Showing papers on "Brillouin scattering published in 2011"

Recent progress in Brillouin scattering based fiber sensors.

Abstract: Brillouin scattering in optical fiber describes the interaction of an electro-magnetic field (photon) with a characteristic density variation of the fiber. When the electric field amplitude of an optical beam (so-called pump wave), and another wave is introduced at the downshifted Brillouin frequency (namely Stokes wave), the beating between the pump and Stokes waves creates a modified density change via the electrostriction effect, resulting in so-called the stimulated Brillouin scattering. The density variation is associated with a mechanical acoustic wave; and it may be affected by local temperature, strain, and vibration which induce changes in the fiber effective refractive index and sound velocity. Through the measurement of the static or dynamic changes in Brillouin frequency along the fiber one can realize a distributed fiber sensor for local temperature, strain and vibration over tens or hundreds of kilometers. This paper reviews the progress on improving sensing performance parameters like spatial resolution, sensing length limitation and simultaneous temperature and strain measurement. These kinds of sensors can be used in civil structural monitoring of pipelines, bridges, dams, and railroads for disaster prevention. Analogous to the static Bragg grating, one can write a moving Brillouin grating in fibers, with the lifetime of the acoustic wave. The length of the Brillouin grating can be controlled by the writing pulses at any position in fibers. Such gratings can be used to measure changes in birefringence, which is an important parameter in fiber communications. Applications for this kind of sensor can be found in aerospace, material processing and fine structures.

Stimulated optomechanical excitation of surface acoustic waves in a microdevice.

Abstract: Brillouin interactions between sound and light can excite mechanical resonances in photonic microsystems, with potential for sensing and frequency reference applications. The authors demonstrate experimental excitation of mechanical resonances ranging from 49 to 1,400 MHz using forward Brillouin scattering.

Slope-assisted fast distributed sensing in optical fibers with arbitrary Brillouin profile.

Abstract: We present a novel method, based on stimulated Brillouin scattering (SBS), for the simultaneous distributed measurement of fast strain variations along the entire length of the sensing fiber. A specially synthesized and adaptable probe wave is used to place the Brillouin interaction always on the slope of the local Brillouin gain spectrum, allowing a single pump pulse to sample fast strain variations along the full length of a fiber with an arbitrary distribution of the Brillouin frequency shift. In this early demonstration of the method, strain vibrations of a few hundred Hz are demonstrated, simultaneously measured on two different sections of an 85m long fiber, having different static Brillouin shifts and with a spatial resolution of 1.5m.

Widely Tunable Single-Passband Microwave Photonic Filter Based on Stimulated Brillouin Scattering

Abstract: A new ultrawide continuously tunable single-passband microwave photonic filter with very high resolution, is presented. It is based on a stimulated Brillouin scattering technique using a phase modulated optical signal and a dual-sideband suppressed-carrier pump. Results are presented which demonstrate a 1- to 20-GHz measured tuning range, together with continuous tuning, extremely high resolution with a -3-dB bandwidth of only 20 MHz, a single passband, shape-invariant tuning, and a high out-of-band rejection of 31 dB.

Multistage VIPA etalons for high-extinction parallel Brillouin spectroscopy

Abstract: We demonstrate a high-resolution high-extinction parallel spectrometer for Brillouin spectroscopy of turbid samples. Cascading multiple VIPA etalons in the cross-axis configuration allowed us to achieve a high extinction ratio of up to 80 dB with sub-GHz resolution. Using a three-stage VIPA, we obtained the Brillouin spectra from Intralipid solutions at concentrations up to 10%.

Brillouin scattering gain bandwidth reduction down to 3.4MHz.

Abstract: We present a simple method for the stimulated Brillouin scattering (SBS) gain bandwidth reduction in an optical fiber. We were able to reduce the natural bandwidth of 20MHz to around 3.4MHz by a superposition of the gain with two losses produced by the same source. This reduced bandwidth can drastically enhance the performance of many different applications which up to now were limited by the minimum of the natural SBS bandwidth.

