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International audience; We demonstrate the fabrication of arsenic-and antimony-free chalcogenide glasses compatible with glass fiber processing. Optical fibers with distinct index profiles are presented and characterized, namely, single-material fibers with or without a suspended core and standard step-index fibers with varying core diameter. In addition, we evidence their potential for nonlinear photonic devices in the mid-infrared spectral region by means of super-continuum generation experiments in the femtosecond regime. Spectral broadenings extend on several octaves in the mid-infrared from 2 to 14 μm.

National audience

International audience; The investigation of some solar radiations of interest for astrophysicists requires optics in the 80–130 nm vacuum ultra-violet spectral range (VUV). In this domain, where both transmittance and reflectance of most materials are very low, the measurement of optical constants is specifically difficult, and optical data are consequently often either inexistent or uncertain. Reliable modelling of optical components for VUV, like polarizing multi-layered mirrors, necessitates prior measurement of complex indices of the thin films involved in the coating. Fluorides like MgF2 or AlF3 are among the rare materials capable to contribute to multi-layer mirrors in the VUV. We have determined optical constants of thin films of these two materials by using a two media reflectance method at normal incidence and a graphical determination particularly suited to this VUV region, which we presented in a previous paper. Optical constants are determined in the range 60–124 nm with 2 nm step, and are compared to existing data. On the basis of these measured indices, polarizing mirrors for k1 = 121.6 nm or k2 = 103.2 nm have been modelled and fabricated. Their reflectance measured versus incidence angle by using monochromatized synchrotron radiation at the above wavelengths is found in agreement with the calculated predictions.

International audience; We present the operating principle and a first experimental characterization of a holographic rangefinder, that couples a two wave mixing phase demodulation set-up with a frequency modulated laser source. In its first implementation, the system allows millimetre sensitivity on tens of meters measurement range with the ability to work with scattering surfaces

International audience; We present an experimental demonstration of stimulated Raman scattering in a hollow core photonic crystal fibre filled with ethanol. By combining the original transmission properties of these fibres with a highly nonlinear liquid we have realized a very efficient Raman generator. This technique can be applied to other nonlinear mechanisms and opens the way towards the realisation of new fibered components for optical systems

The increase in fiber laser and amplifier output power is limited by nonlinear effects and material damage due to the high power density, especially in pulsed operation. Output powers of several hundreds watts have recently been achieved with large-mode-area quasi-singlemode fibers. To further increase the core diameter, an original alternative approach consists in correcting the beam profile after a multimode fiber amplifier by a nonlinear beam cleanup method. We report the conversion of a multimode and depolarized output beam of a highly multimode diode-pumped Yb-doped fiber amplifier to a diffraction limited, linearly polarized beam by two original beam cleanup methods: • the first converts the multimode beam to a singlemode beam using self-referencing two wave mixing process in an infrared sensitive photorefractive crystal (Rh:BaTiO3). With this setup, up to 11.6 W singlemode output is achieved with a 78% multimode to singlemode photorefractive conversion efficiency, • the second converts a multimode beam into a singlemode beam by use of the Brillouin effect in a multimode gradient-index (GI) fiber with a self-aligned loop geometry. A preliminary conversion from a M 2 = 6.5 beam into a M 2 = 1.3 beam with 31% efficiency is reported. To cite this article: L. Lombard et al., C. R. Physique 7 (2006).

International audience; A new method to determine complex amplitudes of index and absorption gratings in photorefractive multiple quantum wells is presented. In usual method to evaluate these parameters, spectral measurement of absorption change due to the applied field over a wide wavelength range is required and the index change is calculated through the Kramers-Krönig's relationship. In our method, only a set of measured data for photorefractive two-wave mixing set-up with small sinusoidal phase modulation for fixed wavelength is needed. This is thus well adapted to insitu characterization of systems that operate at a given wavelength. Real and imaginary part of the gains owing to the index and the absorption gratings are calculated from the output signals of the system. We apply this method to our photorefractive multiple quantum devices operating at 1064 nm, and obtain consistent results

International audience; We present two beam coupling characterization of Ba0.77Ca0.23TiO3, a ferroelectric material with no phase transition around room temperature that shows high photorefractive gain (7cm-1 with ordinary polarization and 15cm-1 with extraordinary polarization). We measure the electrooptic coefficients of Ba0.77Ca0.23TiO3. These values are compared to estimated theoretical values, calculated using a model that allows to deduce the tetragonal phase parameter (Pockels and piezoelectrics coefficients) from the parameters of the high temperature cubic phase (Kerr and electrostriction coefficients)

International audience; We present and characterize theoretically and experimentally a photorefractive velocimeter. This device, based on two-wave mixing in a rapid photorefractive crystal, measures the instantaneous velocity of a vibrating target. It is particularly adapted to the measurement of high-amplitude (up to several mm) low-frequency (up to several kHz) vibrations. Instantaneous velocities as high as 25 mm s-1 are expected to be measured with common photorefractive semiconductors and CW lasers

