arXiv subjects

Yan Pennec

Publications and source records attributed to Yan Pennec.

At least 19 recordsLinked to original sources

arXiv2026

Implementation of Reservoir Computing Using Coupled Microelectromechanical Drum Resonators via Sideband-Pumped Phonon-Cavity Dynamics

Reservoir computing is a bio-inspired machine learning paradigm that exploits the intrinsic dynamics of nonlinear systems with fading memory for efficient temporal information processing. Microelectromechanical resonators offer a promising platform for reservoir computing as they inherently possess the requisite nonlinear and temporal properties while also facilitating the integration of sensing and computing within a single platform. In this work, we experimentally demonstrate a physical reservoir computing platform based on two capacitively coupled drum resonators, operating in the MHz frequency regime. Taking advantage of the concept of phonon-cavity electromechanics, a pump tone is applied at the sideband of the phonon cavity while probing one of the coupled modes, analogous to optomechanical systems, thereby creating nonlinear dynamics in energy transfer between the two resonators. Physical reservoir computing is implemented by exploiting the nonlinear response induced through pump amplitude modulation in combination with a time-delay feedback loop, and the performance is evaluated using both parity and Normalized Auto-Regressive Moving Average benchmarks. This work demonstrates a compact microelectromechanical platform for the integration of sensing and reservoir computing. Moreover, the sideband pumping scheme can further extend conventional single resonator reservoir computing to a multimode architecture.

physics.app-ph↗

arXiv2025

Material-Specific Mapping of Plasmonic Modal Dispersion via Discrete Momentum-Space Probes

Accurate measurement of surface plasmon polariton (SPP) dispersion remains challenging, as conventional angle-resolved techniques are limited by surface quality, diffraction artifacts, and geometry-induced band folding. Here, we show that SPP dispersion can be reconstructed from transmission spectra of plasmonic gratings with subwavelength apertures acting as Fabry-P\'erot (FP) cavities. The approach harnesses modal hybridization between localized FP modes and SPPs, resolved using non-Hermitian eigenmode decomposition and validated by finite-difference time-domain simulations. {\omega}-k dispersion mapping is achieved by varying the grating periodicity, with each structure probing a distinct in-plane momentum state. Geometry- and material-dependent corrections for aperture-induced leakage and dispersive phase shifts yield reconstructed relations in close agreement with eigenmode calculations across non-dispersive, Drude, and Drude-Lorentz models as well as experimental optical datasets spanning metals, oxides, and nitrides. The method is material-agnostic and requires no momentum-resolved instrumentation. Sensitivity to fabrication-induced wall roughness is also assessed: FP resonance positions remain spectrally stable with no measurable linewidth broadening across the explored perturbation range, and the modal field topology is largely preserved throughout. However, transmitted amplitude decreases monotonically owing to enhanced ohmic absorption at the perturbed boundaries.

physics.optics↗

arXiv2024

Relation between interface symmetry and propagation robustness along domain walls based on valley topological photonic crystals

Valley photonic crystals provide efficient designs for the routing of light through channels in extremely compact geometries. The topological origin of the robust transport and the specific geometries under which it can take place have been questioned in recent works. In this article, we introduce a design for valley photonic crystals with richer arrangement possibilities than the standard valley photonic crystals based on two holes of different sizes in the unit cell. Our approach is based on the permutation of three sets of rhombi in an hexagonal lattice to investigate the interplay between Berry curvature, valley Chern number and chirality of interfaces to achieve robust edge-modes propagation along domain walls. We study three types of interfaces with different symmetries: the non-chiral interface with glide-mirror symmetry commonly used in honeycomb-type valley crystals, and two chiral interfaces with or without inversion symmetry of the adjacent bulk lattices. In the latter case, no valley topology is expected. We show that for the three families, edges preserving the shape of the interface through 120{\deg} sharp corners can sustain edge-modes with comparable robustness. Moreover, interfaces with glide-mirror symmetry offer promising performances in circuits with more exotic configurations, like 60{\deg} and 90{\deg} corners or arbitrary curves in which valley preservation is not guaranteed. Our work raises questions about the topological origin of the robustness of transport in valley photonic crystals, discusses the role of the chirality of the interfaces in the propagation around sharp corners, and provides a lattice scheme with broad design possibilities.

physics.optics↗

arXiv2023

Scattering-matrix approach for a quantitative evaluation of the topological protection in valley photonic crystals

