Showing papers on "Brillouin scattering published in 1993"
TL;DR: A novel distributed temperature sensor that uses the temperature dependence of the frequency at which the loss is maximized in the interaction between a cw laser and a pulsed laser with a 32-km sensing length is presented.
Abstract: We present a novel distributed temperature sensor that uses the temperature dependence of the frequency at which the loss is maximized in the interaction between a cw laser and a pulsed laser. With a 32-km sensing length, a temperature resolution of 1°C has been achieved; it is also shown that a spatial resolution of 5 m may be obtained.
229 citations
TL;DR: An experimental distributed temperature sensor that uses the temperature dependence of the Brillouin frequency shift and has observed a temperature resolution of 1 degrees C and obtained a spatial resolution of 10 m.
Abstract: We describe an experimental distributed temperature sensor that uses the temperature dependence of the Brillouin frequency shift. When a 22.2-km sensing length is used, we have observed a temperature resolution of 1°C and have obtained a spatial resolution of 10 m.
166 citations
TL;DR: In this article, an optical fiber cable that can suppress stimulated Brillouin scattering (SBS) has been developed, which was caused by a sinusoidal fiber strain distribution of + or 0.35%, which was generated in fiber by a strain holding, double-stranded cable.
Abstract: An optical fiber cable that can suppress stimulated Brillouin scattering (SBS) has been developed. Fiber cabling expanded the Brillouin gain bandwidth from 50 MHz to 400 MHz (9 dB). The expansion was caused by a sinusoidal fiber strain distribution of +or-0.35%, which was generated in fiber by a strainholding, double-stranded cable. This work explains the relationship between the cable structure and fiber strain, as well as with the Brillouin gain bandwidth expansion. Fiber loss caused by cabling was studied and found to be small; also, the strained fiber reliability of the cable is assured with the use of carbon-coated fiber. >
133 citations
TL;DR: In this article, the SBS threshold can be increased by providing a low frequency sine wave dither to the laser pre-bias current, which is shown to increase the bit error rate.
Abstract: The stimulated Brillouin scattering (SBS) process limits the maximum power that can be transmitted in low-loss optical fibers in multigigabit fiber optic systems. It is shown that recently observed large optical fluctuations resulting from SBS degrade the signal-to-noise ratio and consequently the system bit error rate. Since SBS has potentially the lowest power threshold of all fiber nonlinearities: it is critical that it be addressed. It is shown that the SBS threshold can be increased by providing a low frequency sine wave dither to the laser pre-bias current. It is found that a modulation index as low as 2% can quadruple the SBS threshold. Measurements with a 1.5- mu m externally modulated laser at 2.5 Gb/s indicate that this dither in no way degrades the performance in the presence of chromatic dispersion. >
101 citations
01 Jan 1993
TL;DR: In this article, the SBS threshold can be increased by providing a low-frequency sine-wave dither to the laser pre- bias current in the presence of chro-matic dispersion.
Abstract: Severe degradations in the bit-error-rate perfor- mance in multigigabit fiber-optic systems may result from the stimulated Brillouin scattering process in optical fibers. The SBS process has long been known to limit the maximum power that can be transmitted in low-loss optical fibers. In this paper we show that recently observed large optical fluctuations result- ing from SBS degrade the signal-to-noise ratio and consequently the system bit error rate. Since SBS has potentially the lowest power threshold of all fiber nonlinearities, it is critical that it be addressed. It is shown that the SBS threshold can be increased by providing a low-frequency sine-wave dither to the laser pre- bias current. We find that a modulation index as low as 2% can quadruple the SBS threshold. Measurements with a 1.5-pm externally modulated laser at 2.5 Gb / s indicate that this dither in no way degrades the performance in the presence of chro- matic dispersion.
100 citations
TL;DR: Theoretical and experimental results for stimulated Brillouin gain spectroscopy in anisotropic media are presented in this paper, where the coupling between arbitrary pump and Stokes waves and the corresponding acoustic wave is formulated in terms of the elastic displacement vector and the photoelastic tensor.