International audience; We present the experimental investigation of a photorefractive ring phase modulation amplifier, that is not resonant and that can work with distorted beams. We show that with this geometry an amplification by a factor 5 of a phase modulation signal is possible. We also show that this strong amplification is alleviated by the presence of losses in the ring. These losses lead to a real gain in signal to noise ratio of a factor 3, that nevertheless expresses that with such a system the photon noise limit of laser ultrasonics system can be overpassed. The losses are also responsible for the strong sensitivity of the system to the vibrations, which puts a strong limitation of the ring amplifier

International audience; We solve the problem of the transmission of time modulated signals in a two beam coupling photorefractive set-up using an absorbing material. We obtain an analytical expression that describes this phenomenon in absence of pump beam depletion due to beam coupling. We use this expression to analyse the influence of absorption on the photorefractive build-up. We also describe, using this model, the photorefractive beamsplitter response. It is also showed that the π/2 phase shift between illumination and index gratings is detrimental to a linear detection of the phase variation of the signal beam

International audience; We present a photorefractive investigation of the vanadium doped CdTe at different wavelengths from 1.06 μm to 1.55 μm. The sensitivity and performances of different samples grown with different conditions are deduced. We compare these performances with the ones of the undoped GaAs in the same wavelength range

International audience; We present experimental studies of photorefractive effect in non-photorefractive orientations of LEC-grown GaAs crystals. Picosecond DFWM experiments, carried out in different samples, show that forbidden photorefractive signal correlates well with dislocation density and confirms hypothesis that the effect arises from strain fields around growth-defects

International audience; We present a theoretical and experimental analysis of photorefractive two-beam coupling in undoped GaAs as a function of temperature. The theoretical treatment includes the metastable state of the EL2 defect with its optical properties (optical generation and optical recovery) in the photorefractive model. Three major features are predicted by this model: First, a change of the sign of the photorefractive beam coupling gain around 150 K; second, an enhancement of the space-charge field by a factor of 2 compared to the diffusion field; and, finally, the appearance of a strong peak due to an absorption grating around 150 K. All these features are actually observed experimentally with a good correlation between experimental data and theoretical simulation.

International audience; We present photorefractive measurements at 1.06 mgrm and 1.3 mgrm performed in electron-irradiated GaAs. Irradiation with electrons of kinetic energies ge1 MeV introduces intrinsic electrically active defects which modify the Fermi-level position and allow to modify the electron-hole competition mechanism of the photorefractive effect. Furthermore, it is shown that the optical absorption in the 1.3-1.5 mgrm spectral range can be increased, which might allow to enlarge the useful spectral range of GaAs towards optical telecommunication windows. The native and irradiation-induced defects are assessed by electron paramagnetic resonance and optical absorption spectroscopy conducted at T=300 K and 77 K. The direct influence of an irradiation-induced mid-gap defect on the photorefractive effect is experimentally and theoretically demonstrated

International audience; The AC field technique leading to the enhancement of the photorefractive effect is applied to Vanadium-doped Cadmium Telluride. Net photorefractive gain is obtained for the three wavelengths studied : 1.06μm, 1.32μm and 1.55μm. We observed a change in the sign of the photorefractive gain between 1.06μm and 1.55μm, which represents the first evidence of an electron-hole competition in this material. Theoretical interpretation is performed using an extension of the AC field theoretical model with bipolar conduction

The existence of strontium barium niobate crystals (SrxBa1-xNb2O6, noted SBN:100x) was first reported in 1960 (Francombe, 1960) and first large SBN single crystals were grown by Ballman and Brown over the range 0.25

For many years twin beams originating from parametric down-converted light beams have aroused great interest and attention in the photonics community. One particular aspect of the twin beams is their peculiar intensity correlation functions, which are related to the coincidence rate of photon pairs. Here we take advantage of the huge bandwidth offered by two-photon absorption in a semiconductor to quantitatively determine correlation functions of twin beams generated by spontaneous parametric down-conversion. Compared with classical incoherent sources, photon extrabunching is unambiguously and precisely measured, originating from exact coincidence between down-converted pairs of photons, travelling in unison. These results strongly establish that two-photon counting in semiconductors is a powerful tool for the absolute measurement of light beam photon correlations at ultrashort timescales., The second order correlation function g(2) is used to test quantum correlation properties of light. Here, two-photon counting is used to measure g(2) and an extrabunching effect is demonstrated, providing evidence that two-photon counting is an appropriate method for measuring light beam photon correlations.

