Optical complex media as universal reconfigurable linear operators. Matthès, M. W., P. Del Hougne, J. De Rosny, G. Lerosey, and S. M. Popoff. Optica 6, no. 4 (2019): 465–472.
Résumé: © 2019 Optical Society of America. Performing linear operations using optical devices is a crucial building block in many fields ranging from telecommunications to optical analog computation and machine learning. For many of these applications, key requirements are robustness to fabrication inaccuracies, reconfigurability, and scalability. We propose a way to perform linear operations using complex optical media such as multimode fibers or scattering media as a computational platform driven by wavefront shaping. Given a large random transmission matrix representing light propagation in such a medium, we can extract any desired smaller linear operator by finding suitable input and output projectors. We demonstrate this concept by finding input wavefronts using a spatial light modulator that cause the complex medium to act as a desired complexvalued linear operator on the optical field. We experimentally build several 16 × 16 operators and discuss the fundamental limits of the scalability of our approach. It offers the prospect of reconfigurable, robust, and easytofabricate linear optical analog computation units.


Smart radio environments empowered by reconfigurable AI metasurfaces: an idea whose time has come. Renzo, M. D., M. Debbah, D. T. PhanHuy, A. Zappone, M. S. Alouini, C. Yuen, V. Sciancalepore, G. C. Alexandropoulos, J. Hoydis, H. Gacanin et al. Eurasip Journal on Wireless Communications and Networking 2019, no. 1 (2019).
Résumé: © 2019, The Author(s). Future wireless networks are expected to constitute a distributed intelligent wireless communications, sensing, and computing platform, which will have the challenging requirement of interconnecting the physical and digital worlds in a seamless and sustainable manner. Currently, two main factors prevent wireless network operators from building such networks: (1) the lack of control of the wireless environment, whose impact on the radio waves cannot be customized, and (2) the current operation of wireless radios, which consume a lot of power because new signals are generated whenever data has to be transmitted. In this paper, we challenge the usual “more data needs more power and emission of radio waves” status quo, and motivate that future wireless networks necessitate a smart radio environment: a transformative wireless concept, where the environmental objects are coated with artificial thin films of electromagnetic and reconfigurable material (that are referred to as reconfigurable intelligent metasurfaces), which are capable of sensing the environment and of applying customized transformations to the radio waves. Smart radio environments have the potential to provide future wireless networks with uninterrupted wireless connectivity, and with the capability of transmitting data without generating new signals but recycling existing radio waves. We will discuss, in particular, two major types of reconfigurable intelligent metasurfaces applied to wireless networks. The first type of metasurfaces will be embedded into, e.g., walls, and will be directly controlled by the wireless network operators via a software controller in order to shape the radio waves for, e.g., improving the network coverage. The second type of metasurfaces will be embedded into objects, e.g., smart tshirts with sensors for health monitoring, and will backscatter the radio waves generated by cellular base stations in order to report their sensed data to mobile phones. These functionalities will enable wireless network operators to offer new services without the emission of additional radio waves, but by recycling those already existing for other purposes. This paper overviews the current research efforts on smart radio environments, the enabling technologies to realize them in practice, the need of new communicationtheoretic models for their analysis and design, and the longterm and open research issues to be solved towards their massive deployment. In a nutshell, this paper is focused on discussing how the availability of reconfigurable intelligent metasurfaces will allow wireless network operators to redesign common and wellknown network communication paradigms.
MotsClés: 6G wireless; Environmental AI; Reconfigurable intelligent metasurfaces; Smart radio environments


Lefthanded band in an electromagnetic metamaterial induced by subwavelength multiple scattering. Yves, S., T. Berthelot, M. Fink, G. Lerosey, and F. Lemoult. Applied Physics Letters 114, no. 11 (2019).
Résumé: © 2019 Author(s). Due to the deep subwavelength unit cell in metamaterials, the quasistatic approximation is usually employed to describe the propagation. By making pairs of resonators, we highlight that multiple scattering also occurs at this scale and results in the existence of a dipolar resonance, which leads to a negative index of refraction when we consider several resonators. We experimentally verify the possibility of obtaining a negative index of refraction in periodic metamaterials in two different ways and eventually demonstrate the subwavelength recovery of several point sources in both cases.


Optimally diverse communication channels in disordered environments with tuned randomness. del Hougne, P., M. Fink, and G. Lerosey. Nature Electronics 2, no. 1 (2019): 36–41.
Résumé: © 2019, The Author(s), under exclusive licence to Springer Nature Limited. Multichannel wireless systems have become a standard solution to address our information society’s everincreasing demand for information transfer. The capacity that such systems can achieve is ultimately limited by the channel diversity in a given propagation medium, and numerous approaches to reduce channel crosstalk by engineering software or hardware details of the signals and antenna arrays have been proposed. Here we show that optimal channel diversity can be achieved by physically shaping the propagation medium itself. Using a reconfigurable metasurface placed inside a random environment, we tune the disorder and impose perfect orthogonality of wireless channels. We report experiments in the microwave domain in which we impose equal weights of the channel matrix eigenvalues for up to 4 × 4 systems, and almost equal weights in larger systems. We also demonstrate enhanced wireless image transmission in an office room in which we augmented the 3 × 3 system’s number of effectively independent channels from two to the optimum of three.


Measuring Dirac Cones in a Subwavelength Metamaterial. Yves, S., T. Berthelot, M. Fink, G. Lerosey, and F. Lemoult. Physical Review Letters 121, no. 26 (2018).
Résumé: © 2018 American Physical Society. The exciting discovery of bidimensional systems in condensed matter physics has triggered the search of their photonic analogues. In this Letter, we describe a general scheme to reproduce some of the systems ruled by a tightbinding Hamiltonian in a locally resonant metamaterial; by specifically controlling the structure and the composition it is possible to engineer the band structure at will. We numerically and experimentally demonstrate this assertion in the microwave domain by reproducing the band structure of graphene, the most famous example of those 2D systems, and by accurately extracting the Dirac cones. This is direct evidence that opting for a crystalline description of those subwavelength scaled systems, as opposed to the usual description in terms of effective parameters, makes them a really convenient tabletop platform to investigate the tantalizing challenges that solidstate physics offer.


Doubly negative bubbly metamaterials. Lanoy, M., J. H. Page, G. Lerosey, F. Lemoult, V. Leroy, and A. Tourin. In 2018 12th International Congress on Artificial Materials for Novel Wave Phenomena, METAMATERIALS 2018, 246–248., 2018.
Résumé: © 2018 IEEE. Thanks to their particularly efficient, low frequency Minnaert resonance, air bubbles are known to be excellent candidates for the realization of acoustic metamaterials. Here, we demonstrate that the introduction of pairwise spatial correlations between the bubbles can result in double negativity. This can occur when the bubble pairs are arranged either in random or periodic configurations. Predictions for both types of structure will be presented and the influence of dissipation on the doubly negative behaviour discussed.


Leveraging Chaos for WaveBased Analog Computation: Demonstration with Indoor Wireless Communication Signals. Del Hougne, P., and G. Lerosey. Physical Review X 8, no. 4 (2018).
Résumé: © 2018 authors. Published by the American Physical Society. In sight of fundamental thermal limits on further substantial performance improvements of modern digital computational processing units, wavebased analog computation is becoming an enticing alternative. A wave, as it propagates through a carefully tailored medium, performs the desired computational operation. Yet, the necessary designs are so intricate that experimental demonstrations will necessitate further technological advances. Here, we show that, counterintuitively, the carefully tailored medium can be replaced with a random medium, subject to an appropriate shaping of the incident wave front. Using tunable metasurface reflectarrays, we demonstrate our concept experimentally in a chaotic microwave cavity. We conclude that offtheshelf wireless communication infrastructure in combination with a simple reflectarray suffices to perform analog computation with WiFi waves reverberating in a room.