Abstract: Theory and measurements are presented for stimulated Brillouin gain spectroscopy in anisotropic media. The coupling between arbitrary pump and Stokes waves and the corresponding acoustic wave is formulated in terms of the elastic displacement vector and the photoelastic tensor. A propagation equation that fully includes transient effects is obtained for the Stokes wave. In the limit of small-signal gains this propagation equation can be solved analytically, yielding expressions that relate experimentally accessible quantities to material properties. Absolute Brillouin steady-state gain coefficients, linewidths, and frequency shifts are thereby determined in a number of optical materials at 532 nm. The Brillouin gain coefficient for fused silica is measured by three techniques, providing the reference for absolute gain measurements. Quantitative agreement is found between theory and experiment for transient effects on stimulated Brillouin scattering.
78 citations
TL;DR: Findings settle a recent discussion about whether there are deterministically chaotic features present in the dynamics of SBS in fibers by revealing that for the limiting case of vanishing external reflectivity, the dynamics is purely stochastic.
Abstract: We report on experimental investigations of stimulated Brillouin scattering (SBS) in single-mode optical fibers, taking fully into account the influence of external feedback from the fiber ends. A threshold condition for arbitrary external reflectivity is derived. Detailed time-series analysis reveals that for the limiting case of vanishing external reflectivity, the dynamics is purely stochastic. For finite reflectivities, the observed dynamics is periodic provided environmental perturbations are suppressed. These findings settle a recent discussion about whether there are deterministically chaotic features present in the dynamics of SBS in fibers.
78 citations
TL;DR: Time-domain reflectometry of spontaneous Brillouin scattering in a single-mode optical fiber is performed with a coherent self-heterodyne detection system containing a recently proposed external frequency translator and a single light-wave source.
Abstract: Time-domain reflectometry of spontaneous Brillouin scattering in a single-mode optical fiber is performed with a coherent self-heterodyne detection system containing a recently proposed external frequency translator and a single light-wave source. The light wave is divided into probe and reference light waves. The frequency of the probe light wave is upconverted by the translator by an amount approximately equal to the Brillouin frequency shift. The frequency-converted probe is launched into the fiber and spontaneously Brillouin scattered. As the frequency of the scattered probe is downconverted to near that of the reference light wave, coherent self-heterodyne detection of spontaneous Brillouin scattering becomes possible without having to use a fast-speed detector.
77 citations
TL;DR: In this article, the sound velocities of the longitudinal and transverse vibrational modes in various directions have been measured by Brillouin scattering on high-quality twin-free single crystals of tetragonal PbTiO3.
Abstract: The sound velocities of the longitudinal and transverse vibrational modes in various directions have been measured by Brillouin scattering on high-quality twin-free single crystals of tetragonal PbTiO3. By using these velocities and the dielectric permittivity measured by the impedance method, a complete set of coefficients for the electromechanical properties has been determined at ambient temperature. They are the six elastic stiffness moduli, CEijkl, three piezoelectric stress constants, erij, and four dielectric permittivity constants, eTij and esij.
71 citations
TL;DR: This work has developed a technique for studying the elasticity of single crystals of solid hydrogen and related materials at very high pressures and used the method to determine the second-order elastic moduli of single-crystal n-type hydrogen to 24 GPa at 295 K.
Abstract: We have developed a technique for studying the elasticity of single crystals of solid hydrogen and related materials at very high pressures and used the method to determine the second-order elastic moduli of single-crystal n-type hydrogen to 24 GPa at 295 K. The method involves the measurement of acoustic velocities as a function of crystallographic direction by Brillouin scattering in a diamond anvil cell with the orientation of the single crystals determined by synchrotron x-ray diffraction. Between 6 and 24 GPa, the adiabatic bulk modulus of ${\mathrm{H}}_{2}$ increases by more than a factor of 3 and the shear modulus increases by more than a factor of 4. The acoustic anisotropy of hydrogen decreases from 11% to 6% for compressional waves and from 23% to 14% for shear waves. The data are also used to calculate thermodynamic properties of hydrogen at high pressures. By including the observed velocity anisotropy, the equation of state of ${\mathrm{H}}_{2}$ derived from Brillouin data is in agreement with previous results derived solely from x-ray diffraction.
