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Background:Primary Sjögren Syndrome (pSS) is a chronic autoimmune disease characterized by epithelial atrophy, mononuclear infiltration in exocrine glands resulting in the defective function of these glands. In pSS, atrophy of the epithelium is caused by an increased amount of apoptosis.Objective:The main aim of this study is to investigate the role of the apoptosis-related factors by studying Bcl-2, Fas and FasL expression in relation to the extent of inflammation as well as the effect of therapy on the expression of these mediators.Methods:In pSS patients (n=62) documented for their serological and clinical features, Fas, FasL and Bcl-2 plasma levels were assessed using enzyme-linked immunosorbent assays. In the same context, we investigated their expression by immunohistochemistry analysis in the labial salivary glands samples in association with the extent of inflammation.Results:Interestingly, our results indicated that in pSS patients, the plasmatic Bcl-2, Fas and FasL levels, which appeared to be associated with the severity of inflammation and were significantly elevated in comparison to the healthy controls. Moreover, a significant decrease in all these factors was observed in patients after combined corticosteroids-hydroxychloroquine therapy. Importantly, we report a strong positive correlation between Bcl-2 and NO levels. The immunohistochemical staining reveals a strong Bcl-2 expression in infiltrating mononuclear cells and a total absence in the acinar cells. The Bcl-2 level varies according to the severity of pathology. However, the expression of Fas and FasL was less important and predominantly localized in infiltrating mononuclear cells.Conclusion:Our current study highlights the involvement of Bcl-2, Fas and FasL in pSS glands injury. These factors may act as useful predictor markers of a clinical course in pSS, suggesting a novel approach in the pSS patients monitoring.

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Acoustic wave resonators are promising candidates for gravimetric biosensing. However, they generally suffer from strong acoustic radiation in liquid, which limits their quality factor and increases their frequency noise. This article presents an acoustic radiation-free gravimetric biosensor based on a locally resonant surface phononic crystal (SPC) consisting of periodic high aspect ratio electrodes to address the above issue. The acoustic wave generated in the SPC is slower than the sound wave in water, hence it prevents acoustic propagation in the fluid and results in energy confinement near the electrode surface. This energy confinement results in a significant quality factor improvement and reduces frequency noise. The proposed SPC resonator is numerically studied by finite element analysis and experimentally implemented by an electroplating-based fabrication process. Experimental results show that the SPC resonator exhibits an in-liquid quality factor 15 times higher than a conventional Rayleigh wave resonator at a similar operating frequency. The proposed radiation suppression method using SPC can also be applied in other types of acoustic wave resonators. Thus, this method can serve as a general technique for boosting the in-liquid quality factor and sensing performance of many acoustic biosensors.

Background: Oral aphthosis is one of the major manifestations of Behçet’s disease (BD), a chronic, multisystemic vasculitis. BD etio-pathogenicity related to oral health lack. Objective: This study investigated the possible relationships between poor oral hygiene, oral activity, disease severity and saliva’s Interleukin (IL)-32, IL-6, IL-10 and nitric oxide (NO) levels in Behçet’s patients to determine their role in disease prognosis and their potential therapeutic interest. Method: Fifty-six patients with BD (22 orally active; 34 orally inactive) and 31 healthy subjects have been included in our study. Salivary levels of IL-32, IL-6, and IL-10 were measured using ELISA, while NO levels were assessed by modified Griess’s method. Oral health status and disease severity scores were recorded for each participant. Kruskal-Wallis test and Spearman’s test were performed for statistical analyses. Results: We observed that the tested molecules were increased in BD patients compared to healthy controls (p˂0.05). Moreover, only IL-32 levels were associated with oral activity in patients (p˂0.05). Interestingly, the disease severity score was noted to be correlated positively and significantly with both IL-32 saliva levels (p˂0.01) and plaque index (p˂0.05) in BD patients. Furthermore, IL-32 levels were correlated with plaque index (p˂0.0001). Conclusion: Our results suggest that IL-32, IL- 6, IL-10 and NO were increased in saliva during BD. Our study indicated that IL-32 was associated with the genesis of oral ulcers in response to dental plaque. Ultimately, salivary IL-32 may serve as a prognostic biomarker and a possible therapeutic target for managing Behçet’s disease severity.

