arXiv subjects

Philippe Lalanne

Publications and source records attributed to Philippe Lalanne.

At least 37 records · Page 2Linked to original sources

arXiv2022

WaveY-Net: Physics-augmented deep learning for high-speed electromagnetic simulation and optimization

The calculation of electromagnetic field distributions within structured media is central to the optimization and validation of photonic devices. We introduce WaveY-Net, a hybrid data- and physics-augmented convolutional neural network that can predict electromagnetic field distributions with ultra fast speeds and high accuracy for entire classes of dielectric photonic structures. This accuracy is achieved by training the neural network to learn only the magnetic near-field distributions of a system and to use a discrete formalism of Maxwell's equations in two ways: as physical constraints in the loss function and as a means to calculate the electric fields from the magnetic fields. As a model system, we construct a surrogate simulator for periodic silicon nanostructure arrays and show that the high speed simulator can be directly and effectively used in the local and global freeform optimization of metagratings. We anticipate that physics-augmented networks will serve as a viable Maxwell simulator replacement for many classes of photonic systems, transforming the way they are designed.

physics.app-ph↗

arXiv2021

QNMnonreciprocal_resonators: an openly available toolbox for computing the QuasiNormal Modes of nonreciprocal resonators

QNMnonreciprocal_resonators is an extension (posted in 2021) of the QNMEig solver of the freeware package MAN. It provides a comprehensive presentation of the computation and normalization of electromagnetic quasinormal modes (QNMs) of resonators composed of nonreciprocal materials. It features a theoretical background on the topic and a COMSOL model that illustrates how to put into practice the theory on the example of a Yttrium iron garnet wire in a homogenous background. This document provides the necessary details on how the model is built so that the interested readers may easily modify it for computing QNMs of other nonreciprocal resonators.

physics.optics↗

arXiv2021

Fundamental limitations of Huygens metasurfaces for optical beam shaping

Optical dielectric metasurfaces composed of arrayed nanostructures are expected to enable arbitrary spatial control of incident wavefronts with subwavelength spatial resolution. For phase modulation, one often resorts to two physical effects to implement a 2π-phase excursion. The first effect relies on guidance by tall nanoscale pillars and the second one exploits resonant confinement by nanoresonators with two degenerate Mie-resonances. The first approach requires high aspect ratios, while the second one, known as Huygens metasurfaces, is much flatter, and thus easier to manufacture. We compare the two approaches, more focusing on conceptual rather than technological issues, and identify fundamental limitations with the latter. We explain the origin of the limitations based on general arguments, such as reciprocity, multimode/monomode operation and symmetry breaking.

physics.optics↗

arXiv2021

Hot electron generation through near-field excitation of plasmonic nanoresonators

We theoretically study hot electron generation through the emission of a dipole source coupled to a nanoresonator on a metal surface. In our hybrid approach, we solve the time-harmonic Maxwell's equations numerically and apply a quantum model to predict the efficiency of hot electron generation. Strongly confined electromagnetic fields and the strong enhancement of hot electron generation at the metal surface are predicted and are further interpreted with the theory of quasinormal modes. In the investigated nanoresonator setup, both the emitting source and the acceptor resonator are localized in the same volume, and this configuration looks promising to achieve high efficiencies of hot electron generation. By comparing with the efficiency calculated in the absence of the plasmonic nanoresonator, that is, the dipole source is located near a flat, unstructured metal surface, we show that the effective excitation of the modes of the nanoresonator boosts the generation efficiency of energetic charge carriers. The proposed scheme can be used in tip-based spectroscopies and other optoelectronic applications.

physics.optics↗

arXiv2020

Deep learning enabled design of complex transmission matrices for universal optical components