In this work, we use valley-topological triangular resonators coupled to an input waveguide to evaluate the quality of the topological protection. To that purpose, we first analyze via numerical simulations the existence of backward scattering at cavity corners or transmission with pseudo-spin conversion at the splitter between the input waveguide and the cavity. We evidence that a breakdown of topological protection takes place, in particular at sharp corners, which results in transmission minima and split-resonances, otherwise non-existent. In order to evaluate the small coupling coefficients associated to this breakdown, a phenomenological model based on an exact parameterization of scattering matrices at splitters and corners of the resonators is then introduced. By comparison with the numerical simulations, we are able to quantify the loss of topological protection at sharp bends and splitters. Finally, we use the obtained set of phenomenological parameters to compare the predictions of the phenomenological model with full numerical simulations for fractal-inspired cavities based on the Sierpi\'nski triangle construction. We show that the agreement is overall good, but shows more differences for the cavity composed of the smallest triangles. Our results suggest that even in a system exempt of geometrical and structural defects, topological protection is not complete at corners, sharp bends and splitters. However, simpler but predictive calculations can be realized with a phenomenological approach, allowing simulations of very large devices beyond the reach of standard simulation methods, which is crucial to design photonic devices which gather compactness and low losses through topological conduction of electromagnetic waves.

physics.optics↗

arXiv2020

Vertical engineering for large stimulated Brillouin scattering in unreleased silicon-based waveguides

Strong acousto-optic interaction in silicon-based waveguides generally requires releasing of the silicon core to avoid mechanical leakage into the underlying silica substrate. This complicates fabrication, limits thermalization, reduces the mechanical robustness and hinders large area optomechanical devices on a single chip. Here, we overcome this limitation by employing vertical photonic-phononic engineering. Specifically, the insertion of a thick silicon nitride layer between the silicon guiding core and the silica substrate contributes to reduce GHz-frequencies phonon leakage enabling large values of the Brillouin gain in an unreleased platform. We get values of the Brillouin gain around 300 (Wm)$^{-1}$ for different configurations, which could be further increased by operation at cryogenic temperatures. These values should enable to observe Brillouin-related phenomena in cm-scale waveguides or in more compact ring resonators. This finding could pave the way towards large-area unreleased cavity and waveguide optomechanics on silicon chips.

physics.optics↗

arXiv2019

Polarization-dependent and Valley-protected Lamb Waves in Asymmetric Pillared Phononic Crystals

We present the realization of the topological valley-protected zero-order antisymmetric (A0) or symmetric (S0) and zero-order shear-horizontal (SH0) Lamb waves at different domain walls based on topologically distinct asymmetric double-sided pillared phononic crystals. The elastic periodic structures have either the triangular or the honeycomb symmetry and give rise to a double-negative branch in the dispersion curves. By artificially folding the doubly negative branch, a degenerate Dirac cone is achieved. Different polarization-dependent propagation along the same primary direction along the constituent branches are presented. Moreover, divergent polarization-dependent phenomena along different primary directions along a given branch are also reported. By imposing two large space-inversion symmetry (SIS) breaking perturbations the topological phase transition is obtained. We show that the Berry curvature becomes strongly anisotropic when the wave vector gets away from the valleys. Further, we demonstrate the unidirectional transport of A0, S0, and SH0 Lamb waves at different domain walls in straight or Z-shape wave guides. In the large SIS breaking case, we show negligible reflection at the zigzag outlet of the straight wave guide and occurrence of weak inter-valley scattering at the bending corners of the Z-shape wave guide. For a larger strength of SIS breaking, the edge states are gapped and strong reflection at the zigzag outlet and bending corners is observed. The topological protection cannot be guaranteed any more in that case.

physics.app-ph↗

arXiv2019

Valley and pseudospin-valley topologically protected edge states in symmetric pillared phononic crystals

We present a symmetric double-sided pillared phononic crystals (PPnCs) that can emulate both quantum spin Hall effect (QSHE) and quantum valley Hall effect (QVHE) by solely imposing different geometric perturbations. Indeed, the Dirac cones can occur in the low (deep subwavelength) and high frequency regime by judiciously turning the parameters of the attached pillars and even a double Dirac cone can be achieved. We realize the valley-protected, the pseudospin-protected or the pseudospin-valley coupled edge states with the proposed platform. Besides, we show a variety of refraction phenomena (positive, negative and evanescent) of the valley-polarized edge state at the zigzag termination when emulating QVHE. Further, we illustrate the valley-dependent feature of the pseudospin-valley coupled edge state and demonstrate the valley based splitting of the pseudospin-protected edge states in a Y-junction wave guide.

