[Show abstract][Hide abstract] ABSTRACT: We present a strategy for simulating the scattering effect of an array of self-aggregated (SA) metal nanoparticles (NPs) on the light absorption in solar cells. We include size and shape effects of the NPs, the effect of a layered substrate and the effect of the interaction between NPs. The simulation relies on realistic characterization by SEM microscopy of the random NP arrays. Time and memory limitations of numerical approaches are overcome using semianalytical expressions. Size and shape considerations deal with truncated-sphere shapes by using a polarisability tensor. This is a development of other models leading to equivalent dipoles from the external source and the radiated fields from the rest of NPs. Once an equivalent array of 3-D dipoles is found, the total electromagnetic field and optical simulations are performed. The general trends show good agreement with experimental measurements. A critical analysis of the model is presented, and some improvement strategies are discussed for future studies.
[Show abstract][Hide abstract] ABSTRACT: Incandescent 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.
[Show abstract][Hide abstract] ABSTRACT: We investigate the optical phenomenon responsible for the colored shine that sometimes appears at the surface of ink layers in the specular direction, often called bronzing or gloss differential. It seems to come from the wavelength-dependent refractive index of the ink, which induces a wavelength-dependent reflectance of the ink-air interface. Our experiments on cyan and magenta inkjet inks confirm this theory. Complex refractive indices can be obtained from measurements of the spectral reflectance and transmittance of a transparency film coated with the ink. We propose a correction of the classical Clapper-Yule model in order to include the colored gloss in the prediction of the spectral reflectance of an inked paper. We also explored effects of scattering by the micrometric or nanometric roughness of the ink surface. The micrometric roughness, easy to model with a geometrical optics model, can predict the spreading of the colored gloss over a large cone. Electromagnetic models accounting for the effect of the nanometric roughness of the surface also predict the attenuation of short wavelengths observed under collimated illumination.
[Show abstract][Hide abstract] ABSTRACT: Mid to far infrared is an important wavelength band for detection of substances. Incandescent sources are often used in infrared spectroscopy because they are simple and cost effective. They are however broadband and quasi isotropic. As a result, the total efficiency in a detection system is very poor. Yet it has been shown recently that thermal emission can be designed to be directional and/or monochromatic. To do so amounts to shape the emissivity. Any real thermal source is characterized by its emissivity, which gives the specific intensity of the source compared to the blackbody at the same temperature. The emissivity depends on the wavelength and the direction of emission and is related to the whole structure of the source (materials, geometry below the wavelength-scale.). Emissivity appears as a directional and chromatic filter for the blackbody radiation. Playing with materials and structure resonances, the emissivity can be designed to optimize the properties of an incandescent source. We will see how it is possible to optimize a plasmonic metasurface acting as an incandescent source, to make it directional and quasi monochromatic at a chosen wavelength. We will target a CO2 detection application to illustrate this topic.
No preview · Article · Jan 2015 · Proceedings of SPIE - The International Society for Optical Engineering
[Show abstract][Hide abstract] ABSTRACT: Hybrid silicon photonics offers novel opportunities to control light propagation with nanostructured media on the silicon side. In the specific case of oxide-free heteroepitaxial bonding of III-V layers on silicon, it is particularly crucial to assess the role of nanostructures in the post-bonding situation. We propose here a method of internal light source and integrated prism deviation to evaluate the effective index of small sub-wavelength periodic shallow holes that are completely embedded and do not lend themselves to alternative such as e.g. ellipsometry. We achieve a precision $\Delta n < 0.01$ , a good accuracy both for the understanding and optimization of optical components performances. Measured data are in good agreement with the theoretical expectation, as obtained using an improved homogenization strategy and further confirmed by 3D Bloch mode calculation.
No preview · Article · Oct 2014 · Journal of Lightwave Technology
[Show abstract][Hide abstract] ABSTRACT: Oxide-free bonding of indium phosphide epitaxial layers onto silicon-on-insulator (SOI) offers good thermal and electrical contact. These properties are retained if guidance engineering of the resulting stack is performed by nanostructuring the silicon layer to produce a lower effective index layer. We discuss the optical characterization of such a system by a simple prism deviation method for a thin stack, or diffraction to the air for a more multimode stack, adding a superperiod to the nanostructure.
[Show abstract][Hide abstract] ABSTRACT: We provide a self-consistent electromagnetic theory of the link between spatial coherence and optical resonances in three-dimensional open and dissipative photonic systems. The theory that relies on the concept of quasinormal modes with complex frequencies provides an accurate modal expansion of the imaginary part of the Green tensor that correctly treats the effects of radiative leakage, absorption, and dispersion. It represents a powerful tool for calculating and understanding the degree of spatial coherence in complex photonic or plasmonic systems that are governed by a small number of resonances. Comparisons with fully vectorial calculations evidence the high accuracy of the predictions achieved by our semianalytical treatment in the case of coupled photonic-crystal microcavities and plasmonic nanoantennas made of metallic nanorods.