The rising need for hybrid physical platforms has triggered a renewed interest for the development of agile radio-frequency phononic circuits with complex functionalities. The combination of travelling waves with resonant mechanical elements appears as an appealing means of harnessing elastic vibration. In this work, we demonstrate that this combination can be further enriched by the occurrence of elastic non-linearities induced travelling surface acoustic waves (SAW) interacting with a pair of otherwise linear micron-scale mechanical resonators. Reducing the resonator gap distance and increasing the SAW amplitude results in a frequency softening of the resonator pair response that lies outside the usual picture of geometrical Duffing non-linearities. The dynamics of the SAW excitation scheme allows further control of the resonator motion, notably leading to circular polarization states. These results paves the way towards versatile high-frequency phononic-MEMS/NEMS circuits fitting both classical and quantum technologies., 8 pages; 7 figures

International audience; A novel Lamb wave resonator with fully suppressed acoustic radiation in water is proposed for high-resolution mass-sensitive detection of biomolecules. The elimination of acoustic radiation is achieved by slowing down the Lamb wave to a velocity lower than the sound speed in water. This enables high-quality-factor resonance in water and reduces the sensing frequency noise. High aspect ratio electrodes (HAREs) are used to slow down the Lamb wave. The elastic resonance and large surface area of the HAREs can also enhance the mass sensitivity of the device. The improved mass sensitivity together with the low frequency noise substantially improves the overall sensing resolution. Although reducing the plate thickness can also slow down the Lamb wave, it makes the device very fragile and not practical to use. In contrast, slowing down the Lamb wave by increasing electrode height allows the use of thick plates which is robust. In this article, the behavior and performance of the proposed high aspect ratio electrode Lamb wave resonator (HARE-LWR) are theoretically analyzed using finite element method simulations. Optimum design parameters were found through the simulations. Reported results show that a significant figure of merit improvement was achieved by the proposed HARE-LWR design.

Les cristaux phononiques sont de structures artificielles formees d'une distribution periodique d'au moins deux materiaux, pouvant presenter des bandes de frequences dans lesquelles la propagation des ondes acoustiques ou elastiques est evanescente. L'observation de proprietes de propagation particulieres a des basses frequences, souvent liees a des conditions de resonances, a ouvert la voie aux metamateriaux acoustiques, une classe de materiaux dont le comportement effectif est sans equivalent a l'etat naturel. Cet article vise a illustrer les proprietes originales et les perspectives d'applications des cristaux phononiques et des metamateriaux acoustiques.

Primary Sjogren's syndrome (pSS) is a systemic autoimmune disorder with a complex pathophysiology primarily affecting exocrine glands, leading to compromised secretory function. Recent studies imply that many inflammatory mediators, such as pro-inflammatory cytokines and nitric oxide, are critical in the development and perpetuation of pSS systemic manifestations. In the current study, we aimed to investigate the ex vivo immunomodulatory effect of cardamonin (C16H14O4), on pro-inflammatory cytokines, TNF-α, IL-6 and inducible nitric oxide synthase (iNOS) expression during pSS. For this purpose, peripheral blood mononuclear cells isolated from pSS patients and healthy controls were cultured with different concentrations of cardamonin. Cytokine levels were measured by ELISA and NO production was assessed using the Griess method. Inducible nitric oxide synthase expression and NF-κB activity were analyzed by immunofluorescence staining. Our results suggest that cardamonin inhibits TNF-α, IL-6 and NO production and downregulates iNOS expression and NF-κB activation. Collectively, our results highlight the ex vivo immunomodulatory effects of cardamonin on pro-inflammatory cytokine production and NO pathway in pSS patients. Therefore, cardamonin is a potential candidate for controlling inflammation during pSS.