physics.app-ph↗

arXiv2018

Exploring rotational resonance in elastic metamaterial plates to realize doubly negative property

We report the realization of simultaneously negative effective mass density and shear modulus in a single-phase asymmetric double-sided pillared metamaterial. The negative effective mass density is achieved by the combination of bending and compressional resonances of one pillar whereas the rotational resonance of the other pillar leads to the negative effective shear modulus. The coupling between these two pillars is investigated to describe the formation of the doubly negative property. Then, a pillared system featuring chirality is designed in order to make efficient the excitation of the rotational vibration, the occurrence of which is demonstrated by the transmission spectrum. Finally, numerical simulations of the zero-index refraction are carried out to prove the occurrence of the doubly negative property.

physics.app-ph↗

arXiv2016

Spatio-Temporal Imaging of the Acoustic Field Emitted by a Single Copper Nanowire Copper Nanowires Fabrication

The monochromatic and geometrically anisotropic acoustic field generated by 400 nm and 120 nm diameter copper nanowires simply dropped on a 10 $μ$m silicon membrane is investigated in transmission using three-dimensional time-resolved femtosecond pump-probe experiments. Two pump-probe time-resolved experiments are carried out at the same time on both side of the silicon substrate. In reflection, the first radial breathing mode of the nanowire is excited and detected. In transmission, the longitudinal and shear waves are observed. The longitudinal signal is followed by a monochromatic component associated with the relaxation of the nanowire's first radial breathing mode. Finite Difference Time Domain (FDTD) simulations are performed and accurately reproduce the diffracted field. A shape anisotropy resulting from the large aspect ratio of the nanowire is detected in the acoustic field. The orientation of the underlying nanowires is thus acoustically deduced.

cond-mat.mes-hall↗

arXiv2016

Phonon-Plasmon Interaction in Metal-Insulator-Metal Localized Surface Plasmon Systems

We investigate theoretically and numerically the coupling between elastic and localized surface plasmon modes in a system of gold nanocylinders separated from a thin gold film by a dielectric spacer of few nanometers thickness. That system supports plasmon modes confined in between the bottom of the nanocylinder and the top of the gold film, which arise from the formation of interference patterns by short-wavelength metal-insulator-metal propagating plasmon. First we present the plasmonic properties of the system though computer-simulated extinction spectra and field maps associated to the different optical modes. Next a simple analytical model is introduced, which allows to correctly reproduce the shape and wavelengths of the plasmon modes. This model is used to investigate the efficiency of the coupling between an elastic deformation and the plasmonic modes. In the last part of the paper, we present the full numerical simulations of the phononic properties of the system, and then compute the acousto-plasmonic coupling between the different plasmon modes and five acoustic modes of very different shape. The efficiency of the coupling is assessed first by evaluating the modulation of the resonance wavelength, which allows comparison with the analytical model, and finally in term of time-modulation of the transmission spectra on the full visible range, computed for realistic values of the deformation of the nanoparticle.

physics.optics↗

arXiv2015

Resonant and Non-Local Properties of Phononic Metasolids

We derive a general theory of effective properties in metasolids based on phononic crystals with low frequency resonances. We demonstrate that in general these structures need to be described by means of a frequency-dependent and non-local anisotropic mass density, stiffness tensor and a third- rank coupling tensor, which shows that they behave like a non-local Willis medium. The effect of non-locality and coupling tensor manifest themselves for some particular resonances whereas they become negligible for other resonances. Considering the example of a two-dimensional phononic crystal, consisting of triangular arrangements of cylindrical shells in an elastic matrix, we show that its mass density tensor is strongly resonant and anisotropic presenting both positive and negative divergent values, while becoming scalar in the quasi-static limit. Moreover, it is found that the negative value of transverse component of the mass density is induced by a dipolar resonance, while that of the vertical component is induced by a monopolar one. Finally, the dispersion relation obtained by the effective parameters of the crystal is compared with the band structure, showing a good agreement for the low-wave number region, although the non-local effects are important given the existence of some resonant values of the wave number.

cond-mat.mtrl-sci↗

arXiv2015

Gradient Index Devices for the Simultaneous Focusing of the S0 and A0 Lamb Modes

Gradient index devices for the simultaneous control of the S 0 and A 0 Lamb modes are presented and numerically analysed. It is found a special relationship between the refractive indexes for these two modes which allows their simultaneous control by means of graded phononic crystals and thickness variations of the plate. A flat gradient index lens and a circular Luneburg lens are designed. Numerical simulations show that the performance of these devices is good for the two modes in a broadband frequency region, and that this approach can be used to design more advanced refractive devices for the total control of guided vibrational modes.

