Slow-wave effect and mode-profile matching in Photonic Crystal microcavities

Physical mechanisms involved in the light confinement in photonic crystal slab microcavities are investigated. We first present a full three-dimensional numerical study of these microcavities. Then, to gain physical insight into the confinement mechanisms, we develop a Fabry-Perot model. This model provides accurate predictions and sheds new light on the physics of light confinement. We clearly identify two mechanisms to enhance the Q factor of these microcavities. The first one consists in improving the mode-profile matching at the cavity terminations and the second one in using a slow wave in the cavity.Comment: accepted for publication in Phys. Rev. B, 8 pages, 4 figure

Optical extinction in a single layer of nanorods

We demonstrate that almost 100 % of incident photons can interact with a monolayer of scatterers in a symmetrical environment. Nearly-perfect optical extinction through free-standing transparent nanorod arrays has been measured. The sharp spectral opacity window, in the form of a characteristic Fano resonance, arises from the coherent multiple scattering in the array. In addition, we show that nanorods made of absorbing material exhibit a 25-fold absorption enhancement per unit volume compared to unstructured thin film. These results open new perspectives for light management in high-Q, low volume dielectric nanostructures, with potential applications in optical systems, spectroscopy, and optomechanics

Difference between penetration and damping lengths in photonic crystal mirrors

Different mirror geometries in two-dimensional photonic crystal slabs are studied with fully-vectorial calculations. We compare their optical properties and, in particular, we show that, for heterostructure mirrors, the penetration length associated with the delay induced by distributed reflection is not correlated to the characteristic damping length of the electromagnetic energy distribution in the mirror. This unexpected result evidences that the usual trade-off between short damping lengths and large penetration lengths that is classically encountered in distributed Bragg reflectors can be overcome with carefully designed photonic crystal structures.Comment: to be published in Applied Physics Letters, 4 pages, 4 figure

Tomographic imaging by coding and reconstruction

We present the various researches we made on tomographic imaging by coding and reconstruction . These works are based on two chief kinds of methods : Coding Aperture Imaging and Transaxial Tomography, each of them including theoretical studies and realization of tomographic systems for definite applications . In this paper, we mainly present the more recent studies concerning reconstruction problems from missing data, with development of an original method by "constrained natural pixels", and implementation of multislit coding in micro-imaging of laser plasmas .Nous présentons les divers travaux que nous avons réalisés sur l'imagerie tomographique par codage et reconstruction . Ces travaux sont axés sur deux grands types de méthodes : l'Imagerie par Ouverture de Codage et la Tomographie Axiale Transverse, et comprennent, pour chacune d'elles, des études théoriques et la conception de systèmes tomographiques pour des applications bien précises . Dans cet article, nous présentons essentiellement les études les plus récentes qui concernent les problèmes de reconstruction à données incomplètes, avec le développement d'une méthode originale par «pixels naturels avec contrainte», et la mise en ceuvre d'un codage par multifentes en micro-imagerie de plasmas laser

Plasmonic Metasurface for Directional and Frequency-Selective Thermal Emission

International audienceIncandescent filaments and membranes are often used as infrared sources despite their low efficiency, broad angular emission, and lack of spectral selectivity. Here, we introduce a metasurface to control simultaneously the spectrum and the directivity of blackbody radiation. The plasmonic metasurface operates reliably at 600 °C with an emissivity higher than 0.85 in a narrow frequency band and in a narrow solid angle. This emitter paves the way for the development of compact, efficient, and cheap IR sources and gas detection systems

Efficient light coupling into a photonic crystal waveguide with flatband slow mode

We design an efficient coupler to transmit light from a strip waveguide into the flatband slow mode of a photonic crystal waveguide with ring-shaped holes. The coupler is a section of a photonic crystal waveguide with a higher group velocity, obtained by different ring dimensions. We demonstrate coupling efficiency in excess of 95% over the 8 nm wavelength range where the photonic crystal waveguide exhibits a quasi constant group velocity vg = c/37. An analysis based on the small Fabry-P\'erot resonances in the simulated transmission spectra is introduced and used for studying the effect of the coupler length and for evaluating the coupling efficiency in different parts of the coupler. The mode conversion efficiency within the coupler is more than 99.7% over the wavelength range of interest. The parasitic reflectance in the coupler, which depends on the propagation constant mismatch between the slow mode and the coupler mode, is lower than 0.6% within this wavelength range.Comment: 11 pages, 7 figures, submitted to Photonics and Nanostructures - Fundamentals and Application