In this paper, we report on the observation of nonlinear effects in a nanostrip phononic metasurface (NPM) that enable the tuning of resonance frequencies at 1.42 GHz. The NPM resonator made of periodic nanostrip array is fabricated on a lithium niobate substrate. Each of the nanostrip is 250-nm wide and is made of 680-nm-thick SiO2 layer stacking on 50-nm Al metal electrodes. Finite element analysis reveals that the device operates in a vertically polarized (compression) mode with substantial acoustic energy confined in the nanostrips, leading to a local resonance at low acoustic velocity. Due to the nonlinearity, the resonance frequency of the device decreases quadratically with the increase of stimulation power from 10 to 30 dBm. The underlying mechanism of the nonlinearity is found to be the power-dependent coupling of the adjacent nanostrips. This coupling induces softening of the substrate surface region, which reduces the acoustic velocity and hence the bulk radiation. As a result, the quality factor of the NPM resonator is found to improve with the increase of stimulation power. The power-dependent coupling of nanostrips in the NPM resonator demonstrates a reliable method for the realization of nonlinearity in phononic metasurfaces, which would significantly enrich the mechanisms for the manipulation of surface acoustic waves at high frequencies.

Coupling between surface acoustic waves (SAW) and arrays of mechanical resonators has appeared early in SAW history as a potential means to slow down wave propagation through mass-loading, in particular by creating corrugations on the substrate surface. This concept has been revisited over the past few years in the context of locally-resonant phononic crystals where pillars deposited on a homogeneous surface were shown to hybridize with SAW to form band gaps conditioned by the pillar resonance frequencies. Most of the works reported in the literature focus on the interaction between propagating waves and a collection of resonators. We recently considered the interaction of SAW with isolated mechanical resonators and shown that elastic energy can be strongly confined in subwavelength, micron-scale structures. In this work, we experimentally investigate the coupling characteristics of pairs of pillars driven by SAW. The objective here is to set the basics for the realization of waveguides based on compact chains of phononic resonators.

International audience; Acousto-optical modulators usually rely on coherent diffraction of light by a moving acoustic wave, leading to bulky devices with a long interaction length. We propose a subwavelength acousto-optical structure that instead relies on a double resonance to achieve strong modulation at near-infrared wavelengths. A periodic array of metal ridges on a piezoelectric substrate defines cavities that create a resonant dip in the optical transmission spectrum. The ridges simultaneously support large flexural vibrations when resonantly excited by a radio-frequency signal, effectively deforming the cavities and leading to strongly nonlinear acousto-optical modulation. The nano-optical structure could find applications in highly compact photonic devices.

International audience; We propose to achieve manipulation of mechanical vibrations at the micron scale by exploiting the interaction of individual, isolated mechanical resonators with surface acoustic waves. We experimentally investigate a sample consisting of cylindrical pillars individually grown by focused-ion-beam-induced deposition on a piezoelectric substrate, exhibiting different geometrical parameters and excited by a long-wavelength surface elastic wave. The mechanical displacement is strongly confined in the resonators, as shown by field maps obtained by laser scanning interferometry. A tenfold displacement field enhancement compared to the vibration at the surface is obtained, revealing that the energy is efficiently coupled. The spatial distribution of the elastic energy at the surface is governed by the geometrical characteristics of the resonators and can therefore be controlled by frequency tuning the elastic wave source. The results show the potential of the proposed approach to achieve dynamic control of surface phonons at the microscale or nanoscale.

Investigations of the surface acoustic wave (SAW) properties of phononic crystals in which the periodic modulation occurs on the traction-free surface did not take place until the late 1990s. Theoretical investigations initially focused on isotropic materials before being extended to the case of general anisotropy or to piezoelectric phononic crystals (PC) a few years later. Initially, experimental studies of SAW in 2D PCs were conducted on periodic structures at the millimeter scale exhibiting band gaps frequency in the range of a couple of MHz or lower. Surface modes as well as localization phenomena in linear and point defects were also demonstrated. In contrast, studies in the micrometer scale which may find applications in radio frequency (RF) communications or in MEMS devices have not started before the middle of the last decade. We propose in this chapter to report on some results obtained on the investigation of 2D SAW phononic band gap structures. The theoretical formulations of the plane-wave expansion (PWE) and of the finite difference time domain (FDTD) methods for SAWs are briefly summarized, and calculated results of SAW propagation and related phenomena such as band gaps and waveguiding are presented. Experiments conducted in PC at the micron scale allowing to demonstrate phononic band gaps and potential applications to SAW resonator devices are eventually reported.