Layer potential approach for fast eigenvalue characterization of the Helmholtz equation with mixed boundary conditions. Dupré, M., M. Fink, J. Garnier, and G. Lerosey. Computational and Applied Mathematics 37, no. 4 (2018): 4675–4685.
Résumé: © 2018, SBMAC – Sociedade Brasileira de Matemática Aplicada e Computacional. Our goal is to propose an efficient approach to characterize the eigenvalues and eigenfunctions of the Helmholtz equation with mixed (Dirichlet and Neumann) boundary conditions. Our approach is based on layer potentials. We extend the eigenvalue characterization known for Neumann boundary conditions to the case of mixed boundary conditions. The problem is motivated by the need of such methods for realtime wavefield shaping by electronically tunable surfaces.
MotsClés: Boundary integral equation; Eigenvalue problem; Layer potential


Precise Localization of Multiple Noncooperative Objects in a Disordered Cavity by Wave Front Shaping. Del Hougne, P., M. F. Imani, M. Fink, D. R. Smith, and G. Lerosey. Physical Review Letters 121, no. 6 (2018).
Résumé: © 2018 authors. Published by the American Physical Society. Published by the American Physical Society under the terms of the »https://creativecommons.org/licenses/by/4.0/» Creative Commons Attribution 4.0 International license. Further distribution of this work must maintain attribution to the author(s) and the published article's title, journal citation, and DOI. Complicated multipath trajectories of waves in disordered cavities cause object localization to be very challenging with traditional raytracing approaches. Yet it is known that information about the object position is encoded in the Green's function. After a calibration step, traditional timereversal approaches retrieve a source's location from a broadband impulse response measurement. Here, we show that a nonemitting object's scattering contribution to a reverberant medium suffices to localize the object. We demonstrate our finding in the microwave domain. Then, we further simplify the scheme by replacing the temporal degrees of freedom (d.o.f.) of the broadband measurement with spatial d.o.f. obtained from wave front shaping. A simple electronically reconfigurable reflectarray inside the cavity dynamically modulates parts of the cavity boundaries, thereby providing spatial d.o.f. The demonstrated ability to localize multiple noncooperative objects with a singlefrequency scheme may have important applications for sensors in smart homes.


Dynamic Metasurface Aperture as Smart AroundtheCorner Motion Detector. Del Hougne, P., M. F. Imani, T. Sleasman, J. N. Gollub, M. Fink, G. Lerosey, and D. R. Smith. Scientific Reports 8, no. 1 (2018).
Résumé: © 2018 The Author(s). Detecting and analysing motion is a key feature of Smart Homes and the connected sensor vision they embrace. At present, most motion sen sors operate in lineofsight Doppler shift schemes. Here, we propose an alternative approach suitable for indoor environments, which effectively constitute disordered cavities for radio frequency (RF) waves; we exploit the fundamental sensitivity of modes of such cavities to perturbations, caused here by moving objects. We establish experimentally three key features of our proposed system: (i) ability to capture the temporal variations of motion and discern information such as periodicity (“smart”), (ii) non lineofsight motion detection, and (iii) singlefrequency operation. Moreover, we explain theoretically and demonstrate experimentally that the use of dynamic metasurface apertures can substantially enhance the performance of RF motion detection. Potential applications include accurately detecting human presence and monitoring inhabitants' vital signs.


Topological spoof plasmon polaritons based on C6symmetric crystalline metasurfaces. Fleury, R., S. Yves, T. Berthelot, M. Fink, F. Lemoult, and G. Lerosey. In 2017 11th International Congress on Engineered Material Platforms for Novel Wave Phenomena, Metamaterials 2017, 109–111., 2017.
Résumé: © 2017 IEEE. We demonstrate topological surface polaritons that propagate on the surface of a twodimensional (2D) metamaterial made of a subwavelength periodic arrangement of electromagnetic resonators. Such surface modes are obtained at the boundary between 2D domains of distinct topologies, characterized by nonzero spinChern invariants, where a spin degree of freedom is induced by relying on sixfold rotational (C6) crystal symmetry combined with timereversal symmetry. Experiments are conducted in the microwave regime to corroborate the analytical and numerical predictions. Our proposal enables robust subwavelength guiding of electromagnetic waves on a surface along predefined paths.


Shaping Microwave Fields Using Nonlinear Unsolicited Feedback: Application to Enhance Energy Harvesting. Del Hougne, P., M. Fink, and G. Lerosey. Physical Review Applied 8, no. 6 (2017).
Résumé: © 2017 American Physical Society. Wavefront shaping has emerged over the past decade as a powerful tool to control wave propagation through complex media, initially in optics and more recently also in the microwave domain with important applications in telecommunication, imaging, and energy transfer. The crux of implementing wavefront shaping concepts in real life is often its need for (direct) feedback, requiring access to the target to focus on. Here, we present the shaping of a microwave field based on indirect, unsolicited, and blind feedback which may be the pivotal step towards practical implementations. With the example of a radiofrequency harvester in a metallic cavity, we demonstrate tenfold enhancement of the harvested power by wavefront shaping based on nonlinear signals detected at an arbitrary position away from the harvesting device.


Acoustic double negativity induced by position correlations within a disordered set of monopolar resonators. Lanoy, M., J. H. Page, G. Lerosey, F. Lemoult, A. Tourin, and V. Leroy. Physical Review B 96, no. 22 (2017).
Résumé: © 2017 American Physical Society. Using a multiple scattering theory algorithm, we investigate numerically the transmission of ultrasonic waves through a disordered locally resonant metamaterial containing only monopolar resonators. By comparing the cases of a perfectly random medium with its pair correlated counterpart, we show that the introduction of short range correlation can substantially impact the effective parameters of the sample. We report, notably, the opening of an acoustic transparency window in the region of the hybridization band gap. Interestingly, the transparency window is found to be associated with negative values of both effective compressibility and density. Despite this feature being unexpected for a disordered medium of monopolar resonators, we show that it can be fully described analytically and that it gives rise to negative refraction of waves.


Multiple scattering limit in optical microscopy. Badon, A., A. C. Boccara, G. Lerosey, M. Fink, and A. Aubry. Optics Express 25, no. 23 (2017): 28914–28934.
Résumé: © 2017 Optical Society of America. Optical microscopy offers a unique insight of biological structures with a submicrometer resolution and a minimum invasiveness. However, the inhomogeneities of the specimen itself can induce multiple scattering of light and optical aberrations which limit the observation to depths close to the surface. To predict quantitatively the penetration depth in microscopy, we theoretically derive the singletomultiple scattering ratio in reflection. From this key quantity, the multiple scattering limit is deduced for various microscopic imaging techniques such as confocal microscopy, optical coherence tomography and related methods.


Crystalline Soda Can Metamaterial exhibiting Graphenelike Dispersion at subwavelength scale. Yves, S., F. Lemoult, M. Fink, and G. Lerosey. Scientific Reports 7, no. 1 (2017).
Résumé: © 2017 The Author(s). Graphene, a honeycomb lattice of carbon atoms ruled by tightbinding interaction, exhibits extraordinary electronic properties due to the presence of Dirac cones within its band structure. These intriguing singularities have naturally motivated the discovery of their classical analogues. In this work, we present a general and direct procedure to reproduce the peculiar physics of graphene within a very simple acoustic metamaterial: a double lattice of soda cans resonating at two different frequencies. The first triangular sublattice generates a bandgap at low frequency, which induces a tightbinding coupling between the resonant defects of the second honeycomb one, hence allowing us to obtain a graphenelike band structure. We prove the relevance of this approach by showing that both numerical and experimental dispersion relations exhibit the requested Dirac cone. We also demonstrate the straightforward monitoring of the coupling strength within the crystal of resonant defects. This work shows that crystalline metamaterials are very promising candidates to investigate tantalizing solidstate physics phenomena with classical waves.


Slow waves in locally resonant metamaterials line defect waveguides. Kaina, N., A. Causier, Y. Bourlier, M. Fink, T. Berthelot, and G. Lerosey. Scientific Reports 7, no. 1 (2017).
Résumé: © 2017 The Author(s). Many efforts have been devoted to wave slowing, as it is essential, for instance, in analog signal computing and is one prerequisite for increased wave/matter interactions. Despite the interest of many communities, researches have mostly been conducted in optics, where wavelengthscaled structured composite media are promising candidates for compact slow light components. Yet their structural scale prevents them from being transposed to lower frequencies. Here, we propose to overcome this limitation using the deep subwavelength scale of locally resonant metamaterials. We experimentally show, in the microwave regime, that introducing coupled resonant defects in such metamaterials creates subwavelength waveguides in which wave propagation exhibit reduced group velocities. We qualitatively explain the mechanism underlying this slow wave propagation and demonstrate how it can be used to tune the velocity, achieving group indices as high as 227. We conclude by highlighting the three beneficial consequences of our line defect slow wave waveguides: (1) the subwavelength scale making it a compact platform for low frequencies (2) the large group indices that together with the extreme field confinement enables efficient wave/matter interactions and (3) the fact that, contrarily to other approaches, slow wave propagation does not occur at the expense of drastic bandwidth reductions.


