Jean Toulouse

Phase diagram of the relaxor ferroelectric (1-x)Pb(Zn1/3Nb2/3)O3-xPbTiO3

Recently, a new orthorhombic phase has been discovered in the ferroelectric system (1-x)Pb(Zn1/3Nb2/3)O3-xPbTiO3 (PZN-xPT) for x=9%, and for x=8% after the application of an electric field. In the present work, synchrotron x-ray measurements have been extended to higher concentrations 10%≤x≤15%. The orthorhombic phase was observed for x=10%, but, surprisingly, for x≥11% only a tetragonal phase was found down to 20 K. The orthorhombic phase thus exists only in a narrow concentration range with near-vertical phase boundaries on both sides. This orthorhombic symmetry (MC type) is in contrast to the monoclinic MA-type symmetry recently identified at low temperatures in the Pb(Zr1-xTix)O3 (PZT) system over a triangle-shaped region of the phase diagram in the range x=0.46–0.52. To further characterize this relaxor-type system, neutron inelastic scattering measurements have also been performed on a crystal of PZN-xPT with x=15%. The anomalous soft-phonon behavior (‘‘waterfall’’ effect) previously observed for x=0% and 8% is clearly observed for the 15% crystal, which indicates that the presence of polar nanoregions extends to large values of x.

Spontaneous and stimulated Brillouin scattering gain spectra in optical fibers

We study the Brillouin scattering behavior in several single-mode fibers with different waveguide characteristics in terms of their longitudinal mode structures in the gain spectrum, linewidth narrowing, and stimulated Brillouin scattering (SBS) threshold levels. Evolution from spontaneous to SBS is investigated by monitoring the Brillouin line-shape and the behavior of the longitudinal acoustooptic resonance modes that exist in the core. We compare our results with the current theory of Brillouin scattering generated from noise in the undepleted pump approximation. We also present experimentally Brillouin gain spectra in the highly depleted pump regime, where there is no analytical solution, by showing the evolution of the gain spectrum as a function of the injected laser intensity.

Polarized Raman study of the phonon dynamics inPb(Mg1/3Nb2/3)O3crystal

Pb(Mg 1 / 3 Nb 2 / 3 )O 3 is one of the simplest members of the class of lead relaxors and often serves as a model system for more complicated compounds. In this paper, we analyze both polarized and depolarized Raman-scattering spectra, measured in the temperature range between 1000 and 100 K, using a multiple-peak decomposition. Based on this analysis, we propose a comprehensive picture of the structural transformations in the crystal and associated dynamics. According to our model, the formation of the Fm3m symmetry in the chemically ordered regions as well as the appearance and freezing of the polar nanoregions are the consequences of the same phenomenon: the off-centered displacements of ions and their fast reorientational thermal motion. Short-lived dynamic lattice distortions are present even at the highest measured temperatures. From the Burns temperature, T d ∼620 K, their motion becomes progressively more restricted. Temperature T* ∼350 K marks the beginning of the freezing process which continues down to the temperature of the electric-field-induced phase transition, T d 0 ∼210 K. Raman scattering exists due to the presence of local lattice distortions. It is characterized by phonons with different wave vectors interacting with dynamic and static disorder.

Optical nonlinearities in fibers: review, recent examples, and systems applications

Optical nonlinearities give rise to many ubiquitous effects in optical fibers. These effects are interesting in themselves and can be detrimental in optical communications, but they also have many useful applications, especially for the implementation of all-optical functionalities in optical networks. In the present paper, we briefly review the different kinds of optical nonlinearities encountered in fibers, pointing out the essential material and fiber parameters that determine them. We describe the effects produced by each kind of nonlinearity, emphasizing their variations for different values of essential parameters. Throughout the paper, we refer to recent systems applications in which these effects have been dealt with or exploited.