Transparent electrodes made of ultra thin metals have recently been demonstrated with performances comparable to those offered by transparent conductive oxides (TCOs), which are traditionally used in applications such as photovoltaic cells, light emitting devices, photodetectors and electro-optical modulators. In this work we report highly uniform, optically transparent and electrically conductive nickel films. Their good performance, combined with low cost and simplicity in processing, make ultra thin Ni films highly competitive, even with respect to the latest developments in TCO technology. Nickel films can be easily incorporated into an industrial process flow and could therefore be an attractive alternative to TCOs in many industrial applications.

International audience; Control of sound in phononic band-gap structures promises novel control and guiding mechanisms. Designs in photonic systems were quickly matched in phononics, and rows of defects in phononic crystals were shown to guide sound waves effectively. The vast majority of work in such phononic guiding has been in the frequency domain, because of the importance of the phononic dispersion relation in governing acoustic confinement in waveguides. However, frequency-domain studies miss vital information concerning the phase of the acoustic field and eigenstate coupling. Using a wide range of wavevectors k, we implement an ultrafast technique to probe the wave field evolution in straight and L-shaped phononic crystal surface-phonon waveguides in real- and k-space in two spatial dimensions, thus revealing the eigenstate-energy redistribution processes and the coupling between different frequency-degenerate eigenstates. Such use of k-t space is a first in acoustics, and should have other interesting applications such as acoustic-metamaterial characterization.

A scheme is demonstrated for optical pumping of a vertical-external-cavity surface-emitting laser. The scheme is based on absorption of the pump light within the wells of the multiple-quantum-well gain structure rather than the conventional approach of absorption of a shorter wavelength in the barrier regions. The operation of a laser around 850 nm pumped by an 808 nm source demonstrates the potential of this technique for allowing operation at a significantly shorter range of wavelengths for these devices in general and specific application of high-brightness pump lasers for devices in this spectral region. A further advantage is the smaller quantum defect which results in reduced heating of the gain medium. These advantages are achieved while maintaining a slope efficiency of up to 18%, which is comparable to results obtained with a traditional pumping scheme with a similar gain medium.

International audience; We demonstrate efficient three-dimensional surface acoustic wave guidance and confinement in a high-aspect ratio electrode transducer. Each electrode acts as an elastic resonator that is evanescently coupled to its neighbors. We observe high amplitude displacement fields confined within the high aspect ratio electrodes. The stored surface waves are found to present a general shear polarization instead of the sagittal polarization expected for classical Rayleigh waves. The elastic energy is mostly distributed in the mass-loaded areas, and waves propagate within the transducer without diffraction, even for very low acoustic apertures. VC 2013 American Institute of Physics.

International audience; The propagation of surface acoustic waves in two-dimensional phononic crystals of pillars on a surface is investigated experimentally for hexagonal and honeycomb lattice symmetries. A random array of pillars is also compared to the periodic phononic crystals. Taking into account that the geometrical and physical characteristics of the pillars are the same in all cases, it is shown that the locally resonant band gap in the low frequency range is almost independent of periodicity and resilient to randomness. In contrast, the Bragg band gap disappears with the random array.

Efficient acoustic waveguides with a confinement in 3-dimensional space were obtained using high aspect ratio interdigital transducers (HAR IDTs). Energy trapping at the substrate surface is ensured by mass loading effect, while lateral confinement is preserved while reducing the acoustic aperture of the HAR IDTs down to one acoustic wavelength. A detailed analysis of such HAR IDTs fabricated on X-cut lithium niobate, with Y-propagating waves is presented. Reflection scattering parameter measurements were performed and are here reported. They show the existence of several modes with a resonance frequency much lower than the one expected for a Rayleigh wave. The wave velocity is indeed reduced from 3639 m/s down to 781 m/s. Using heterodyne laser scanning interferometry, measurements of out-of-plane displacement induced by the generated surface waves were performed. The measurement results show that the elastic energy is strongly localized within the acoustic aperture of the transducer.