National audience

International audience; Les mémoires holographiques sont connues pour leurs très fortes capacités. Nous présentons ici une architecture de mémoire optique inspirée de la photographie interférentielle de Lippmann, architecture très voisine de l'holographie, mais néanmoins plus simple à mettre en œuvre. Nous montrons, que moyennant des règles de conception très simples, une telle architecture de Lippmann avec un multiplexage des pages de données en longueur d'onde doit présenter des capacités de stokage similaires à celles des montages holographiques.

Slow-mode micro-structured waveguides enable a large enhancement of optical nonlinearities. Using a generalization of the local field factor theory of nonlinear homogeneous media, we review the impact of the group velocity reduction on the hierarchy of the semi-conductor nonlinearities. As an illustration, we experimentally and theoretically reported an intrinsic limitation concerning the Raman amplification of short pulses in silicon nanowires through the self-phase modulation induced by both the optical Kerr effect and free-carrier refraction. Hence, we provide a fundamental insight on the nonlinear interaction of short pulses for the design of future slow-mode devices.

International audience; We consider the Raman amplification problem for silicon waveguides in the regime in which both the pump and signal pulses are relatively short but wide enough that their duration exceeds the phonon lifetime (about 3 ps in silicon). We use the coupled pump-signal equations for numerical simulations that include all competing nonlinear effects such as self- and cross-phase modulations, two-photon and free-carrier absorptions, and changes in the refractive index induced by the free carriers. However, numerical simulations do not provide much physical insight. For this reason, we also develop an approximate analytic approach for solving the Raman amplification problem. We introduce the concept of an effective Raman gain and show analytically how it depends on the pump bandwidth. As the pump spectrum broadens inside the silicon waveguide, the effective Raman gain is reduced considerably. We obtain an analytical form of the nonlinear phase accumulated during propagation inside a silicon waveguide and use it to calculate the total spectral broadening experienced by a pump pulse. Using this result, we can predict changes in the effective Raman gain as a function of pump pulse energy. A comparison of our predictions with the recent experimental data shows that our model is reasonable and captures the essential physics.

Nowadays, the holographic data storage presents a renewed interest. It seems well placed to lead a new generation of optical storage capacity and playback speeds much higher than current optical discs based on the recording onto a surface. In this thesis, we propose a new architecture for optical data storage that is based on the principle of Lippmann photography interferential. Information are included in the volume of the recording material in the form of pages of data multiplexing in wavelength by exploiting the Bragg selectivity. This technique, although very similar to holography, had never been considered for high storage capacities. The aim of the thesis was to analyze this new architecture to determine the conditions that can lead to very high capacities. This analysis was based on a numerical simulation tool of diffraction process involved in this memory interferential. It allowed us to define two conditions under which these high capacities are achievable. In accordance with these conditions, we developed a demonstrator called "Lippmann’s memory" and have thus demonstrated experimentally that the capacity is proportional to the thickness of the recording material. With such an architecture, Terabyte disks of 12 cm in diameter are expected.; Le stockage de données par holographie suscite un intérêt renouvelé. Il semble bien placé pour conduire à une nouvelle génération de mémoires optiques aux capacités et débits de lecture bien supérieurs à ceux des disques optiques actuels basés sur l’enregistrement dit surfacique. Dans ce travail de thèse, nous proposons une nouvelle architecture de stockage optique de données qui s’inspire du principe de la photographie interférentielle de Lippmann. Les informations y sont inscrites dans le volume du matériau d’enregistrement sous la forme de pages de données par multiplexage en longueur d’onde en exploitant la sélectivité de Bragg. Cette technique, bien que très voisine de l’holographie, n’avait jamais été envisagée pour le stockage à hautes capacités. L’objectif de la thèse a été d’analyser cette nouvelle architecture afin de déterminer les conditions pouvant conduire à de très hautes capacités. Cette analyse s’est appuyée sur un outil de simulation numérique des processus de diffraction en jeu dans cette mémoire interférentielle. Elle nous a permis de définir deux conditions sous lesquelles ces hautes capacités sont atteignables. En respectant ces conditions, nous avons conçu un démonstrateur de mémoire dit de « Lippmann » et avons ainsi démontré expérimentalement que la capacité est bien proportionnelle à l’épaisseur du matériau d’enregistrement. Avec une telle architecture, des capacités de l’ordre du Téraoctet sont attendues pour des disques de 12 cm de diamètre.

Efficient polarizing as well as non-polarizing mirrors for a wavelength of λ=121.6 nm (hydrogen Lyman-α radiation) are necessary to achieve an experimental determination of the magnetic field in the solar corona through the Hanle effect. We have designed, realized and characterized such mirrors. These consist of glass coated with a thin-film stack. The coatings use the most reflective (Al) and most transparent (fluorides) materials at this wavelength. Different coatings were explored which involve an increasing number of films in the coating stack. At the incident angle of maximum polarization where the p-polarized reflectivity R p is minimized, an s-polarized reflectivity R s as high as 69% is experimentally obtained with a coating made of a Fabry–Perot resonator. To our knowledge, this value is the highest ever reported for a polarizing mirror at this wavelength. Additionally, efficient non-polarizing mirrors have been designed and realized by using a two-layer coating (MgF2/Al/glass). By optimizing the fluoride layer thickness, a mirror with non-polarizing properties in the whole range of incident angles was realized.