Stimulated Brillouin scattering slow light in optical fibers [Invited]

Abstract: Stimulated Brillouin scattering (SBS) has become a favorable underlying mechanism in many demonstrations of all-optical variable delay in standard fibers, often referred to as slow and fast light. Over 100 journal papers and numerous conference sessions have been dedicated to SBS slow light since 2005. In this paper, recent research in this area is reviewed. Following a short introduction to the topic, several specific trends in contemporary work are highlighted: the optimization of the SBS pump spectrum for extended slow light delay and reduced pulse distortion; SBS slow light demonstrations in nonstandard, highly nonlinear fibers; applications of SBS slow light to the delay of analog waveforms; and the role of polarization. Finally, a brief concluding perspective is provided.

Band diagram of spin waves in a two-dimensional magnonic crystal.

Abstract: The dispersion curves of collective spin-wave excitations in a magnonic crystal consisting of a square array of interacting saturated nanodisks have been measured by Brillouin light scattering along the four principal directions of the first Brillouin zone. The experimental data are successfully compared to calculations of the band diagram and of the Brillouin light scattering cross section, performed through the dynamical matrix method extended to include the dipolar interaction between the disks. We found that the fourfold symmetry of the geometrical lattice is reduced by the application of the external field and therefore equivalent directions of the first Brillouin zone are characterized by different dispersion relations of collective spin waves. The dispersion relations are explained through the introduction of a bidimensional effective wave vector that characterizes each mode in this magnonic metamaterial.

Distributed Brillouin sensing with sub-meter spatial resolution: modeling and processing

Abstract: A general analytic solution for Brillouin distributed sensing in optical fibers with sub-meter spatial resolution is obtained by solving the acoustical-optical coupled wave equations by a perturbation method. The Brillouin interaction of a triad of square pump pulses with a continuous signal is described, covering a wide range of pumping schemes. The model predicts how the acoustic wave, the signal amplitude and the optical gain spectral profile depend upon the pumping scheme. Sub-meter spatial resolution is demonstrated for bright-, dark- and π-shifted interrogating pump pulses, together with disturbing echo effects, and the results compare favorably with experimental data. This analytic solution is an excellent tool not only for optimizing the pumping scheme but also for post-processing the measured data to remove resolution degrading features.

Complete All-Optical Silica Fiber Isolator via Stimulated Brillouin Scattering

Abstract: This study demonstrates the theoretical operation of an all-optical silica fiber isolator using stimulated Brillouin scattering. Two pump sources that copropagate through a double-mode fiber generate acoustic waves through electrostriction. These acoustic waves then induce unidirectional interband optical transitions between a separate pair of signal sources. With 1 W of total input pump power, complete optical isolation is achieved with a silica rod waveguide of radius 0.67 μm over a length of approximately 12 m, with pumps operating at a wavelength of 1.55 μm and signals at 1.50 μm.

Spatially resolved Brillouin spectroscopy to determine the rheological properties of the eye lens

Abstract: Presbyopia is closely associated with the loss of accommodation, and hence with a decline in the viscoelastic properties of the human eye lens. In this article we describe a method for obtaining spatially resolved in vivo measurements of the rheological properties of the eye lens, based on the spectroscopic analysis of spontaneous Brillouin scattering using a virtually imaged phased array (VIPA). The multi-pass configuration enhances resolution to the extent that measurements are possible in elastic biological tissue characterized by intense scattering. We also present spatially resolved measurements obtained in extracted animal eyes and lenses. The results yield entirely new insights into the aging process of the eye lens.