International audience; We here report on the fabrication of electroplated nickel (Ni) masks for dry etching of sub-micron patterns in lithium niobate (LiNbO3). This process allows obtaining 350-nm thick Ni masks defining high air filling fraction holey arrays (e.g. openings of 1800 nm in diameter with inter-hole spacing of 300 nm, or 330 nm diameter holes spaced by 440 nm). The mask profile is perfectly vertical (angle ≈ 90°). The obtained metallic masks are used to realise photonic and phononic crystals. High aspect ratio and dense arrays of holey patterns were defined and transferred into LiNbO3 through RIE (Reactive Ionic Etching) in sulphur hexafluoride (SF6) chemistry. Nanometric holes exhibiting sidewall slope angles of the order of 60° have in this way been etched in LiNbO3. The LiNbO3/Ni selectivity is close to 6 and the etch rate around 6 nm/min.

Like photonic crystals have revolutionized the way of manipulating optical waves at the sub-micron scale, phononic crystals have more recently played similar decisive role for sound waves, or more generally elastic waves. Then, the idea of coupling light and sound in purposely designed microstructures is now emerging. In this respect, the periodic, wavelength-scale (for both optic and high-frequency acoustic waves) transverse air-hole microstructure of photonic crystal fibers (PCFs) provides additional degrees of freedom for light-sound interactions. PCFs can indeed exhibit photonic and phononic bandgap effects, allowing for tight confinement and joint waveguiding of both types of waves [1]. Electrostriction-driven Brillouin phenomena, namely backward Stimulated Brillouin Scattering (SBS) and forward Guided Acoustic Wave Brillouin Scattering (GAWBS), constitute an important category of such opto-acoustic coupling. The geometry of PCFs can dramatically modify the Brillouin spectrum, the gain and the stimulated Brillouin threshold, globally yielding much richer opto-acoustic dynamics and spectral features than in conventional fibers [2-11]. Specific transverse or longitudinal guided acoustics modes in the 100 MHz-10 GHz range can thus be selectively excited, resonantly enhanced and tightly confined within the microstructure, with an intimate dependence on its μm or sub-μm geometry. All these specific features have great potential for developing novel PCF-based distributed Brillouin sensors [6,7,12-14], for high-resolution longitudinal mapping of the intrinsic fluctuations of the fiber microstructure [15], and more generally for developing original tools of optical signal processing [1-4,9,16,17]. This talk will give a comprehensive overview of these original behaviors in a range of PCFs.

International audience; Fabrication processes implemented for the realization of micron-sized patterns in lithium niobate are presented, in view of applications to nanophotonics and phononics. Collective processes based on reactive ion etching in fluorine chemistries as well as FIB milling are discussed.

Scholte-Stoneley waves (SSW) propagate at the interface of a fluid medium and a solid medium. Their velocity is smaller than the transverse and longitudinal velocities in the solid, and smaller than the sound velocity in the fluid. We consider in this work 2D silicon-water phononic crystals (PC) and study bulk wave to SSW modal conversion at the PC surface. We report on a new theoretical and experimental investigation of conditions for Scholte-Stoneley waves generation on 2D corrugated silicon plate. The obtained experimental results confirm the SSW generation through diffraction. They appear at cut-off frequencies for diffraction orders from the classical grating law.

International audience; Using a modified Proton Exchange process we have realized Photonic Wires in X-cut LiNbO3. They exhibit highly confined mode, low propagation losses, low strain induced polarization coupling and no reduction of the nonlinear properties.

International audience; Solutions for the development of compact RF passive transducers as an alternative to standard surface or bulk acoustic wave devices are receiving increasing interest. This article presents results on the development of an acoustic band-pass filter based on periodically poled ferroelectric domains in lithium niobate. The fabrication of periodically poled transducers (PPTs) operating in the range of 20 to 650 MHz has been achieved on 3-in (76.2-mm) 500-μm-thick wafers. This kind of transducer is able to excite elliptical as well as longitudinal modes, yielding phase velocities of about 3800 and 6500 ms(-1), respectively. A new type of acoustic band-pass filter is proposed, based on the use of PPTs instead of the SAWs excited by classical interdigital transducers. The design and the fabrication of such a filter are presented, as well as experimental measurements of its electrical response and transfer function. The feasibility of such a PPT-based filter is thereby demonstrated and the limitations of this method are discussed.

