in measurement of Brillouin gain spectrum and Brillouin frequency shift. The results reveal the necessity of adopting polarization scrambler into the system, and astutely choosing the correct pump power in order to reduce fluctuations in the Brillouin signals.

The Brillouin gain properties in a double-clad As2Se3 photonic crystal fiber (PCF) are simulated based on the finite-element method (FEM). The results indicate that the Brillouin gain spectrum (BGS) of our proposed chalcogenide PCF exhibits a multipeaked behavior and has a high Brillouin gain coefficient. We also find that a larger size of inner cladding air holes will lead to a more pronounced second peak in the BGS. On the other hand, the size of the outer cladding has nearly no effect on the BGS behavior. Through these results, one can tailor the Stimulated Brillouin scattering effect in PCFs for a wide range of applications.

We modeled the shape of the Brillouin gain spectrum (BGS) produced in an optical fiber wherein spatially and temporally nonuniform strains are simultaneously produced. On the basis of BGS observation experiments, the validity of the model is demonstrated.

A technique to measure nonlinear processes, such as stimulated Brillouin scattering, with a very-high signal-to-noise ratio (SNR) is presented. Brillouin gain measurement with 77 dB SNR is demonstrated over a 2m-long section of single-mode fiber.

We propose and experimentally demonstrate an averaging-free vector BOTDA system, which enables both distributed Brillouin gain and Brillouin phase shift detection without trace averaging. A 4m spatial resolution over 18.3 km is realized.

A Brillouin/erbium fiber laser (BEFL) which uses 4-m erbium-doped fiber as both the Brillouin gain and linear gain media is presented and its applications in an interferometric fiber sensor are investigated.

International audience; Brillouin gain coefficient is usually evaluated using well-established pump-probe technique. We report a technique based upon the cavity ringdown method that enables to characterize this fundamental parameter directly in a Brillouin laser cavity. Indeed, within a unique experimental setup, material gain, optical cavity parameters and laser properties can be extracted. This method would be particularly suitable for micro-resonator lasers intracavity material Brillouin gain determination.

We demonstrate the giant enhancement of stimulated Brillouin scattering in an As2S3 chalcogenide half suspended-core rectangle waveguide through simulation experiments. The half suspended-core waveguid is charactered by an effective length of 3.9 cm and a cross-section of 0.9 µm × 0.9 µm, which is supported by SiO2 ridge glass. Through simulation experments, the Brillouin gain obtained is 54 dB for a pump power of just 248 mW. The 3-dB bandwidth can reduce to 8.2 MHz. A huge advantage of this structure is that it can obtain huge Brillouin gain and tiny 3-dB bandwidth for a low pump power and minute extension. This demonstration provides a feasible way for on-chip stimulated Brillouin scattering, which is important for microwave signal processing.

We demonstrate a BOTDA system based on optimized compensation scheme for the propagation loss of the pump pulse by distributed Brillouin amplification. Near-constant Brillouin gain is obtained in the distributed measurement of Brillouin frequency along 51 km optical fiber with 20 cm spatial resolution.

Brillouin gain spectra of few mode fibres are modelled and compared to measurements. Spectral differences for various optical modes are explained by the different overlaps with the guided acoustic modes.

In distributed Brillouin optical fiber sensor when the length of the perturbation to be detected is much smaller than the spatial resolution that is defined by the pulse width, the measured Brillouin gain spectrum (BGS) experiences two or multiple peaks. In this work, we propose and demonstrate a technique using differential pulse pair Brillouin optical time-domain analysis (DPP-BOTDA) based on double-peak BGS to enhance small-scale events detection capability, where two types of single mode fiber (main fiber and secondary fiber) with 116 MHz Brillouin frequency shift (BFS) difference have been used. We have realized detection of a 5-cm hot spot at the far end of 24-km single mode fiber by employing a 50-cm spatial resolution DPP-BOTDA with only 1GS/s sampling rate (corresponding to 10 cm/point). The BFS at the far end of 24-km sensing fiber has been measured with 0.54 MHz standard deviation which corresponds to a 0.5°C temperature accuracy. This technique is simple and cost effective because it is implemented using the similar experimental setup of the standard BOTDA, however, it should be noted that the consecutive small-scale events have to be separated by a minimum length corresponding to the spatial resolution defined by the pulse width difference.

Very recently, for higher-speed distributed measurements of strain and temperature, we have developed a new configuration of Brillouin optical correlation-domain reflectometry (BOCDR) — slope-assisted (SA-) BOCDR —, which utilizes the spectral power of Brillouin gain spectrum. Its basic operation has already been clarified and further studies are being carried out extensively. However, a detailed study on the measurement sensitivity has not been performed yet. Hence, in this work, we experimentally investigate how the spatial resolution and the incident power affect the measurement sensitivity of SA-BOCDR.