Subwavelength focusing and imaging from the far field using time reversal in subwavelength scaled resonant media. Lemoult, F., M. Dupre, M. Fink, and G. Lerosey. In International Conference on Transparent Optical Networks., 2017.
Résumé: © 2017 IEEE. In this talk we will show how the use of time dependent and broadband wave fields, in conjunction with media structured at the subwavelength scale and supporting resonant eigenmodes, permits to beat the diffraction limit from the far field for imaging or focusing purposes. Examples will be given in the microwave, the acoustic, and the optical domain.


Topological acoustic polaritons: Robust sound manipulation at the subwavelength scale. Yves, S., R. Fleury, F. Lemoult, M. Fink, and G. Lerosey. New Journal of Physics 19, no. 7 (2017).
Résumé: © 2017 IOP Publishing Ltd and Deutsche Physikalische Gesellschaft. Topological insulators, a hallmark of condensed matter physics, have recently reached the classical realm of acoustic waves. A remarkable property of timereversal invariant topological insulators is the presence of unidirectional spinpolarized propagation along their edges, a property that could lead to a wealth of new opportunities in the ability to guide and manipulate sound. Here, we demonstrate and study the possibility to induce topologically nontrivial acoustic states at the deep subwavelength scale, in a structured twodimensional metamaterial composed of Helmholtz resonators. Radically different from previous designs based on nonresonant sonic crystals, our proposal enables robust sound manipulation on a surface along predefined, subwavelength pathways of arbitrary shapes.
MotsClés: acoustic metamaterials; polaritons; quantum spin Hall effect; topological insulators


Crystalline metamaterials for topological properties at subwavelength scales. Yves, S., R. Fleury, T. Berthelot, M. Fink, F. Lemoult, and G. Lerosey. Nature Communications 8 (2017).
Résumé: The exciting discovery of topological condensed matter systems has lately triggered a search for their photonic analogues, motivated by the possibility of robust backscatteringimmune light transport. However, topological photonic phases have so far only been observed in photonic crystals and waveguide arrays, which are inherently physically wavelength scaled, hindering their application in compact subwavelength systems. In this letter, we tackle this problem by patterning the deep subwavelength resonant elements of metamaterials onto specific lattices, and create crystalline metamaterials that can develop complex nonlocal properties due to multiple scattering, despite their very subwavelength spatial scale that usually implies to disregard their structure. These spatially dispersive systems can support subwavelength topological phases, as we demonstrate at microwaves by direct field mapping. Our approach gives a straightforward tabletop platform for the study of photonic topological phases, and allows to envision applications benefiting the compactness of metamaterials and the amazing potential of topological insulators.


Smart optical coherence tomography for ultradeep imaging through highly scattering media. Badon, A., D. Li, G. Lerosey, A. C. Boccara, M. Fink, and A. Aubry. Science Advances 2, no. 11 (2016).


Spatiotemporal imaging of light transport in highly scattering media under white light illumination. Badon, A., D. Li, G. Lerosey, A. C. Boccara, M. Fink, and A. Aubry. Optica 3, no. 11 (2016): 1160–1166.


Spatiotemporal imaging of light transport in strongly scattering media. Badon, A., D. Li, G. Lerosey, C. Boccara, M. Fink, and A. Aubry. In 2016 URSI International Symposium on Electromagnetic Theory, EMTS 2016, 272–275., 2016.
Résumé: © 2016 IEEE.We report on the passive measurement of timedependent Green's functions in the optical frequency domain with lowcoherence interferometry. Inspired by previous studies in acoustics and seismology, we show how the mutual coherence function of a broadband and incoherent wavefield can directly yield the Green's functions between scatterers of a complex medium. Both the ballistic and multiple scattering components of the Green's function are retrieved. This simple and powerful approach directly yields a wealth of information about the medium under investigation. In particular, it allows to investigate locally the growth of the diffusive halo within the scattering medium. Local measurements of transport parameters can thus be performed and allow to image a strongly scattering layer with a unprecedented resolution of a few transport mean free paths. This constitutes a major breakthrough compared to stateoftheart techniques such as optical diffuse tomography.


Intensityonly measurement of partially uncontrollable transmission matrix: demonstration with wavefield shaping in a microwave cavity. Del Hougne, P., B. Rajaei, L. Daudet, and G. Lerosey. Optics Express 24, no. 16 (2016): 18631–18641.


Spatiotemporal Wave Front Shaping in a Microwave Cavity. Del Hougne, P., F. Lemoult, M. Fink, and G. Lerosey. Physical Review Letters 117, no. 13 (2016).


Soda cans metamaterial: A subwavelengthscaled phononic crystal. Lemoult, F., N. Kaina, M. Fink, and G. Lerosey. Crystals 6, no. 7 (2016).
Résumé: © 2016 by the authors; licensee MDPI, Basel, Switzerland.Photonic or phononic crystals and metamaterials, due to their very different typical spatial scales—wavelength and deep subwavelength—and underlying physical mechanisms—Bragg interferences or local resonances—, are often considered to be very different composite media. As such, while the former are commonly used to manipulate and control waves at the scale of the unit cell, i.e., wavelength, the latter are usually considered for their effective properties. Yet we have shown in the last few years that under some approximations, metamaterials can be used as photonic or phononic crystals, with the great advantage that they are much more compact. In this review, we will concentrate on metamaterials made out of soda cans, that is, Helmholtz resonators of deep subwavelength dimensions. We will first show that their properties can be understood, likewise phononic crystals, as resulting from interferences only, through multiple scattering effects and Fano interferences. Then, we will demonstrate that below the resonance frequency of its unit cell, a soda can metamaterial supports a band of subwavelength varying modes, which can be excited coherently using time reversal, in order to beat the diffraction limit from the far field. Above this frequency, the metamaterial supports a band gap, which we will use to demonstrate cavities and waveguides, very similar to those obtained in phononic crystals, albeit of deep subwavelength dimensions. We will finally show that multiple scattering can be taken advantage of in these metamaterials, by correctly structuring them. This allows to turn a metamaterial with a single negative effective property into a negative index metamaterial, which refracts waves negatively, hence acting as a superlens.
MotsClés: Acoustics; Metamaterial; Multiple scattering; Phononic crystals


Using subwavelength diffraction gratings to design open microwave cavities. Dupre, M., M. Fink, and G. Lerosey. In 2013 7th International Congress on Advanced Electromagnetic Materials in Microwaves and Optics, METAMATERIALS 2013, 133–135., 2013.
Résumé: Weintroduce an open microwave cavity that has a wall replaced by a subwavelength grating. Usually, subwavelength gratings show very low transmission. In our experiment, this phenomenon is compensated by the microwave cavity that finally allows all the energy to be transmitted. We study the far field emission of this system and show that coupling the cavity with a subwavelength grating gives rise to a zero order emission only at discrete angles and frequencies. We study the relations between angles of emissions and frequencies, the influence of geometric parameters such as the grating fill factor and the behavior of a chaotic cavity. We show that it allows us to make a configurable system that may have many applications in the fields of communications, detection and imaging, and may allow the study of open microwave cavities on a fundamental point of view. © 2013 IEEE.


Time reversal focusing and the diffraction limit. Fink, M., J. De Rosny, G. Lerosey, and A. Tourin. In Proceedings of the International School of Physics “Enrico Fermi”, 155–177. Vol. 173., 2011.
Résumé: Time reversal mirrors refocus an incidentwave field to the position of the original source, regardless of the complexity of the propagation medium. TRMs have now been implemented in a variety of physical scenarios from GHz Microwaves to MHz Ultrasonics and to hundreds of Hz in ocean acoustics. Common to this broad range of scales is a remarkable robustness exemplified by observations at all scales that the more complex the medium (random or chaotic), the sharper the focus. A TRM acts as an antenna that uses complex environments to appear wider than it is, resulting, for a broadband pulse, in a refocusing quality that does not depend on the TRM aperture. Moreover, when the complex environment is located in the near field of the source, time reversal focusing opens completely new approaches to superresolution. We will shown that, for a broadband source located inside a random metamaterial, a TRM located in the far field radiates a timereversed wave that interacts with the random medium to regenerate not only the propagating but also the evanescent waves required to refocus below the diffraction limit. © 2011 by Società Italiana di Fisica.