[EN] We discuss theoretically the simultaneous existence of phoxonic, i.e., dual phononic and photonic, band gaps in a periodic silicon strip waveguide. The unit-cell of this one-dimensional waveguide contains a hole in the middle and two symmetric stubs on the sides. Indeed, stubs and holes are respectively favorable for creating a phononic and a photonic band gap. Appropriate geometrical parameters allow us to obtain a complete phononic gap together with a photonic gap of a given polarization and symmetry. The insertion of a cavity inside the perfect structure provides simultaneous confinement of acoustic and optical waves suitable to enhance the phonon-photon interaction. © 2011 Copyright 2011 Author(s)., This work was supported by the European Commission Seventh Framework Programs (FP7) under the FET-Open project TAILPHOX No 233883.

International audience; We report on the observation of elastic waves propagating in a two-dimensional phononic crystal composed of air holes drilled in an aluminum nitride membrane. The theoretical band structure indicates the existence of an acoustic band gap centered around 800 MHz with a relative bandwidth of 6.5% that is confirmed by gigahertz optical images of the surface displacement. Further electrical measurements and computation of the transmission reveal a much wider attenuation band that is explained by the deaf character of certain bands resulting from the orthogonality of their polarization with that of the source.

International audience; We show that an appropriate mass-loading, placed on the surface and in between the electrodes of a coplanar acoustic LiNbO3 superlattice, can counteract lateral diffraction of surface acoustic waves (SAWs). The strong confinement corresponds to a SAW mode, whose displacement is measured using laser interferometry. The proposed SAW confinement method has also potentials in acousto-optic devices, as we demonstrate a threefold reduction in the electrical power required for complete optical switching in mass-loaded superlattice with respect to similar unloaded structure. The devices have also the advantage not to suffer additional acoustic or optical loss due to the mass-loading structure.

International audience; We observe experimentally the propagation of surface-guided waves in a hypersonic phononic crystal, both in the radiative and nonradiative regions of the spectrum. Combining electrical measurements in reflection and transmission as well as optical maps of the surface displacement, a band gap extending from 0.6 to 0.95 GHz is identified in a square lattice array of 1 μm radius air holes milled in lithium niobate. The optical measurements reveal the transmission of surface-guided waves above the band gap, well inside the sound cone.

International audience; We report on the experimental study of the propagation of surface guided waves in a periodic arrangement of pillars on a semi-infinite medium. Samples composed of nickel pillars grown on a lithium niobate substrate were prepared and wide bandwidth transducers were used for the electrical generation of surface elastic waves. We identify a complete band gap for surface guided waves appearing at frequencies markedly lower than the Bragg band gap. Using optical measurements of the surface vibrations and by comparison with a finite element model, we argue that the low frequency band gap arises because of local resonances in the pillars. When resonance is reached, the acoustic energy is confined inside the pillars and transmission through the array is strongly reduced. At higher frequencies and inside the Bragg band gap, the incident surface elastic waves are almost completely reflected and the observed exponential decay of the transmission is similar to the case of phononic crystals made of holes in a substrate.

International audience; We consider launching a monochromatic surface acoustic wave packet on a large set of random scatterers. The interference of the multiple scattered waves creates a random pattern of ripples on the crystal surface that is recorded by optical interferometry. The Fourier transform of the amplitude and phase data of the measured wave field unveils the complete slowness curve, i.e., the wave-vector as a function of the propagation angle. A simple acoustic speckle model is proposed to explain this observation.

International audience; When phononic crystal were first introduced in the early 1990's, their ability to prohibit acoustic wave propagation was first demonstrated for bulk waves. Since then, it has been shown that these artificial materials offer unprecedented ways of steering the course of any type of elastic waves, bulk or guided. A series of works has then focused on investigating the effects these artificial materials could have on already confined surface-guided waves, an interest clearly driven by the prominent position surface acoustic waves and their combination with piezoelectric solids occupy in the vast field of wireless telecommunication systems. Theoretical reports stated that complete surface wave band gaps could be obtained in perfect 2D structures. Experimental demonstrations did not live up to one's expectations, though: significant energy loss was observed for frequencies supposedly lying above the bandgap and coupling of the acoustic energy to the bulk substrate was blamed. The radiation of these modes located above a sound line - defined by the dispersion relation of the bulk mode with the lowest velocity - seemed to cast a genuine stumbling block on the development of phononic structures relying on surface waves. Yet, if losses are unavoidable there, configurations do exist that can make them acceptable. In this paper, we will focus more closely on recent theoretical and experimental results that show, through the simulation, fabrication and characterization of a hypersonic phononic crystal, not only that bandgaps can be obtained at near-GHz frequencies, but also that a clear transmission of the signal can be observed even for modes lying within the sound cone.