Solid-core tellurite glass fiber for infrared and nonlinear applications

By optimizing glass composition and using a multistage dehydration process, a ternary 80TeO(2)-10ZnO-10Na(2)O glass is obtained that shows excellent transparency in the wavelength range from 0.38 microm up to 6.10 microm. Based on this optimized composition, we report on the fabrication of a single-mode solid-core tellurite glass fiber with large mode area of 103 microm(2) and low loss of 0.24-0.7 dB/m at 1550 nm. By using the continuous-wave self-phase modulation method, the non-resonant nonlinear refractive index n(2) and the effective nonlinear parameter gamma of this made tellurite glass fiber were estimated to be 3.8x10(-19) m(2)/W and 10.6 W(-1) x km(-1) at 1550 nm, respectively.

Characterization of new erbium-doped tellurite glasses and fibers

Tellurite glasses are promising candidates for optical fiber laser and amplifier applications because of their excellent optical and chemical properties. The emission spectrum from erbium in tellurite glasses is almost twice as broad as the corresponding spectrum in silica. In this presentation, we report the results of a two-prong investigation of new tellurite glasses: a Raman study that provides detail information on the microscopic structure of these glasses, and a study of the erbium emission in fibers fabricated from these glasses. Specifically, we report on the emission from fibers of different lengths and for different pumping schemes.

Unique characteristic features of stimulated Brillouin scattering in small-core photonic crystal fibers

We present extensive stimulated Brillouin scattering (SBS) results from experiments and modeling for four different photonic crystal fibers (PCFs) with core diameters ranging from 8 to 1.7 μm. These results reveal several SBS characteristic features of small-core PCFs, high thresholds, and acoustic peaks, which are due to their antiguiding nature and highly multimode acoustic character. The nature of what we believe to be new acoustic modes is examined in the light of the large variations observed in the Brillouin gain, Brillouin threshold, and Brillouin shift with decreasing core diameter and optical wavelength.

Fabrication and characterization of a water-free mid-infrared fluorotellurite glass

Using a physical and chemical dehydration technique and a high-pressure, ultradry O2 atmosphere in a semiclosed steel-chamber furnace, we fabricated a group of fluorotellurite glasses with a composition of (90-x)TeO2-xZnF2-10Na2O (mol.%, x=0-30). For x=30, no OH absorption was observed in the range of 0.38-6.1 μm. This is the first report of a water-free mid-IR fluorotellurite glass, to our knowledge, offering the common advantages of a robust oxide glass and an IR-transparent fluoride one. Besides optimized linear transmittance and absorption, the nonlinear refractive indices and Raman gain coefficients are reduced. These results are discussed in the context of mid-IR high-power laser generation and transmission.

Theory of stimulated Raman scattering cancellation in wavelength-division-multiplexed systems via spectral inversion

By exploiting the reflection symmetry of the underlying evolution equations, we theoretically demonstrate that stimulated Raman scattering crosstalk in continuous-wave wavelength-division-multiplexed systems can be totally eliminated using spectral inversion techniques. We show that this result is always true, irrespective of the shape of the Raman gain curve or the loss/gain profile along the optical fiber system. These results are illustrated by means of relevant examples.

Diffuse Neutron Scattering Study of a Disordered Complex Perovskite Pb(Zn1/3Nb2/3)O3Crystal

Diffuse scattering around the (110) reciprocal lattice point has been investigated by elastic neutron scattering in the paraelectric and the relaxor phases of the disordered complex perovskite crystal-Pb(Zn1/3Nb2/3)O3(PZN). The appearance of a diffuse intensity peak indicates the formation of polar nanoregions at temperature T*, approximately 40K above Tc=413K. The analysis of this diffuse scattering indicates that these regions are in the shape of ellipsoids, more extended in the direction than in the direction. The quantitative analysis provides an estimate of the correlation length, \xi, or size of the regions and shows that \xi ~1.2\xi , consistent with the primary or dominant displacement of Pb leading to the low temperature rhombohedral phase. Both the appearance of the polar regions at T*and the structural transition at Tc are marked by kinks in the \xi curve but not in the \xi one, also indicating that the primary changes take place in a direction at both temperatures.