Recent breakthroughs in photonics-based quantum, neuromorphic and analogue processing have pointed out the need for new schemes for fully programmable nanophotonic devices. Universal optical elements based on interferometer meshes are underpinning many of these new technologies, however this is achieved at the cost of an overall footprint that is very large compared to the limited chip real estate, restricting the scalability of this approach. Here, we consider an ultracompact platform for low-loss programmable elements using the complex transmission matrix of a multi-port multimode waveguide. We propose a deep learning inverse network approach to design arbitrary transmission matrices using patterns of weakly scattering perturbations. The demonstrated technique allows control over both the intensity and phase in a multiport device at a four orders reduced device footprint compared to conventional technologies, thus opening the door for large-scale integrated universal networks.

physics.optics↗

arXiv2020

Mode volume of electromagnetic resonators: let us try giving credit where it is due

The mode volume is a very important figure of merits, which transversally arouse the physics and applications of electromagnetic cavities. Its modern definition was not obtained simply, and I try to briefly summarize the evolution of ideas. I also incidentally address considerations on scientific publishing policy in the epilogue.

physics.optics↗

arXiv2020

Shape deformation of nanoresonator: a quasinormal-mode perturbation theory

When material parameters are fixed, optical responses of nanoresonators are dictated by their shapes and dimensions. Therefore, both designing nanoresonators and understanding their underlying physics would benefit from a theory that predicts the evolutions of resonance modes of open systems---the so-called quasinormal modes (QNMs)---as the nanoresonator shape changes. QNM perturbation theories (PTs) are one ideal choice. However, existing theories developed for material changes are unable to provide accurate perturbation corrections for shape deformations. By introducing a novel extrapolation technique, we develop a rigorous QNM PT that faithfully represents the electromagnetic fields in perturbed domain. Numerical tests performed on the eigenfrequencies, eigenmodes and optical responses of deformed nanoresonators evidence the predictive force of the present PT, even for large deformations. This opens new avenues for inverse design, as we exemplify by designing super-cavity modes and exceptional points with remarkable ease and physical insight.

physics.optics↗

arXiv2020

MetaNet: A new paradigm for data sharing in photonics research

Optimization methods are playing an increasingly important role in all facets of photonics engineering, from integrated photonics to free space diffractive optics. However, efforts in the photonics community to develop optimization algorithms remain uncoordinated, which has hindered proper benchmarking of design approaches and access to device designs based on optimization. We introduce MetaNet, an online database of photonic devices and design codes intended to promote coordination and collaboration within the photonics community. Using metagratings as a model system, we have uploaded over one hundred thousand device layouts to the database, as well as source code for implementations of local and global topology optimization methods. Further analyses of these large datasets allow the distribution of optimized devices to be visualized for a given optimization method. We expect that the coordinated research efforts enabled by MetaNet will expedite algorithm development for photonics design.

physics.optics↗

arXiv2020

Long-lifetime coherence in a quantum emitter induced by a metasurface

An anisotropic quantum vacuum (AQV) has been predicted to induce quantum interferences during the spontaneous emission process in an atomic $V$-transition [G. S. Agarwal, Phys. Rev. Lett. 84, 5500 (2000)]. Nevertheless, the finite lifetime of the excited states is expected to strongly limit the observability of this phenomenon. In this paper, we predict that an AQV can induce a long-lifetime coherence in an atomic $Λ$-transition from the process of spontaneous emission, which has an additional advantage of removing the need for coherent laser excitation. We also carry out two metasurface designs and compare their respective efficiencies for creating an AQV over remote distances. The detection of this coherence induced by a metasurface, in addition to being yet another vindication of quantum electrodynamics, could pave the way towards the remote distance control of coherent coupling between quantum emitters, which is a key requirement to produce entanglement in quantum technology applications.

quant-ph↗

arXiv2020

Intrinsic multipolar contents of nanoresonators for tailored scattering

We introduce a theoretical and computational method to design resonant objects, such as nanoantennas or meta-atoms, exhibiting tailored multipolar responses. In contrast with common approaches that rely on a multipolar analysis of the scattering response of an object upon specific excitations, we propose to engineer the \textit{intrinsic} (i.e., excitation-independent) multipolar content and spectral characteristics of the natural resonances -- or quasinormal modes -- of the object. A rigorous numerical approach for the multipolar decomposition of resonances at complex frequencies is presented, along with an analytical model conveying a direct physical insight into the multipole moments induced in the resonator. Our design strategy is illustrated by designing a subwavelength optical resonator exhibiting a Janus resonance that provides side-dependent coupling to waveguides over the full linewidth of the resonance and on a wide angular range for linearly-polarized incident planewaves. The method applies to all kinds of waves and may open new perspectives for subwavelength-scale manipulation of scattering and emission.

