Optical resonators are widely used in modern photonics. Their spectral response and temporal dynamics are fundamentally driven by their natural resonances, the so-called quasinormal modes (QNMs), with complex frequencies.For optical resonators made of dispersive materials, the QNM computation requires solving a nonlinear eigenvalue problem. This rises a difficulty that is only scarcely documented in the literature. We review our recent efforts for implementing efficient and accurate QNM-solvers for computing and normalizing the QNMs of micro-and nanoresonators made of highly-dispersive materials. We benchmark several methods for three geometries, a twodimensional plasmonic crystal, a two-dimensional metal grating, and a three-dimensional nanopatch antenna on a metal substrate, in the perspective to elaborate standards for the computation of resonance modes.

We demonstrate the efficacy of nanostructured thin film silicon solar cells to trap and absorb approximately 75% of all sunlight incident (400 nm-1200 nm) with an equivalent bulk thickness of only 1 micron of silicon. This is achieved by sculpting the collection zone into a three-dimensional, simple-cubic-symmetry, photonic crystal consisting of modulated silicon nanowires embedded in SiO 2 and sitting on a quartz substrate with no metallic mirrors. A specific modulation of the radius of nanowires provides antireflection, strong light trapping, and back-reflection mechanisms in targeted spectral regions. This modulation is linear at the top of the nano-rods leading to nanocones at the solar cell to air boundary. These silicon nanocones are very good absorbers at short wavelengths and act as broadband coupler to a light-trapping region below at longer wavelengths. In the light trapping region the modulation is periodic to form a simple cubic photonic crystal exhibiting a broad spectrum of strong parallel interface refraction resonances. Here, light incident from most angles is deflected into slow group velocity modes with energy flow nearly parallel to the interface, long dwell times, and strong light intensity enhancement (up to 150 times the incident intensity) in specific regions. Finally, a stronger and chirped modulation of the nanowire underneath provides back-reflection by means of a one-dimensional depth-dependent photonic stopgap. The possibility of absorbing light at energies below the electronic band gap of silicon is illustrated using a graded index Si x Ge 1Àx alloy in the bottom section of each nanowire. Each nanowire is amenable to a radial P-N junction for proximal charge carrier separation and efficient collection of photo-generated current.

We show the important role played by the multipolar coupling between the illuminating field and magneto-electric scatterers even in the small particle limit (λ/10). A general multipolar method is presented which, for the case of planar non centrosymmetric particles, generates a simple expression for the polarizability tensor that directly links the dipolar moment to the incident field. The relevancy of this approach is demonstrated by comparing thoroughly the dipolar moments predicted by the method with full numerical calculations.

The main goal of the method proposed in this paper is the numerical study of various kinds of anisotropic gratings deposited on isotropic substrates, without any constraint upon the diffractive pattern geometry or electromagnetic properties. To that end we propose a new FEM (Finite Element Method) formulation which rigorously deals with each infinite issue inherent to grating problems. As an example, 2D numerical experiments are presented in the cases of the diffraction of a plane wave by an anisotropic aragonite grating on silica substrate (for the two polarization cases and at normal or oblique incidence). We emphasize the interesting property that the diffracted field is non symmetric in a geometrically symmetric configuration.

In this Letter, we describe a very general procedure to obtain a causal fit of the permittivity of materials from experimental data with very few parameters. Unlike other closed forms proposed in the literature, the uniqueness of this approach lies in its independence on the material or frequency range at stake. Many illustrative numerical examples are given, and the accuracy of the fitting is compared to other expressions in the literature.

Numerical calculation of modes in dispersive and absorptive systems is performed using the finite element method. The dispersion is tackled in the frame of an extension of Maxwell's equations where auxiliary fields are added to the electromagnetic field. This method is applied to multi-domain cavities and photonic crystals including Drude and Drude-Lorentz metals. Numerical results are compared to analytical solutions for simple cavities and to previous results of the literature for photonic crystals, showing excellent agreement. The advantages of the developed method lie on the versatility of the finite element method regarding geometries, and in sparing the use of tedious complex poles research algorithm. Hence the complex spectrum of resonances of non-hermitian operators and dissipative systems, like two-dimensional photonic crystal made of absorbing Drude metal, can be investigated in detail. The method is used to reveal unexpected features of their complex band structures.

We propose a novel formulation of the finite element method adapted to the calculation of the vector field diffracted by an arbitrarily shaped crossed-grating embedded in a multilayered stack and illuminated by an arbitrarily polarized plane wave under oblique incidence. A complete energy balance (transmitted and reflected diffraction efficiencies and losses) is deduced from field maps. The accuracy of the proposed formulation has been tested using classical cases computed with independent methods. Moreover, to illustrate the independence of our method with respect to the shape of the diffractive object, we present the global energy balance resulting from the diffraction of a plane wave by a lossy thin torus crossed-grating. Finally, computation time and convergence as a function of the mesh refinement are discussed. As far as integrated energy values are concerned, the presented method shows a remarkable convergence even for coarse meshes.

Plasmonic oligomers are near-field coupled assemblies of metallic nanoparticles. Both their scattering/absorption spectra and the spatial distribution of the electromagnetic field can be tailored through the hybridization of plasmonic modes hosted by individual particles. Such a control on the field distribution opens new routes to deliver light at a deep subwavelength scale in targeted locations ("hot spots"). However, active control of hot spots in plasmonic oligomers and their observation in the near field are highly challenging. Here, we propose to use a two-photon absorption process in azopolymer in the near infrared to imprint from the far field the near field distribution around a trimer antenna. The trimer antenna comprises two nanogaps separated by a quarter of the wavelength in the polymer and is designed to allow for the switch on a single nanogap when illuminated at 900 nm by a 2 collimated beam at an oblique incidence. The monitoring of the topographical depletions in the photopolymer proves that it is possible to address a single hot spot in the structure and to remotely switch its location in the two nanogaps on demand, simply by illuminating with an opposite oblique incidence. This work shows that bonding and anti-bonding gap modes can be selectively excited resulting in controlled hot spot locations. Two-photon absorption by azobenzene-containing photopolymer turns out to be a reliable approach for investigating confined plasmonic fields in the near infrared with a 20 nm resolution.