Fundamentals of Nonlinear Optics

Abstract: Introduction Historical Background Unifying Themes Overview of Nonlinear Effects Covered in this Book Labeling Conventions and Terminology Units Linear Optics Introduction Tensor Properties of Materials Wave Equation Determining e-Waves and o-Waves in Crystals Index Ellipsoid Applications Introduction to the Nonlinear Susceptibility Introduction Classical Origin of the Nonlinearity Details of the Nonlinear Susceptibility, chi(2) Connection between Crystal Symmetry and the d-Matrix Electro-Optic Effect Three-Wave Processes in the Small-Signal Regime Introduction to the Wave Equation for Three Fields Birefringent Phase Matching Tuning Curves and Phase-Matching Tolerances Taylor Series Expansion Techniques for Determining Bandwidth Noncollinear Phase Matching Quasi-Phase Matching Introduction to Quasi-Phase Matching Linear and Nonlinear Material Considerations QPM with Periodic Structures QPM Calculation: An Example Fourier Transform Treatment of QPM Tolerances Fabricating Quasi-Phase-Matched Structures Three-Wave Mixing beyond the Small-Signal Limit Introduction DFG with a Single Strong Pump DFG with Strong Pump and Loss Solutions for All Three Coupled Amplitude Equations Spontaneous Parametric Scattering (Optical Parametric Generation) chi(2) Devices Introduction Optimizing Device Performance: Focusing Resonator Devices chi(3) Processes Introduction Nonlinear Polarization for chi(3) Processes Wave Equation for chi(3) Interactions Self-Induced Effects Parametric Amplifiers Noncollinear Processes Degenerate Four-Wave Mixing Z -Scan Raman and Brillouin Scattering Introduction Spontaneous Raman Scattering Stimulated Raman Scattering Anti-Stokes Generation Raman Amplifiers Photoacoustic Effects: Raman-Nath Diffraction Brillouin Scattering Nonlinear Optics Including Diffraction and Dispersion Introduction Spatial Effects Temporal Effects Solutions to the Nonlinear Envelope Equation Appendix A: Complex Notation Appendix B: Sellmeier Equations Appendix C: Programming Techniques Appendix D: Exact Solutions to the Coupled Amplitude Equations Index Problems, References, and Further Reading appear at the end of most chapters.

FSBS resonances observed in a standard highly nonlinear fiber

Abstract: Forward stimulated Brillouin scattering (FSBS) is observed in a standard 2-km-long highly nonlinear fiber. The frequency of FSBS arising from multiple radially guided acoustic resonances is observed up to gigahertz frequencies. The tight confinement of the light and acoustic field enhances the interaction and results in a large gain coefficient of 34.7 W−1 at a frequency of 933.8 MHz. We also find that the profile on the anti-Stokes side of the pump beam have lineshapes that are asymmetric, which we show is due to the interference between FSBS and the optical Kerr effect. The measured FSBS resonance linewidths are found to increase linearly with the acoustic frequency. Based on this scaling, we conclude that dominant contribution to the linewidth is from surface damping due to the fiber jacket and structural nonuniformities along the fiber.

0.16 nm spaced multi-wavelength Brillouin fiber laser in a figure-of-eight configuration

Abstract: A stable and compact multi-wavelength Brillouin fiber laser (BFL) operating at room temperature is experimentally demonstrated using a 100 m long photonic crystal fiber (PCF) in conjunction with a figure-of-eight configuration. At a Brillouin pump (BP) level of 15.3 dBm, 7 simultaneous lines with 20 GHz or 0.16 nm line spacing is achieved by removing the odd-order Stokes lines. The anti-Stokes lines are also generated via four wave mixing process in the laser cavity. Compared with the Erbium-based multi-wavelength laser, this BFL has advantages in term of channel spacing and flexibility in the choice of operating wavelength. The output spectrum of the proposed BFL can be tuned by 80 nm, dependent on the availability of an appropriate BP source. The multi-wavelength BFL shows a good stability with power fluctuations of less than 0.5 dB over more than 3 h.

Sharp tunable optical filters based on the polarization attributes of stimulated Brillouin scattering

Abstract: Sharp and highly-selective tunable optical band-pass filters, based on stimulated Brillouin scattering (SBS) amplification in standard fibers, are described and demonstrated. Polarization pulling of the SBS-amplified signal wave is used to increase the selectivity of the filters to 30 dB. Pump broadening via synthesized direct modulation was used to provide a tunable, sharp and uniform amplification window: Pass-band widths of 700 MHz at half maximum and 1GHz at the −20dB points were obtained. The central frequency, bandwidth and shape of the filter can be arbitrarily set. Compared with scalar SBS-based filters, the polarization-enhanced design provides a higher selectivity and an elevated depletion threshold.

