GaTe-Sb2Te3 thin-films phase change characteristics

International audienceA radio frequency magnetron co-sputtering technique exploiting GaTe and ${\rm Sb}_2 {\rm Te}_3$SbTe targets was used for the fabrication of Ga-Sb-Te thin films. Prepared layers cover broad region of chemical composition (${\sim}{10.0 {-} 26.3}\,\, {\rm at.}$∼10.0-26.3at. % of Ga, ${\sim}{19.9 {-} 34.4}\,\, {\rm at.}$∼19.9-34.4at. % of Sb) while keeping Te content fairly constant (53.8-55.6 at. % of Te). Upon crystallization induced by annealing, large variations in electrical contrast were found, reaching a sheet resistance ratio of ${{R}_{\rm annealed}}/{{R}_{\rm as - deposited}}\;\sim{2.2} \times {{10}^{ - 8}}$R/R∼2.2×10 for the ${{\rm Ga}_{26.3}}{{\rm Sb}_{19.9}}{{\rm Te}_{53.8}}$GaSbTe layer. Phase transition from the amorphous to crystalline state further leads to huge changes of optical functions demonstrated by optical contrast values up to $|\Delta n| + |\Delta k| = {4.20}$|Δn|+|Δk|=4.20 for ${{\rm Ga}_{26.3}}{{\rm Sb}_{19.9}}{{\rm Te}_{53.8}}$GaSbTe composition

Démonstration expérimentale et étude numérique des ondes plasmons-solitons

International audienceNous avons conçu et fabriqué des structures plasmoniques nonlinéaires planaires à base de verres de chalcogénure et d’or où nous avons pu observer pour la première fois les ondes nonlinéaires plasmons-solitons décrites théoriquement dès les années 80. Des comparaisonssatisfaisantes avec les résultats de modèles numériques spécifiques sont aussi décrites

Experimental demonstration of soliton-plasmon coupling in planar waveguides

International audienceMerging the fields of plasmonics and nonlinear optics authorizes a variety of fascinating and original physical phenomena. In this study, we specifically study the combination of the strong light confinement ability of surface plasmon polaritons (SPP) with the beam self-trapping effect that occur in nonlinear optical Kerr medium. Although this idea of plasmon-soliton has been the subject of several theoretical or numerical articles, no experimental evidence has been revealed yet. One reason is that in the proposed configurations the requested nonlinear refractive index change amplitude to generate a plasmon-soliton is too high to be reached in available material. Another limitation is due to the large propagation losses associated with plasmons. In the present study, a proper architecture has been designed and then fabricated allowing the first experimental observation of hybrid coupling between a spatial optical soliton and a SPP in a metal-Kerr dielectric structure. To be able to trigger the nonlinearity at moderate light power and simultaneously to allow propagation over several millimetres distance, a metal-dielectric structure was designed. It consists of a four-layer planar geometry made of a transparent Kerr dielectric layer placed on a lower refractive index medium, with on its top surface a thin dielectric layer covered by a metallic film deposited on top. The Kerr medium is a 3µm thick chalcogenide film (Ge28.1Sb6.3Se65.6) with a high refractive index deposited by RF magnetron sputtering on an oxidized silicon substrate. The thickness of the thin SiO2 layer is 10 nm while the top gold layer is 30 nm. Samples are about 5-6 mm along propagation direction (z-axis). As shown by numerical simulations, the designed planar nonlinear waveguide with its top silica and gold layer supports a fundamental TE mode profile at NIR wavelengths whose transverse profile along y (perpendicular to the layers) is not affected by the metal layer while the TM mode is clearly localized near the SiO2-metal-chalcogenide interfaces due to its plasmonic part. The estimated nonlinear parameter γ of the TM mode is nearly three times larger than the TE one. Consequently, in nonlinear regime an enhanced self-focusing effect is expected for this TM wave. Experiments are performed with a tunable optical parametric oscillator emitting 200 fs pulses at 1.55 µm with a repetition rate of 80 MHz. The experimental analysis consists in injecting a typical 4 × 30 μm2 (FWHM in x-y cross section) elliptical laser beam into the waveguide and monitoring the output beam spatial profile evolution versus light power. Different arrangements are tested that unambiguously reveal the plasmon-soliton coupling. For instance, experiments are conducted with and without the metallic layer and for both TE and TM polarizations. In addition, different positions on the sample of the metal part with several lengths chosen between 0.1 to 2mm are tested. Additional experiments are in progress to analyze the beam evolution with near-field scanning microscopy and simulations of the beam propagation in the full structure are developed to reach a better and fully quantitative description of the observed phenomena

