Brillouin Gain Coefficient Research Articles

Brillouin-gain coefficients of chalcogenide glasses

We derived the relation between a figure of merit, M1, for the diffraction efficiency of acousto-optical devices and the Brillouin-gain coefficient, gB. We then estimated the values of gB and the phonon lifetime for typical As2S3 and As2Se3 chalcogenide glasses from known acousto-optical parameters. We found that the magnitude of gB for these two glasses is greater than 20 times that of fused silica.

Simulating and Designing Brillouin Gain Spectrum in Single-Mode Fibers

For many fiber applications, the Brillouin gain spectrum (BGS) contains important information including the Brillouin frequency shift, the Brillouin spontaneous linewidth, and the Brillouin gain coefficient. This paper is the first, to the best of our knowledge, to present an accurate numerical simulation of the BGS in single-mode fibers. The simulated and measured BGS were in good agreement. Through repeated numerical simulations, we revealed a tendency of the peak Brillouin gain coefficient that determines the stimulated Brillouin scattering threshold.

Stimulated Brillouin scattering in multimode fibers for optical phase conjugation

Stimulated Brillouin backscattering (SBS) is studied in multimode glass fibers with core diameters between 25 and 200 μm . The SBS threshold energy, and damage threshold were measured. High SBS reflectivities over 80% are obtained with 30 ns laser pulses at 1.06 μm wavelength. The experimental results regarding the SBS reflectivity are compared with an analytical calculation for a plane wave model of the SBS process. The Brillouin gain coefficient of the fibers appeared to be about equal to the bulk gain coefficient.

Transient stimulated Brillouin scattering in a fiber ring resonator and its effect on optical Kerr bistability

We numerically investigate the transient interaction between optical Kerr bistability and stimulated Brillouin scattering (SBS) when an intense optical pulse is incident in a short fiber ring resonator. An initial phase detuning of the ring resonator and the difference in the phase shift between the pump wave and the created Stokes wave are taken into account in the three-wave SBS model. The ratio of the Brillouin gain coefficient to the nonlinear refractive index of the fiber, which is termed the relative Brillouin gain coefficient, is used as a key parameter for examining the conditions for obtaining optical Kerr bistability in a fiber ring resonator. The numerical results show that optical Kerr bistability cannot be obtained in a ring resonator made from a conventional fused-silica fiber because of the generation of SBS. However, if other fibers with relative Brillouin gain coefficients at least 1 order smaller than that of fused-silica fibers are used, we can suppress SBS and hence obtain optical Kerr bistability. Moreover, we investigate theoretically and experimentally the dynamics of SBS in a fused-silica fiber ring resonator irradiated by a Gaussian pulse. The relaxation and pulsation in the Stokes signal depend strongly on the initial phase detuning of the ring resonator. The experimental results obtained with a single-frequency pulsed YAG laser agree qualitatively with theoretical predictions.

Characterisation of Liquid Brillouin Media at 532 nm

A number of transparent liquids have been evaluated for use in stimulated Brillouin scattering at 532 nm. Measurements were made of frequency shift, SBS threshold, reflectivity and optical breakdown properties. It was found that the alkanes, and in particular n-pentane, performed well and measurements were made of Brillouin gain coefficient and phonon lifetimes. It is suggested that these liquids are promising candidates for use in self-pumped phase conjugate mirrors, high gain Brillouin amplifiers and four-wave mixing mirrors.

Brillouin gain spectrum characterization in single-mode optical fibers

A novel method for Brillouin gain spectrum measurements in optical fibers is presented. It is based on the pump and probe technique with the specificity to use a single laser source together with an external modulator to generate the interacting lightwaves. The high accuracy and inherent stability of the technique makes it suitable for calibration and reference measurements. Different fibers with different refractive index profiles have been tested and characterized. The problem of the evolution of the polarization of the interacting waves is addressed in the article and a polarization insensitive determination of the actual Brillouin gain coefficient is made possible through two successive measurements with different polarizations. The effects of strain and temperature on the Brillouin gain spectrum are also fully characterized.