Operation of Brillouin dynamic grating in single-mode optical fibers.

Abstract: The first (to our knowledge) observation of Brillouin dynamic grating in conventional single-mode fibers is reported, and the characterization is demonstrated with respect to the external parameters for the grating generation. When a 100 m single-mode fiber is used, a reflectance of 8% with a spectral bandwidth as low as 2.4 MHz is achieved, which is less than 10% of ordinary Brillouin gain bandwidth.

Nonlinear effects in optical fibers

Abstract: Preface. 1 Introduction. References. 2 Electromagnetic Wave Propagation. 2.1 Wave Equation for Linear Media. 2.2 Electromagnetic Waves. 2.3 Energy Density and Flow. 2.4 Phase Velocity and Group Velocity. 2.5 Reflection and Transmission of Waves. 2.6 The Harmonic Oscillator Model. 2.7 The Refractive Index. 2.8 The Limit of Geometrical Optics. Problems. References. 3 Optical Fibers. 3.1 Geometric Optics Description. 3.2 Wave Propagation in Fibers. 3.3 Fiber Attenuation. 3.4 Modulation and Transfer of Information. 3.5 Chromatic Dispersion in Single-Mode Fibers. 3.6 Polarization-Mode Dispersion. Problems. References. 4 The Nonlinear Schrodinger Equation. 4.1 The Nonlinear Polarization. 4.2 The Nonlinear Refractive Index. 4.3 Importance of Nonlinear Effects in Fibers. 4.4 Derivation of the Nonlinear Schrodinger Equation. 4.5 Soliton Solutions. 4.6 Numerical Solution of the NLSE. Problems. References. 5. Nonlinear Phase Modulation. 5.1 Self-Phase Modulation. 5.2 Cross-Phase Modulation. Problems. References. 6. Four-Wave Mixing. 6.1 Wave Mixing. 6.2 Mathematical Description. 6.3 Phase Matching. 6.4 Impact and Control of FWM. 6.5 Fiber Parametric Amplifiers. 6.6 Parametric Oscillators. 6.7 Nonlinear Phase Conjugation with FWM. 6.8 Squeezing and Photo-Pair Sources. Problems. References. 7 Intrachannel Nonlinear Effects. 7.1 Mathematical Description. 7.2 Intrachannel XPM. 7.3 Intrachannel FWM. 7.4 Control of Intrachannels Nonlinear Effects. Problems. References. 8 Soliton Lightwave Systems. 8.1 Soliton Properties. 8.2 Perturbation of Solitons. 8.3 Path-Averaged Solitons. 8.4 Soliton Transmission Control. 8.5 Dissipative Solitons. 8.6 Dispension-Managed Solitons. 8.7 WDM Soliton Systems. Problems. References. 9 Other Applications of Optical Solitons. 9.1 Soliton Fiber Lasers. 9.2 Pulse Compression. 9.3 Fibers Bragg Gratings. Problems. References. 10 Polarization Effects. 10.1 Coupled Nonlinear Schrodinger Equations. 10.2 Nonlinear Phase Shift. 10.3 Solitons in Fibers with Constant Birefringence. 10.4 Solitons in Fibers with Randomly Varying Birefringence. 10.5 PMD-Induced Soliton Pulse Broadening. 10.6 Dispersion-Managed Solitons and PMD. Problems. References. 11 Stimulated Raman Scattering. 11.1 Raman Scattering in the Harmonic Oscillator Model. 11.2 Raman Gain. 11.3 Raman Threshold. 11.4 Impact of Raman Scattering on Communication Systems. 11.5 Raman Amplification. 11.6 Raman Fiber Lasers. Problems. References. 12 Stimulated Brillouin Scattering. 12.1 Light Scattering at Acoustic Waves. 12.2 The Coupled Equations for Stimulated Brillouin Scattering. 12.3 Brillouin Gain and Bandwidth. 12.4 Threshold of Stimulated Brillouin Scattering. 12.5 SBS in Active Fibers. 12.6 Impact of SBS on Communication Systems. 12.7 Fiber Brillouin Amplifiers. 12.8 SBS Slow Light. 12.9 Fiber Brillouin Lasers. Problems. References. 13 Highly Nonlinear and Microstructured Fibers. 13.1 The Nonlinear Parameter in Silica Fibers. 13.2 Microstructured Fibers. 13.3 Non-Silica Fibers. 13.4 Soliton Self-Frequency Shift. 13.5 Four-Wave Mixing. 13.6 Supercontinuum Generation. Problems. References. 14 Optical Signal Processing. 14.1 Nonlinear Sources for WDM Systems. 14.2 Optical Regeneration. 14.3 Optical Pulse Train Generation. 14.4 Wavelength Conversion. 14.5 All-Optical Switching. Problems. References. Index.