[EN] We demonstrate theoretically that photons and acoustic phonons can be simultaneously guided and slowed down in specially designed nanostructures. Phoxonic crystal waveguides presenting simultaneous phononic and photonic band gaps were designed in perforated silicon membranes that can be conveniently obtained using silicon-on-insulator technology. Geometrical parameters for simultaneous photonic and phononic band gaps were first chosen for optical wavelengths around 1550 nm, based on the finite element analysis of a perfect phoxonic crystal of circular holes. A plain core waveguide was then defined, and simultaneous slow light and elastic guided modes were identified for some waveguide width. Joint guidance of light and elastic waves is predicted with group velocities as low as c/25 and 180 m/s, respectively. © 2011 Optical Society of America., This research has received funding from the European Community's Seventh Framework Programme (FP7/2007-2013) under grant agreement number 233883 (TAILPHOX).

International audience; We report on an integrated acousto-optic filter in domain inverted LiNbO(3) using a coplanar electrode configuration, which can achieve complete optical switching at electrical powers as low as 50mW. These values are more than one order of magnitude lower than previously reported results [Opt. Lett. 34, 3205 (2009)]. In order to design the low power consumption devices, we have calculated surface acoustic wave excitation, propagation and acousto-optic interaction in the domain inverted LiNbO(3) superlattice using scalar approximation and FEM analysis. Results from both modeling techniques are in good agreement with the experiments, including direct measurement of the acoustic displacement using laser interferometry and acousto-optic performance.

International audience; A phononic crystal exhibiting a band gap in the near-gigahertz frequency range for surface acoustic waves was fabricated in a lithium niobate substrate. Reflection and transmission properties of the sample were characterized both electrically and optically, by means of embedded broadband interdigitated transducers and optical heterodyne interferometry, respectively. Measurements performed for (XZ) propagating surface waves show the existence of a band gap between 660 and 900 MHz. Optical measurements confirm that the phononic crystal behaves as a perfect mirror for waves propagating at frequencies within the band gap. Outside of the band gap, transmission can be observed for frequencies below, but also above the forbidden frequency range, hence showing that losses experienced by high frequency surface acoustic waves, i.e. for modes located beyond the sound line, can be partially overcome.

International audience; We report on the experimental observation of a one-octave-large omnidirectional elastic band gap for longitudinal waves in a three-dimensional phononic crystal consisting of face-centered-cubic arrays of close-packed steel beads in a solid epoxy matrix. The 60% relative width of the band gap is larger than expected based on the contrast in material properties, and is confirmed by band structure diagram and transmission spectra computations. The coupling between shear and longitudinal polarizations is pointed out as a mechanism for enlarging the band gap by comparing with the steel beads in water matrix case.

International audience; The diffraction of elastic waves on a two-dimensional finite phononic crystal is investigated by a plane wave technique. It is first remarked that a full solution to the phononic crystal problem requires that all modes of the periodic structure (Bloch waves) are indentified and incorporated in the solution, including evanescent Bloch waves. An extended plane-wave expansion (PWE) method is used to obtain the complex band structure of the phononic crystal, but also the band structure of diffracted waves in the incident and exit media. Complex isofrequency curves are presented and show sharp variations of the Bloch wave vector with the angle of propagation. Finally, the complex band structures are used to formulate a reflection/transmission problem similar to the one leading to Fresnel formulas for homogeneous media. Some examples of diffracted field computations are given.

International audience; We report on two approaches to achieve ultra-smooth structures on lithium niobate (LiNbO3) substrates. The first method relies on ICP-RIE (inductively coupled-reactive ionic etching) or on RIE, and is exploited here for the fabrication of rods with smooth etched surfaces. A series of tests have been performed with fluorine gases. Nanometric rods with 200, 400 or 600 nm diameters, with a periodicity of 400, 800 and 1200 nm respectively and etched angles close to 68 for the RIE process and 75 for the ICP-RIE process have been fabricated. The second process is based on ''optical grade dicing'' and is dedicated to the fabrication of deep-etched ridge waveguides. First optical characterization results are reported. They show optical propagation losses value close to 0.1 dB/cm.