Exploiting spatiotemporal degrees of freedom for farfield subwavelength focusing using time reversal in fractals. Dupré, M., F. Lemoult, M. Fink, and G. Lerosey. Physical Review B – Condensed Matter and Materials Physics 93, no. 18 (2016).
Résumé: © 2016 American Physical Society. Materials which possess a high local density of states varying at a subwavelength scale theoretically permit the focusing of waves onto focal spots much smaller than the free space wavelength. To do so, metamaterials – manmade composite media exhibiting properties not available in nature – are usually considered. However, this approach is limited to narrow bandwidths due to their resonant nature. Here, we prove that it is possible to use a fractal resonator alongside time reversal to focus microwaves onto λ/15 subwavelength focal spots from the far field, on extremely wide bandwidths. We first numerically prove that this approach can be realized using a multiplechannel time reversal mirror that utilizes all the degrees of freedom offered by the fractal resonator. Then, we experimentally demonstrate that this approach can be drastically simplified by coupling the fractal resonator to a complex medium, here a cavity, that efficiently converts its spatial degrees of freedom into temporal ones. This makes it possible to achieve deep subwavelength focusing of microwave radiation by time reversing a single channel. Our method can be generalized to other systems coupling complex media and fractal resonators.


Negative refractive index and acoustic superlens from multiple scattering in single negative metamaterials. Kaina, N., F. Lemoult, M. Fink, and G. Lerosey. Nature 525, no. 7567 (2015): 77–81.


Symmetry issues in the hybridization of multimode waves with resonators: An example with Lamb waves metamaterial. Rupin, M., P. Roux, G. Lerosey, and F. Lemoult. Scientific Reports 5 (2015).
Résumé: Locally resonant metamaterials derive their effective properties from hybridization between their resonant unit cells and the incoming wave. This phenomenon is well understood in the case of plane waves that propagate in media where the unit cell respects the symmetry of the incident field. However, in many systems, several modes with orthogonal symmetries can coexist at a given frequency, while the resonant unit cells themselves can have asymmetric scattering crosssections. In this paper we are interested in the influence of symmetry breaking on the hybridization of a wave field that includes multiple propagative modes. The A 0 and S 0 Lamb waves that propagate in a thin plate are good candidates for this study, as they are either antisymmetric or symmetric. First we designed an experimental setup with an asymmetric metamaterial made of long rods glued to one side of a metallic plate. We show that the flexural resonances of the rods induce a break of the orthogonality between the A 0/S 0 modes of the freeplate. Finally, based on numerical simulations we show that the orthogonality is preserved in the case of a symmetric metamaterial leading to the presence of two independent polariton curves in the dispersion relation.


WaveField Shaping in Cavities: Waves Trapped in a Box with Controllable Boundaries. Dupré, M., P. Del Hougne, M. Fink, F. Lemoult, and G. Lerosey. Physical Review Letters 115 (2015): 017701.


Optical detection and imaging in complex media: How the memory effect can help overcome multiple scattering. Badon, A., D. Li, G. Lerosey, A. C. Boccara, M. Fink, and A. Aubry. In CLEO: QELS – Fundamental Science, CLEO_QELS 2015, 1551p., 2015.
Résumé: We report on imaging in random scattering media. Our approach is based on the measurement of a reflection matrix between a spatial light modulator and a camera. We take advantage of the memory effect to filter the multiple scattering noise and improve the detection and imaging of objects embedded in scattering media. © 2014 Optical Society of America.


Overcoming multiple scattering for detection and imaging in strongly scattering media. Badon, A., D. Li, G. Lerosey, C. Boccara, M. Fink, and A. Aubry. In Adaptive Optics: Analysis, Methods and Systems, AO 2015, 289., 2015.
Résumé: We report on imaging through thick scattering media based on a matrix approach of wave propagation. We show how to overcome multiple scattering and demonstrate imaging of targets beyond several transport mean free paths. © 2015 OSA.


Retrieving timedependent Green's functions in optics with lowcoherence interferometry. Badon, A., G. Lerosey, A. C. Boccara, M. Fink, and A. Aubry. In CLEO: QELS – Fundamental Science, CLEO_QELS 2015, 1551p., 2015.
Résumé: We report on the passive measurement of timedependent Green's functions in optics with lowcoherence interferometry. Inspired by previous studies in acoustics and seismology, we show how the correlations of a broadband and incoherent wavefield can directly yield the Green's functions between scatterers of a complex medium. © 2014 Optical Society of America.


Image transmission through a scattering medium: Inverse problem and sparsitybased imaging. Gigan, S., S. M. Popoff, A. Liutkus, D. Martina, O. Katz, G. Chardon, R. Carminati, G. Lerosey, M. A. Fink., A. C. Boccara et al. In 2014 13th Workshop on Information Optics, WIO 2014., 2014.
Résumé: © 2014 IEEE. We demonstrate how to measure accurately the transmission matrix of a complex medium. With this information, we show how to focus light, recover an image, and even perform efficient reconstruction of a sparse object.


Retrieving timedependent green's functions in optics with lowcoherence interferometry. Badon, A., G. Lerosey, A. C. Boccara, M. Fink, and A. Aubry. Physical Review Letters 114, no. 2 (2015).
Résumé: © 2015 American Physical Society. We report on the passive measurement of timedependent Green's functions in the optical frequency domain with lowcoherence interferometry. Inspired by previous studies in acoustics and seismology, we show how the correlations of a broadband and incoherent wave field can directly yield the Green's functions between scatterers of a complex medium. Both the ballistic and multiple scattering components of the Green's function are retrieved. This approach opens important perspectives for optical imaging and characterization in complex scattering media.


Timedriven superoscillations with negative refraction. Dubois, M. A., E. Bossy, S. Enoch, S. Guenneau, G. Lerosey, and P. Sebbah. Physical Review Letters 114, no. 1 (2015).
Résumé: © 2015 American Physical Society. The flatlens concept based on negative refraction proposed by Veselago in 1968 has been mostly investigated in the monochromatic regime. It was recently recognized that time development of the superlensing effect discovered in 2000 by Pendry is yet to be assessed and may spring surprises: Timedependent illumination could improve the spatial resolution of the focusing. We investigate dynamics of flexural wave focusing by a 45°tilted square lattice of circular holes drilled in a duralumin plate. Timeresolved experiments reveal that the focused image shrinks with time below the diffraction limit, with a lateral resolution increasing from 0.8λ to 0.35λ, whereas focusing under harmonic excitation remains diffraction limited. Modal analysis reveals the role in pulse reconstruction of radiating lens resonances, which repeatedly selfsynchronize at the focal spot to shape a superoscillating field.


Shaping complex microwave fields in reverberating media with binary tunable metasurfaces. Kaina, N., M. Dupre, G. Lerosey, and M. Fink. Scientific reports 4 (2014): 6693.


Experimental Demonstration of Ordered and Disordered Multiresonant Metamaterials for Lamb Waves. Rupin, M., F. Lemoult, G. Lerosey, and P. Roux. Physical Review Letters 112, no. 23 (2014).


Imaging with nature: compressive imaging using a multiply scattering medium. Liutkus, A., D. Martina, S. Popoff, G. Chardon, O. Katz, G. Lerosey, S. Gigan, L. Daudet, and I. Carron. Scientific reports 4 (2014): 5552.


Using Subwavelength Diffraction Gratings to Design Open Electromagnetic Cavities. Dupre, M., M. Fink, and G. Lerosey. Physical Review Letters 112, no. 4 (2014).


Composite media mixing Bragg and local resonances for highly attenuating and broad bandgaps. Kaina, N., M. Fink, and G. Lerosey. Scientific Reports 3 (2013).
Résumé: In this article, we investigate composite media which present both a local resonance and a periodic structure. We numerically and experimentally consider the case of a very academic and simplified system that is a quasione dimensional split ring resonator medium. We modify its periodicity to shift the position of the Bragg bandgap relative to the local resonance one. We observe that for a wellchosen lattice constant, the local resonance frequency matches the Bragg frequency thus opening a single bandgap which is at the same time very wide and strongly attenuating. We explain this interesting phenomenon by the dispersive nature of the unit cell of the medium, using an analogy with the concept of white light cavities. Our results provide new ways to design wide and efficient bandgap materials.