We propose a method to manipulate the SBS process in optical fiber. By adjusting its doping level and structure, a desired single-peak BGS with a bandwidth of ∼17MHz and a Brillouin gain coefficient of ∼2.45 m−1·W−1 can be achieved.

The impact of probe power on the distortions of both pump pulse and Brillouin gain/loss spectrum in single-tone probe based BOTDA system is experimentally investigated for the first time. The results indicate probe power limitations in a couple of recent techniques, offering practical probe power thresholds securing the robustness in such methods.

This paper proposes a novel method based on differential π-phase-shift long-pulse-width pair to narrow the Brillouin gain spectrum for improving the frequency accuracy in Brillouin optical time-domain analysis (BOTDA) system. This is the first approach to reduce the bandwidth of Brillouin gain spectrum for distributed sensing to the best of our knowledge. The temporal and spectral Brillouin responses for the proposal are analytically solved, and the key parameters such as pulse width and the length of π-phase-shift pulse section are investigated. Theoretical analysis and experimental results demonstrate that the proposal could achieve 17 MHz Brillouin gain spectrum bandwidth and a fixed spatial resolution of 2.5 m simultaneously, without signal-to-noise ratio penalty. This Brillouin gain spectrum is 3 times narrower than that obtained using standard single-pulse based BOTDA method with same spatial resolution, resulting in3times frequency accuracy improvement. Furthermore, such a significantly narrowed Brillouin gain spectrum provides more tolerance to the small temperature change when hot spots are introduced, giving rise to the sharper rising/falling edge of the Brillouin frequency shift profile along the sensing fiber. This way, more precise temperature/strain measurement can be obtained.

Brillouin gain spectra (BGS) in an As2Se3 photonic crystal fiber (PCF) are investigated numerically. The profiles of the BGS are simulated by calculating the characteristics of different-order optical and acoustic waves in the PCFs with different core diameters. For the small-core PCF, there are two peaks in BGS, but there is only one peak for the large-core PCF. We also reveal that in the small-core PCF, the difference of Brillouin frequency shift between the LP01 and LP11 modes is obvious, while it is not obvious in the large-core PCF. The Brillouin threshold increases with the core diameter increasing.

A triple Brillouin frequency spacing Brillouin fiber laser sensor for temperature measurement is proposed and demonstrated. Fiber under test 1 (FUT1) with 10 km SMF and FUT2 with 5 km SMF are used as Brillouin gain medium and generate the 1st-order Stokes (S1) and 3rd-order Stokes (S3) and 2nd-order Stokes (S2) respectively. Only the pump and S3 circulate in the ring with two optical circulators of three and four port. External perturbations can be effectively reduced and Brillouin gain bandwidth not is deteriorated with 10 MHz bandwidth. About 3 MHz/°C sensitivity is consistent with the theoretical value and ±0.05 dB power fluctuation and 0.2 °C temperature stability are obtained. The proposed structure makes it convenient for more applications.

Theoretical investigations of stimulated brillouin scattering-based tunable slow light in (i) Er-doped tellurite and (ii) undoped tellurite fibers are reported. Maximum allowable pump power for undistorted output pulse, Brillouin gain, time-delay, figure-of-merit, and time-delay slop efficiency of both the fibers has been obtained. We have found that (i) Brillouin gain up to ~91 dB and time delay of 140 ns can be achieved using 1100 mW pump power in 2 m Er-doped fiber and (ii) Brillouin gain up to ~86 dB and time delay of ~227 ns using 23 mW pump power in 100 m undoped tellurite fiber can be achieved. Simulated results indicate that the time delay in fibers can be tuned with the pump power to obtain tunable slow light features in these fibers. We feel that detailed theoretical investigations and simulations carried out in the study have potential impact in the design and development of slow light-based photonic devices.

In this study, the impact of Stimulated Brillouin Scattering (SBS) and effective core area and the Brillouin gain coefficient on On-Off Key (OOK) and phase modulation formats is investigated. In comparison with OOK formats, Return to Zero-Differential Phase Shift Keying (RZ-DPSK) revealed more robustness against the SBS effect with regards to jitter. The generated jitter due to power increment from 0 to 6 dBm was measured. The results show 0.1232, 0.1054, 0.0683 and 0.0544 bit period jitter for NRZ-OOK, RZ-OOK 0.5, NRZ-DPSK and RZ DPSK respectively. Furthermore, it is shown that SBS effect changes the behavior of system with regards to bit rate variation. It is shown that lower bit rate, does not guarantee higher performance. For instance, while the log BER at 2 Gb/sec is -11 for RZ-OOK 0.5, -9 for CSRZ,-10 for NRZ-DPSK and -16 for RZ-DPSK, at 8 Gb/sec they hit a peak with -16, -20, -21 and -36, respectively.

