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Nonlinear all-optical technology is an ultimate route for the next-generation ultrafast signal processing of optical communication systems. New nonlinear functionalities need to be implemented in photonics, and complex oxides are considered as promising candidates due to their wide panel of attributes. In this context, yttria-stabilized zirconia (YSZ) stands out, thanks to its ability to be epitaxially grown on silicon, adapting the lattice for the crystalline oxide family of materials. We report, for the first time to the best of our knowledge, a detailed theoretical and experimental study about the third-order nonlinear susceptibility in crystalline YSZ. Via self-phase modulation-induced broadening and considering the in-plane orientation of YSZ, we experimentally obtained an effective Kerr coefficient of n ^ 2 YSZ = 4.0 ± 2 × 10 − 19 m 2 · W − 1 in an 8% (mole fraction) YSZ waveguide. In agreement with the theoretically predicted n ^ 2 YSZ = 1.3 × 10 − 19 m 2 · W − 1 , the third-order nonlinear coefficient of YSZ is comparable with the one of silicon nitride, which is already being used in nonlinear optics. These promising results are a new step toward the implementation of functional oxides for nonlinear optical applications.

The emerging interest in integrated optical technologies raises the need for precise characterisation techniques for waveguides presenting nonlinearities. Here we propose a non-interferometric measurement to accurately characterise the Kerr contribution in hybrid waveguides and illustrate its performances using SiN waveguides with a GSS chalcogenide top-layer. The sensitivity of our technique in terms of nonlinear phase reaches 10 mrad and its accuracy makes possible to extract the nonlinear contributions from the top-layer.

International audience; Background: Liquid filled hollow core fiber Raman wavelength converters are devices enabling to red-shift the wavelength of laser beams delivered by either fixed wavelength or tunable lasers. Most of the reported converters operate in a pulsed regime with pulse durations comprised between a few hundreds of picoseconds and up to a few nanoseconds, and energy of a few micro-Joules. However, and depending on the pulse duration, the optimization of Raman converters turns to be rather challenging since the desired forward Raman scattering may compete with counter-propagating nonlinear effects like Raman and Brillouin back-scatterings. The Brillouin back-scattering is especially hard to cancel since the Brillouin gains are usually larger than the Raman gains. Techniques have already been investigated but are not fully satisfactory. Our aim in this paper is to propose a technique to optimize the Raman forward scattering and to minimize these back-scattering effects.Methods: We compare the interaction lengths in the forward and backward directions in the above-mentioned temporal regimes. If the fiber length is higher that the backward effective length of interaction then the backward effects should decrease at the benefit of the forward Raman scattering. Numerical simulations enable to estimate more precisely how long the fiber should be to get large Raman conversion efficiency and negligible Brillouin scattering.Results and discussion: To validate this technique we build two identical Raman converters differing only by the fiber lengths (0.5 m and 1.5 m). We present the experimental setup. The experimental results are confronted to the numerical simulations. As expected increasing the fiber length strongly decreases the Brillouin scattering.Conclusions: We have proposed a simple and efficient solution to minimize Brillouin back-scattering in Raman wavelength converters by optimizing the fiber length. The experimental demonstration was conducted with low energy (≈ 6 μJ) but the energies should scale with the fiber effective area if more energy is needed, without affecting the conversion efficiencies.

We demonstrated a class of highly nonlinear hybrid waveguide structures based on infiltration of As2S3 chalcogenide glass into silicon slot waveguides. The nonlinear properties of the hybrid waveguides were precisely quantified via a bidirectional top-hat D-scan method, enabling a direct comparison between properties measured using different device geometries. We experimentally demonstrate hybrid As2S3-Si slot waveguides with a two-photon absorption (TPA) figure of merit exceeding 2 at near infrared wavelengths. These waveguides largely satisfy the critical criterion for efficient nonlinear integrated photonics (FOMTPAwg>1), allowing phase shifts greater than π with minimal overall losses. These results pave the way for efficient and robust ultrafast all-optical devices and circuits in large-scale silicon photonics technology.