Ultra small mode volume defect cavities in spatially ordered and disordered metamaterials. Kaina, N., F. Lemoult, M. Fink, and G. Lerosey. Applied Physics Letters 102, no. 14 (2013).
Résumé: In this letter, we study metamaterials made out of resonant electric wires arranged on a spatial scale much smaller than the free space wavelength, and we show that they present a hybridization band that is insensible to positional disorder. We experimentally demonstrate defect cavities in disordered and ordered samples and prove that, analogous to those designed in photonic crystals, those cavities can present very high quality factors. In addition, we show that they display mode volumes much smaller than a wavelength cube, owing to the deep subwavelength nature of the unit cell. We underline that this type of structure can be shrunk down to a period close of a few skin depth. Our approach paves the way towards the confinement and manipulation of waves at deep subwavelength scales in both ordered and disordered metamaterials. © 2013 AIP Publishing LLC.
MotsClés: Defect cavity; Display modes; Freespace wavelengths; High quality factors; Positional disorder; Spatial scale; Subwavelength; Subwavelength scale; Defects; Metamaterials


Acoustooptic imaging: Merging the best of two worlds. Lerosey, G., and M. Fink. Nature Photonics 7, no. 4 (2013): 265–267.


Wave propagation control at the deep subwavelength scale in metamaterials. Lemoult, F., N. Kaina, M. Fink, and G. Lerosey. Nature Physics 9, no. 1 (2013): 55–60.
Résumé: The ability to control wave propagation is of fundamental interest in many areas of physics. Photonic crystals proved very useful for this purpose but, because they are based on Bragg interferences, these artificial media require structures with large dimensions. Metamaterials, on the other hand, can exhibit very deep subwavelength spatial scales. In general they are studied for their bulk effective properties that lead to effects such as negative refraction. Here we go beyond this effective medium paradigm and we use a microscopic approach to study metamaterials based on resonant unit cells. We show that we can tailor unit cells locally to shape the flow of waves at deep subwavelength scales. We validate our approach in experiments with both electromagnetic and acoustic waves in the metre range demonstrating cavities, waveguides, corners and splitters with centimetrescale dimensions, an order of magnitude smaller than previous proposals. © 2013 Macmillan Publishers Limited.


Exploiting the timereversal operator for adaptive optics, selective focusing and scattering pattern analysis. Popoff, S. M., A. Aubry, G. Lerosey, M. Fink, A. C. Boccara, and S. Gigan. In 2012 Conference on Lasers and ElectroOptics, CLEO 2012., 2012.
Résumé: We report on the optical measurement of the backscattering matrix in a weakly scattering medium. A decomposition of the time reversal operator allows selective and efficient focusing on individual scatterers, even through an aberrating layer. © 2012 OSA.
MotsClés: Backscattering matrix; Decomposition of the time reversal operator; Optical measurement; Scattering medium; Scattering pattern; Timereversal operator; Lasers; Optical data processing; Scattering


Dispersion in media containing resonant inclusions: Where does it come from? Lemoult, F., M. Fink, and G. Lerosey. In 2012 Conference on Lasers and ElectroOptics, CLEO 2012., 2012.
Résumé: Propagation media containing resonant inclusions have been studied for over a century in acoustics, electromagnetism or solid state physics. There exist some in nature, such as dielectrics, which contain enormous amounts of atoms. To calculate those materials permittivities one considers that each atom “sees” the same electromagnetic field and calculates the average field that takes into account an incoming wave as well as the overall response of the ensemble of atoms [1]. This macroscopic view assumes that there is no variations of the electromagnetic field at the scale of the interatomic distance. © 2012 OSA.
MotsClés: Average field; Interatomic distances; Propagation media; Electromagnetic fields; Lasers; Atoms


Compact MIMO antenna arrays using metamaterial hybridization band gaps. Lerosey, G., C. Leray, F. Lemoult, J. De Rosny, and A. Tourin. In IEEE Antennas and Propagation Society, APS International Symposium (Digest), 774–777., 2012.
Résumé: In this talk, we show how the concept of hybridization band gap in metamaterials can be utilized to create antennas for MIMO applications. Those strongly decoupled antennas present at the same time a very small form factor and a very low correlation. To that aim, we first explain briefly the concept of hybridization between a resonator and the free space waves continuum. Then we expose the methodology we use to design multiports antennas based on that concept. We present results of several antennas designed using this idea, especially in the wifi bands, and give potential solutions for multiband compact MIMO antennas for LTE applications. © 2012 IEICE.
MotsClés: Free spaces; Low correlation; MIMO antenna; MIMO applications; Multiband; Potential solutions; Small form factors; Antenna arrays; Approximation theory; Energy gap; Metamaterials; Metamaterial antennas


Far field subwavelength imaging of magnetic patterns. Ourir, A., G. Lerosey, F. Lemoult, M. Fink, and J. De Rosny. Applied Physics Letters 101, no. 11 (2012).
Résumé: Far field imaging of subwavelength magnetic objects in real time is a very challenging issue. We propose an original solution based on a planar array of closely spaced split ring resonators. Hybridization between the resonators of such metalens induces subwavelength modes with different frequencies. Thanks to these high Q resonating modes, Purcell like effect allows an evanescent source, close to the metalens, to emit waves that can be collected efficiently in the far field. We present the first microwave experimental demonstration of such metalens to image of a subwavelength magnetic pattern. Numerical simulation shows that this approach is still valid at THz frequencies. © 2012 American Institute of Physics.
MotsClés: Different frequency; Far field; Farfield imaging; Magnetic patterns; MetaLens; Planar arrays; Real time; Split ring resonator; Subwavelength; Subwavelength imaging; THz frequencies; Physical properties; Physics


A polychromatic approach to farfield superlensing at visible wavelengths. Lemoult, F., M. Fink, and G. Lerosey. Nature Communications 3 (2012).
Résumé: Breaking the diffraction barrier in the visible part of the electromagnetic spectrum is of fundamental importance. Farfield subwavelength focusing of light could, for instance, drastically broaden the possibilities available in nanolithography, lightmatter interactions and sensing at the nanoscale. Similarly, imaging with a nanometric resolution could result in incredible breakthroughs in soft matter and biology. There have been numerous proposals in this regard based on metamaterials, structured illumination methods or diffractive optical components. The common denominator of all these approaches resides in their monochromatic nature. Here we show that using polychromatic light in dispersive metamaterials allows us to circumvent many limitations associated with previous monochromatic approaches. We design a plasmonic metalens based on metallic nanorods that, when used with broadband light fields, can beat the diffraction limit for imaging and focusing from the far field. © 2012 Macmillan Publishers Limited. All rights reserved.
MotsClés: nanomaterial; nanorod; article; diffraction; electromagnetic field; electromagnetic radiation; imaging system; lens; light; polychromatic light; spectral sensitivity


Hybridization band gap based smart antennas: Deep subwavelength yet directional and strongly decoupled MIMO antennas. Lerosey, G., C. Leray, F. Lemoult, J. De Rosny, A. Tourin, and M. Fink. In Proceedings of 6th European Conference on Antennas and Propagation, EuCAP 2012, 2697–2701., 2012.
Résumé: In this paper, we show how the concept of hybridization band gaps can be utilized to create antennas for MIMO applications. Those strongly decoupled antennas present at the same time a very small form factor and a very low correlation. To that aim, we first explain briefly the concept of hybridization between a resonator and the free space waves continuum. Then we expose the methodology we use to design multiports antennas based on that concept. We present numerical and experimental results of 2 ports MIMO antennas at 2.45 GHz, printed on a PCB, whose areas are smaller than 2.6*2.6 cm 2. The two ports display experimentally peak gains of a about 4 dB, efficiencies of 80%, a coupling lower than 30 dB and a correlation lower than 0.1. © 2012 IEEE.
MotsClés: compact antenna arrays; electromagnetic band gap antennas; metamaterials; MIMO antennas; photonic crystals; Smart antennas; Compact antenna; Electromagnetic band gap antennas; Free spaces; Low correlation; MIMO antenna; MIMO applications; Peak gain; Small form factors; Subwavelength; Approximation theory; Energy gap; Metamaterials; Photonic crystals; Smart antennas; Metamaterial antennas


Controlling waves in space and time for imaging and focusing in complex media. Mosk, A. P., A. Lagendijk, G. Lerosey, and M. Fink. Nature Photonics 6, no. 5 (2012): 283–292.
Résumé: In complex media such as white paint and biological tissue, light encounters nanoscale refractiveindex inhomogeneities that cause multiple scattering. Such scattering is usually seen as an impediment to focusing and imaging. However, scientists have recently used strongly scattering materials to focus, shape and compress waves by controlling the many degrees of freedom in the incident waves. This was first demonstrated in the acoustic and microwave domains using time reversal, and is now being performed in the optical realm using spatial light modulators to address the many thousands of spatial degrees of freedom of light. This approach is being used to investigate phenomena such as optical superresolution and the time reversal of light, thus opening many new avenues for imaging and focusing in turbid media. © 2012 Macmillan Publishers Limited. All rights reserved.