69 citations
TL;DR: This paper used Brillouin scattering to investigate the elastic properties of water under negative pressures and found that nucleation occurs long before reaching the mechanical instability region where the bulk modulus is zero.
Abstract: Using Brillouin scattering we have investigated the elastic properties of water under negative pressures. The samples were H2O liquid–vapor inclusions in α‐quartz which could be heated to their homogenization temperatures (in the range 120–370 °C); on cooling, negative pressures as high as 1000 bars were reached before a vapor bubble nucleated. The velocity of sound results obtained from our Brillouin experiments indicate that nucleation occurs long before reaching the mechanical instability region where the bulk modulus is zero.
TL;DR: In this paper, the authors measured the overall bandwidth of guided acoustic-wave Brillouin scattering in optical fibers with different fiber core diameters and compared the relative intensity of the light scattering produced by the different acoustic modes.
Abstract: The overall bandwidth of guided acoustic-wave Brillouin scattering has been measured in optical fibers with different fiber core diameters. The relative intensity of the light scattering produced by the different acoustic modes is compared with theory and shows good agreement when the optical fiber has its polymer jacket removed. The mode intensities and linewidths in a jacketed optical fiber are modified by the selective damping of individual guided acoustic modes.
TL;DR: In this paper, the configurational compressibility of diopside and anorthite liquids has been determined from comparison between high-temperature ultrasonic (relaxed Vp) data and extrapolated Brillouin (unrelaxing Vp and Vs) values, the relative importance of vibrational and configural contributions can be markedly different for the compressibility and heat capacity of silicate melts.
Abstract: The compressional Vpand shear Vs wave velocities of diopside (CaMgSi2O6), anorthite (CaAl2Si2O8), and grossular (Ca3Al2Si3O12) glasses and liquids have been measured by high-resolution Brillouin spectroscopy up to 1200 or 1400 K. For all three materials, marked breaks in the wave velocity-temperature relationships are observed at temperatures consistent with the glass transition temperatures observed in viscosity and calorimetry experiments. From comparisons between high-temperature ultrasonic (relaxed Vp) data and extrapolated Brillouin (unrelaxed Vp and Vs) values, the configurational compressibility of diopside and anorthite liquids has been determined. The relative importance of vibrational and configurational contributions can be markedly different for the compressibility and heat capacity of silicate melts.
TL;DR: The dual-pulse-excited fiber ring is used to generate squeezed vacuum that, when injected into a measuring Mach–Zehnder interferometer, improves its sensitivity by 3 dB beyond the shot-noise limit.
Abstract: A novel scheme employing two pulses separated by a short time delay is used to cancel the phase noise from guided-acoustic-wave Brillouin scattering in a fiber ring interferometer. The dual-pulse-excited fiber ring is used to generate squeezed vacuum that, when injected into a measuring Mach–Zehnder interferometer, improves its sensitivity by 3 dB beyond the shot-noise limit.
TL;DR: Molecular dynamics calculations revealed that a pressure-induced «amorphized» solid is disordered and anisotropic but not structurally related to an isotropic quenched melt.
Abstract: Molecular dynamics calculations revealed that a pressure-induced ``amorphized'' solid is disordered and anisotropic but not structurally related to an isotropic quenched melt. The results explain the anomalous elastic behavior observed via Brillouin scattering on \ensuremath{\alpha}-quartz [L. E. McNeil and M. Grimsditch, Phys. Rev. Lett. 68, 83 (1991)]. The reversal in frequency shifts for sound propagation in the perpendicular and parallel directions is due to the unequal densification in the a and c directions. The helical chains are found to recover upon depressurizing. Anisotropy of pressure amorphized solids is thus a general property, and pressure-induced amorphization is not related to melting.