High power narrow-band fiber-based ASE source

Abstract: In this paper we describe a high power narrow-band amplified spontaneous emission (ASE) light source at 1030 nm center wavelength generated in an Yb-doped fiber-based experimental setup. By cutting a small region out of a broadband ASE spectrum using two fiber Bragg gratings a strongly constrained bandwidth of 12 ± 2 pm (3.5 ± 0.6 GHz) is formed. A two-stage high power fiber amplifier system is used to boost the output power up to 697 W with a measured beam quality of M2≤1.34. In an additional experiment we demonstrate a stimulated Brillouin scattering (SBS) suppression of at least 17 dB (theoretically predicted ~20 dB), which is only limited by the dynamic range of the measurement and not by the onset of SBS when using the described light source. The presented narrow-band ASE source could be of great interest for brightness scaling applications by beam combination, where SBS is known as a limiting factor.

Impact of Raman scattering and modulation instability on the performances of Brillouin sensors

Abstract: The impact of Raman scattering and modul ation instability is studied in Brillouin time-domain analysis systems. It turns out to be very detrimental for long-range sensing as a result of the extended interaction length combined to the high pump peak pulse power. The conditions under which these effects limit the sensing range are determined and the modeling is very well confirmed by experimental results. Keywords: Fibre optics, optical fibre sensor, stimulated Brillouin scattering, distributed fibre sensor, non-linear optics, stimulated Raman scattering, modulation instability. 1. INTRODUCTION The recent raising interest in Brillouin fiber sensors for application in civil engineering, in oil & gas industry, in perimeter security and in intrusion detection has stimulated the research efforts to extend the detection range. In time-domain distributed Brillouin sensors (BOTDA) pulses are used to interrogate locally the interaction along the fiber. In order to achieve better performances in terms of range and spatial resolution, pump pulse and signal powers must be raised. These powers cannot be made arbitrarily large and must be kept below the observation threshold of any other noise-fed nonlinear effects. In these systems the most critical nonlinear effects are those in which a signal wave is amplified through a forward interaction, in other words when the background noise is amplified while co-propagating with the pump pulse. In such a situation the interaction length may cover many tens of kilometers and even a weak nonlinear amplification much less efficient than stimulated Brillouin scattering (SBS) may result in a large amplified spontaneous signal that eventually depletes the pump. The id entified nonlinear effects are the modulation instability (MI), which occurs only in fibers presenting an anomalous dispersion at the pump wavelength, and the Raman scattering (RS). A spectral self-broadening of the pump due to MI was observed in sensors based on spontaneous Brillouin scattering

SBS-Based Fiber Optical Sensing Using Frequency-Domain Simultaneous Tone Interrogation

Abstract: A frequency-sweep-free method for stimulated Brillouin scattering (SBS)-based sensing is proposed, having the potential for fast acquisition characteristics. The Brillouin gain spectrum and the Brillouin frequency shift are determined using multiple frequency tones for both the probe and pump. While in this paper, continuous wave probe and pump waves are used to prove the feasibility of the concept, an extension to fast distributed sensing, using pulsed pumps, is also described.

