Two of the most successful microcresonator concepts are the vertical cavity surface emitting laser (VCSEL), where light is confined between distributed Bragg reflectors (DBRs), and the distributed feedback (DFB) laser, where a periodic grating provides positive optical feedback to selected modes in an active waveguide (WG) layer. Our work concerns the combination of both into a composite device, facilitating coherent interaction between both regimes and giving rise to novel laser modes in the system. In a first realization, a full VCSEL stack with an organic active layer is evaporated on top of a diffraction grating with a large period (approximately 1 micron), leading to diffraction of waveguided modes into the surface emission of the device. Here, the coherent interaction between VCSEL and WG modes, as observed in an anticrossing of the dispersion lines, facilitates novel hybrid lasing modes with macroscopic in-plane coherence [1]. In further studies, we decrease the grating period of such devices to realise DFB conditions in a second-order Bragg grating which strongly couples photons via first-order light diffraction to the VCSEL. This efficient coupling can be compared to more classical cascade-coupled cavities and is successfully described by a coupled oscillator model [2]. When both resonators are non-degenerate, they are able to function as independent structures without substantial diffraction losses. The realization of such novel devices provides a promising platform for photonic circuits based on organic microlasers. [1] A. Mischok et al., Adv. Opt. Mater., early online, DOI: 10.1002/adom.201600282, (2016) [2] T. Wagner et al., Appl. Phys. Lett., accepted, in production, (2016)

Hybrid resonators in vertical and lateral direction are introduced by depositing a full vertical cavity surface emitting laser (VCSEL) stack on top of a periodically structured substrate. As a result, waveguided (WG) modes in the cavity plane are scattered into the vertical direction and exhibit linear dispersion curves in addition to the original parabolic cavity mode. A large in-plane coherence length even below threshold enables a coherent interaction of both resonators, as observed in a pronounced anticrossing and hybridization of waveguided and VCSEL modes in the far field spectrum. Resulting from this coupling, both original VCSEL modes as well as hybrid WG-VCSEL modes show stimulated emission. Here, hybrid modes exhibit a macroscopically increased spatial extension of the coherent laser mode, proven by both spatially resolved spectra as well as sharp modes in k-space. The coherent coupling of two conceptually very different devices with perpendicular propagation directions facilitates a multitude of new applications.

A. Mischok and co-workers develop a hybrid waveguide–vertical cavity surface emitting laser on page 1215. An angle-resolved emission spectrum of such a hybrid laser is presented on their cover image. The linear dispersion lines of an organic waveguide are scattered into the surface emission of a microcavity via a high-order diffraction grating and enable the observation of novel hybrid laser modes (red) with a macroscopically increased coherence length.

Two of the most successful microresonator concepts are the vertical cavity surface emitting laser (VCSEL), comprising a vertical cavity of highly reflective DBRs sandwiching an active layer, and the distributed feedback (DFB) laser, where a periodic optical grating selects laser modes from an active waveguide (WG) layer. Here, an organic microcavity is coupled with in-plane periodic photonic wires or dots to facilitate a coherent interaction between waveguided and vertically emitting modes as well as creating an additional in-plane confinement. The vertical positioning of such patterning plays a crucial role in the observable features. While embedding metallic or dielectric wires directly in the cavity layer leads to a strong lateral confinement as well as the observation of photonic Bloch states [1,2], the deposition of the full VCSEL stack on top of a periodic grating reveals novel features. In such a device, we demonstrate the coherent coupling between parabolic VCSEL and linear WG modes in the angle-resolved far field emission. In this system, lasing occurs not only at the VCSEL parabola apex but also at points of hybridization, when the dispersion of modes cross, showing a drastically enhanced in-plane coherence [3]. The coherent coupling of two conceptually different devices with perpendicular propagation directions paired with the macroscopic coherence facilitate a multitude of new applications. [1] Adv. Opt. Mater. 2(8), 746 (2014) [2] Phys. Rev. Appl. 3, 064016 (2015). [3] Adv. Opt. Mater. under review (2016).

We embed periodic SiO2 wires in an organic microcavity, producing a rectangular potential by the different optical thicknesses of the active layer due to the additional SiO2 layer. By mu-photoluminescence spectroscopy, we observe the energy dispersion of the photons and obtain discrete localized below and extended Bloch states above the potential barrier, respectively, showing that electro-magnetic waves can behave like massive particles, such as electrons, in crystal lattices. We investigate the dependencies on wire width and period and use the Kronig-Penney model to describe the photon energy dispersion, including an "effective mass" of a photon propagating through a microcavity implying polarization splitting. We obtain excellent agreement between experiment, simulation and analytical calculation. (C) 2015 Elsevier Ltd. All rights reserved.

Although Cu(In,Ga)Se2 (CIGS) solar cells have the highest efficiency of any thin-film solar cell, especially when sodium is incorporated, the fundamental device properties of ultrafast carrier transport and recombination in such cells remain not fully understood. Here, we explore the dynamics of charge carriers in CIGS absorber layers with varying concentrations of Na by femtosecond (fs) broadband pump-probe reflectance spectroscopy with 120fs time resolution. By analyzing the time-resolved transient spectra in a different time domain, we show that a small amount of Na integrated by NaF deposition on top of sputtered Cu(In,Ga) prior to selenization forms CIGS, which induces slower recombination of the excited carriers. Here, we provide direct evidence for the elongation of carrier lifetimes by incorporating Na into CIGS.