TL;DR: In this paper, the dependence of stimulated Brillouin scattering (SBS) on a graded temperature distribution applied periodically to a polarization-maintaining fiber was investigated and it was shown that SBS intensity decreases with an increase in the temperature difference.
Abstract: The dependence of stimulated Brillouin scattering (SBS) on a graded temperature distribution applied periodically to a polarization-maintaining fiber is investigated. The SBS intensity decreases with an increase in the temperature difference. SBS disappears at a 37 degrees C temperature difference, where a 10-mW pumping light of 1.319- mu m wavelength is launched into a fiber of 1.6-km length. The SBS threshold increases as the temperature difference increases. >
TL;DR: In this paper, the authors describe the principles and recent development of a new technique for measuring temperature and strain distribution using Brillouin backscattering rather than Rayleigh and Raman backscatter.
Abstract: This paper describes the principles and recent development of a new technique for measuring temperature and strain distribution using Brillouin backscatteringrather than Rayleigh and Raman backscattering. The technique is based ontemperature- and strain-induced changes in the Brillouin frequency shift. Experimental sensitivities of 1.2 MHz/K and 5.8 MHz/104 strain are demonstrated at awavelength of 1.32 rim. Two approaches for measuring the weak Brillouin line arediscussed. 1 . INTRODUCTION Fiber-optic sensor systems which can explore the distributed measurand over a wide range are categorized as being distributed or quasi-distributed1. Thedistributed fiber sensor systems usually utilize scattering in an optical fiber astheir sensing mechanism, while the quasi-distributed sensor systems or multi-pointsensor systems only employ a fiber as an optical transmission line and have discrete sensors arranged in the fiber or more complicated fiber networks. Of these, thedistributed fiber sensor systems are very attractive since they can operate over
TL;DR: In this paper, the loss and dispersion properties of fibers with a nonuniform dopant concentration along their length are investigated theoretically and simple equations are obtained for loss estimation and a design procedure by which to achieve SBS suppression.
Abstract: The loss and dispersion properties of fibers with a nonuniform dopant concentration along their length are investigated theoretically and simple equations are obtained for loss and dispersion estimation. These equations are used to discuss fiber properties and a design procedure by which to achieve SBS suppression. The loss increases by 0.02-0.03 dB/km/% and the dispersion decreases by -2.4 ps/km/nm/% as the relative-index change due to dopant increases longitudinally. It is found that a large change in the dopant concentration along a fiber is effective in suppressing SBS. >
TL;DR: In this paper, the Brillouin light scattering was used to obtain elastic and piezoelectric constants for a single domain orthorhombic KNbO3 single crystal at room temperature and pressure.
Abstract: Brillouin light scattering was used to obtain elastic and piezoelectric constants for a single domain orthorhombic KNbO3 single crystal at room temperature and pressure. More than 320 measurements of longitudinal and transverse acoustic wave velocities were obtained in 160 different crystallographic directions. An inversion of these data using the literature values for the dielectric permittivity of KNbO3 resulted in the full set of elastic and piezoelectric constants for the material. It is suggested that the difference between piezoelectric constants obtained by high‐ and low‐frequency methods could be explained by the high‐frequency relaxation‐type dispersion for the dielectric constant e33 in the GHz region by analogy with BaTiO3. The directional dependence of electromechanical coupling for longitudinal and transverse acoustic waves in KNbO3 was analyzed. The obtained elastic constants were (in GPa): CE11=224(4), CE22=273(5), CE33=245(5), CE44=75(1), CE55=28.5(5), CE66=95(2), CE12=102(5), CE13=182(10)...