Exploiting the timereversal operator for adaptive optics, selective focusing, and scattering pattern analysis. Popoff, S. M., A. Aubry, G. Lerosey, M. Fink, A. C. Boccara, and S. Gigan. Physical Review Letters 107, no. 26 (2011).
Résumé: We report on the experimental measurement of the backscattering matrix of a weakly scattering medium in optics, composed of a few dispersed gold nanobeads. The decomposition of the timereversal operator is applied to this matrix and we demonstrate selective and efficient focusing on individual scatterers, even through an aberrating layer. Moreover, we show that this approach provides the decomposition of the scattering pattern of a single nanoparticle. These results open important perspectives for optical imaging, characterization, and selective excitation of nanoparticles. © 2011 American Physical Society.
MotsClés: Backscattering matrix; Experimental measurements; matrix; Nanobeads; Optical imaging; Scattering medium; Scattering pattern; Selective excitations; Single nanoparticle; Timereversal operator; Nanoparticles; Scattering


Controlling light through optical disordered media: Transmission matrix approach. Popoff, S. M., G. Lerosey, M. Fink, A. C. Boccara, and S. Gigan. New Journal of Physics 13 (2011).
Résumé: We experimentally measure the monochromatic transmission matrix (TM) of an optical multiple scattering medium using a spatial light modulator together with a phaseshifting interferometry measurement method. The TM contains all the information needed to shape the scattered output field at will or to detect an image through the medium. We confront theory and experiment for these applications and study the effect of noise on the reconstruction method. We also extracted from the TM information about the statistical properties of the medium and the light transport within it. In particular, we are able to isolate the contributions of the memory effect and measure its attenuation length. © IOP Publishing Ltd and Deutsche Physikalische Gesellschaft.
MotsClés: Attenuation lengths; Disordered media; Light transport; Memory effects; Multiplescattering medium; Phase shifting Interferometry; Reconstruction method; Spatial light modulators; Statistical properties; Transmission matrix; Light modulators; Light transmission


Time reversal in subwavelengthscaled resonant media: Beating the diffraction limit. Lemoult, F., A. Ourir, J. De Rosny, A. Tourin, M. Fink, and G. Lerosey. International Journal of Microwave Science and Technology (2011).
Résumé: Time reversal is a physical concept that can focus waves both spatially and temporally regardless of the complexity of the propagation medium. Time reversal mirrors have been demonstrated first in acoustics, then with electromagnetic waves, and are being intensively studied in many fields ranging from underwater communications to sensing. In this paper, we will review the principles of time reversal and in particular its ability to focus waves in complex media. We will show that this focusing effect depends on the complexity of the propagation medium rather than on the time reversal mirror itself. A modal approach will be utilized to explain the physical mechanism underlying the concept. A particular focus will be given on the possibility to break the diffraction barrier from the far field using time reversal. We will show that finite size media made out of coupled subwavelength resonators support modes which can radiate efficiently in the far field spatial information of the near field of a source. We will show through various examples that such a process, due to reversibility, permits to beat the diffraction limit using far field time reversal, and especially that this result occurs owing to the broadband inherent nature of time reversal. © 2011 Fabrice Lemoult et al.


Revisiting the wire medium: An ideal resonant metalens. Lemoult, F., M. Fink, and G. Lerosey. Waves in Random and Complex Media 21, no. 4 (2011): 591–613.
Résumé: This article is the first one in a series of two dealing with the concept of a 'resonant metalens' we introduced recently. Here, we focus on the physics of a medium with finite dimensions consisting of a square lattice of parallel conducting wires arranged on a subwavelength scale. This medium supports electromagnetic fields that vary much faster than the operating wavelength. We show that such modes are dispersive due to the finiteness of the medium. Their dispersion relation is established in a simple way, a link with designer plasmons is made, and the canalization phenomenon is reinterpreted in the light of our model. We explain how to take advantage of this dispersion in order to code subwavelength wavefields in time. Finally, we show that the resonant nature of the medium ensures an efficient coupling of these modes with free space propagating waves and, thanks to the Purcell effect, with a source placed in the near field of the medium. © 2011 Taylor & Francis.
MotsClés: Conducting wire; Dispersion relations; Efficient coupling; Finite dimensions; Free space; MetaLens; Near fields; Operating wavelength; Purcell effect; Square lattices; Subwavelength; Wavefields; Wire medium; Electromagnetic fields; Wire; Dispersion (waves)


Farfield subwavelength imaging and focusing using a wire medium based resonant metalens. Lemoult, F., M. Fink, and G. Lerosey. Waves in Random and Complex Media 21, no. 4 (2011): 614–627.
Résumé: This is the second article in a series of two dealing with the concept of a 'resonant metalens' we introduced recently. This is a new type of lens capable of coding in time and radiating efficiently in the farfield region subdiffraction information about an object. A proof of the concept of such a lens is performed in the microwave range, using a medium made out of a square lattice of parallel conducting wires with finite length. We investigate a subwavelength focusing scheme with time reversal and demonstrate experimentally spots with focal widths of λ /25. Through a crosscorrelation based imaging procedure we show an image reconstruction with a resolution of λ/80. Eventually we discuss the limitations of such a lens which reside essentially in losses. © 2011 Taylor & Francis.
MotsClés: Conducting wire; Cross correlations; Farfield; Farfield region; Finite length; MetaLens; Square lattices; Subdiffraction; Subwavelength; Time reversal; Wire medium; Image reconstruction; Wire; Focusing


Transmission matrix in optics: Taking advantage of transmission channels for image transmission in disordered materials. Popoff, S. M., G. Lerosey, R. Carminati, M. Fink, A. C. Boccara, and S. Gigan. In 2011 Conference on Lasers and ElectroOptics Europe and 12th European Quantum Electronics Conference, CLEO EUROPE/EQEC 2011., 2011.
Résumé: Recently, a method has been proposed by I. Vellekoop et al. [1] to focus light through a multiple scattering material, using a spatial light modulator as a tool to shape the incoming beam to obtain a maximal interference on a speckle spot of the output speckle pattern. The result is a bright, diffraction limited, spot which can be several hundred times brighter than the rest of the speckle. © 2011 IEEE.
MotsClés: Diffraction limited; Disordered materials; Spatial light modulators; Speckle patterns; Transmission channels; Transmission matrix; Electron optics; Light modulators; Optics; Quantum electronics; Speckle; Light


Acoustic resonators for farfield control of sound on a subwavelength scale. Lemoult, F., M. Fink, and G. Lerosey. Physical Review Letters 107, no. 6 (2011).
Résumé: We prove experimentally that broadband sounds can be controlled and focused at will on a subwavelength scale by using acoustic resonators. We demonstrate our approach in the audible range with soda cans, that is, Helmholtz resonators, and commercial computer speakers. We show that diffractionlimited sound fields convert efficiently into subdiffraction modes in the collection of cans that can be controlled coherently in order to obtain focal spots as thin as 1/25 of a wavelength in air. We establish that subwavelength acoustic pressure spots are responsible for a strong enhancement of the acoustic displacement at focus, which permits us to conclude with a visual experiment exemplifying the interest of our concept for subwavelength sensors and actuators. © 2011 American Physical Society.
MotsClés: Acoustic pressures; Diffraction limited; Farfield; Focal spot; Helmholtz resonators; Sensors and actuators; Strong enhancement; Subdiffraction; Subwavelength; Subwavelength scale; Visual experiments; Acoustic fields; Resonators; Acoustic resonators


Image transmission through an opaque material. Popoff, S., G. Lerosey, M. Fink, A. C. Boccara, and S. Gigan. Nature Communications 1, no. 6 (2010).
Résumé: Optical imaging relies on the ability to illuminate an object, collect and analyse the light it scatters or transmits. Propagation through complex media such as biological tissues was so far believed to degrade the attainable depth, as well as the resolution for imaging, because of multiple scattering. This is why such media are usually considered opaque. Recently, we demonstrated that it is possible to measure the complex mesoscopic optical transmission channels that allow light to traverse through such an opaque medium. Here, we show that we can optimally exploit those channels to coherently transmit and recover an arbitrary image with a high fidelity, independently of the complexity of the propagation. © 2010 Macmillan Publishers Limited. All rights reserved.
MotsClés: article; imaging system; laser diffraction; light scattering; optical tomography; visual system