Spontaneous parametric downconversion (SPDC) sources are an essential element of quantum communication and quantum information processing systems. Their quality can be hampered by spectral, temporal, or spatial distinguishability of the two photons of a generated pair. Even when such defects have been corrected, the ultimate quality of the SPDC source is limited by the intrinsic multiple pair generation. In this paper, the effect of transmission, filtering and detection losses and asymmetrical spectral bandwidths in the photon pair paths on the visibility of the two-photon interference delivered by the SPDC source and its useful pair rate are investigated. In this investigation, two subcases are distinguished: deterministic and statistical splittings of the generated pairs, whatever the coherence of the multiple pairs. We show that the visibility is strongly degraded by a spectral bandwidth asymmetry, while the losses mainly affect the measured coincidence probability. The deterministic splitting configuration is shown to be generally more advantageous, although statistical splitting may present some advantages in applications with a narrow bandwidth requirement, such as those involving quantum memories. Moreover, while pump-induced optical noise only produces small visibility reductions, dark counts of the single-photon detectors are shown to limit the maximum possible visibility, particularly in the case of high-loss photon pair sources. Because our model quantifies the intrinsic limitations due to double pair emission in a simple way, the results presented can be used to optimize the design of SPDC sources and choose the optimum trade-offs between several key parameters such as visibility, generation probabilities, and spectral bandwidth, in particular for small bandwidth SPDC sources in the perspective of quantum networking and computing applications.

Laser induced picosecond transient gratings are used to study carrier transport via free carrier and photorefractive nonlinearities in serni-insulating undoped GaAs and vanadium doped CdTe crystals. Absorption and carrier generation mechanisms are investigated through the variation of grating strengths with input fluence. We show that grating decays are governed by mostly ambipolar diffusion and by its variation with fluence. Ambipolar mobilities are measured: μa≈135 cm2.V-1.s-1 in CdTe and μa≈760 cm2.V-1.s-1 in GaAs.

Characterization of different optical techniques, such as photo-induced current transient spectroscopy (PICTS), absorption, photoconductivity spectra and photorefractive wave mixing, of semi-insulating V-doped Cdytals prepared by the modified Bridgman method are presented. The aim of this joint research programme is to provide information which can lead to the understanding of the complex processes which determine photorefractive effects and to optimize the key parameters.

The PhD dissertation is organized in two parts. In the first part, we present an experimental study of stimulated Raman scattering in a silicon-on-insulator (SOI) nanowire. We demonstrate that the Raman amplification of a narrow-band Stokes wave experiences a saturation effect for high pump intensities because of self phase modulation of the pump beam. Moreover, an analytical model is presented that describes the experimental results remarkably well. The model furthermore provides an estimation of the Raman gain coefficient γR of silicon. The second part is devoted to the experimental study of stimulated Raman scattering in a doubly resonant planar GaAs microcavity. The nonlinear measurements clearly show some totally unexpected results. We experimentally demonstrate that the relaxation of the electrons in the conduction band of GaAs is significantly modified through the interaction with coherently excited Raman phonons.

Semiconductor photonic structures are very interesting for all-optical signal processing due to their strong non-linear properties. Structuring the medium on a small scale enables light localization and therefore enhancement of nonlinear phenomena. However, the extent of this enhancement depends on the order of the nonlinearity, thus introducing new interaction regimes, which are the subject of this manuscript. After describing the theoretical background presenting the enhancement of nonlinear processes through localization in semiconductors, we demonstrate experimentally and quantitatively, for the first time the influence of localization on the enhancement of nonlinearities such as the Kerr effect, two-photon absorption and free-carrier effects, by studying a GaAs photonic crystal. We solve the Raman amplification problem in silicon nanowaveguides, by developing an analytical model that shows the influence of nonlinear phase modulation effects on the decrease of the effective Raman gain in silicon. This model is validated by experimental data. Finally, we study the application of localization to all-optical nonlinear switching. We introduce the concept of nonlinear switching and absorption lengths, which enables us to analyze different materials. We show that pure Kerr switching is unattainable in Si and GaAs (contrary to AlGaAs and GaN), but that switching assisted by free-carrier effects is a possibility for certain microstructure geometries.; Du fait de leurs fortes propriétés non-linéaires, les structures photoniques semi-conductrices sont très intéressantes pour le traitement tout-optique du signal. La structuration à petite échelle permet de localiser la lumière et donc d'exalter les phénomènes non-linéaires, mais avec un pouvoir d'exaltation différent suivant l'ordre de la non-linéarité, introduisant ainsi une nouvelle hiérarchie des régimes d'interaction. Après une description théorique présentant le renforcement des processus non- linéaires par la localisation dans les semi-conducteurs, nous démontrons expérimentalement et quantitativement, pour la première fois, l'influence de la localisation sur l'exaltation des non- linéarités telles que l'effet Kerr, l'absorption à deux photons et les effets de porteurs libres, par l'étude d'un guide à cristal photonique de GaAs. Nous résolvons le problème de l'amplification Raman d'impulsions dans un nanoguide de silicium, en développant un modèle analytique permettant de montrer l'influence des effets de modulation de la phase non-linéaire sur la chute du gain Raman effectif dans le silicium. Ce modèle est validé expérimentalement. Finalement, nous abordons l'application de la localisation à la commutation non- linéaire tout-optique. Nous introduisons la notion de longueurs non-linéaire de commutation et d'absorption permettant d'étudier différents matériaux. Nous montrons que la commutation par effet Kerr pur est impossible pour le Si et le GaAs (contrairement à l'AlGaAs et au GaN), mais qu'une commutation par effet de porteurs libres y est envisageable pour certaines géométries de microstructures.