On-chip stimulated Brillouin scattering

Abstract: We report the first demonstration of on-chip stimulated Brillouin scattering (SBS). SBS is characterized in a chalcogenide (As 2 S 3 ) photonic chip where the measured Brillouin shift and full-width at half-maximum (FWHM) linewidth are 7.7 GHz and 34 MHz respectively. The measured Brillouin gain coefficient (g B ) is 0.715 x 10 -9 m/W, consistent with the theoretical estimate. Keywords: stimulated Brillouin scattering, on-chip,chalcogenide 1. INTRODUCTION Stimulated Brillouin scattering (SBS) is an inelastic scattering process, which results from the interaction of photons with acoustic phonons in a medium [1]. SBS has been exploited in optical fibers to enable a number of important applications such as Brillouin lasers, slow-light, microwave (MW) generation, optical signal-to-noise ratio (OSNR) monitoring, slow-light based true time delay, opto-mechanical oscillator and tailoring optical forces [2-17] . Recently, SBS was characterized in a photonic crystal fiber (PCF) where the strong optical-acoustic confinement allows efficient SBS process [18, 19]. While there have been several detailed studies, both theoretical and experimental, of SBS in optical fibers, the ability to harness SBS in a chip scale device holds the key to realize light-sound and light-light interaction in an integrated optical structure. Realization of on-chip SBS, however, is challenging because many of the optical materials, commonly used in nonlinear optics, have very low Brillouin scattering cr oss-section and therefore long lengths are required at moderate pump powers. Chalcogenide glass, on the other hand, has very large Kerr nonlinearity [20] and Brillouin gain, which enables SBS realization in short fiber length. In this paper, we report our recent results on SBS generation in a chip scale device [21]. SBS was characterized in a 7 cm long chalcogenide (As

Cavity enhanced stimulated Brillouin scattering in an optical chip for multiorder Stokes generation

Abstract: The support of the Australian Research Council (ARC) through its Discovery grant (DP1096838), Centre of Excellence scheme and Federation Fellowship is acknowledged.

Detrimental effect of self-phase modulation on the performance of Brillouin distributed fiber sensors

Abstract: We show that the spectral broadening of the pump pulse through self-phase modulation in a time-domain distributed Brillouin sensor has a considerably detrimental effect in the measurement, especially in the case of long distances and high-resolution pulses. Using 30ns pump pulses with peak power of 276mW, self-phase modulation leads to a doubling of the effective gain linewidth after some 20km, which is equivalent to a contrast loss of 2dB in the measurement. The impact is higher for shorter pulses (higher resolution). The theoretical modeling is fully confirmed by experimental results.

Highly coherent terahertz wave generation with a dual-frequency Brillouin fiber laser and a 1.55 μm photomixer

Abstract: Thanks to a portable dual-frequency Brillouin fiber laser and a 1.55 μm photomixer, we report the generation of a highly coherent kilohertz level submillimeter wave emission. Low-cost telecommunications components are used to achieve very simple source architecture. The photomixer is composed of a unitravelling carrier photodiode integrated with an antenna. An emission at 316 GHz is observed and analyzed thanks to heterodyne detection with a signal-to-noise ratio >65 dB and a ~1 kHz linewidth. The phase noise of the proposed source has the same performance at 1.7 and 316 GHz. We show that this source has comparable or better phase noise compared to electrical oscillators and the tunability is much wider.

Narrow linewidth power scaling and phase stabilization of 2-μm thulium fiber lasers

Abstract: Thulium-doped fiber lasers (TFLs) emitting retina-safe 2-μm wavelengths offer substantial power-scaling advantages over ytterbium-doped fiber lasers for narrow linewidth, single-mode operation. This article reviews the design and performance of a pump-limited, 600 W, single-mode, single-frequency TFL amplifier chain that balances thermal limitations against those arising from stimulated Brillouin scattering (SBS). A simple analysis of thermal and SBS limits is anchored with measurements on kilowatt class Tm and Yb fiber lasers to highlight the scaling advantage of Tm for narrow linewidth operation. We also report recent results on active phase-locking of a TFL amplifier to an optical reference as a precursor to further parallel scaling via coherent beam combining.

