symmetric and antisymmetric band-edge modes exist in distributed feedback surface-emitting semiconductor lasers, with the dominant difference being the radiation loss. Devices generally operate on the low-loss antisymmetric modes, although the power extraction efficiency is low. Here we develop graded photonic heterostructures, which localize the symmetric mode in the device centre and confine the antisymmetric modes close to the laser facet. This modal spatial separation is combined with absorbing boundaries to increase the antisymmetric mode loss, and force device operation on the symmetric mode, with elevated radiation efficiency. Application of this concept to terahertz quantum cascade lasers leads to record-high peakpower surface emission ( > 100 mW) and differential efficiencies (230 mW A − 1 ), together with low-divergence, single-lobed emission patterns, and is also applicable to continuous-wave operation. such flexible tuning of the radiation loss using graded photonic heterostructures, with only a minimal influence on threshold current, is highly desirable for optimizing secondorder distributed feedback lasers.

We demonstrate the possibility to efficiently split the near-field heat flux exchanged between graphene nano-disks by tuning their doping. This result paves the way for the developement of an active control of propagation directions for heat fluxes exchanged in near-field throughout integrated nanostructures networks.The control of electric currents in solids is at the origin of modern computer technology which has revolutionized our daily life. Until the 2000s no thermal counterpart had been developed to control the flow of heat at the nanoscale in a similar manner. In 2006, a step forward in this direction has been done by Li et al.[1] when they introduced the first concept of a thermal transistor for controlling heat fluxes carried by phonons through solid segments. Later, several prototypes of phononic thermal logic gates [2] as well as thermal memories [3] were developed in order to process information by means of the heat fluxes carried by phonons [4]. Besides, different solid-state thermal diodes were conceived [5-9] allowing for rectifying these fluxes in asymmetric solid segments.Very recently, there has been a fast growing interest in developing active functionalties to manage heat transfers by radiation rather than by conduction between contactless solids. Since 2010 several radiative thermal rectifiers [10][11][12][13][14][15][16][17][18][19] have been proposed using spectrally selective nanostructures and phase-changes materials. In 2014 and 2015 a radiative analog of a transistor was suggested theoretically which allows for switching, modulating and amplifying the heat flux exchanged both in the nearfield [21] or far-field regime [22]. Furthermore, a concept of a radiative thermal memory was introduced working in the far-field [23] and the near-field regime [24]. Such devices open the way for new perspectives concerning the development of contactless thermal circuits intended for an active thermal management with photons instead of electrons or phonons. Finally, the thermal diode concept based on phase-change materials has already been tested, experimentally, in the far-field regime [20] in 2014. A review of these recent developments can be found in Ref. [25].In this Letter, we introduce the concept of a heat flux splitter which allows us to tune the direction of propagation of heat flux exchanged in the near-field. To demonstrate the operating modes of this heat splitter we consider a set of three graphene nano-disks in mutual interaction. We show that the heat flux exchanged between these nano-disks cannot only be splitted equally in two predefined directions as for a 50:50 beam splitter, which is trivial, but it can also be oriented in mostly one predefined direction acting like a 99:1 beam splitter by an appropriate tuning of the Fermi levels in the graphene nano-disks. Since this tuning can be achieved by electrical gating, for instance, we thus demonstrate, in particular, that the direction of propagation of the radiative heat flow can be dynamically controlled in nano-architectures by electr...

It is known that the near-field spectrum of the local density of states of the electromagnetic field above a SiC/air interface displays an intense narrow peak due to the presence of a surface polariton. It has been recently shown that this surface wave can be strongly coupled with the sheet plasmon of graphene in graphene-SiC heterosystems. Here, we explore the interplay between these two phenomena and demonstrate that the spectrum of the electromagnetic local density of states in these systems presents two peaks whose position depends dramatically both on the distance to the interface and on the chemical potential of graphene. This paves the way towards the active control of the local density of states.

We propose and demonstrate a hybrid photonic-plasmonic nanolaser that combines the light harvesting features of a dielectric photonic crystal cavity with the extraordinary confining properties of an optical nano-antenna. For this purpose, we developed a novel fabrication method based on multi-step electron-beam lithography. We show that it enables the robust and reproducible production of hybrid structures, using a fully top-down approach to accurately position the antenna. Coherent coupling of the photonic and plasmonic modes is highlighted and opens up a broad range of new hybrid nanophotonic devices.