Integrated photonics has for several years included in its panoply the development of functions based on third-order non-linear optical phenomena, from the generation of supercontinuum or frequency comb sources to metrology or spectroscopy on chip applications. This natural evolution, after the development of high-speed transceivers in the last few years, particularly in silicon photonics, is based on a number of compromises and still has to solve problems, particularly concerning the integration of nonlinear materials on silicon and their exploitation. The work we present addresses two directions. The first is oriented towards the development of a supercontinuum source using Nitrogen-rich photonic circuits from an industrial CMOS platform, while the second aims at the development of hybrid highly nonlinear waveguides significantly reducing the impact of twophoton absorption in the telecom window around 1,55μm by exploiting silicon slot waveguides infiltrated by chalcogenide glasses (As2S3).

International audience; Nanofibers enable exploring evanescent nonlinearities. In this context, we aim to characterize a nanofiber immersed in ethanol. A single mode fiber at 532 nm is used and the nanofiber diameter is increased. Designed tapers are adiabatic in ethanol helping to investigate the stimulated Raman effect.

International audience; Nanofibers are nowadays attracting attention as an interesting tool to explore evanescent nonlinearities. In this context, we propose a full optical characterization of a nanofiber immersed in a Raman liquid in order to control the backward Raman and Brillouin beams that limit the forward Raman effect. Simulations are performed determining the parameters of the nanofibers to be fabricated on this issue for different vectorial modes. An experimental setup is presented enabling us to investigate such a characterization. Further experimental results will be gotten and are expected to lead to novel applications in nonlinear optics.

International audience; In this paper, we report the experimental characterization of highly nonlinear GeSbS chalcogenide glass waveguides. We used a single-beam characterization protocol that accounts for the magnitude and sign of the real and imaginary parts of the third-order nonlinear susceptibility of integrated Ge 23 Sb 7 S 70 (GeSbS) chalcogenide glass waveguides in the near-infrared wavelength range at λ 1580 nm. We measured a waveguide nonlinear parameter of 7.0 0.7 W −1 · m −1 , which corresponds to a nonlinear refractive index of n 2 0.93 0.08 × 10 −18 m 2 ∕W, comparable to that of silicon, but with an 80 times lower two-photon absorption coefficient β TPA 0.010 0.003 cm∕GW, accompanied with linear propagation losses as low as 0.5 dB/cm. The outstanding linear and nonlinear properties of GeSbS, with a measured nonlinear figure of merit FOM TPA 6.0 1.4 at λ 1580 nm, ultimately make it one of the most promising integrated platforms for the realization of nonlinear functionalities.

In this paper, we propose an experimental setup and an uncertainty evaluation to feed our previously proposed semi-analytical model for brisk assessment (SAMBA) of distortions from fiber nonlinearities over heterogeneous fiber spans transmission. We experimentally characterize physical nonlinear parameters required by the SAMBA by setting up a one span test bed and cumulated chromatic dispersion emulation in the transmitter, resulting in a nonlinear noise coefficient curve. We determine the accuracy of our method through the evaluation of the uncertainties impacting the measurement of the nonlinear noise. Finally, we assess the accuracy of our SAMBA performance estimator with a multispan dispersion unmanaged transmission up to 25 spans and show less than 0.5 dB prediction error in the linear and nonlinear regimes.

International audience; We report the characterization of highly nonlinear GeSbS chalcogenide glass integrated waveguides. Linear and nonlinear measurements were performed in the telecom window, illustrating the potential of As-free chalcogenides for photonics applications.

International audience; We report on the linear and nonlinear measurements of GeSbS chalcogenide glasses in waveguide configuration. Single-mode waveguides and ring resonators have been characterized in linear and nonlinear optical regimes around 1.58 µm wavelength demonstrating the interest of using this material for ultrahigh-bandwidth optical communications systems.