TL;DR: In this article, the effects of gain and spontaneous emission on the threshold power of optical fibers are discussed, together with treatments of amplification on the line-narrowing process normally associated with stimulated Brillouin scattering in a lossy medium and the appearance of strong higher order Stokes waves.
Abstract: Stimulated Brillouin scattering in optical fibers is carefully reassessed for the case of distributed optical gain (achievable in optical fibers lightly doped with rare-earth ions) instead of the usual loss. The effects of gain and amplified spontaneous emission on the threshold power are discussed, together with treatments of the effects of amplification on the line-narrowing process normally associated with stimulated Brillouin scattering in a lossy medium and the appearance of strong higher-order Stokes waves. The implications for erbium-doped fiber amplifier systems are explored.
TL;DR: In this article, an acoustic mode frequency, lattice parameter, and refractive index measurements have been carried out on single crystals of cubic stabilized zirconia, ZrO2(xY2O3), in the temperature range 300 to 1450 K, using Brillouin scattering, x-ray diffraction, and interferometric methods, respectively.
Abstract: Acoustic mode frequency, lattice parameter, and refractive index measurements have been carried out on single crystals of cubic stabilized zirconia, ZrO2(xY2O3), in the temperature range 300 to 1450 K, using Brillouin scattering, x‐ray diffraction, and interferometric methods, respectively. Elastic constants Cij and associated quantities such as the bulk modulus B=(C11+2C12)/3, the anisotropy ratio A=2C44/(C11−C12), and the Cauchy relation failure Δ=(C12−C44) have been determined from these measurements. The results show a linear reduction in C11 , C12 , and C44 until a characteristic transition temperature Tc, which depends on the dopant concentration x. The linear decrease is understood in terms of normal thermal expansion. Above Tc (1300 K for x=9.4 mol % and 1050 K for x=24 mol %) there are elastic anomalies; significant reductions in C11, (C11‐C12)/2 and C44 occur, with an increase in C12 . These effects are considered to result from thermally generated disorder. Detailed examination of the temperatu...
Patent•
20 Oct 1993TL;DR: In this paper, an alternating waveform was employed to induce a dither upon the laser output, which caused the laser to be frequency modulated, thereby broadening the effective linewidth of the output and increasing the SBS power threshold.
Abstract: A technique for reducing the power threshold at which stimulated brillouin scattering ("SBS") occurs within an optical fiber by directly modulating a conventional laser generating an optical signal propagated along that fiber. The modulation is accomplished by employing an alternating waveform to induce a dither upon the laser output. The specific frequency of the alternating waveform is chosen to be very much lower than the low frequency cut-off of any receiver coupled to the optical fiber, but sufficiently high enough to efficiently suppress the Brillouin gain. This dithering causes the laser to be frequency modulated, thereby broadening the effective linewidth of the laser output and increasing the SBS power threshold.
TL;DR: In this article, the optical Kerr effect in a reciprocal fiber-optic Brillouin ring laser gyroscope was investigated, and it was found that the Kerr effect, as the major error source of the rotation rate measurement, causes a bias of beat frequency with nonlinear dependence on rotation rate.
Abstract: The optical Kerr effect in a reciprocal fiber-optic Brillouin ring laser gyroscope is investigated. It is found that the Kerr effect, as the major error source of the rotation rate measurement in this gyroscope, causes a bias of beat frequency with nonlinear dependence on rotation rate. A differential Stokes power of 1 mW inside the ring resonator is measured to produce a beat frequency bias of 69 Hz, which agrees well with the theoretical expectation. >
TL;DR: Using Brillouin scattering, the two independent elastic moduli of [ital a]-SiO[sub 2] are measured with increasing and decreasing pressures up to 25 GPa and an estimate of the density is obtained indirectly from the measured refractive index.