Full-text · Article · Mar 2014 · Physical Review A
[Show abstract][Hide abstract] ABSTRACT: Tamm plasmons are interface modes formed at the boundary between a metallic layer and a dielectric Bragg mirror. They present advantages associated both to surface plasmons and to microcavities photonic modes. One of their striking properties is that they can be spatially confined by structuring only the metallic part of the structure, thus reducing the size of the mode and allowing various geometries without altering the optical properties of the active layer. These modes are very good candidates for optimizing the emission properties of semiconductor nanostructures. In particular, due to the relatively low damping and the versatility of the Tamm geometries, they open new perspective for the development of hybrid metal/semiconductor lasers. In this paper, we will show that a laser effect can be achieved in a bidimensional Tamm structure under pulsed optical pumping. We will also demonstrate that the mode can be spatially confined, and that this results in a reduction of the pump power at threshold.
No preview · Article · Feb 2014 · Proceedings of SPIE - The International Society for Optical Engineering
[Show abstract][Hide abstract] ABSTRACT: We have developed a self-consistent electromagnetic theory of the link between light-matter interactions and optical resonances in three-dimensional nanoresonators. The theory that relies on the concept of quasinormal modes with complex frequencies is capable of accurately handling any photonic or plasmonic resonator with strong radiation leakage, absorption and material dispersion. We first provide a simple iterative method to calculate and normalize quasinormal modes that may be implemented with any numerical tool. We then use the modal formalism to derive a modal expansion of the imaginary part of the Green tensor. This modal representation provides a powerful tool to calculate and understand light-matter interactions in complex photonic or plasmonic systems. In particular, we analyze the degree of spatial coherence in nanoantennas made of metallic nanorods.
No preview · Article · Jan 2014 · Proceedings of SPIE - The International Society for Optical Engineering
[Show abstract][Hide abstract] ABSTRACT: We propose a unique approach for light extraction, using engineered nano-particles to efficiently decouple the light guided in transverse-magnetic guided modes into free-space radiation modes that leak out normally to the thin-film stacks. The underlying mechanism takes advantage of a small electric field variation at the nano-particle scale and induces a "polarization conversion," which renders the induced dipole moment perpendicular to the polarization of the incident light. Our analysis is supported by 2D fully vectorial computational results. Potential applications for light emitting or photovoltaic devices are outlined.
Full-text · Article · Dec 2013 · Applied Physics Letters
[Show abstract][Hide abstract] ABSTRACT: We provide a self-consistent electromagnetic theory of the coupling between dipole emitters and dissipative nanoresonators. The theory that relies on the concept of quasinormal modes with complex frequencies provides an accurate closed-form expression for the electromagnetic local density of states of any photonic or plasmonic resonator with strong radiation leakage, absorption, and material dispersion. It represents a powerful tool to calculate and conceptualize the electromagnetic response of systems that are governed by a small number of resonance modes. We use the formalism to revisit Purcell’s factor. The new formula substantially differs from the usual one; in particular, it predicts that a spectral detuning between the emitter and the resonance does not necessarily result in a Lorentzian response in the presence of dissipation. Comparisons with fully vectorial numerical calculations for plasmonic nanoresonators made of gold nanorods evidence the high accuracy of the predictions achieved by our semianalytical treatment.
Full-text · Article · Jun 2013 · Physical Review Letters
[Show abstract][Hide abstract] ABSTRACT: The spontaneous emission of a quantum emitter depends on its
environment. This fundamental effect of quantum electrodynamics has
become a cornerstone of nano-optics, with the objective to control light
absorption and emission at the nanometer scale. At the heart of the
effect lies the emitter-cavity coupling. An important figure of merit is
the famous Q/V ratio introduced by Purcell in 1946 and largely used by
the photonic-crystal community over the last decennia, with Q the
quality factor of the cavity and V the mode volume. Here we revisit the
classical problem of field coupling between quantum emitters and
cavities to encompass the important case of metallic nanoresonators. We
propose a generalized Purcell formula, which substantially differs from
the classical one and which is capable of accurately handling cavity
modes with strong radiative leakage, absorption and material dispersion.
Fully-vectorial numerical calculations obtained for distinct nanocavity
constructs representative of modern studies in nanophotonics provide a
strong support to our theory.