The characterization of a third order nonlinear integrated waveguide is reported for the first time by means of a top-hat Dispersive-Scan (D-Scan) technique, a temporal analog of the top-hat Z-Scan. With a single laser beam, and by carrying two counter-directional nonlinear transmissions to assess the input and output coupling efficiencies, a novel procedure is described leading to an accurate measurement of the TPA figure of merit, the effective Two-Photon Absorption (TPA) and optical Kerr (including the sign) coefficients. The technique is validated in a silicon strip waveguide for which the effective nonlinear coefficients are measured with an accuracy of $\pm 10~\%$, Comment: 5 pages, 4 figures

International audience; Fibered sources of photon pairs can be easily integrated into future quantum communication networks. However, in silica-core fibres, the broadband spectrum of spontaneous Raman scattering strongly contributes to uncorrelated noise photons degrading the quality of the source. To overcome the problem of the silica Raman scattering, a new architecture was recently proposed, with hollow-core photonic crystal fibers (LF-HCPF) whose core and cladding are filled with a non-linear liquid. As opposed to the Raman scattering spectrum of silica, which is broadband and continuous, the Raman scattering spectrum of liquids is composed of narrow lines. Thus, generating photon pairs between these narrow lines permits to avoid the spectral overlap between the SFWM pairs and the Raman photons. A near infra-red LF-HCPCF photon pair source has been demonstrated, featuring a three order of magnitude suppression of the Raman noise [1]. We have also demonstrated the first non-linear LF-PCF with a transmission band and a zero-dispersion-wavelength (ZDW) in the telecom wavelength range combined with a non-linearity of the same order of magnitude as the one of silica, as a first step towards a Raman-free photon pair source in the telecom band [2]. Injecting light on both sides of this fiber in a Sagnac loop configuration can then be used to obtain entanglement.

The difficulty in characterising nonlinear integrated structures lies in assessing the real power injected into the guided mode. Nonlinear characterisations of nano-waveguides currently reported in literature rarely give a precise determination of the coupling efficiency, while it directly affects the nonlinear response. Using a single beam top-hat Dispersive-Scan (D-Scan) method, a temporal analogue of the top-hat Z-Scan [1], we show the first nonlinear waveguide characterisation that simultaneously and accurately measures the input (k in ) and output (k out ) coupling efficiencies, the effective Two-Photon Absorption (γ TPA ) and Kerr (γ) nonlinear parameters. Like in Z-Scan, the D-Scan technique [2] advantageously gives access to the sign of the Kerr coefficient.

Raman wavelength converters based on hollow core microstructured fibres filled with gases or liquids have been widely studied in the last few decades [1, 2]. In these converters the wavelength of a laser pump beam is red-shifted by stimulated Raman scattering in the material filling the core of the fibre, giving rise to new discrete wavelengths that can be used in many domains of applications (biophotonics, environment …). The possibility to strongly confine the pump light over long distances is an asset to get a high conversion efficiency. However if no particular care is taken unwanted non linear effects can occur at the expense of the stimulated forward Raman scattering. These effects are the Raman and Brillouin back-scatterings. In this work we are interested in the optimization of liquid-core Raman converters operating with pulses of a few nanoseconds or less. In these temporal regimes competition between the abovementioned effects are known to be very strong. We validate here a solution to minimize Raman and Brillouin back-scatterings by an appropriate choice of the fibre length. The effective length of interaction L eff in the backward direction is estimated to be cΔt / 2n, where At is the pulse width duration and n the refractive index. In the forward direction, as the dispersion is negligible, this effective length is the length of the fibre L. In liquids, as backward and forward Raman gains are nearly the same, L has just to be slightly higher than L eff to avoid Raman back-scattering. In most liquids and for long pulses Brillouin gain is much higher than Raman gain (typically one order of magnitude). To decrease Brillouin scattering L has to be subsequently higher than Leff. We demonstrate experimentally these trends by building two Raman converters differing only by their lengths. Our initial aim was to realize a Raman converter emitting in the near IR range. The pump source is a microlaser at 532 nm delivering 900 ps pulses at a repetition rate of 4.5 kHz. We choose ethanol as the Raman liquid. When pumped at 532 nm, the first Stokes order of ethanol is at 630 nm and the second Stokes order is at 772 nm, i.e the near IR wavelength we want to generate. A Kagome fibre was used to realize the two converters. When empty this fibre guides in the near IR range over a 1 μm wide transmission band. When filled with ethanol this transmission band is blue-shifted and then covers the pump and the Stokes wavelengths. In our configuration L eff =0.1 m. The lengths of the two converters are 0.5 m and 1.5 m. The results are shown in figure 1. As expected we observed no Raman backscattering in both cases and Brillouin effect is strongly attenuated for the longer fibre. For instance at the critical point (when the output Raman Stokes energy equals the transmitted pump energy), the Brillouin energy is 66% of the forward Raman energy for the 0.5 m fibre and is only 9% for the 1.5 m fibre. As a consequence, the output energy at 772 nm is highly improved and we obtain an output energy of 0.9 μJ at 772 nm for an injected energy of 5.8 μJ.