Hybrid halide perovskites are now considered as key materials for contemporary research in photovoltaics and nanophotonics. In particular, because these materials can be solution processed, they represent a great hope for obtaining low cost devices. While the potential of 2D layered hybrid perovskites for polaritonic devices operating at room temperature has been demonstrated in the past, the potential of the 3D perovskites has been much less explored for this particular application. Here, we report the strong exciton-photon coupling with 3D bromide hybrid perovskite. Cavity polaritons are experimentallly demonstrated from both reflectivity and photoluminescence experiments, at room temperature, in a 3λ/2 planar microcavity containing a large surface spin-coated CH 3 NH 3 PbBr 3 thin film. A microcavity quality factor of 92 was found and a large Rabi splitting of 70 meV was measured. This result paves the way to low-cost polaritonic devices operating at room temperature, potentially electrically injectable as 3D hybrid perovskites present good transport properties.Cavity polaritons are half-light half-matter quasiparticles arising from the strong coupling regime between excitonic and photonic modes [1]. Such regime is achieved when the coupling strength, related to the oscillator strength quantifying the light-matter interaction in a material, is larger than the dissipation rates of uncoupled excitons and cavity photons. Thanks to its hybrid nature, cavity polaritons inherit the best features of both the excitonic and photonic component: strongly nonlinear bosonic particles which can propagate balistically over macroscopic distance, and can be injected/probed via optical means. These fascinating properties suggest not only a playground for studying physics of out of equilibrium Bose Einstein condensation, but also a potential platform for all-optical devices. In the later direction, many proof-of-concepts of polaritonic devices have been reported: polaritonic lasers [2], polariton transistors [3], resonant tunnelling diodes [4], interferometer [5], optical gates [3], and optical router [6]. Most of these demonstrations are in GaAs-based system the most accomplished technologies to engineer cavity polaritons. However, due to the small excitonic effects and oscillator strength in GaAs, their operating regime is limited to cryogenic temperature. For this reason, materials presenting strong excitonic effects at room temperature, such as the high band gap materials GaN [7,8] or ZnO [9, 10] are actively studied. However, the achievement of inorganic semiconductor engineered confined microstructures need sophisticated and high * emmanuelle.deleporte@ens-cachan.fr temperature epitaxial techniques. Looking for low-cost solutions, soft chemistry and low temperature processed materials presenting strong excitonic effects were also considered. The strong coupling regime at room temperature has been demonstrated in planar microcavities containing organic materials [11][12][13][14] or organic-inorganic halide perovskites such ...

In this paper the design, fabrication and characterization of a bioinspired overlayer deposited on a GaN LED is described. The purpose of this overlayer is to improve light extraction into air from the diode's high refractive-index active material. The layer design is inspired by the microstructure found in the firefly Photuris sp. The actual dimensions and material composition have been optimized to take into account the high refractive index of the GaN diode stack. This two-dimensional pattern contrasts other designs by its unusual profile, its larger dimensions and the fact that it can be tailored to an existing diode design rather than requiring a complete redesign of the diode geometry. The gain of light extraction reaches values up to 55% with respect to the reference unprocessed LED.

In this article, we show for the first time, both theoretically and empirically, that plasmonic coupling can be used to generate Localized Surface Plasmon Resonances (LSPRs) in transition metal dimeric nano-antennas (NAs) over a broad spectral range (from the visible to the near infrared) and that the spectral position of the resonance can be controlled through morphological variation of the NAs (size, shape, interparticle distance). First, accurate calculations using the generalized Mie theory on spherical dimers demonstrate that we can take advantage of the plasmonic coupling to enhance LSPRs over a broad spectral range for many transition metals (Pt, Pd, Cr, Ni etc.). The LSPR remains broad for low interparticle distances and masks the various hybridized modes within the overall resonance. However, an analysis of the charge distribution on the surface of the nanoparticles reveals these modes and their respective contributions to the observed LSPR. In the case of spherical dimers, the transfer of the oscillator strengths from the "dipolar" mode to higher orders involves a maximum extinction cross-section for intermediate interparticle distances of a few nanometers. The emergence of the LSPR has been then experimentally illustrated with parallelepipedal NAs (monomers and dimers) made of various transition metals (Pt, Pd and Cr) and elaborated by nanolithography. Absolute extinction cross-sections have been measured with the spatial modulation spectroscopy technique over a broad spectral range (300-900 nm) for individual NAs, the morphology of which has been independently characterized by electron microscopy imaging. A clear enhancement of the LSPR has been revealed for a longitudinal excitation and plasmonic coupling has been clearly evidenced in dimers by an induced redshift and broadening of the LSPR compared to monomers. Furthermore, the LSPR has been shown to be highly sensitive to slight modifications of the interparticle distance. All the experimental results are well in agreement with finite element method (FEM) calculations in which the main geometrical parameters characterizing the NAs have been derived from electron microscopy imaging analysis. The main advantage of dimers as compared to monomers lies in the generation of a well-defined and highly enhanced electromagnetic field (the so-called "hot spots") within the interparticle gap that can be exploited in photo-catalysis, magneto-plasmonics or nano-sensing.

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