Semiconductor photonic structures are very interesting for all-optical signal processing due to their strong non-linear properties. Structuring the medium on a small scale enables light localization and therefore enhancement of nonlinear phenomena. However, the extent of this enhancement depends on the order of the nonlinearity, thus introducing new interaction regimes, which are the subject of this manuscript. After describing the theoretical background presenting the enhancement of nonlinear processes through localization in semiconductors, we demonstrate experimentally and quantitatively, for the first time the influence of localization on the enhancement of nonlinearities such as the Kerr effect, two-photon absorption and free-carrier effects, by studying a GaAs photonic crystal. We solve the Raman amplification problem in silicon nanowaveguides, by developing an analytical model that shows the influence of nonlinear phase modulation effects on the decrease of the effective Raman gain in silicon. This model is validated by experimental data. Finally, we study the application of localization to all-optical nonlinear switching. We introduce the concept of nonlinear switching and absorption lengths, which enables us to analyze different materials. We show that pure Kerr switching is unattainable in Si and GaAs (contrary to AlGaAs and GaN), but that switching assisted by free-carrier effects is a possibility for certain microstructure geometries.; Du fait de leurs fortes propriétés non-linéaires, les structures photoniques semi-conductrices sont très intéressantes pour le traitement tout-optique du signal. La structuration à petite échelle permet de localiser la lumière et donc d'exalter les phénomènes non-linéaires, mais avec un pouvoir d'exaltation différent suivant l'ordre de la non-linéarité, introduisant ainsi une nouvelle hiérarchie des régimes d'interaction. Après une description théorique présentant le renforcement des processus non- linéaires par la localisation dans les semi-conducteurs, nous démontrons expérimentalement et quantitativement, pour la première fois, l'influence de la localisation sur l'exaltation des non- linéarités telles que l'effet Kerr, l'absorption à deux photons et les effets de porteurs libres, par l'étude d'un guide à cristal photonique de GaAs. Nous résolvons le problème de l'amplification Raman d'impulsions dans un nanoguide de silicium, en développant un modèle analytique permettant de montrer l'influence des effets de modulation de la phase non-linéaire sur la chute du gain Raman effectif dans le silicium. Ce modèle est validé expérimentalement. Finalement, nous abordons l'application de la localisation à la commutation non- linéaire tout-optique. Nous introduisons la notion de longueurs non-linéaire de commutation et d'absorption permettant d'étudier différents matériaux. Nous montrons que la commutation par effet Kerr pur est impossible pour le Si et le GaAs (contrairement à l'AlGaAs et au GaN), mais qu'une commutation par effet de porteurs libres y est envisageable pour certaines géométries de microstructures.

International audience; Although wavelength-multiplexed page-oriented Lippmann data storage architectures present similarities with reflection holographic memories, we evidenced that simple rules must be followed to reach the same high storage densities

International audience; We experimentally show that the self-phase modulation of picosecond pump pulses, induced by both the optical Kerr effect and free-carrier refraction, has a detrimental effect on the maximum on-off Raman gain achievable in silicon on insulator nanowave- guides, causing it to saturate, as we confirm with a simple calculation of the Raman gain.

International audience; . We demonstrate the feasibility of efficient polarizing and non-polarizing mirrors at λ = 121..6 nm designed within the framework of the Lyman α Lyot Coronograph Imager project. We have designed, realized and characterized such mirrors Optical constants of the materials involved in the thin film coatings are determined experimentally. Reflectivity measurements in the VUV wavelength domain have been performed at PTB (Synchrotron at BESSY II, Berlin). A s-polarized reflectivity Rs as high as 68% is experimentally obtained with a coating made of a Fabry-Pérot resonator. To our knowledge this value is the highest ever reported for a polarizing mirror at this wavelength.