International audience

We report on the experimental characterization of a novel nonlinear liquid-filled hollow-core photonic-crystal fiber for the generation of photon pairs at telecommunication wavelength through spontaneous four-wave-mixing. We show that the optimization procedure in view of this application links the choice of the nonlinear liquid to the design parameters of the fiber, and we give an example of such an optimization at telecom wavelengths. Combining the modeling of the fiber and classical characterization techniques at these wavelengths, we identify, for the chosen fiber and liquid combination, spontaneous four-wave-mixing phase matching frequency ranges with no Raman scattering noise contamination. This is a first step toward obtaining a telecom band fibered photon-pair source with a high signal-to-noise ratio., Comment: 5 pages, 5 figures, journal

We report on the first third order nonlinear experimental characterization of Ge-rich Si 1.x Ge x waveguides, with Germanium concentrations x ranging from 0.7 to 0.9. The experimental values will be compared with theoretical models. These results will provide helpful insights to assist the design of nonlinear integrated optical based devices in both the near- and mid-IR wavelength ranges.

The enhanced nonlinear interaction in a silicon microcavity under coherent excitation is studied under different conditions. By controlling the pulse frequency drift, we guarantee, at every instant, the coincidence with the frequency resonance of the cavity that in the nonlinear regime suffers from a blue shift in time. This limiting shift effect is caused by the free carriers generated by the strong silicon two-photon absorption. Owing to the linear time-frequency relation of the pulse, the coupling efficiency to the drifted resonance can be maintained, further increasing the blue-shift. We study the input power effect after using different pulse durations.

International audience; The effective Kerr and two photon absorption (TPA) nonlinear parameters of a nano-waveguide are characterized by means of a bi-directional top hat D-Scan technique. This approach requires a single beam and allows the measurement of the coupling efficiencies.

International audience; We measure the span-to-span noise covariance as indicator of Gaussian noise model accuracy over dispersion-managed systems. We found that covariance shouldn’t exceed 1/3 of variance, which occurs once residual dispersion per span exceeds 60ps/nm.