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 ( ${\sim}{\rm 100}~{\rm Hz}$ at ${\sim}{\rm 1}\hbox{-}{\rm kHz}$ 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.

We theoretically and experimentally investigate the conditions of obtaining a narrowband flat-top Brillouin gain spectrum (BGS) based on single-frequency and multi-frequency phase modulations. Using the unequal-amplitude spectral lines, the flat-top BGS can be realized by controlling the intensity ratio and the frequency separation between them. In experiment, we obtain the flat-top gain spectra with the bandwidths of 40 MHz and 125 MHz, and with the top fluctuation of less than 0.21 dB. Based on this, we also achieve low distortion Brillouin amplification of a probe signal pulse and spectrum.

We have experimentally investigated spatial-division multiplexed (SDM) Brillouin optical time-domain analysis in a heterogeneous multicore fiber whose central core and six outer cores are made from different preforms, showing a ∼70 MHz Brillouin frequency shift (BFS) difference between them. It reveals that the heterogeneous central core and the outer cores have different temperature sensitivities, but their strain sensitivities are almost the same. By making use of the distinct temperature coefficients of these two kinds of cores, simultaneous and discriminative temperature and strain measurements are achieved. The bending-induced Brillouin gain spectrum (BGS) broadening issue in off-center cores has been clarified, and a solution has been proposed to eliminate the uncertainty caused by a bending-induced BFS shift, by averaging the BFS variations of two symmetrical outer cores. We show a new perspective for discriminative measurement in Brillouin distributed sensors based on SDM solutions.

We demonstrate a novel technique for distributed Brillouin frequency estimation by fitting the Brillouin transfer function directly in the complex domain. Experimental results show the uncertainty of Brillouin frequency can be significantly reduced compared with the approaches based solely on Brillouin gain or phase. Refereed/Peer-reviewed

The Brillouin backscattered wave was examined in a short-length single-mode fiber at different ambient temperatures using a 1553-nm wavelength laser source. To obtain Brillouin scattering depending on the temperature change in a 95-m long single-mode fiber cable, the Brillouin optical time domain reflectometry (BOTDR) technique was used. In this technique, a 1553 nm wavelength signal was sent from one side of the test fiber. The FC/APC connector was attached to the other end of the test fiber. The temperature parameters of the single-mode fiber cables of different brands and types can be obtained using Brillouin scattering. The Brillouin frequency shift is found 0.93 MHz/$^{\circ}$C. Measured linear change demonstrated its use as the temperature sensor of Brillouin Scattering.

A true-time-delay(TTD) element is demonstrated using on-chip stimulated Brillouin scattering. Record net-Brillouin-gain of 47dB enabled 4ns delay over 100MHz and phase-shift of ∼200°. The TTD element was validated by incorporating it in a two-tap filter.

We simulate giant sideband-resolved interaction between telecom photons and megahertz phonons traveling along a silicon double-slot waveguide. The calculations predict a Rabi flop length below 100 μm and a Brillouin gain coefficient above 109 W−1m−1.

A multi-wavelength Brillouin Erbium Fiber laser (BEFL) with single Brillouin frequency spacing and pulsing characteristics is demonstrated. The proposed multi-wavelength BEFL uses two optical circulators to route the Brillouin Stokes and Brillouin pump (BP) into the cavity. Multi-wavelength combs with 20 lines and spacing of 0.086 nm is obtained by using the non-zero dispersion shifted fiber (NZ-DSF) as the Brillouin gain medium (BGM) and 5 lines with 0.079 nm spacing with 500 m long SMF. Pulsing characteristic is also observed in both multi-wavelength BEFLs. The measured repetition rate are in the kilohertz range due to the long cavity.

We evaluate the Brillouin frequency shift (BFS) determination error when using the Brillouin phase spectrum (BPS) instead of the Brillouin gain spectrum (BGS) in BOTDA setups. We compare the error obtained in the BFS determination in both cases, both with theoretical arguments and experimental data. In comparison to the gain, for an equal SNR and linewidth, the phase generally provides a better fit of the BFS for smaller frequency spans. This result opens a possible way to reduce the measurement time of certain BOTDA systems by using the phase feature, Ministerio de Economía y Competitividad, Comunidad de Madrid, Universidad de Alcalá, European Commission

By analyzing the operation of the slope assisted Brillouin Optical Time-Domain Analysis (BOTDA) method, it comes out that the acquisition rate is practically limited by two fundamental factors: the polarization scrambling frequency and the phase noise from the laser. As regards polarization scrambling, we show experimentally that the scrambling frequency poses a limit on the maximum acquisition rate for a given averaging factor. As regards phase noise, we show numerically and experimentally that the slope assisted method is particularly sensitive to the laser phase noise, due to the specific positioning of the pump-probe frequency shift on the Brillouin Gain Spectrum (BGS).

