Démonstration de l'autofocalisation d'une onde plasmonique

This dissertation contributes to the research area of nonlinear plasmonics an emerging field of optics. The main goal is to demonstrate experimentally the spatial self-trapping of a plasmonic wave.The study begins with the fabrication and the characterization of slab Ge-Sb-Se chalcogenide waveguides. A technique based on the formation of spatial solitons is developed to estimate their Kerr nonlinearities. Linear and nonlinear optical properties of the waveguides are studied at the wavelengths of 1200 nm and 1550 nm.Plasmonic structures are then designed to propagate hybrid plasmon-soliton waves with moderate propagation losses. They are constituted of the previous waveguides covered with nanolayers of silica and gold.Optical characterizations reveal a giant self-focusing undergone by the wave that propagates inside the plasmonic structure. The behavior is present only for TM polarized light as expected from theory. Detailed experimental results of this plasmon enhanced nonlinear self-trapping corresponding to different configurations are presented. Simulations confirm the obtained experimental results.This fundamental demonstration confirms the concept of plasmon-assisted self-focusing while revealing a very efficient nonlinear effect. This opens new perspectives for the development of integrated nonlinear photonic devices as well as new physical phenomena.Cette thèse est une contribution au domaine de recherche de la plasmonique nonlinéaire, domaine émergent de l'optique. L'objectif principal est de démontrer expérimentalement l'autofocalisation d'une onde plasmonique.L'étude débute avec la fabrication et la caractérisation de guides plans en verre de chalcogénure de composition Ge-Sb-Se. Une technique basée sur la formation de solitons spatiaux est développée afin d’estimer leurs non-linéarités Kerr. Les propriétés optiques linéaires et non linéaires de ces guides sont étudiées aux longueurs d’onde de 1200 nm et 1550 nm.Des structures plasmoniques sont ensuite conçues pour propager des ondes hybrides plasmon-solitons avec des pertes de propagation modérées. Elles sont constituées des guides précédents recouverts de nanocouches de silice et d'or.Les caractérisations optiques par couplage plasmon-soliton révèlent une forte autofocalisation subie par l’onde qui se propage à l'intérieur de la structure plasmonique. Comme prévu par la théorie, le comportement est présent uniquement pour une lumière polarisée TM. Des résultats expérimentaux détaillés de cette autofocalisation exaltée par effet plasmonique sont présentés pour différentes configurations. Des simulations confirment les résultats expérimentaux obtenus.Cette démonstration fondamentale vient confirmer le concept d’autofocalisation assistée par plasmon tout en révélant un effet nonlinéaire très efficace. Cela ouvre de nouvelles perspectives pour le développement de dispositifs photoniques non linéaires intégrés ainsi que de nouveaux phénomènes physiques

Experimental demonstration of plasmon-soliton coupling

International audienceMerging the fields of plasmonics and nonlinear optics authorizes a variety of fascinating and original physicalphenomena. In this work, we specifically study the combination of the strong light confinement ability of surfaceplasmon polaritons (SPP) with the beam self-trapping effect in a nonlinear optical Kerr medium. Although this idea ofplasmon-soliton has been the subject of numerous theoretical papers [1], up to now, no experimental evidence had beenrevealed. In the present study, a proper architecture has been designed and fabricated allowing the first experimentalobservation of hybrid coupling between spatial solitons and SPP.To be able to trigger the nonlinearity at moderate light power and simultaneously allow propagation over severalmillimeters, a metal-dielectric structure was first designed. It consists of a four–layer planar geometry made of a Kerrdielectric layer placed on a lower refractive index substrate and covered with a thin dielectric layer followed by a metallicfilm. Performed numerical simulations show that the designed planar waveguide exhibits an enhanced Kerr self-focusingfor the TM0 mode thanks to the plasmonic effect.The experimental analysis consists in injecting a typical 4 × 30 μm2 (FWHM) elliptical beam at 1.55μm from afemtosecond laser into the 5mm long waveguide. The output beam distribution evolution is then monitored versus inputlight intensity. Figure 1 shows the large trapping enhancement observed for a TM mode in presence of the plasmonicstructure (Fig. 1d,e) compared to configurations (Fig. 1b,c and Fig. 1f,g) where plasmonic effect is absent. For an inputintensity of 1.2 GW/cm² the beam is self-confined to a 12μm FWHM (Fig. 1e) while the FWHM is twice (Fig. 1c,g)without plasmonic effect. The proposed plasmonic structure definitely exposes an enhanced self-focusing nonlinearity.The strong light confinement is due to the presence of the hybrid coupling between a plasmon and a soliton waves.Different configurations have also been tested that unambiguously reveal this plasmon-soliton coupling

