Evolutionary optimization of all-dielectric magnetic nanoantennas

Magnetic light and matter interactions are generally too weak to be detected, studied and applied technologically. However, if one can increase the magnetic power density of light by several orders of magnitude, the coupling between magnetic light and matter could become of the same order of magnitude as the coupling with its electric counterpart. For that purpose, photonic nanoantennas have been proposed, and in particular dielectric nanostructures, to engineer strong local magnetic field and therefore increase the probability of magnetic interactions. Unfortunately, dielectric designs suffer from physical limitations that confine the magnetic hot spot in the core of the material itself, preventing experimental and technological implementations. Here, we demonstrate that evolutionary algorithms can overcome such limitations by designing new dielectric photonic nanoantennas, able to increase and extract the optical magnetic field from high refractive index materials. We also demonstrate that the magnetic power density in an evolutionary optimized dielectric nanostructure can be increased by a factor 5 compared to state of the art dielectric nanoantennas. In addition, we show that the fine details of the nanostructure are not critical in reaching these aforementioned features, as long as the general shape of the motif is maintained. This advocates for the feasibility of nanofabricating the optimized antennas experimentally and their subsequent application. By designing all dielectric magnetic antennas that feature local magnetic hot-spots outside of high refractive index materials, this work highlights the potential of evolutionary methods to fill the gap between electric and magnetic light-matter interactions, opening up new possibilities in many research fields.Comment: 13 pages, 4 figure

Dielectric nanoantennas to manipulate solid-state light emission

International audienc

Optical horn antennas for efficiently transferring photons from a quantum emitter to a single-mode optical fiber

International audienceWe theoretically demonstrate highly efficient optical coupling between a single quantum emitter and a monomode optical fiber over remarkably broad spectral ranges by extending the concept of horn antenna to optics. The optical horn antenna directs the radiation from the emitter toward the optical fiber and efficiently phase-matches the photon emission with the fiber mode. Numerical results show that an optical horn antenna can funnel up to 85% of the radiation from a dipolar source within an emission cone semi-angle as small as 7 degrees (antenna directivity of 300). It is also shown that 50% of the emitted power from the dipolar source can be collected and coupled to an SMF-28 fiber mode over spectral ranges larger than 1000 nm, with a maximum energy transfer reaching 70 %. This approach may open new perspectives in quantum optics and sensing

An achiral magnetic photonic antenna as a tunable nanosource of superchiral light

Sensitivity to molecular chirality is crucial for many fields, from biology and chemistry to the pharmaceutical industry. By generating superchiral light, nanophotonics has brought innovative solutions to reduce the detection volume and increase sensitivity at the cost of a non-selectivity of light chirality or a strong contribution to the background. Here, we theoretically propose an achiral plasmonic resonator, based on a rectangular nanoslit in a thin gold layer behaving as a magnetic dipole, to generate a tunable nanosource of purely superchiral light. This nanosource is free of any background, and the sign of its chirality is externally tunable in wavelength and polarization. These properties result from the coupling between the incident wave and the magnetic dipolar character of our nano-antenna. Thus, our results propose a platform with deep subwavelength detection volumes for chiral molecules in particular, in the visible, and a roadmap for optimizing the signal-to-noise ratios in circular dichroism measurements to reach single-molecule sensitivity

Broadband plasmonic nanoantennas for multi-color nanoscale dynamics in living cells

Recently, the implementation of plasmonic nanoantennas has opened new possibilities to investigate the nanoscale dynamics of individual biomolecules in living cell. However, studies have yet been restricted to single molecular species as the narrow wavelength resonance of gold-based nanostructures precludes the simultaneous interrogation of different fluorescently labeled molecules. Here we exploited broadband aluminum-based nanoantennas carved at the apex of near-field probes to resolve nanoscale-dynamic molecular interactions on intact living cell membranes. Through multicolor excitation, we simultaneously recorded fluorescence fluctuations of dual-color labeled transmembrane receptors known to form nanoclusters in living cells. Fluorescence cross-correlation studies revealed transient interactions between individual receptors in regions of ~60 nm. Moreover, the high signal-to-background ratio provided by the antenna illumination allowed us to directly detect fluorescent bursts arising from the passage of individual receptors underneath the antenna. Remarkably, by reducing the illumination volume below the characteristic receptor nanocluster sizes, we resolved molecular diffusion within nanoclusters and distinguished it from nanocluster diffusion. Spatiotemporal characterization of transient interactions between molecules is crucial to understand how they communicate with each other to regulate cell function. Our work demonstrates the potential of broadband photonic antennas to study multi-molecular events and interactions in living cell membranes with unprecedented spatiotemporal resolution