Abstract: Using Brillouin scattering we have measured the two independent elastic moduli of a-${\mathrm{SiO}}_{2}$ with increasing and decreasing pressures up to 25 GPa. For descending pressures the shear constant shows irreversible behavior similar to that previously reported for the longitudinal mode. Although the bulk modulus at a given pressure can be evaluated from the measured elastic constants, the irreversible changes which occur on densification preclude the possibility of evaluating the density as a function of pressure by an integration of the compressibility. An estimate of the density is obtained indirectly from the measured refractive index.
Patent•
11 Jun 1993
TL;DR: In this paper, an optical transmission system comprising a method and apparatus for cancelling noise in the output from a light source for broadening the line width of light source so as to increase stimulated Brillouin scattering threshold in a standard single mode fiber with a dispersion null at 1310 nm and for using a linearized external modulator to modulate the amplified output of a distributed feedback laser providing and output at 1550 nanometers.
Abstract: An optical transmission system (1) is provided comprising a method and apparatus for cancelling noise (4-6) in the output from a light source (2) for broadening the line width of a light source so as to increase stimulated Brillouin scattering threshold in a standard single mode fiber with a dispersion null at 1310 nm and for using a linearized external modulator to modulate the amplified output of a distributed feedback laser (15) providing and output at 1550 nanometers for use on a standard single mode fiber optic cable (9) with a dispersion null at 1310 nm.
TL;DR: In this paper, an experimental and theoretical study of stimulated Brillouin scattering (SBS) in laser produced plasma using a laser pump with a duration of 8-10 psec is presented.
Abstract: This paper presents an experimental and theoretical study of stimulated Brillouin scattering (SBS) in laser produced plasma using a laser pump with a duration of 8–10 psec. The experiments were performed in a preformed plasma to minimize the flow velocity and have the same plasma conditions over a large range of laser intensities. The reflectivity was then compared to theoretical results over an intensity range of 1013–2×1015 W/cm2. A short pulse was used so that the SBS was in the temporally growing regime and saturation was not an issue.
TL;DR: In this paper, the elastic constants of yttrium aluminum garnet have been measured in the temperature range 300-1450 K using a combination of Brillouin scattering and refractive index measurements.
Abstract: Elastic constants of yttrium aluminum garnet have been measured in the temperature range 300–1450 K using a combination of Brillouin scattering and refractive index measurements. Associated quantities such as the bulk modulus, anisotropy ratio, and thermo‐optic coefficient have been determined.
TL;DR: A conventional Cole-Davidson model for the memory function was found to be inadequate due to the neglect of β relaxation, and an empirical memory function including both a and β relaxation was constructed, found to provide good fits to the spectra for the whole temperature range studied.
Patent•
17 Mar 1993TL;DR: In this article, an optical signal generator, an optical communication system, and a method for searching for a Fresnel reflection point in an optical transmission line make use of characteristic features of stimulated Brillouin scattering.
Abstract: An optical signal generator, an optical communication system, and a method for searching for a Fresnel reflection point in an optical transmission line make use of characteristic features of stimulated Brillouin scattering (SBS). In the optical signal generator, exciting light supplied to an optical transmission line, formed of a nonlinear optical medium, showing stimulated Brillouin scattering, is amplitude-modulated with an information signal. The threshold value for stimulated Brillouin scattering in the optical medium is positioned between a high level and a low level of the modulated waveform.
Journal Article•
TL;DR: In this article, a Brillouin-scattering experiment was performed on the ionic glass former CaKNO 3 to determine the temperature dependence of the nonergodicity parameter f(T) of mode-coupling theory.
Abstract: A Brillouin-scattering experiment was performed on the ionic glass former CaKNO 3 to determine the temperature dependence of the nonergodicity parameter f(T) of mode-coupling theory. The spectra were analysed using a generalised hydrodynamics formulation with most of the parameters fixed by previously reported experimental results. A conventional Cole-Davidson model for the memory function was found to be inadequate due to the neglect of β relaxation. An empirical memory function including both a and β relaxation was therefore constructed, based on a previous depolarised-light-scattering study. It was found to provide good fits to the spectra for the whole temperature range studied