physics.optics↗

arXiv2019

Global polarizability matrix method for efficient modeling of light scattering by dense ensembles of non-spherical particles in stratified media

We introduce a numerical method that enables efficient modelling of light scattering by large, disordered ensembles of non-spherical particles incorporated in stratified media, including when the particles are in close vicinity to each other, to planar interfaces and/or to localized light sources. The method consists in finding a small set of fictitious polarizable elements -- or numerical dipoles -- that quantitatively reproduces the field scattered by an individual particle for any excitation and at an arbitrary distance from the particle surface. The set of numerical dipoles is described by a global polarizability matrix that is determined numerically by solving an inverse problem relying on fullwave simulations. The latter are classical and may be performed with any Maxwell's equations solver. Spatial non-locality is an important feature of the numerical dipoles set, providing additional degrees of freedom compared to classical coupled dipoles to reconstruct complex scattered fields. Once the polarizability matrix describing scattering by an individual particle is determined, the multiple scattering problem by ensembles of such particles in stratified media can be solved using a Green tensor formalism and only few numerical dipoles, thereby with a low physical memory usage, even for dense systems in close vicinity to interfaces. The performance of the method is studied with the example of large high-aspect-ratio high-index dielectric cylinders. The method is easy to implement and may offer new possibilities for the study of complex nanostructured surfaces, which are becoming widespread in emerging photonic technologies.

physics.optics↗

arXiv2019

Quasinormal-mode modeling and design in nonlinear nano-optics

Based on quasinormal-mode theory, we propose a novel approach enabling a deep analytical insight into the multi-parameter design and optimization of nonlinear photonic structures at subwavelength scale. A key distinction of our method from previous formulations relying on multipolar Mie-scattering expansions is that it directly exploits the natural resonant modes of the nanostructures, which provide the field enhancement to achieve significant nonlinear efficiency. Thanks to closed-form expression for the nonlinear overlap integral between the interacting modes, we illustrate the potential of our method with a two-order-of-magnitude boost of second harmonic generation in a semiconductor nanostructure, by engineering both the sign of $χ^{(2)}$ at subwavelength scale and the structure of the pump beam.

physics.optics↗

arXiv2019

Non-uniqueness of the Quasinormal Mode Expansion of Electromagnetic Lorentz Dispersive Materials

Any optical structure possesses resonance modes and its response to an excitation can be decomposed onto the quasinormal and numerical modes of discretized Maxwell's operator. In this paper, we consider a dielectric permittivity that is a N-pole Lorentz function of the pulsation $ω$. We propose a common formalism and obtain different formulas for the modal expansion. The non-uniqueness of the excitation coeffcient is due to a choice of the linearization of Maxwell's equation with respect to $ω$ and of the form of the source term. We make the link between the numerical discrete modal expansion and analytical formulas that can be found in the literature. We detail the formulation of dispersive Perfectly Matched Layers (PML) in order to keep a linear eigenvalue problem. We also give an algorithm to regain an orthogonal basis for degenerate modes. Numerical results validate the different formulas and compare their accuracy.

physics.comp-ph↗

arXiv2019

Quasinormal-mode analysis of grating spectra at fixed incidence angles

Grating spectra exhibit sharp variations of the scattered light, known as grating anomalies. The latter are due to resonances that have fascinated specialists of optics and physics for decades and are nowadays used in many applications. We present a comprehensive theory of grating anomalies, and develop a formalism to expand the field scattered by metallic or dielectric gratings into the basis of its natural resonances, thereby enabling the possibility to reconstruct grating spectra measured for fixed illumination angles as a sum over every individual resonance contribution with closed-form expressions. This gives physical insights into the spectral properties and a direct access to the resonances to engineer the spectral response of gratings and their sensitivity to tiny perturbations.