physics.class-ph↗

arXiv2015

Combined photonic-plasmonic modes inside photonic crystal cavities

In this article, we present a numerical study of the optical properties of a metal nanowire interacting with a localized cavity in a two dimensional photonic crystal. The nature of the modes, their wavelength and width are investigated as a function of the particle radius. It is shown in particular that a particle with diameter about the lattice constant presents very narrow resonances corresponding to hybrid photonic-plasmonic modes, where increased lifetime is attributed to the decrease of the radiative losses by interaction with the photonic crystal. These results open interesting applications in areas where narrow plasmonic resonances are required, as in LSP-resonance based biosensing.

physics.optics↗

arXiv2014

Effective Medium Theory for Elastic Metamaterials in Thin Elastic Plates

An effective medium theory for resonant and non-resonant metamaterials for flexural waves in thin plates is presented. The theory provides closed-form expressions for the effective parameters of arrangement of inclusions or resonators in thin plates as a function of the filling fraction of the inclusions, their physical properties and the frequency. It is shown that positive or negative effective elastic parameters are possible depending on the symmetry of the resonance but, unlike it happens for bulk elastic waves, the responsible for the negative mass density behaviour is the monopolar term, while the negative Young's modulus and Poisson's ratio is due to the combination of monopolar and quadrupolar resonances, showing also that, at least for the first order in the scattering coefficients, the dipolar resonance plays no role in the description of the effective medium. Several examples are given for both non-resonant and resonant effective parameters and the results are verified by multiple scattering theory.

cond-mat.mtrl-sci↗

arXiv2014

Omnidirectional refractive devices for flexural waves based on graded phononic crystals

Different omnidirectional refractive devices for flexural waves in thin plates are proposed and numerically analyzed. Their realization is explained by means phononic crystal plates, where a previously developed homogenization theory is employed for the design of graded index refractive devices. These devices consist of a circular cluster of inclusions with properly designed gradient in their radius. With this approach, the Luneburg and Maxwell lenses and a family of beam splitters for flexural waves are proposed and analyzed. Results show that these devices work properly in a broadband frequency region, being therefore an efficient approach for the design of refractive devices specially interesting for nano-scale applications.

cond-mat.mtrl-sci↗

arXiv2012

Optical absorption of silicon nanowires

We report on simulations and measurements of the optical absorption of silicon nanowires (NWs) versus their diameter. We first address the simulation of the optical absorption based on two different theoretical methods : the first one, based on the Green function formalism, is useful to calculate the scattering and absorption properties of a single or a finite set of NWs. The second one, based on the Finite Difference Time Domain (FDTD) method is well-adapted to deal with a periodic set of NWs. In both cases, an increase of the onset energy for the absorption is found with increasing diameter. Such effect is experimentally illustrated, when photoconductivity measurements are performed on single tapered Si nanowires connected between a set of several electrodes. An increase of the nanowire diameter reveals a spectral shift of the photocurrent intensity peak towards lower photon energies, that allows to tune the absorption onset from the ultraviolet radiations to the visible light spectrum.

cond-mat.mtrl-sci↗

arXiv2012

Phonons in Slow Motion: Dispersion Relations in Ultra-Thin Si Membranes

We report the changes in dispersion relations of hypersonic acoustic phonons in free-standing silicon membranes as thin as \sim 8 nm. We observe a reduction of the phase and group velocities of the fundamental flexural mode by more than one order of magnitude compared to bulk values. The modification of the dispersion relation in nanostructures has important consequences for noise control in nano and micro-electromechanical systems (MEMS/NEMS) as well as opto-mechanical devices.

cond-mat.mes-hall↗

arXiv2005

Magnetic relaxation of exchange biased (Pt/Co) multilayers studied by time-resolved Kerr microscopy

Magnetization relaxation of exchange biased (Pt/Co)5/Pt/IrMn multilayers with perpendicular anisotropy was investigated by time-resolved Kerr microscopy. Magnetization reversal occurs by nucleation and domain wall propagation for both descending and ascending applied fields, but a much larger nucleation density is observed for the descending branch, where the field is applied antiparallel to the exchange bias field direction. These results can be explained by taking into account the presence of local inhomogeneities of the exchange bias field.

cond-mat.other↗