Strong multipolar transition enhancement with graphene nanoislands

During the past half century, a major approximation was natural in the field of light-matter interaction: the point-dipole model. It was assumed that the wavelength is much larger than the size of the emitting atom or molecule, so that the emitter can be described as a single or a collection of elementary dipoles. As it is legitimate for visible light, the approximation does no longer hold near plasmonic nanostructures, where the effective wavelength can drop below 10 nm. In that case deviations arise from the approximate model. First, the emitter spatial extent influences the far-field spectrum. Second, high-order transitions beyond the dipolar ones are not forbidden anymore. Going beyond the approximation requires intensive numerical efforts to compute the photonic response over the spatial extent of the emitter, since the complete Green's function is required. Here, we develop a general model that computes the multipolar transition rates of a quantum emitter in a photonic environment, by computing the Green's function through an eigenpermittivity modal expansion. We apply the method on graphene nanoislands, and we demonstrate a local breakdown of the selection rules, with quadrupolar transition rates becoming 100 times larger than dipolar ones.Comment: 21 pages and 8 pages supplementary informatio

Dual-interface grating supercelles for broadband absorption

Here, we propose the usage of dual-interface grating (DIG) supercells with multiperiodicity as shown in Fig. 1(c) and numerically study their extensive mode-coupling possibilities. We consider a-Si solar cell systems which have active layer thickness that is comparable to the size of the grating geometry. At such thickness regime, the grating structure heavily affects the eigenfield profiles of the guided modes. We show how DIG supercells offer much possibility in improving higher order diffraction coupling conditions to guided modes, while maintaining lower order diffraction coupling efficiency. In addition, including symmetry-breaking or blazing properties in DIG structures can lead to excite previously inaccessible modes efficiently, and thus further broadens the enhancement range

Strong coupling and symmetry breaking in plasmonic structures

editorial reviewe

Temperature-induced stochastic resonance in Kerr photonic cavities for frequency shift

peer reviewedDriven nonlinear photonic cavities are widely studied because they exhibit many interesting effects, such as nonreciprocity, thermal effects, and frequency conversion. Specifically, adding noise to a modulated nonlinear system can lead to stochastic resonance (SR), which corresponds to periodic transitions between stable states. In this work, we study the outgoing power and spectra from a nonlinear-driven photonic cavity coupled to an external port. Using a Langevin framework, we show that the system temperature induces SR in the bistable regime, which we study in detail to exploit for enhanced frequency shift. In this way, the thermal fluctuations of the system itself can function as a driver for effective sideband generation, enabling shift efficiencies of up to 40%. We extensively explore various regimes in order to understand and maximize the process

Fano resonance engineering in slanted cavities with hyperbolic metamaterials

peer reviewe

Strong multipolar transition enhancement with graphene nanoislands

peer reviewedFor a long time, the point-dipole model was a central and natural approximation in the field of photonics. This approach assumes that the wavelength is much larger than the size of the emitting atom or molecule so that the emitter can be described as a single or a collection of elementary dipoles. This approximation no longer holds near plasmonic nanostructures, where the effective wavelength can reach the nanometer-scale. In that case, deviations arise and high-order transitions, beyond the dipolar ones, are not forbidden anymore. Typically, this situation requires intensive numerical efforts to compute the photonic response over the spatial extent of the emitter wavefunctions. Here, we develop an efficient and general model for the multipolar transition rates of a quantum emitter in a photonic environment by computing Green's function through an eigen permittivity modal expansion. A major benefit of this approach is that the position of the emitter and the permittivity of the material can be swept in a rapid way. To illustrate, we apply the method on various forms of graphene nanoislands, and we demonstrate a local breakdown of the selection rules, with quadrupolar transition rates becoming 100 times larger than dipolar ones

Graphene ribbons for tunable coupling with plasmonic subwavelength cavities

peer reviewedSince graphene supports low loss plasmonic guided modes in the infrared range, we theoretically investigate the coupling of these modes in patterned sheets with nano-cavities. We calculate cavity modes and (potentially critical) coupling in filter-type circuits, with resonances observed as multiple minima in the reflection spectrum. The origin and properties of the cavity modes are fully modeled by coupled mode theory, exploring for various positions of the cavity with respect to the access waveguide. A useful resonance frequency shift is examined by modifying the graphene doping (e.g. via voltage tuning). The deeply subwavelength cavity modes reach quality factors up to 42 for ribbons of 30 nm width around 5 µm wavelength. These resonances provide opportunities for ultra-compact optoelectronic circuits