Experimental demonstration of plasmon-soliton waves

International audienceWe report the experimental observation of plasmon-soliton coupling. The demonstration is performed in a chalcogenide- based four-layer planar geometry designed to limit plasmon propagation losses while exhibiting efficient Kerr self-focusing at moderate power. The observations reveal a strongly enhanced self-focusing undergone by a self-trapped beam propagating inside the structure. As expected, only TM polarized waves exhibit such a behavior. Different experimental arrangements are tested that unambiguously reveal the nonlinear plasmon-soliton coupling which is corroborated by numerical simulation

Experimental proof and modelling of plasmon-soliton coupling and propagation in a nonlinear plasmonic structure

National audienceWhile plasmonics has seen numerous striking experimental results during the last decade, there is only very few dealing with nonlinear integrated plasmonics. This last research topic addresses photonic devices in which waveguide aspects are predominant and nonlineareffects emerges from bulk term. Our current work belongs to this difficult but promising topic. We have obtained the first experimental proof of the coupling between a plasmon and a spatial soliton. This demonstration have been realized in a layered planar structure where the nonlinear layer is made of a specific chalcogenide glass ensuring both a high nonlinear coefficient, a low two-photon absorption, and a relatively high power damage threshold. In its plasmonic part, the chalcogenide layer is separated from the 32 nm thick gold layer by a 10 nm thick silica layer whom the thickness was optimized by modal numerical simulations in order to ensure a high effective nonlinearity of the plasmonic structure. Our experimental results reveal a strong reinforcement of the self-focusing of the incident beam only when it passes through the plasmonic part of the structure. This effect occurs when TM polarized waves are launched while no reinforcement is observed when TE polarized waves are considered. This is one of the signatures of the plasmon-soliton coupling. Power dependency of the recorded spatial profiles has also been studied together with the impact of the localization of the plasmonic structure relatively to the input facet of the light beam. In order to get a better understanding of these phenomena, we have build a spatial nonlinear propagation model taking into account two spatial dimensions and the different field profiles along the full structure (with/without the gold layer). We get a good agreement between the experimental data and the numerical results

Measurement of ultrafast optical Kerr effect of Ge–Sb–Se chalcogenide slab waveguides by the beam self-trapping techniqueKerr solitons

International audiencee present a reliable and original experimental technique based on the analysis of beam self-trapping to measure ultrafast optical nonlinearities in planar waveguides. The technique is applied to the characterization of Ge-Sb-Se chalcogenide films that allow Kerr induced self-focusing and soliton formation. Linear and nonlinear optical constants of three different chalcogenide waveguides are studied at 1200 and 1550 nm in femtosecond regime. Waveguide propagation loss and two photon absorption coefficients are determined by transmission analysis. Beam broadening and narrowing results are compared with simulations of the nonlinear Schrödinger equation solved by BPM method to deduce the Kerr n2 coefficients. Kerr optical nonlinearities obtained by our original technique compare favorably with the values obtained by Z-scan technique. Nonlinear refractive index as high as (69 ± 11) × 10-18m2 / W is measured in Ge12.5Sb25Se62.5 at 1200 nm with low nonlinear absorption and low propagation losses which reveals the great characteristics of our waveguides for ultrafast all optical switching and integrated photonic devices