physics.optics↗

arXiv2019

A General Theoretical and Experimental Framework for Nanoscale Electromagnetism

Local, bulk response functions, e.g permittivity, and the macroscopic Maxwell equations completely specify the classical electromagnetic problem, which features only wavelength $λ$ and geometric scales. The above neglect of intrinsic electronic length scales $L_{\text{e}}$ leads to an eventual breakdown in the nanoscopic limit. Here, we present a general theoretical and experimental framework for treating nanoscale electromagnetic phenomena. The framework features surface-response functions---known as the Feibelman $d$-parameters---which reintroduce the missing electronic length scales. As a part of our framework, we establish an experimental procedure to measure these complex, dispersive surface response functions, enabled by quasi-normal-mode perturbation theory and observations of pronounced nonclassical effects---spectral shifts in excess of 30% and the breakdown of Kreibig-like broadening---in a quintessential multiscale architecture: film-coupled nanoresonators, with feature-sizes comparable to both $L_{\text{e}}$ and $λ$.

physics.optics↗

arXiv2018

Attenuation of slow Metal-Insulator-Metal plasmonic waveguides, from Joule absorption to roughness-induced backscattering

By combining analytical and numerical approaches, we theoretically investigate the effect of fabrication imperfections, e.g. roughness at metal interfaces, on nanometer metal-insulator-metal waveguides supporting slow gap-plasmon modes. Realistic devices with vapor deposition- and chemically-grown metal films are considered. We obtain quantitative predictions for the attenuations induced by absorption and by backscattering, and analytically derive how both attenuations scale with respect to the group velocity. Depending on the material parameters and fabrication quality, roughness-induced backscattering is find to be a significant additional source of attenuation for small group velocities, which is often neglected in the literature.

physics.optics↗

arXiv2018

Rigorous modal analysis of plasmonic nanoresonators

The specificity of modal-expansion formalisms is their capabilities to model the physical properties in the natural resonance-state basis of the system in question, leading to a transparent interpretation of the numerical results. In electromagnetism, modal-expansion formalisms are routinely used for optical waveguides. In contrast, they are much less mature for analyzing open non-Hermitian systems, such as micro and nanoresonators. Here, by accounting for material dispersion with auxiliary fields, we considerably extend the capabilities of these formalisms, in terms of computational effectiveness, number of states handled and range of validity. We implement an efficient finite element solver to compute the resonance states, and derive new closed-form expressions of the modal excitation coefficients for reconstructing the scattered fields. Together, these two achievements allow us to perform rigorous modal analysis of complicated plasmonic resonators, being not limited to a few resonance states, with straightforward physical interpretations and remarkable computation speeds. We particularly show that, when the number of states retained in the expansion increases, convergence towards accurate predictions is achieved, offering a solid theoretical foundation for analyzing important issues, e.g. Fano interference, quenching, coupling with the continuum, which are critical in nanophotonic research.

physics.optics↗

arXiv2018

Ultrafast perturbation maps as a quantitative tool for testing of multi-port photonic devices

Advanced photonic probing techniques are of great importance for the development of non-contact wafer-scale testing of photonic chips. Ultrafast photomodulation has been identified as a powerful new tool capable of remotely mapping photonic devices through a scanning perturbation. Here, we develop photomodulation maps into a quantitative technique through a general and rigorous method based on Lorentz reciprocity that allows the prediction of transmittance perturbation maps for arbitrary linear photonic systems with great accuracy and minimal computational cost. Excellent agreement is obtained between predicted and experimental maps of various optical multimode-interference devices, thereby allowing direct comparison of a device under test with a physical model of an ideal design structure. In addition to constituting a promising route for optical testing in photonics manufacturing, ultrafast perturbation mapping may be used for design optimization of photonic structures with reconfigurable functionalities.

physics.optics↗