Beam self-action in planar chalcogenide waveguides

International audienceWe present a new experimental technique based on the analysis of beam self-action to measure optical nonlinearity in planar waveguides. This technique is applied to analyze the nonlinear properties of slab chalcogenide waveguides that can develop Kerr induced self-focusing or self-defocusing, depending upon the waveguide structure and composition. Optical nonlinearity in chalcogenide waveguide is studied in the 1200 nm to 1550 nm wavelength range in femtosecond regime. Results of the proposed technique compare favorably with n2 values obtained with the Z-scan technique. In addition, beam self-trapping in the chalcogenide waveguides due to material photosensitivity is also observe

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

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 and numerical study of plasmon-soliton waves

International audienceMerging the fields of plasmonics and nonlinear optics authorizes a variety of fascinating and original physical phenomena. In this work, we specifically study the combination of the strong light confinement ability of surface plasmon polaritons (SPP) with the beam self-trapping effect in a nonlinear optical Kerr medium. Although this idea of plasmon-soliton has been the subject of numerous theoretical papers since the eighties [1–4], up to now, no experimental evidence had been revealed yet. In the present study, a proper structure (Fig. 1a) has been designed and fabricated allowing the first experimental demonstration of these hybrid nonlinear waves merging spatial solitons and SPP

Linear and nonlinear optical properties of co-sputtered Ge-Sb-Se amorphous thin films

International audienceAmorphous Ge-Sb-Se thin films were co-sputtered from ${{\rm GeSe}_4}$GeSe and ${{\rm Sb}_2}{{\rm Se}_3}$SbSe targets. Depending on the film composition, linear optical properties were studied by ellipsometry. The Kerr coefficient and two-photon absorption coefficient were estimated using Sheik-Bahae's formalism for co-sputtered films of ${{\rm GeSe}_4} {\text -} {\rm Sb}_2{{\rm Se}_3}$GeSe-SbSe compared to ${{\rm GeSe}_2}{\text -}{\rm Sb}_2{{\rm Se}_3}$GeSe-SbSe pseudo-binary system and ${{\rm As}_2}{{\rm Se}_3}$AsSe as reference. The Kerr coefficient was found within the range of 4.9 {\unicode {x2013}}- 21 \times {10^{ - 18}}4.9--21×10. Quantitatively by means of a figure of merit at 1.55 µm, thin films with compositions of ${{\rm Ge}_7}{\rm Sb}_{25}{\rm Se}_{68}$GeSbSe and ${{\rm Ge}_9}{\rm Sb}_{20}{\rm Se}_{71}$GeSbSe having an estimated Kerr coefficient of about ${10.1} \times {10^{ - 18}}\;{{\rm m}^2}{{\rm W}^{ - 1}}$10.1×10mW and ${13.4} \times {10^{ - 18}}\;{{\rm m}^2}{{\rm W}^{ - 1}}$13.4×10mW should be considered for the future nonlinear optical integrated platforms. Such compositions being close to ${({{\rm GeSe}_4})_{50}}{({{\rm Sb}_2}{{\rm Se}_3})_{50}}$(GeSe)(SbSe) pseudo-binary (i.e., ${\rm Ge}_{7.5}{\rm Sb}_{25.0}{\rm Se}_{67.5}$GeSbSe) provides just the trade-off between a high Kerr coefficient and low optical losses related to two-photon absorption

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

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