Silicon photonics is a disruptive technology poised to revolutionize several areas of our society. It has often been considered as the natural step forward to overcome some of the inherent bottlenecks of current microelectronics technology. Importantly, photonic integrated circuits can be implemented using CMOS-like fabrication processes, hence benefiting from a mature technology that provides low-cost mass fabrication using advanced tools. A large pool of Si components has been demonstrated, standing for low-loss waveguides, filters, micro-ring resonators, Mach-Zehnder interferometers, array waveguide gratings or photonic crystals, among others [1]. Similarly, the incorporation of Ge in Si photonic platforms has yield the demonstration of several active optical devices such as high-speed optical modulators and photodetectors with unprecedented performance [2]. In addition, strong electro-absorption and electro-refraction has been demonstrated in Ge/SiGe quantum wells showing strong Quantum Confined Stark Effects (QCSE), allowing for efficient optoelectronic modulation and detection at telecom wavelengths [3]. Interestingly, tuning the QW design allows fine tuning of the absorption band edge of devices over a wideband range. Moreover, light emission from the direct bandgap transition HH1-CΓ1 has also been reported in SiGe/Ge quantum wells, opening the route towards the development of light emitting devices fully integrated in a silicon chip [4]. Noticeably, all the above described activities are meant to develop Si-based photonic platforms in the near-infrared wavelength range, where most applications are foreseen. Lately, however, there is an increasing interest in the exploitation of Ge-based photonic platforms at longer wavelengths up to the mid-infrared [5]. Having Ge a transparency window up to 15 µm, there are good prospects for the development of advanced photonic sensing platforms leveraging from the strong mid-IR molecular absorption bands of several chemical and biological substances. Besides, Ge-based platforms have also been proposed as ideal candidates to exploit the nonlinear properties at mid-IR wavelengths, owing to a higher χ(3) nonlinearity and the absence of two-photon absorption beyond λ ≈ 3.15 µm [6]. Important benefits are also expected in data communications, taking advantage from the two atmospheric transparency windows at λ ≈ 3-5 µm and λ ≈ 8-13 µm and the relaxed wavelength regulations put in place. Thus, in this presentation we will show our recent work on the development of Ge-based photonic devices for telecom and mid-IR applications. For that, a review of the advanced optoelectronic devices demonstrated so far in our group will be presented, including high-speed SiGe/Ge QWs electro-absorption modulators and detectors exploiting the QCSE. Then, further insight on the room temperature luminescence of QWs will be provided, followed by its integration in light emitting diodes in waveguide configuration for planar emission. In addition, a novel mid-IR photonic platform based on Ge-rich graded-index SiGe alloys will be presented. This platform offers an interesting set of advantages over other existing mid-IR approaches such as low-loss propagation and optimal modal area over an unprecedentedly broadband wavelength range [7]. As a consequence, the first demonstration of ultra-wideband mid-IR Mach-Zehnder interferometers operating from λ = 5.5 µm to 8.5 µm was performed using the graded-index SiGe platform [8]. Finally, the third-order nonlinear properties of this platform will be discussed, supported by experimental data on Ge-rich SiGe waveguides using a bidirectional top hat D-scan method [9]. Promising results were obtained, thus providing a promising scenario to develop broadband optical sources based on the supercontinuum generation. References [1] D. Thomson et al. ‘Roadmap on silicon photonics’, Journal of Optics, 2016, 18(7), 073003 (2016). [2] Y. Ishikawa, et al. ‘Germanium for silicon photonics,’ Thin Solid Films, 518(6), S83-S87 (2010). [3] P. Chaisakul, et al. ‘Integrated germanium optical interconnects on silicon substrates,’ Nature Photonics, 8(6), 482-488 (2014). [4] P. Chaisakul, et al. ‘Room temperature direct gap electroluminescence from Ge/Si0. 15Ge0. 85 multiple quantum well waveguide,’ Applied Physics Letters, 99(14), 141106 (2011). [5] R. Soref, ‘Mid-infrared photonics in silicon and germanium,’ Nature photonics, 4(8), 495-497 (2010). [6] L. Zhang, et al.’Nonlinear Group IV photonics based on silicon and germanium: from near-infrared to mid-infrared,’ Nanophotonics, 3(4-5), 247-268 (2014). [7] J. M. Ramirez et al. ‘Low-loss Ge-rich Si0.2Ge0.8 waveguides for mid-infrared photonics,’ Opt. Lett. 42(1) 105-108 (2017) [8] V. Vakarin et al. ‘Ultra-wideband Ge-rich silicon germanium integrated Mach-Zehnder interferometer for mid-infrared spectroscopy,’ Opt. Lett. 42(17), 3482-3485 (2017) [9] J. M. Ramirez et al. ‘Ge-rich graded-index SiGe waveguides with broadband tight mode confinement and flat anomalous dispersion for nonlinear mid-infrared photonics,’ Opt. Express, 25(6), 6561-6567 (2017) Figure 1

The χ(3) nonlinear properties of slotted hybrid silicon photonic waveguides infiltered with third-order nonlinear materials (NM) are studied by calculating the effective nonlinear susceptibilities associated to the silicon and cladding material, respectively. Optimization of the geometry of silicon-slotted waveguides is performed to engineer the nonlinear figure of merit (FOMTPA) of the guided mode up to 4.25, which is related to the balance between the Kerr and the TPA effects. The importance of engineering the nonlinear FOMTPA is illustrated by simulating the self-phase modulation effect in slotted hybrid silicon photonic waveguides.