Acoustic coefficients of P_2O_5-doped silica fiber: acoustic velocity, acoustic attenuation, and thermo-acoustic coefficient

Abstract: We present measurements and modeling of the effect of P2O5 doping on the acoustic damping and temperature sensitivity coefficients of silica fibers. In particular, the Brillouin gain spectrum of a highly P-doped fiber is measured and investigated at different temperatures. It is found that the acoustic damping coefficient (proportional to the Brillouin spectral width) of phosphorus pentoxide (1.41 × 105 m−1 for bulk P2O5 at 11 GHz) is similar to, but larger than, that of germanium dioxide. Additionally, the acoustic velocity (and thereby the Stokes’ shift) is found to be much less dependent on temperature in P2O5 ( + 0.12 m/s/°C) than in SiO2 ( + 0.56 m/s/°C). Using these coefficients (the thermo-acoustic coefficients), the modeled and unique slopes of the Stokes’-shift-versus-temperature curves for the four observed acoustic modes each lie within 3% of the measured values. Finally, utilizing both the thermo-optic and thermo-acoustic coefficients, a design example is presented where a composition is determined for which the dependence of the Brillouin frequency shift on temperature is minimized. In this example, the calculated temperature sensitivity is less than 5 kHz/°C over the temperature range −100 °C < T < 100 °C for the molar composition 0.54P2O5:0.46SiO2.

Streicker Bridge: a comparison between Bragg-grating long-gauge strain and temperature sensors and Brillouin scattering-based distributed strain and temperature sensors

Abstract: The Streicker Bridge at Princeton University campus has been equipped with two fiber-optic sensing technologies: discrete long-gauge sensing, based on Fiber Bragg-Gratings (FBG), and truly-distributed sensing, based on Brillouin Optical Time Domain Analysis (BOTDA). The sensors were embedded in concrete during the construction. The early age measurements, including hydration swelling and contraction, and post-tensioning of concrete were registered by both systems and placed side by side in order to compare their performances. Aside from the usual behavior, an unusual increase in strain was detected by several sensors in various cross-sections. The nature of this event is still under investigation, but preliminary study indicates early-age cracking as the cause. The comparison between the two monitoring systems shows good agreement in the areas where no unusual behavior was detected, but some discrepancies are noticed at locations where unusual behavior occurred and during the early age of concrete. These discrepancies are attributed to the spatial resolution of the distributed monitoring system and the temperature influences at early age. In this paper, general information concerning the Streicker Bridge project is given. The monitoring systems and their specifications are briefly presented. The monitoring data are analyzed and a comparison between the two systems is performed.

One-laser-based generation/detection of Brillouin dynamic grating and its application to distributed discrimination of strain and temperature.

Abstract: This paper presents a novel scheme to generate and detect Brillouin dynamic grating in a polarization-maintaining optical fiber based on one laser source. Precise measurement of Brillouin dynamic grating spectrum is achieved benefiting from that the pump, probe and readout waves are coherently originated from the same laser source. Distributed discrimination of strain and temperature is also achieved with high accuracy.

Ultrasonic wave transport in a system of disordered resonant scatterers: Propagating resonant modes and hybridization gaps

Abstract: We present the results of ultrasonic pulse propagation experiments on suspensions of plastic spherical scatterers immersed in water. This system was selected to study the effects of scattering resonances on wave transport. By separating the coherent ballistic component from the multiply scattered wave field, both the dispersion relations and the diffusive propagation of ultrasound were investigated. We show that the dispersion relation is marked by a series of hybridization gaps due to the coupling between the propagating modes of surrounding fluid and the scattering resonances. Effects of dissipation on the formation of the gaps were investigated. We find evidence in our ultrasonic data for the existence of a (slowly propagating) second longitudinal mode, also seen in Brillouin scattering experiments, that arises from the coupling between the resonant scatterers. These results are interpreted with an effective medium model based on the spectral function approach, which gives an excellent description of the dispersion relations in this system. Measurements of the multiply scattered ultrasound allow both the diffusion coefficient and the absorption time to be measured as a function of frequency. The relationship between the diffusion coefficient and the ballistic data is discussed, while the measurement of the absorption time from the decay of the multiply scattered coda enables the absorption and scattering lengths to be separated. These ultrasonic measurements and their interpretation based on the spectral function approach give a very complete picture of wave transport in this strongly scattering resonant system.