Enhancing Magnetic Light Emission with All-Dielectric Optical Nanoantennas

Electric and magnetic optical fields carry the same amount of energy. Nevertheless, the efficiency with which matter interacts with electric optical fields is commonly accepted to be at least 4 orders of magnitude higher than with magnetic optical fields. Here, we experimentally demonstrate that properly designed photonic nanoantennas can selectively manipulate the magnetic versus electric emission of luminescent nanocrystals. In particular, we show selective enhancement of magnetic emission from trivalent europium-doped nanoparticles in the vicinity of a nanoantenna tailored to exhibit a magnetic resonance. Specifically, by controlling the spatial coupling between emitters and an individual nanoresonator located at the edge of a near field optical scanning tip, we record with nanoscale precision local distributions of both magnetic and electric radiative local densities of states (LDOS). The map of the radiative LDOS reveals the modification of both the magnetic and electric quantum environments induced by the presence of the nanoantenna. This manipulation and enhancement of magnetic light-matter interaction by means of nanoantennas opens up new possibilities for the research fields of opto-electronics, chiral optics, nonlinear&nano-optics, spintronics and metamaterials, amongst others.Peer ReviewedPostprint (author's final draft

Light funneling from a photonic crystal laser cavity to an optical nano-antenna: toward antenna-based laser nano-emission

International audienceWe show that the near-field coupling between a photonic crystal microlaser and a nanoantenna can enable hybrid photonic systems that are both physically compact and highly efficient at transferring optical energy into the nano-antenna. Up to 19.4% of the laser power from a micron-scale photonic crystal laser cavity is experimentally transferred to a bowtie aperture nano-antenna (BNA) whose area is 400-fold smaller than the overall emission area of the microlaser. Instead of a direct deposition of the nano-antenna onto the photonic crystal, it is fabricated at the apex of a fiber tip to be accurately placed in the near-field volume of the microlaser. Such light funneling within a hybrid structure provides a path for overcoming the diffraction limit in optical energy transfer to the nanoscale and should thus open promising avenues in the nanoscale enhancement and confinement of light in compact architectures, impacting applications such as biosensing, optical trapping, heating, spectroscopy, and nanoimaging

Enhancement and Inhibition of Spontaneous Photon Emission by Resonant Silicon Nanoantennas

Substituting noble metals for high-index dielectrics has recently been proposed as an alternative strategy in nanophotonics to design broadband optical resonators and circumvent the Ohmic losses of plasmonic materials. In this paper, we demonstrate that subwavelength silicon nanoantennas can manipulate the photon emission dynamics of fluorescent molecules. In practice, we show that dielectric nanoantennas can both increase and decrease the local density of optical states at room temperature, a process that is inaccessible with noble metals at the nanoscale. Using scanning probe microscopy, we analyze quantitatively, in three dimensions, the near-field interaction between a 100-nm fluorescent nanosphere and silicon nanoantennas with diameters ranging between 170 and 250 nm. Associated with numerical simulations, these measurements indicate increased or decreased total spontaneous decay rates by up to 15% and a gain in the collection efficiency of emitted photons by up to 85%. Our study demonstrates the potential of silicon-based nanoantennas for the low-loss manipulation of solid-state emitters at the nanoscale and at room temperature

Manipulating Electric and Magnetic Light-matter interactions at the nanoscale

The interactions between light and matter are present absolutely everywhere around us, and since Maxwell's work, we understand them in a much clearer way. However, we are always discovering new facets of these interactions. In particular, since the revolution in nanofabrication techniques and ever-increasing computing capabilities, we are now able to design and fabricate objects of nanometric dimensions with totally new optical properties that are not possible with macroscopic materials. This revolution has led to new scientific and technological applications, the firsts of which have been developed in our laboratories only a few years ago. For example, we can cite applications in the medical field, to kill cancer cells, in photovoltaics, to create more efficient solar panels, in cosmetics, for specific properties of sun creams, in our screens, to obtain higher quality images and colors, or in space to create ultra-reflective solar sails, etc. Of course, we are still far from controlling humans with nanorobots using the 5G network, but the advances are still significant.Nanophotonics is remarkable in that it is now used in many fields of research. Something that was probably not foreseen at the beginning of near-field optics, the precursor field of nanophotonics. We can mention quantum information, certain parts of chemistry and biology, certain computer components, etc.In this manuscript, I will describe, through a few chapters, the most significant researches that have shaped my research career until today. In particular, I will detail a few selected studies that illustrate my main work themes, notably my work on the manipulation and increase of electric and magnetic optical fields and their coupling to matter.In the first part, I will describe how nanostructuring matter at nanometric scales can manipulate the electric and magnetic fields of light. In particular, by choosing suitable materials and shapes, I will explain how increasing these fields by several orders of magnitude is achievable. In the second part, I will describe examples of manipulating electric quantum emitters' emission via optical nano-antennas designed to control and concentrate the optical electric field. Finally, in the last part, I will explain how photonic nano-antennas engineered to exalt the optical magnetic field also allows manipulating quantum emitters' emission, this time, magnetic ones.Les interactions entre la lumière et la matière sont présentes absolument partout autour de nous, et depuis les travaux de Maxwell, nous les comprenons de manière beaucoup plus claire. Cependant, nous découvrons toujours de nouvelles facettes de ces interactions. En particulier, depuis la révolution des techniques de nanofabrication et l'augmentation constante des capacités de calcul, nous sommes désormais en mesure de concevoir et de fabriquer des objets de dimensions nanométriques présentant des propriétés optiques totalement nouvelles, impossibles à obtenir avec des matériaux macroscopiques. Cette révolution a conduit à de nouvelles applications scientifiques et technologiques, dont les premières ont été développées dans nos laboratoires il y a seulement quelques années. Par exemple, nous pouvons citer des applications dans le domaine médical, pour tuer les cellules cancéreuses, dans le domaine photovoltaïque, pour créer des panneaux solaires plus efficaces, dans le domaine cosmétique, pour des propriétés spécifiques des crèmes solaires, dans nos écrans, pour obtenir des images et des couleurs de meilleure qualité, ou encore dans le domaine spatial pour créer des voiles solaires ultra-réfléchissantes, etc. Bien sûr, nous sommes encore loin de contrôler les humains avec des nanorobots en utilisant le réseau 5G, mais les avancées sont tout de même significatives.La nanophotonique est remarquable dans la mesure où elle est désormais utilisée dans de nombreux domaines de recherche. Quelque chose qui n'était probablement pas prévu au début de l'optique en champ proche, le domaine précurseur de la nanophotonique. On peut citer l'information quantique, certaines parties de la chimie et de la biologie, certains composants informatiques, etc.Dans ce manuscrit, je vais décrire, à travers quelques chapitres, les recherches les plus significatives qui ont façonné ma carrière de chercheur jusqu'à aujourd'hui. En particulier, je détaillerai quelques études choisies qui illustrent mes principaux thèmes de travail, notamment mes travaux sur la manipulation et l'augmentation des champs optiques électriques et magnétiques et leur couplage à la matière.Dans la première partie, je décrirai comment la nanostructuration de la matière à des échelles nanométriques permet de manipuler les champs électriques et magnétiques de la lumière. En particulier, en choisissant des matériaux et des formes adaptés, j'expliquerai comment il est possible d'augmenter ces champs de plusieurs ordres de grandeur. Dans la deuxième partie, je décrirai des exemples de manipulation de l'émission d'émetteurs quantiques électriques via des nano-antennes optiques conçues pour contrôler et concentrer le champ électrique optique. Enfin, dans la dernière partie, j'expliquerai comment les nano-antennes photoniques conçues pour exalter le champ magnétique optique permettent également de manipuler l'émission d'émetteurs quantiques, magnétiques cette fois