Additional electromagnetic waves and stimulated light scattering in the vicinity of an excitonic resonance.

The excitation of additional waves caused by a spatial dispersion transforms the stimulated Raman and Brillouin scattering in the vicinity of the excitonic resonance into a kind of a four-wave mixing. The parametric coupling of four exciton polariton waves (EPW's) on the nonlinear polarization caused by the nonlinear polariton-phonon interaction results in the amplification of the Stokes additional wave. The Raman and Brillouin gain coefficients of the Stokes waves depending on the amplitudes and the wave vectors of both pumping EPW's essentially differ from the ones in the case without additional waves. The nonlinear Raman or Brillouin polarization containing additional waves generates a spectrum of scattered harmonics which consists of 20 harmonics with the combination wave vectors and frequencies instead of one anti-Stokes wave and one wave with the frequency lower than the Stokes frequency in the case without additional waves. The results obtained show that stimulated light scattering can be an effective method for the experimental investigation of additional waves and additional boundary conditions due to the amplification of additional waves. \textcopyright{} 1996 The American Physical Society.

Effect of optical breakdown on stimulated Brillouin scattering in focused beam cells

The effect of optical breakdown on the reflection of focused beam stimulated Brillouin backscattering (SBS) cells is studied theoretically. The threshold for SBS is inversely proportional to the breakdown intensity and the square of the stationary Brillouin gain coefficient if the threshold for optical breakdown is low. Two values of the steady-state reflectance are possible if optical breakdown and SBS have approximately the same threshold.

High-resolution stimulated Brillouin gain spectroscopy in glasses and crystals

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.

Intrinsic Brillouin linewidths and stimulated Brillouin gain coefficients in glasses studied by inelastic light scattering

Rayleigh–Brillouin scattering measurements on various multicomponent halide glasses and some selected oxide glasses were performed. The Brillouin linewidth measurements, the Brillouin intensities, and Brillouin frequency shifts allowed us to calculate the phonon attenuation, Pockels elasto-optic coefficients, and the stimulated Brillouin scattering gain coefficients. Brillouin linewidths obtained experimentally range between the limit of 21 MHz for an 88BeF2–12ThF4 glass and 213 MHz for a zirconium barium lanthanum fluoride glass. The parameter obtained in this study shows that the threshold power for the onset of stimulated Brillouin scattering in some halide glasses is greater than that for silicate glasses, which has important ramifications as a selection criterion for halide-based glasses as single-mode optical waveguide materials.

Gain saturation in fiber Raman amplifiers due to stimulated Brillouin scattering

The effects of stimulated Brillouin scattering (SBS) on Raman gain are explored. Measurements of gain in a fiber Raman amplifier show a saturation at low gain levels. Experimental data and a theoretical model are presented, demonstrating that this saturation is due to pump depletion by SBS. This effect also leads to Raman gain fluctuations arising from mode partitioning in a multimode pump laser. Two ways to avoid the deleterious effects of SBS on the performance of Raman amplifiers are suggested. One is to use a multimode semiconductor laser with a modal linewidth of the order of a few hundred megahertz, which leads to a strongly reduced Brillouin gain coefficient. The second approach is to use very short pump pulses in a backward configuration. >

Direct measurement of the acoustic decay times of hypersonic waves generated by SBS

The acoustic decay time of hypersound generated by stimulated Brillouin scattering (SBS) has been measured in several heavy gases (Xe, SF 6 , CCIF 3 , C 2 F 6 ) over a range of pressures. A straightforward optical probing technique is used whereby the decay time can be measured directly with high precision. A theoretical formulation of the decay mechanisms in a polyatomic gas is presented, and it is shown both theoretically and experimentally that vibrational relaxation can become the major decay process at high gas density. The Brillouin gain coefficient and acoustic frequency are also experimentally determined or calculated for the gases investigated. Two Brillouin-active gases (CCIF 3 and C 2 F 6 ) with high Brillouin gains, which have not been studied previously, have been characterized. A study of the gas C 2 F 6 near its critical point showed a large variation of the acoustic velocity which reaches a minimum value in the vicinity of its critical density.