Optical fibres heavily doped with alumina are shown to exhibit an exceptionally low Brillouin gain coefficient and an athermal Brillouin frequency response. Such fibres could prove useful for applications that employ fibre sensing or require high-power fibre laser systems.

We have developed a theoretical approach to simulate stimulated Brillouin scattering (SBS) generation in photonic crystal fiber (PCF). The threshold condition for the SBS occurrence has been derived as a function of fiber parameters and input pump power. A particular emphasis is given to the influence of the input pump power and fiber length on the Brillouin gain in the PCF. To assess threshold pump power accurately, the pump depletion effect has been included by employing the 1% criterion. This simulation can anticipate the Brillouin threshold gain value precisely. The threshold gain varies from 14 to 18 depending on the PCF length.

We studied the impact of optical pulse coding techniques on Brillouin optical time-domain analysis (BOTDA) systems experimentally. The results show that complementary-coding-based schemes can provide significant enhanced signal-to-noise ratio (SNR) to the BOTDA system. Using complementary coding, the average time can be reduced significantly and so does the measurement time. The complementary-coded pulses with individual pulse duration of 0.1 ns allowed us to realize temperature sensing over 50 m of single-mode fiber with 1-cm spatial resolution.

We review the fundamental properties of Brillouin scattering in a perfluorinated graded-index polymer optical fiber (PFGI-POF) with 120 μm core diameter. The experiments were performed at 1.55 μm telecommunication wavelength. The Brillouin frequency shift (BFS) and the Brillouin bandwidth were 2.83 GHz and 105 MHz, respectively. The Brillouin gain coefficient was calculated to be 3.09 × 10−11 m/W, which was comparable to that of fused silica fibers. The Brillouin threshold power of the 100 m POF was estimated to be as high as 24 W, which can be, for practical applications, reduced by using POFs with smaller cores. These properties were compared with those of silica-based graded-index multi-mode fibers. We also investigated the BFS dependences on strain and temperature. They showed negative dependences with coefficients of −121.8 MHz/% and −4.09 MHz/K, respectively, which are −0.2 and −3.5 times as large as those in silica fibers. These BFS dependences indicate that the Brillouin scattering in PFGI-POFs can be potentially applied to high-accuracy temperature sensing with reduced strain sensitivity.

We present measurements of the Brillouin frequency shift in an optical fiber using a 1550 nm distributed feedback laser diode(DFB-LD) as a light source. By modulating the probe light with an electro-optic modulator, we confirm the stimulated Brillouin gain spectrum(BGS) and spontaneous BGS using the coherent detection method. We also confirm the applicability of the technique to distributed temperature sensors that measure the change in Brillouin frequency shift due to temperature variations.

A technique to develop all-fiber devices based on the customization of Brillouin gain spectrum is proposed in this article. It is based on the proper concatenation and elongation of optical fibers. To check experimentally the proposed technique, an optical device with a “like W” stimulated Brillouin scattering shape was implemented. Our experiment shows a 3-dB bandwidth of 219 MHz with two reject bands placed at 10.7855 and 10.876 GHz, respectively, from the pump wavelength. Optical devices such as Brillouin amplifiers or Brillouin filters can be developed using the proposed technique. © 2010 Wiley Periodicals, Inc. Microwave Opt Technol Lett 52:787–790, 2010; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/mop.25033

The Brillouin fiber amplifier (BFA) has been used in Brillouin optical time (frequency) domain analyzer based sensors. The performance of this sensor depends on pump depletion which occurs when the threshold is reached and when the Brillouin gain is saturated. Although threshold definitions are common for Brillouin fiber generators (BFG), there is no explicit threshold definition for BFA. More importantly we find the maximum gain point corresponds to the optimized distributed sensing system where the depletion effect remains small to moderate. We find that only the method based on the determination of the power for which the pump becomes depleted, and hence, the Stokes gain saturated (i.e. inflexion method), remains valid for BFA. We also derive an analytical relation accounting for the various sensor key parameters such as fiber type and length as well as input Stokes power. The thresholds obtained with the analytical relation are within 10% of experimental and numerical values, which is maximum power that can be launched for a given optimum sensing configuration.

Tento dokument je zaměřen na simulaci a analýzu S-band multi-vlnových délek výkonného Ramanova laseru Brillouine s využitím vláken Bragg a Ramanového zesilovače v kruhové dutině. Raman zesilovače se používají pro zesílení signálu průměrného výkonu modelu. This paper is focusing on simulation and analyzing of S-band multi-wavelength Brillouine Raman fiber laser performance utilizing fiber Bragg grating and Raman amplifier in ring cavity. Raman amplifier average power model is employed for signal amplification