International audience; Nowadays, holographic data storage is considered as one of the most serious candidates for the next generation of high capacity optical disks. In this paper, we present the study of a novel optical data storage system based on Lippmann photography. Interferential photography invented by Lippmann in 1891 was the first practical way of making colour photographs. Based on this technique, we propose to record wavelength-multiplexed data in a page-oriented architecture. Initially, we present numerical simulations with the aim to use thick media for the recording and exploring the theoretical capacity of storage, and we have demonstrated that with this architecture we can reach data capacities as large as for holography, of order of TeraBytes for an optical disk of 120 mm of diameter. Therefore, we describe the implementation of an experimental set-up for the recording and retrieval of many images using a resolution target, mask or SLM as data pages, a holographic material as recording medium and a CCD for the detection. With this novel architecture, we obtain experimental results that validate our previous theoretical approach. So, theory and experiment confirm the enormous potential of Lippmann technique for reaching very high capacities.

National audience

International audience; We study the photon correlation properties of broadband parametric down-converted light. The measurement of the photon correlation is carried out thanks to a modified Hanbury Brown-Twiss interferometer based on two photon absorption in GaAs detector. Since this method is not affected by the phase matching conditions of the detecting apparatus (so called “final state post-selection”), the detection bandwidth can be extremely large. This is illustrated by studying, with the same apparatus, the degree of second order coherence of parametric light in both degenerate and non-degenerate cases. We show that our experiment is able to determine the coherent as well as the incoherent contributions to the degree of second order coherence of parametric light with a time resolution in the fs range scale.

mini-colloque 18 " Photostructuration des polymères pour les micro et nanotechnologies "; National audience

International audience; La modulation électro-optique est une fonction clef dans le domaine des technologies optiques, généralement assurée par des cristaux ferroélectriques tels que le niobate de lithium (LN). La mise en œuvre de l'effet électro-optique dans un film mince offre la possibilité de réduire de plusieurs ordres de grandeur la tension de modulation (du kV au Volt) et la taille des composants. Elle ouvre également la voie, par micro-nano structuration des films, à la réalisation de composants actifs à bande interdite photonique électriquement accordable. De multiples fonctionnalités nouvelles peuvent être envisagées. L'enjeu est considérable dans le domaine du transport de l'information et des composants photoniques. Notre objectif était donc le développement de films actifs aux propriétés électro-optiques (effet Pockels) héritées de celles du cristal et nous avons choisi le niobate de strontium barium SBN (SrxBa1-xNb2O6) à cause de son exceptionnel coefficient électro-optique à l'état cristallin. Nous avons obtenu des films épitaxiés sur des substrats MgO recouverts de platine en utilisant la technique de pulvérisation RF magnétron de cibles céramiques [1,2]. Ces films présentent une très forte non-linéarité diélectrique, des propriétés ferroélectriques et électro-optiques [3]. Les méthodes qui ont été mises au point pour déterminer les coefficients électro-optiques d'un film mince s'appuient généralement sur des approximations drastiques, des relations présupposées entre les coefficients, et elles négligent souvent les autres effets du champ (piézoélectricité et électro-absorption). La méthode que nous avons mise au point ne fait appel à aucune de ces approximations et détermine simultanément les différentes contributions à la réponse observée (électro-optique, piézoélectricité, électro-absorption). Nous présentons cette méthode et les propriétés électro-optiques ainsi déterminées d'un film SBN. Nous montrons que piézoélectricité et électro-absorption contribuent de façon significative à la réponse globale à basse fréquence. Les propriétés électro-optiques du film (r33=39 pm/V) sont inférieures à celles du cristal massif SBN de même composition (r33=237 pm/V) mais supérieures à celles d'un cristal de niobate de lithium (r33=31 pm/V). Les filières film mince LN [4,5] et SBN sont comparées en tenant compte de la différence entre les permittivités diélectriques de ces deux matériaux. Références : [1] M. Cuniot-Ponsard, J.M. Desvignes, B. Ea-Kim, E. Leroy, J. Appl. Phys. 93(3),1718-1724 (2003). [2] M. Cuniot-Ponsard, J.M. Desvignes, A. Bellemain, Journal of Materials Science 41, 5302-5309 (2006) [3] N. Boulay, M. Cuniot-Ponsard, J.M. Desvignes, A. Bellemain, Ferroelectrics, 353, 10-20 (2007) [4] P. Rabiei and P. Günter, Appl. Phys. Lett. 85 (20), 4603 (2004) [5] H. Akazawa and M. Shimada, J. Appl. Phys. 98 113501 (2005)

International audience; We anticipate that the capacity of Lippmann storage in thick holographic material should be the same as for conventional wavelength multiplexed holographic materials. First experimental tests are presented.

