In the last decades, designs of most incandescent sources have been realized by heating the whole device. Here we propose a novel approach consisting in taking advantage of hot nanoemitters that can be cooled in a few tens of nanoseconds. It offers a new opportunity for high speed modulation and for enhanced agility in the active control of polarization, direction and wavelength of emission. To compensate the weak thermal emission of isolated nanoemitters, we propose to insert them in some complex environments, such as e.g. the gap of cold nanoantenna, which allow a significant thermal emission enhancement of the hot nanovolume. In order to optimize this kind of device, a fully vectorial upper bound for the thermal emission of a hot nanoparticle in a cold environment is derived. This criterion is very general since it is equivalent to an absorption cross-section upper bound for the nanoparticle. Moreover, it is an intrinsic characteristic of the environment regardless of the nanoparticle, so it allows to decouple the design of the environment from the one of the hot nanovolume. It thus provides a good figure of merit to compare the ability of different systems to enhance thermal emission of hot nanoemitters.
We model a photonic crystal slab as a Fabry-Perot resonator with two propagating Bloch waves in the periodic medium. This provides a semi-analytical recipe for the computation of photonic crystal slab modes' dispersion and quality factors. We apply for the search and study of bound states in the continuum, which exist above the light line, among the leaky modes, but nevertheless are decoupled from the continuum of propagating modes and are confined inside the periodic medium. We identify them as a set of optogeometric parameters for which the quality factor of a given photonic crystal mode goes to infinity. Also, we illustrate a simple example of the vertical symmetry breaking by adding a semi-infinite dielectric substrate, and comment on some other asymmetric configurations.
Photonic and plasmonic resonators are dielectric or metallic optical devices that confine light at a scale smaller than the wavelength. The eigenmodes of the system are obviously powerful and intuitive tools to describe light scattering and light-matter interactions mediated by the resonant structure. However, owing to the presence of energy dissipation (by radiation or absorption), using the eigenmodes of nanoresonators is an open issue that has been partly solved only recently. We have developed a modal formalism that relies on the concept of quasinormal modes with complex eigenfrequencies. The theory is capable of handling any photonic or plasmonic resonator with strong radiation leakage, absorption and material dispersion. The normalization of the quasinormal modes constitutes one of the key points of the modal formalism; only a proper and efficient normalization method can ensure both a good accuracy and a high versatility of the theory. Different methods for normalizing quasinormal modes have been published recently. We benchmark these methods on the generic example of a plasmonic nanoantenna lying over a substrate.
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.
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.
From a microscopic point of view, we theoretically investigate fishnet metamaterials. We formulate the construction of
the fundamental Bloch mode by tracking the flows of energy through the fishnet structure. The analysis is supported by a
closed-form semi-analytical model based on surface-plasmon coupled-mode equations. The model provides an accurate
formula for the fishnet refractive index, including the real (negative-valued) and imaginary parts. The model simply
explains how the surface plasmon modes couple in the structure and it shines new light on the fishnet negative-index
paradigm at optical frequencies. It possesses broad flexibility in geometrical and material parameter tailoring of fishnet
properties, even including the gain-assisted case.
Optical microcavities offer the ability to create extremely low-threshold lasers with high modulation bandwidth. In such microcavity devices, the fraction β of spontaneous emission into the lasing mode can become close to one and the step-like "threshold" gradually disappears. To implement such high-β devices, one can exploit Cavity Quantum ElectroDynamics effects, more precisely spontaneous emission enhancement. The concomitant effect of spontaneous emission acceleration is the preferential funnelling of spontaneous emission into the cavity mode. In our work, the cavity is a double- heterostructure cavity etched on a suspended membrane and contains InAs quantum dots. Lasing is achieved with β-factors higher than 0.44 and is sustained by less than 10 quantum dots.
Diffractive optical elements in the form of surface-relief 'blaze' (echelette-type) structures diamond-turned onto the surface of conventional refractive lens elements are well-established and widely used. However, they suffer from limited broadband diffraction efficiency, which prevents the full benefits of hybrid optics from being realised. A family of diffractive optics, the blazed-binary optical element, is investigated to improve the broadband efficiency.
Blazed-binary optical elements are diffractive components, composed of subwavelength (ie. with size smaller than the wavelength) ridges, pillars or other simple geometries carefully etched in a dielectric film, that mimic standard blazed-echelette diffractive elements. Their operation exploits effective-medium theory. We show that by exploiting the high dispersion of artificial material, diffractive optical elements which are blazed over a broad spectral range can be synthesized. A blazed-binary grating is designed to validate the broadband behaviour and practical aspects are investigated through the manufacture of sub-wavelength structures in a Gallium Arsenide substrate.
An accurate three-dimensional method to calculate the Bloch modes of photonic crystal waveguides is proposed. Good agreement with available experimental and numerical data is obtained. The originality of the method lies in the fact that the Bloch modes are seen as the electromagnetic fields associated to the complex poles of an in-plane transversal scattering matrix. In comparison with previous approaches, the computational domain discretized is smaller and a higher accuracy for the losses of photonic crystal waveguides is achieved.