Etude et développement de nano-antennes fibrées pour la microscopie en champ proche optique et la nano-photonique

In the first part of this manuscript, we use in our advantage the concept of optical nano-antennas, toget new solutions on the interpretation problems of scanning near-field optical microscope (SNOM)images. Indeed, it is known that some of the developed nano-antennas can express dipolarbehaviours. In this manuscript, we show how a bowtie nano-aperture (dipolar nano-antenna)embedded at the apex of a SNOM probe, can be used to detect and collect only one component ofthe electric near-field. This result is demonstrated as well theoretically, by the use of FDTD (FiniteDifference Time Domain) codes, as experimentally, by the characterisation with this tip, of dielectricsamples (diffraction grating and photonic crystals) and metallic ones (random plasmonic medium).In a second part, we show how the tip previously described, can be used as a detector of the signalfrom single emitter (SE). We study in this part the coupling and interactions between those twoobjects. After a full description of a two level system characteristics, we show theoretically the effectof our probe on the reduction of the excited state life time and the enhancement of thefluorescence of the SE, in both regime, saturated and non-saturated. Then we describeexperimentally how our special tip reduces the excited state life time of quantum dots placed at theapex of it, respect to more conventional SNOM probes as the dielectric and the circular apertureones.Dans la première partie de cette thèse, nous tirons parti du concept de nano-antenne optique afind'apporter une solution innovante au problème d'interprétation de la microscopie champ procheoptique (SNOM). En effet, il est connu que certaines nano-antennes développent des réponsesoptiques dipolaires. Dans cette thèse nous démontrons comment l’utilisation d’une nano-ouverturepapillon (nano-antenne dipolaire), à l’extrémité d’une pointe SNOM, permet de détecter et collecteruniquement une seule composante du champ proche électrique. Ce résultat est démontré d’unpoint de vue théorique par l’utilisation de simulation FDTD (Finite Difference Time Domain) et d’unpoint de vue expérimental par la caractérisation, par cette pointe innovante, d´échantillonsdiélectriques (réseaux, cristaux photoniques) et métalliques (milieux désordonnés plasmoniques).Dans une deuxième partie, nous démontrons comment la sonde développée dans la premièrepartie, peut être utilisée comme détecteur du signal émis par un nano-émetteurs (NE) unique. Il estétudié dans cette partie l’effet de couplage entre ces deux objets. Dans un premier temps, après ladescription complète des grandeurs caractéristiques d’un NE, nous démontrons théoriquementl’effet de la pointe sur la réduction du temps de vie de l’état excité et l’augmentation de lafluorescence d’un NE, en régime saturé et non saturé. Puis dans un deuxième temps nousdémontrons expérimentalement comment cette sonde réduit le temps de vie de l’état excité deboites quantiques placées à son extrémité, en comparaison de pointes SNOM plus conventionnellestelle que la pointe diélectrique et la pointe à ouverture circulaire