La première partie du manuscrit est consacrée au fonctionnement de sources à diode laser en montage de type cavité étendue et qui intègre un filtre holographique. Ce filtre intra-cavité est dynamique est constitué de l'association d'un matériau photoréfractif et d'un réflecteur. Nous montrons que ce filtre est équivalent à un filtre Fabry-Perot dont l'un des miroirs est constitué par un réseau de Bragg photoréfractif enregistré par la structure de modes du laser. Ses caractéristiques sont décrites en détail. Une brève analyse de stabilité d'un laser auto-organisable illustre le processus de sélection entre les modes, induit par le filtre Fabry-Perot photoréfractif. Nous avons alors étudié des fonctionnements de sources à diode laser montée en cavité étendue utilisant comme réflecteur distant un filtre Fabry-Perot photoréfractif. Dans le cas des diodes laser qualifiées de limitée par diffraction, où l'émission laser est supportée par un seul mode transverse, cette configuration originale force l'oscillation de la source sur un seul mode longitudinal et ce, sur une large plage de courant d'injection. Ce comportement a été démontré pour des longueurs d'onde de fonctionnement allant de 630 à 1550 nm et des puissances de sortie variant de quelques dizaines de milliWatt au Watt. Enfin, nous avons démontré qu'un tel filtre dynamique utilisé avec des diodes laser à ruban large, supportant plusieurs modes transverse, introduit également des pertes sélectives sur la structure transverse des modes. L'application dans ce dernier cas est l'amélioration de la brillance de sources à diode laser de puissance. Enfin, nous présentons le fonctionnement original d'une source à diode laser accordable dont la longueur d'onde de fonctionnement est fixée par l'injection optique temporaire d'un faisceau issu d'un laser maître. Cette source présente la particularité de disposer dans sa cavité d'un milieu holographique dynamique de type photoréfractif qui lui permet, après arrêt de l'injection, de conserver un fonctionnement à la longueur d'onde préalablement imposée par le laser maître. En utilisant un laser maître accordable en longueur d'onde, nous avons réalisé l'adressage optique d'une telle source suivant un peigne de longueurs d'onde quasi périodique. La seconde partie du manuscrit traite des études sur le renforcement des interactions nonlinéaires dans des milieux micro-structurés en semi-conducteurs. La première étape a nécessité le développement complet d'une source OPO accordable en longueur d'onde et délivrant des impulsions picosecondes. Nous rapportons la première démonstration expérimentale et quantitative sur le lien entre la propagation d'une impulsion en régime de lumière lente et l'exaltation des nonlinéarités. Nous avons en particulier étudié les phénomènes d'absorption à deux photons (TPA) et d'auto-modulation de phase induits par les effets Kerr optique et de réfraction par les porteurs libres (FCR) générés par TPA. Par un ajustement de nos courbes expérimentales, sans paramètre ajustable (en s'appuyant sur la valeur de la vitesse de groupe mesurée en régime de propagation linéaire), nous avons démontré de manière quantitative l'effet de l'exaltation des nonlinéarités par l'effet du ralentissement de la lumière. Parallèlement, nous avons initié une étude consacrée à la diffusion Raman stimulée dans des nano-structures semi-conductrices. Nous avons démontré, dans des nanoguides de silicium sur isolant, une saturation du facteur d'amplification Raman par l'élargissement spectral des impulsions pompe par des effets d'automodulation de phase nonlinéaire. Enfin, nous présentons nos résultats expérimentaux sur le fonctionnement d'une microcavité doublement résonnante en régime de diffusion Raman stimulée.

We experimentally and theoretically study self-phase modulation by Kerr effect in a liquid filled hollow core photonic crystal fiber. We perform a complete characterization of the linear optical properties of the hollow core photonic band gap fiber filled with deuterated acetone to determine all the characteristics of the propagation mode. The nonlinear coefficient of the fiber is determined by fitting the output spectra broadened by self-phase modulation with a new analytical expression giving the spectra of a secant hyperbolic pulse transmitted through a Kerr media. The experiment allows a precise determination of the nonlinear index change of acetone-d6 equal to (1.15$\pm$0.17)x10-19 m2W-1., to be published in JOSAB