No preview · Article · Mar 2013 · Proceedings of SPIE - The International Society for Optical Engineering
[Show abstract][Hide abstract] ABSTRACT: We review the properties of the generation of surface plasmons by
subwavelength isolated slits in metal films and by small ensembles of
slits. After an introduction, in Section 2, we recall the theoretical
modal formalism that allows us to calculate the generation efficiency of
SPP from the total field scattered by an indentation on a metal film. We
also rapidly discuss the main results known of the SPP generation
efficiency by subwavelength tiny slits or grooves. In Section 3, we
consider the special case of wavelength-large slits that support two
propagative modes and that allow us to dynamically control the direction
of generated surface plasmons. In Section 4, we conclude by describing a
compact and efficient device capable of launching SPPs in a single
direction with a normally incident beam.
Full-text · Article · Mar 2013 · Proceedings of SPIE - The International Society for Optical Engineering
[Show abstract][Hide abstract] ABSTRACT: We compute the radiative heat transfer between nanostructured gold plates in
the framework of the scattering theory. We predict an enhancement of the heat
transfer as we increase the depth of the corrugations while keeping the
distance of closest approach fixed. We interpret this effect in terms of the
evolution of plasmonic and guided modes as a function of the grating's
Full-text · Article · Mar 2012 · Journal of Physics Conference Series
[Show abstract][Hide abstract] ABSTRACT: Through a fully analytical model [Phys. Rev. B 78, 245108 (2008)], we
investigate the impact of several disorder models on backscattering
losses in photonic crystal waveguides. To evaluate their relative
relevance, we compare the predictions with loss measurements. The
comparison suggests that a long-range disorder at the scale of every
hole has to be considered in disorder model, in addition to the more
classical hole surface roughness.
No preview · Article · Feb 2012 · Proceedings of SPIE - The International Society for Optical Engineering
[Show abstract][Hide abstract] ABSTRACT: The photoluminescence of nitrogen-vacancy (NV) centers in diamond
nanoparticles exhibits specific properties as compared to NV centers in bulk
diamond. For instance large fluctuations of lifetime and brightness from
particle to particle have been reported. It has also been observed that for
nanocrystals much smaller than the mean luminescence wavelength, the particle
size sets a lower threshold for resolution in Stimulated Emission Depletion
(STED) microscopy. We show that all these features can be quantitatively
understood by realizing that the absorption-emission of light by the NV center
is mediated by the diamond nanoparticle which behaves as a dielectric
[Show abstract][Hide abstract] ABSTRACT: Slow light devices such as photonic crystal waveguides (PhCW) and coupled resonator optical waveguides (CROW) have much promise for optical signal processing applications and a number of successful demonstrations underpinning this promise have already been made. Most of these applications are limited by propagation losses, especially for higher group indices. These losses are caused by technological imperfections ("extrinsic loss") that cause scattering of light from the waveguide mode. The relationship between this loss and the group velocity is complex and until now has not been fully understood. Here, we present a comprehensive explanation of the extrinsic loss mechanisms in PhC waveguides and address some misconceptions surrounding loss and slow light that have arisen in recent years. We develop a theoretical model that accurately describes the loss spectra of PhC waveguides. One of the key insights of the model is that the entire hole contributes coherently to the scattering process, in contrast to previous models that added up the scattering from short sections incoherently. As a result, we have already realised waveguides with significantly lower losses than comparable photonic crystal waveguides as well as achieving propagation losses, in units of loss per unit time (dB/ns) that are even lower than those of state-of-the-art coupled resonator optical waveguides based on silicon photonic wires. The model will enable more advanced designs with further loss reduction within existing technological constraints.
[Show abstract][Hide abstract] ABSTRACT: A novel metal-coated nanocylinder-cavity architecture fully compatible with III-V GaInAs technology and benefiting from a broad spectral range enhancement of the local density of states is proposed as an integrated source of nonclassical light. Because of a judicious selection of the mode volume, the cavity combines good collection efficiency (≈45%), large Purcell factors (≈15) over a 80 nm spectral range, and a low sensitivity to inevitable spatial mismatches between the single emitter and the cavity mode. This represents a decisive step towards the implementation of reliable solid-state devices for the generation of entangled photon pairs at infrared wavelengths.
Full-text · Article · Oct 2010 · Physical Review Letters
[Show abstract][Hide abstract] ABSTRACT: We report statistical fluctuations for the transmissions of a series of photonic-crystal waveguides (PhCWs) that are supposedly identical and that only differ because of statistical structural fabrication-induced imperfections. For practical PhCW lengths offering tolerable -3dB attenuation with moderate group indices (n(g) approximately 60), the transmission spectra contains very narrow peaks (Q approximately 20,000) that vary from one waveguide to another. The physical origin of the peaks is explained by calculating the actual electromagnetic-field pattern inside the waveguide. The peaks that are observed in an intermediate regime between the ballistic and localization transports are responsible for a smearing of the local density of states, for a rapid broadening of the probability density function of the transmission, and bring a severe constraint on the effective use of slow light for on-chip optical information processing. The experimental results are quantitatively supported by theoretical results obtained with a coupled-Bloch-mode approach that takes into account multiple scattering and localization effects.