The χ(3) nonlinear properties of slotted hybrid silicon photonic waveguides infiltrated with third-order nonlinear materials (NM) are studied by modelling the self-phase modulation (SPM). The broadness and intensity of SPM spectrum are investigated through nonlinear FOM TPA optimization to inhibit the detrimental two-photo absorption in slot waveguides, which demonstrates slot waveguides with higher FOM TPA could perform as wide but much more intense broadened spectrum than those with low FOM TPA , even though high FOM TPA slot waveguides intrinsically have larger effective mode areas, namely weaker Kerr effects. This study will draw attention to future nonlinear optimization of hybrid silicon waveguides to make balance between effective mode areas related Kerr effects and FOM TPA related TPA inhibition.

The χ(3) nonlinear properties of slotted crystalline silicon photonic waveguides filled with third-order nonlinear materials (NM) are studied by calculating the effective nonlinear susceptibilities associated to the silicon and cladding material, respectively. The adopted approach circumvents the assumptions that the introduced NM dominates the nonlinear behavior of the slotted waveguide and that strong light confinement in the slot allows neglecting the two-photon absorption (TPA) process in the silicon rails. Optimization of the geometry of silicon-slotted waveguides is performed on the basis of the nonlinear figure of merit (FOM(TPA)) of the guided mode, which is related to the balance between the Kerr and the TPA effects, allowing to reach a FOM(TPA)=4.25. The obtained results reveal the importance of properly choosing the waveguide width of the silicon rails in order to minimize the TPA effect even by tolerating a reduced overall nonlinearity.

Third-order nonlinear effects in silicon photonics are traditionally spoiled by free carrier effects. Optimization of the geometry of silicon slotted waveguides has been performed on the basis of the FOMTPA of the guided mode and has revealed the importance of properly choosing the waveguide width of the silicon rails in order to minimize TPA.

International audience; The large field enhancement that can be achieved in high quality factor and small mode volume photonic crystal microcavities leads to strengthened nonlinear interactions. However, the frequency shift dynamics of the cavity resonance under a pulsed excitation, which is driven by nonlinear refractive index change, tends to limit the coupling efficiency between the pulse and the cavity. As a consequence, the cavity enhancement effect cannot last for the entire pulse duration, limiting the interaction between the pulse and the intra-cavity material. In order to preserve the benefit of light localization throughout the pulsed excitation, we report the first experimental demonstration of coherent excitation of a nonlinear microcavity, leading to an enhanced intra-cavity nonlinear interaction. We investigate the nonlinear behavior of a Silicon-based microcavity subject to tailored positively chirped pulses, enabling to increase the free carrier density generated by two-photon absorption by up to a factor of 2.5 compared with a Fourier-transform limited pulse excitation of equal energy. It is accompanied by an extended frequency blue-shift of the cavity resonance reaching 19 times the linear cavity bandwidth. This experimental result highlights the interest in using coherent excitation to control intra-cavity light-matter interactions and nonlinear dynamics of microcavity-based optical devices.

The crystal-to-hexagonal columnar mesophase transition in solution-grown single crystals of poly(di-n-propyl siloxane), PDPS, was studied in situ with selected-area electron diffraction and variable-temperature atomic force microscopy. It was observed that, upon the transition, the hexagonal columnar mesophase displays two mutually orthogonal orientations of the lattice. The 2a* and 2b* reciprocal lattice vectors of the α-phase crystal coincide with the a* vectors of each of the two differently oriented mesophase lattices. The in situ atomic force microscopy study of the evolution of a single PDPS crystal upon heating shows that crystal thickening can occur via a short-term dwelling in the mesophase. The high chain mobility in the mesophase can account for the exceptional range of accessible crystal thicknesses of PDPS, which is much larger than that observed for polyethylene single crystals.

Polarized attenuated total reflection Fourier transform infrared spectra were recorded on multilayer stacks of native gastric tubulovesicle membranes. The spectral intensity and linear dichroism were measured for average thicknesses ranging between 0 and 100 bilayers. Atomic force microscopy was used to investigate the orientation of the membranes at the top of the stack. Height profiles were obtained along randomly drawn lines and slopes were computed over various distances. Orientation distribution functions were obtained from the slopes and decomposed into Legendre polynomials. It was found that the second Legendre polynomials coefficient characterizing the membrane orientation was always larger than 0.9. It could therefore be concluded that the membrane tilt does not significantly contribute to the infrared dichroism, even for the largest thicknesses tested.