International audience; The electro-optic (EO) light modulation is a key function in light-wave technologies. It is mostly realized by exploiting the linear EO Pockels effect in ferroelectric bulk crystals like lithium niobate (LN) for primary example. Optimizing the performance of EO modulation has led to develop EO thin film waveguides. By using the Crystal Ion Slicing (CIS) and wafer bonding technique [1] or epitaxial thin film deposition [2], some research groups have thus succeeded in increasing the EO performance of LN modulators until a value close to the theoretical limit for LN. Any further significant improvement in the EO modulation performances can then only arise from changing LN for a material with better electro-optic properties. Beside LN, the ferroelectric materials which have been considered in the literature in view of preparing electro-optic thin films are mainly BaTiO3 (BT), (Ba,Sr)TiO3 (BST), (Pb,La)(Zr,Ti)O3 (PLZT), and (Sr,Ba)Nb2O6 (SBN). Electro-optic coefficients higher than that of LN crystal by more than two orders of magnitude have been reported for some of these films [3-6]. In addition to increasing drastically the EO modulation performances, the implementation of the Pockels EO effect in thin film waveguides opens up the path to the realization of electrically-tunable photonic crystal (PC) devices. The position and shape of a photonic band gap are dependent on the refractive index of the propagating medium and therefore can be electro-optically controlled. This EO control considerably extends the scope of PC structures potential functionalities, and should play a main role in the future deployment of the photonic technology. The great potential of EO thin films is linked to our ability to prepare highly EO and well-controlled thin films in the configurations required. A reliable method of characterizing the electric-field-induced response of a thin film is an essential tool for progressing in this field. The electric-field-induced response is a combination of inverse piezoelectric, electro-optic and electro-absorptive effects. In this presentation we propose a method which allows determining simultaneously these three contributions to the global effect experimentally observed. A specific feature of this method is its high level of self-consistency. The difficulties and reliability of electro-optic characterization are discussed. The method is used to characterize the electric-field-induced response of an epitaxial (Sr,Ba)Nb2O6 (SBN) thin film, which we prepared.

We experimentally show that the self-phase modulation of picosecond pump pulses, induced by both the optical Kerr effect and free-carrier refraction, has a detrimental effect on the maximum on-off Raman gain achievable in silicon on insulator nanowaveguides, causing it to saturate. A simple calculation of the Raman gain coefficient from the measured broadened output pump spectra perfectly matches the saturated behavior of the amplified Raman signal observed experimentally at different input pump powers., Accepted for publications in Applied Physics Letters

International audience; Lippmann photography is a more than one century old interferometric process invented for recording colored images in thick black and white photographic emulsions. After a comparison between this photographic process and Denisyuk holography, we feature some hints to apply this technique to high density data storage by wavelength multiplexing in a page-oriented approach in thick media. For the first time we experimentally investigate this approach. We anticipated that this storage architecture should allow capacities as large as for conventional holography

We present a Raman generator based on a 35 cm long hollow core photonic crystal fiber entirely filled with ethanol emitting on a nearly-Gaussian beam. The power conversion efficiency from the pump at 532 nm to the first Stokes order of ethanol at 630 nm is 67%. Temporal profiles, mode patterns and power stability are also analyzed.

National audience; Les niobates sont des matériaux ferroélectriques de référence dans le domaine électro-optique : LN (LiNbO3) est le cristal industriel standard et SBN:x (SrxBa1-xNb2O6) présente le coefficient électro-optique diagonal r33 le plus élevé jamais mesuré sur un cristal. La préparation de ces matériaux sous forme de film mince permet de réunir potentiellement les conditions d'un guidage d'onde efficace et d'une modulation électro-optique très basse tension. Elle ouvre également la voie, par micro-nano structuration des films, à la réalisation de composants actifs à bande interdite photonique électriquement accordable, par effet Pockels. Les applications potentielles sont multiples. Néanmoins le développement des films ferroélectriques pour la mise en œuvre de l'effet électro-optique est resté très limité : la réalisation de films minces de LiNbO3 fait toujours l'objet de recherches en cours , et les tentatives consacrées à des matériaux alternatifs sont restées sans suite. Pourtant l'enjeu est considérable dans le domaine du transport de l'information et des composants photoniques. Notre objectif était donc le développement de films actifs aux propriétés électro-optiques (effet Pockels) héritées de celles du cristal. Le matériau choisi est le niobate de strontium-barium (Srx Ba1-xNb2 O6 - SBN:x), un matériau ferroélectrique qui présente à l'état de cristal massif des propriétés électro-optiques exceptionnelles (r33 voisin de 200 pm/V pour x= 60%), très supérieures à celles du niobate de lithium (LiNbO3, r33 = 31 pm/ V). Nous avons obtenu des films épitaxiés sur des substrats MgO recouverts de platine en utilisant la technique de pulvérisation RF magnétron de cibles céramiques. Ces films présentent une très forte non-linéarité diélectrique, des propriétés ferroélectriques et électro-optiques. Les méthodes qui ont été mises au point pour déterminer les coefficients électro-optiques d'un film mince s'appuient généralement sur des approximations drastiques, des relations présupposées entre les coefficients, et négligent en particulier les autres effets du champ (piézoélectricité et électro-absorption). La méthode que nous avons mise au point ne fait appel à aucune de ces approximations et met en évidence le poids des différentes contributions. Nous présentons cette méthode et les propriétés électro-optiques ainsi déterminées sur les films de SBN. Ces propriétés électro-optiques sont supérieures à celles du niobate de lithium massif et ouvrent la voie à la conception de composants photoniques actifs, miniaturisés et électriquement accordables.