Measuring and exploiting the transmission matrix in optics. Popoff, S. M., G. Lerosey, R. Carminati, M. Fink, A. C. Boceara, and S. Gigan. In Lasers and ElectroOptics/Quantum Electronics and Laser Science Conference: 2010 Laser Science to Photonic Applications, CLEO/QELS 2010., 2010.
Résumé: We introduce a method to measure the transmission matrix of a complex medium. This matrix exhibits statistical properties in good agreement with random matrix theory and allows light focusing and imaging through the random medium. ©2010 IEEE.
MotsClés: Complex medium; Light focusing; matrix; Random matrix theory; Random medium; Statistical properties; Transmission matrix


Theory of electromagnetic timereversal mirrors. De Rosny, J., G. Lerosey, and M. Fink. IEEE Transactions on Antennas and Propagation 58, no. 10 (2010): 3139–3149.
Résumé: The theory of monochromatic timereversal mirrors (TRM) or equivalently phase conjugate mirrors is developed for electromagnetic waves. We start from the fundamental timesymmetry of the Maxwell's equations. From this symmetry, a differential expression similar to the Lorentz reciprocity theorem is deduced. The radiating conditions on TRM are expressed in terms of 6dimension Green's functions. To predict the time reversal focusing on antenna arrays, a formalism that involves impedance matrix is developed. We show that antenna coupling can dramatically modify the focal spot. Especially, we observe, that in some circumstances, subwavelength focusing on a bidimensional array may arise. © 2010 IEEE.
MotsClés: Antenna arrays; diffraction; microwaves; phase conjugate mirrors; plasmonic; subwavelength focusing; timereversal; timesymmetry; Phase conjugate mirrors; Plasmonic; Subwavelength; Timereversal; timesymmetry; Antenna phased arrays; Diffraction; Electromagnetic waves; Electromagnetism; Focusing; Green's function; Maxwell equations; Mirrors; Plasmons; Radio waves; Antennas


Resonant metalenses for breaking the diffraction barrier. Lemoult, F., G. Lerosey, J. De Rosny, and M. Fink. Physical Review Letters 104, no. 20 (2010).
Résumé: We introduce the resonant metalens, a cluster of coupled subwavelength resonators. Dispersion allows the conversion of subwavelength wave fields into temporal signatures while the Purcell effect permits an efficient radiation of this information in the far field. The study of an array of resonant wires using microwaves provides a physical understanding of the underlying mechanism. We experimentally demonstrate imaging and focusing from the far field with resolutions far below the diffraction limit. This concept is realizable at any frequency where subwavelength resonators can be designed. © 2010 The American Physical Society.
MotsClés: Diffraction barrier; Diffraction limits; Far field; MetaLens; Purcell effect; Subwavelength; Subwavelength resonators; Temporal signatures; Underlying mechanism; Wavefields; Resonators


Experimental validation of time reversal ultra wideband communication system for high data rates. Naqvi, I. H., G. E. Zein, G. Lerosey, J. De Rosny, P. Besnier, A. Tourin, and M. Fink. IET Microwaves, Antennas and Propagation 4, no. 5 (2010): 643–650.
Résumé: An experimental validation of high data rate communication for a time reversal (TR) ultra wideband (UWB) communication system is performed using binary pulse amplitude modulation (BPAM) in two different dense multipath propagation channels for different data rates (15.62Mbps≤Rb≤1Gbps). From the measured received signals, signal, interference and noise contributions are separated. At very high data rates, interference has the most dominant contribution of all. Furthermore, without any processing and equalisation at the receiver, bit error rate (BER) performance is compared for different Rb It is shown that for Rb≤125Mbps, TR system gives a good BER performance. Finally, the authors introduce a modified TR scheme in which total bandwidth of the TR system is divided into Nsubbands contributing equal power in the power spectral density (PSD). This technique enables a flat PSD of the TR transmitted signal, reduces inter symbol interference (ISI) and therefore improves the BER performance of the system. © 2010 © The Institution of Engineering and Technology.
MotsClés: BER performance; Bit error rate performance; Data rates; Dense multipath; Dominant contributions; Equalisation; Experimental validations; High data rate; High data rate communications; Noise contributions; Propagation channels; Received signals; Time reversal; Transmitted signal; Ultrawideband communications; Amplitude modulation; Broadband networks; Communication systems; Data flow analysis; Power spectral density; Pulse amplitude modulation; Satellite communication systems; Bit error rate


NanoOptics: YagiUda antenna shines bright. Lerosey, G. Nature Photonics 4, no. 5 (2010): 267–268.


NanoOptics: YagiUda antenna shines bright. Lerosey, G. Nature Photonics (2010).


Measuring the transmission matrix in optics: An approach to the study and control of light propagation in disordered media. Popoff, S. M., G. Lerosey, R. Carminati, M. Fink, A. C. Boccara, and S. Gigan. Physical Review Letters 104, no. 10 (2010).
Résumé: We introduce a method to experimentally measure the monochromatic transmission matrix of a complex medium in optics. This method is based on a spatial phase modulator together with a fullfield interferometric measurement on a camera. We determine the transmission matrix of a thick random scattering sample. We show that this matrix exhibits statistical properties in good agreement with random matrix theory and allows light focusing and imaging through the random medium. This method might give important insight into the mesoscopic properties of a complex medium. © 2010 The American Physical Society.
MotsClés: Complex medium; Disordered media; Fullfield; Interferometric measurement; matrix; Mesoscopic properties; Random matrix theory; Random medium; Random scattering; Spatial phase modulator; Statistical properties; Transmission matrix; Light; Light propagation; Light transmission


Manipulating Spatiotemporal Degrees of Freedom of Waves in Random Media. Lemoult, F., G. Lerosey, J. De Rosny, and M. Fink. Physical Review Letters 103, no. 17 (2009).
Résumé: We show that all the spatiotemporal degrees of freedom available in a complex medium can be harnessed and converted into spatial ones. This is demonstrated experimentally through an instantaneous spatial inversion, using broadband ultrasonic waves in a multiple scattering sample. We show theoretically that the inversion convergence is governed by the total number of degrees of freedom available in the medium for a fixed bandwidth and demonstrate experimentally its use for complex media investigation. We believe our approach has potential in sensing, imagery, focusing, and telecommunication. © 2009 The American Physical Society.
MotsClés: Complex media; Complex medium; Degrees of freedom; Number of degrees of freedom; Waves in random media; Ultrasonics; Mechanics


Timereversed waves and superresolution. Fink, M., J. de Rosny, G. Lerosey, and A. Tourin. Comptes Rendus Physique 10, no. 5 (2009): 447–463.
Résumé: Timereversal mirrors (TRMs) refocus an incident wavefield to the position of the original source regardless of the complexity of the propagation medium. TRMs have now been implemented in a variety of physical scenarios from GHz microwaves to MHz ultrasonics and to hundreds of Hz in ocean acoustics. Common to this broad range of scales is a remarkable robustness exemplified by observations at all scales that the more complex the medium (random or chaotic), the sharper the focus. A TRM acts as an antenna that uses complex environments to appear wider than it is, resulting for a broadband pulse, in a refocusing quality that does not depend on the TRM aperture. Moreover, when the complex environment is located in the near field of the source, timereversal focusing opens completely new approaches to superresolution. We will show that, for a broadband source located inside a random metamaterial, a TRM located in the far field radiated a timereversed wave that interacts with the random medium to regenerate not only the propagating but also the evanescent waves required to refocus below the diffraction limit. This focusing process is very different from that developed with superlenses made of negative index material only valid for narrowband signals. We will emphasize the role of the frequency diversity in timereversal focusing. To cite this article: M. Fink et al., C. R. Physique 10 (2009). © 2009.
MotsClés: Metamaterials; Timereversal mirror


Subwavelength dynamic focusing in plasmonic nanostructures using time reversal. Bartal, G., G. Lerosey, and X. Zhang. Physical Review B – Condensed Matter and Materials Physics 79, no. 20 (2009).
Résumé: We employ time reversal for deep subwavelength focusing in plasmonic periodic nanostructures. The strong anisotropy enables propagating modes with very large transverse wave vector and moderate propagation constant, facilitating transformation of diffractionlimited plane waves to high K Bloch waves in the plasmonic nanostructure. Time reversal is used to excite the waves in the nanostructure at the exact amplitude and phase to focus the incident light to dimensions well below the diffraction limit at any point in the structure, exemplifying a true subdiffractional confinement and resolution. © 2009 The American Physical Society.