The atomic force microscopy study of thermal behavior of truncated crystal of LPE alternately crystallized from n-octane at Tc1=98 and Tc2=95°C was performed. It was found that the morphological evolution during annealing of iso-height crystal regions is nonuniform.

The Common Agricultural Policy (CAP) of the European Union, technological developments, and commercial pressures to maximise returns and minimise costs, have given rise to a marked intensification of agriculture, particularly in the last 30 years. This highly intensified agriculture has resulted in environmental problems such as erosion. More recently, the CAP reform has introduced agri-environmental measures as a means of combating soil erosion. However, even though the 1992 CAP reform was meant to contribute to overall grassland stabilisation, recent studies point to continued agronomic pressures to plough up grassland. This paper presents a brief synthesis of crop trends and environmental impacts on erosion in Upper Normandy, France. Our analysis is based on data from the French agricultural censuses and on some remote sensing results from the FLOODGEN European project. We also used the simulation capacity of the runoff and erosion STREAM model to test the consequences of grassland decrease in agricultural catchments and to show the efficiency of some agri-environmental measures. Results show that Upper Normandy has lost 200,000 ha of permanent grassland between 1970 and 2000. A simulation performed with the STREAM model shows that the ploughing up of 17% of permanent grassland leads to a sharp rise both in runoff volume (>75%) and soil loss (>85%) within a catchment basin.

L'insertion d'un cristal photorefractif a l'interieur de la cavite d'un laser permet de fortement reduire le nombre de modes laser. Les modes enregistrent dans le cristal un hologramme qui modifie en retour leurs pertes. Il en resulte une tres forte selection entre les modes et qui, sous certaines conditions, force le laser a osciller sur un seul mode. L'hologramme etant systematiquement adapte a la structure de modes emis par le laser, on parle alors de cavites laser auto-organisables. Nous presentons les resultats qui ont ete obtenus sur le filtrage de modes longitudinaux dans des lasers de type quatre niveaux fonctionnant en regimes continu et impulsionnel, ainsi que dans des lasers a semi-conducteurs. En outre, nous montrons que l'insertion d'un tel cristal peut avoir comme application la stabilisation d'un mode. Le laser est alors monomode, l'inscription d'un hologramme par ce mode diminue ses pertes et etend son domaine de stabilite.

International audience; nonlinear properties of slotted silicon photonic waveguides filled with third-order nonlinear materials (NM, DDMEBT polymer) are quantitatively studied by separately calculating the effective nonlinearity susceptibilities associated to the silicon and cladding material, respectively. Optimization of the silicon slotted waveguide geometry is performed and focused on the optimization of optical power confinement in the high FOMTPA cladding material and of Aeff(NM)/Aeff(Si). The simulated nonlinear wave evolution results show the importance of properly choosing the silicon rail and slot widths in order to minimize the influence of the two-absorption process and associated free carrier effects (free carrier absorption, free carrier refraction).

Mixed Langmuir–Blodgett films of behenic acid (docosanoic acid) and glucose oxidase have been elaborated. The resulting films transferred on muscovite have been studied by scanning force microscopy. The general organization of the mixed film has been observed. Lateral force microscopy coupled with topographic data obtained with the contact mode, and a selective solubilization process have made possible the distinction between enzyme and behenic acid domains. The general organization of the mixed film may be described as quasi circular domains of glucose oxidase surrounded by a behenic acid monolayer. Both of them are organized on a sublayer of glucose oxidase molecules adsorbed on muscovite.

The dynamic organization of a mixed Langmuir film of glucose oxidase and behenic acid has been studied. Samples of the mixed film transferred after different relaxation times were analyzed by UV-Vis and IR spectroscopies and by lateral force microscopy. The results demonstrate that the enzyme molecules present at the air/water interface arc progressively covered by the behenic acid film. Moreover, we observe an increase of the quantity of glucose oxidase in the mixed film with lime, showing that the adsorption of glucose oxidase under the behenic acid film continues during and after the relaxation process.