We investigate, using the Plane Wave Expansion method and an energy balance criterion, the polarization states of elastic waves in a two dimensional phononic crystal made of vacuum holes in a silicon host matrix. Pure modes can be identified for the out of plane polarization while a continuous variation of the in-plane polarization with the Bloch wave vector can be observed. The study is then extended to two-dimensional phononic crystal waveguides by using the super- cell technique. The dependence of the elastic wave polarization state on the wave guide width is investigated and shows as well a continuous variation with the Bloch wave vector. Moreover, the variation of the width of the waveguide can be used to tune both the dispersion and the polarization of guided waves.

International audience; We consider the problem of designing waveguides in nanostructures presenting simultaneously phononic and photonic band gaps. We specifically opt for designs in perforated silicon membranes that can be conveniently obtained using silicon-on- insulator technology. Geometrical parameters for simultaneous photonic and phononic band gaps are first chosen, based on the finite element analysis of a perfect phoxonic crystal of circular holes. A plain core waveguide is then defined, and simultaneous slow light and elastic guided modes are identified. Joint confinement of light and elastic waves with group velocities reduced by a factor of a few tens is predicted.

defect We report on the theoretical and experimental evidence for the occurrence of an omnidirectional elastic band gaps in one-dimensional phononic crystal structures. The structure is constituted by a periodically layered mirror deposited on a specific substrate that exhibits total reflection of waves for all incident angles and polarizations in a given frequency range. We study in this paper the influence of the nature and the filling fraction of the layered structures as well as of the substrate nature on the omnidirectional band gap. By introducing a defect piezoelectric layer in the finite size layered structure, selective resonance modes can occur within the omnidirectional bang gap under certain conditions. In this case, the elastic energy is confined to the defect layer. The frequencies of the defect modes are sensitive to the nature of the material and to the layer thicknesses. We excite the localized mode in the defect layer via interdigital transducers deposited on the substrate surface. We show a high frequency one port resonator at 4.3 GHz with high phase velocity of 43 km/s. The omnidirectional character of the band gap is crucial to confine the elastic energy in the layer.

[EN] We discuss the simultaneous existence of phononic and photonic band gaps in a periodic array of holes drilled in a Si membrane. We investigate in detail both the centered square lattice and the boron nitride (BN) lattice with two atoms per unit cell which include the simple square, triangular and honeycomb lattices as particular cases. We show that complete phononic and photonic band gaps can be obtained from the honeycomb lattice as well as BN lattices close to honeycomb. Otherwise, all investigated structures present the possibility of a complete phononic gap together with a photonic band gap of a given symmetry, odd or even, depending on the geometrical parameters. (C) 2010 Optical Society of America, This work is supported in part by the European Commission Seventh Framework Programme (FP7) under the FET-Open project TAILPHOX No 233833 and by Ministry of Higher Education and Research, Nord-Pas de Calais Regional Council and FEDER through the 'Contrat de Projets Etat Region (CPER) 2007-2013'.

International audience; The possibility to obtain hypersonic phononic band gaps in artificial crystals presenting submicron lattice parameters has shown that phononic and photonic crystals can be made of comparable dimensions, hence opening the way to simultaneous elastic and electromagnetic band gaps. We here focus on the theoretical investigation of air/lithium niobate 2D phoxonic crystals. The conditions for the existence of a full photonic band gap in this material are demanding, due to its relatively low refractive index and its elastic anisotropy which slightly hinders the opening of large phononic band gaps. The most commonly used singleatom lattices, i.e. square and hexagonal, as well as multipleatom hexagonal lattices were considered. In each case, photonic and phononic band structures were computed independently. It is observed that decreasing the symmetry of the lattice by adding atoms of different sizes inside the unit cell leads to larger phoxonic band gaps. Examples of designs for operation at an optical wavelength of 1.55 μm are given. The corresponding phononic frequencies are in the Gigahertz range.