Controlling the phase and amplitude of plasmon sources at a subwavelength scale. Lerosey, G., D. F. P. Pile, P. Mathieu, G. Bartel, and X. Zheng. Nano Letters 9, no. 1 (2009): 327–331.
Résumé: We present a new class of nanoscale plasmonίc sources based on subwavelength dielectric cavities embedded in a metal siab. Exploiting the streng dispersion near the FabryPerot resonance in such a resonator, we control the phase and the amplitude of the generated plasmons at the subwavelength scale. As an example, we present a subwavelength unidirectional plasmonic antenna utilizing interference between two plasmonic cavίty sources wίth matched phase and amplitude.© 2009 American Chemcal Society.
MotsClés: Dielectric cavities; Fabryperot resonances; Nanoscale; New class; Sub wavelengths; Subwavelength scale; Optical data storage; Plasmons; nanomaterial; article; chemical model; chemistry; computer simulation; conformation; crystallization; macromolecule; materials testing; methodology; nanotechnology; particle size; refractometry; surface plasmon resonance; surface property; ultrastructure; Computer Simulation; Crystallization; Macromolecular Substances; Materials Testing; Models, Chemical; Molecular Conformation; Nanostructures; Nanotechnology; Particle Size; Refractometry; Surface Plasmon Resonance; Surface Properties


Focusing beyond the diffraction limit with farfield time reversal. Lerosey, G., J. De Rosny, A. Tourin, and M. Fink. Science 315, no. 5815 (2007): 1120–1122.
Résumé: We present an approach for subwavelength focusing of microwaves using both a timereversal mirror placed in the far field and a random distribution of scatterers placed in the near field of the focusing point. The farfield timereversal mirror is used to build the timereversed wave field, which interacts with the random medium to regenerate not only the propagating waves but also the evanescent waves required to refocus below the diffraction limit. Focal spots as small as onethirtieth of a wavelength are described. We present one example of an application to telecommunications, which shows enhancement of the information transmission rate by a factor of 3.
MotsClés: diffraction; microwave radiation; telecommunication; wavelength; acoustics; article; diffraction; lens; lithotripsy; microwave radiation; priority journal; scanning near field optical microscopy; sound transmission; technology; telecommunication; time; ultrasound


Time reversal telecommunications in complex environments. Tourin, A., G. Lerosey, J. de Rosny, A. Derode, and M. Fink. Comptes Rendus Physique 7, no. 7 (2006): 816–822.
Résumé: The time reversal technique is well known in acoustics and has lead to remarkable applications in ultrasound and underwater acoustics. Here we propose to apply it to MIMO (Multiple Input – Multiple Output) UWB (Ultra Wide Band) communication: in a first 'training' step, the intended user transmits an electromagnetic pulse that propagates in a medium, where it undergoes multiple reflections. The resulting signals are recorded at the base station by one or more antennas, time reversed and used to precode the transmitted symbols. The resulting sequences are sent back by the antennas. The timereversed wave retraces its former paths and leads to a focus of the message in space and time at the receiver. The equalization step is thus simplified since TR compensates for the reverberation caused by the channel. Furthermore, TR takes advantage of the multipaths to increase the signal strength at the receiver and to improve spatial focusing. To cite this article: A. Tourin et al., C. R. Physique 7 (2006). © 2006 Académie des sciences.
MotsClés: MIMO; Multiple scattering; Reverberation; Time reversal; UWB


Time reversal of wideband microwaves. Lerosey, G., J. De Rosny, A. Tourin, A. Derode, and M. Fink. Applied Physics Letters 88, no. 15 (2006).
Résumé: In this letter, time reversal is applied to wideband electromagnetic waves in a reverberant room. To that end a multiantenna time reversal mirror (TRM) has been built. A 150 MHz bandwidth pulse at a central frequency of 2.45 GHz is radiated by a monopolar antenna, spread in time due to reverberation, recorded at the TRM, time reversed, and retransmitted. The timereversed wave converges back to its source and focus in both time and space. The time compression is studied versus the number of antennas in the TRM and its bandwidth. The focal spot is also measured thanks to an eightchannel receiving array. © 2006 American Institute of Physics.
MotsClés: Arrays; Bandwidth; Microwave antennas; Mirrors; Reverberation; Monopolar antenna; Receiving array; Time reversal mirror (TRM); Microwaves


Time reversal of electromagnetic waves and telecommunication. Lerosey, G., J. De Rosny, A. Tourin, A. Derode, G. Montaldo, and M. Fink. Radio Science 40, no. 6 (2005).
Résumé: [1] Time reversal (TR) communication in various configurations (single input, single output (SISO); multiple inputs, single output (MISO); or multiple inputs, multiple outputs (MIMO)) is studied. In particular, we report an experimental demonstration of time reversal focusing with electromagnetic waves in a SISO scheme. An antenna transmits a 1 μs electromagnetic pulse at a central frequency of 2.45 GHz in a highQ cavity. Another antenna records the strongly reverberated signal. The timereversed wave is built and transmitted back by the same antenna acting now as a time reversal mirror. The wave is found to converge to its initial source and is compressed in time. The quality of focusing is determined by the frequency bandwidth and the spectral correlations of the field within the cavity. A spatial focusing of the compressed pulse is also shown. This experiment is the first step for a communication scheme based on time reversal. It would be very interesting for ultrawideband communication in complex media since TR would permit compensation for delay spreading. MISO and MIMO TR communications are discussed on the basis of smallscale experiments with ultrasound. In particular, the binary error rate of the method is studied as a function of both data rate and external noise. A simple theoretical approach explains the results. Copyright 2005 by the American Geophysical Union.
MotsClés: Antennas; Bandwidth; Error analysis; Functions; Telecommunication systems; Binary error rate; Complex media; Ultrawideband communication; Electromagnetic waves


Telecommunication in a disordered environment with iterative time reversal. Montaldo, G., G. Lerosey, A. Derode, A. Tourin, J. de Rosny, and M. Fink. Waves Random Media 14, no. 3 (2004): 287–302.
Résumé: We present a method to transmit digital information through a highly scattering medium in a MIMOMU (multiple input multiple output multiple users) context. It is based on iterations of a timereversal process, and permits us to focus short pulses, both spatially and temporally, from a base antenna to different users. This iterative technique is shown to be more efficient (lower intersymbol interference and lower error rate) than classical timereversal communication, while being computationally light and stable. Experiments are presented: digital information is conveyed from 15 transmitters to 15 receivers by ultrasonic waves propagating through a highly scattering slab. From a theoretical point of view, the iterative technique achieves the inverse filter of propagation in the subspace of nonnull singular values of the timereversal operator. We also investigate the influence of external additive noise, and show that the number of iterations can be optimized to give the lowest error rate. © 2004 IOP Publishing Ltd.
MotsClés: Antenna lobes; Antennas; Digital communication systems; Eigenvalues and eigenfunctions; Iterative methods; Matrix algebra; Signal receivers; Transmitters; Ultrasonic propagation; Multiple input multiple output multiple users; Short pulses; Time reversal method; Electromagnetic wave scattering


Time reversal of electromagnetic waves. Lerosey, G., J. De Rosny, A. Tourin, A. Derode, G. Montaldo, and M. Fink. Physical Review Letters 92, no. 19 (2004): 193904–1.
Résumé: A onechannel electromagnetic timereversal mirror (TRM) was used for investigating the feasibility of time reversal focusing with electromagnetic waves in the GHz range. Two omnidirectional antennas with a frequency of 2.45 GHz and two transceiver circuit boards were also used for the investigations. The baseband signals were time reversed and the wave carriers were phase conjugated in order to avoid digitizing the radio signals at GHz frequencies. The circuit boards demodulated the radio frequency signal back to the baseband. The frequency bandwidth and the spectral correlations determined the quality of focusing.
MotsClés: Analog to digital conversion; Bandwidth; Correlation methods; Demodulation; Light scattering; Light transmission; Low pass filters; Mirrors; Monochromators; Signal receivers; Signal to noise ratio; Transceivers; Ultrasonic effects; Wireless telecommunication systems; Phase conjugation; Quasimonochromatic signals; Spectral correlations; Time reversal mirrors (TRM); Antenna radiation