International audience; Coherent excitation of a nonlinear semiconductor microcavity is theoretically reported. It intends to counterbalance the frequency drift of the cavity resonance driven by the nonlinear refractive effects, which causes a limitation in the energy coupling efficiency of an input pulse into the cavity resonance. We show that exciting such a nonlinear microcavity with tailored chirped pulses allows to maintain the benefit of light localization and to further enhance light-matter interactions, opening the way to the realization of highly efficient nonlinear devices.

International audience; Two-photon counting (TPC) interferometry has been realized by measuring the electrical current due to two-photon absorption in the space charge layer of a semiconductor detector located at the output port of an interferometer. We apply this technique to study the correlation properties of twin beams issued from parametric fluorescence. We describe in details how the different second-order correlation functions (interbeam, intrabeam) can be extracted at the femtosecond timescale from raw data. The values of these correlation functions determined by our experiments are in excellent agreement with theory. More precisely, extrabunching in twin beams is unambiguously demonstrated and theoretically described using two models: a comprehensive multimode quantum optics model and a simpler classical stochastic approach. Given the high brightness of our twin-beam source, both theories yield similar results. Finally, convenient analytical expressions of the correlation functions were derived from both theories, expressions in which we have been able to relate specific terms to accidental and exact coincidences between photons. Two-photon interferometry thus determines to which extent twin photons are twin. This technique should become a useful tool for future quantum optics developments.

International audience; We report our recent efforts for the design and fabrication of comb slot photonic crystal waveguides in silicon on insulator photonics. The main issues related to dispersion engineering, investigation of slow mode optical losses, and modal confinement metrics, have been investigated in various geometries. Nonlinear χ (3) optical properties have then been explored using a pump probe picosecond experiment and the obtained trends and results are discussed. OCIS codes: (130.5296) Photonic crystal waveguides, (130.4310) Nonlinear 1. Introduction Silicon photonics has received a strong interest in the last years, and the main efforts of the recent period have been focused on high-frequency active devices such as optical modulators and integrated detectors. To go beyond the data rates practically achievable using optoelectronic components and to reduce the energy ber bit of on-chip optical data transmissions, which appears to be a key metrics for future applications, an interesting opportunity is to exploit nonlinear optics to achieve all-optical signal processing. The main drawback of silicon is this purpose is the absence of second order nonlinear effects (χ (2)) and the strong free-carrier phenomena (Free Carrier Dispersion: FCR, Free Carrier Absorption) accompanying the Kerr effect when using χ (3)-processes. To address this issue and improve the functionality of photonic devices, the introduction of a slot in the silicon waveguide provides a way to confine light in the low index material due to the strong discontinuity at the index contrast interface [1]. Chosen according to its second and third order non-linear susceptibilities χ (2) and χ (3) , the low index material can dramatically enhance the non-linear effects in the photonic crystal waveguides. χ (2) electro-optic modulation [2] in slotted photonic crystals and χ (3) Four-Wave Mixing in slot waveguides [3] have been for example successfully demonstrated. But slotted waveguides can be also very useful for sensing thanks to the infiltration, because the analytes can interact with the extrema of the electric field, not only its evanescent part [4].

The formation of behenic acid monolayers at the air/water interface has been studied in the presence of glucose oxidase. When the enzyme is present in the subphase, spreading of behenic acid at the air/water interface leads to the formation of a mixed film of glucose oxidase and behenic acid. The pressure–area isotherms performed with various concentrations of the enzyme in the subphase showed the incorporation of the enzyme in the monolayer. The dynamics of the mixed films was studied by following the evolution of the film area at a constant pressure and the evolution of the pressure at a constant area. Glucose oxidase dramatically stabilizes the behenic acid film. A limit pressure of incorporation of glucose oxidase in the behenic acid film at the air/water interface was observed at 28 m N /m.

Mixed behenic acid/glucose oxidase ( BA GOx ) films were transferred onto CaF2 slides and gold substrates and characterized by IR and/or UV-visible spectroscopies. The results obtained were confirmed by the study of pressure-area isotherms and led to a diagrammatic model of the structure elaborated by Langmuir—Blodgett technology. This structure could present some domains with GOx organized as islets.