By adding photonic wire structures to an organic microcavity, we create an additional confinement and a Bloch-like band structure in the dispersion of periodically structured cavities. We experimentally observe spontaneous and stimulated emission from the ground and different excited discrete modes at room temperature. By changing the spatial gain distribution via a two-beam interference, we are able to directly control the laser emission from both extended and confined modes of such organic photonic wires. Both spatial distribution and dispersion exhibit coherent emission from tunable modes, which we describe with an analytical model and numerical simulations, in agreement with our measurements.

L'invention concerne un element de filtrage optique (50) qui est destine a des moyens (70) de conversion d'informations spectrales en informations de position et sur lequel est monte un detecteur (30) destine a detecter des signaux, ledit element de filtrage optique comprenant au moins deux micro-resonateurs (10, 11) ; un micro-resonateur (10 ; 11) comprend au moins - deux structures de couche reflechissantes (4, 6, 8, 9), recouvrant la surface, qui sont constituees d'au moins une couche de matiere (2) d'indice de refraction eleve et d'au moins une couche de matiere (3) de faible indice de refraction dans une sequence alternee, et - au moins une couche de resonance (5 ; 7), recouvrant la surface, qui sont disposees entre les deux structures de couche reflechissantes (4, 6, 8, 9) recouvrant la surface. Selon l'invention, l'element de filtrage (50) comprend au moins un substrat transparent (1), a faces planes et paralleles, destine au decouplage optique des deux micro-resonateurs (10, 11) ; le premier micro-resonateur (10 ; 11) se trouve sur une premiere des deux surfaces opposees (51 ; 52) du substrat (1) ; le second micro-micro-resonateur (11 ; 10) se trouve sur le substrat (1) sur l'une seconde surface (54) du substrat (1), opposee a la premiere surface (51) ; et la couche de resonance (5 ; 7) d'au moins un micro-resonateur (10 ; 11) et/ou la structure de couche reflechissante (4, 6, 8, 9), entourant la couche de resonance (5 ; 7), ont une epaisseur variable le long d'un axe horizontal (25) de l'element de filtrage (50).

We investigate the angle-resolved emission of a multimode organic microcavity in a microscope, setup with a high numerical aperture. In the angle-integrated spectra, we observe the formation of narrow deep minima and maxima typical for Fano-like interference in microcavities. Our experimental angle-resolved transmission and emission spectra agree well with corresponding numerical simulations using a transfer-matrix technique, confirming the Fano-like interference of the adjacent antiphase modes.

Organic microcavities comprising the host: guest emitter system Alq(3):DCM off er an interesting playground to experimentally study the dispersion characteristics of laterally patterned microlasers due to the broad emission spectrum and large oscillator strength of the organic dye. By structuring of metallic or dielectric sublayers directly on top of the bottom mirror, we precisely manipulate the mode structure and influence the coherent emission properties of the device. Embedding silver layers into a microcavity leads to an interaction of the optical cavity-state in the organic layer and the neighboring metal which red-shifts the cavity resonance, creating a Tamm-plasmon-polariton state. A patterning of the metal can in turn be exploited to fabricate deep photonic wells of micron-size, efficiently con fining light in lateral direction. In periodic arrays of silver wires, we create a Kronig-Penney-like optical potential in the cavity and in turn observe optical Bloch states spanning over several photonic wires. We modify the Kronig-Penney theory to analytically describe the full far-field emission dispersion of our cavities and show the emergence of either zero-, pi-, or 2 pi-phase-locking in the system. By investigating periodic SiO2 patterns, we experimentally observe stimulated emission from the ground and different excited discrete states at room temperature and are able to directly control the laser emission from both extended and confined modes of the photonic wires at room-temperature.

We discuss approaches to increase the light outcoupling efficiency in organic microcavity (MC) lasers and organic light-emitting diodes (OLEDs). We find that the introduction of metals into the cavities leads to additional Tamm-plasmon polariton modes, while the corrugation of metal contacts, such as perforated μ-size holes or a periodic array of metal stripes, leads to 2D confinement of the cavity modes, which in turn reduces the lasing threshold in MCs. Furthermore, we elucidate light loss mechanisms in OLEDs and reveal how external dielectric layers and periodic gratings can be used to enhance outcoupling from the OLED cavity.

We investigate the formation of optical modes in organic microcavities with an incorporated perforated silver layer. The metal leads to a formation of Tamm-plasmon-polaritons and thus separates the sample into metal-free or metal-containing areas, supporting different resonances. This mode splitting is exploited to confine photons in elliptic holes and triangular cuts, forming distinctive standing wave patterns showing the strong lateral confinement. A comparison with a Maxwell-Bloch based rate equation model clearly shows the nonlinear transition into the lasing regime. The concentration of the electric field density and inhibition of lateral loss channels in turn decreases the lasing threshold by up to one order of magnitude, to 0.1 nJ. By spectroscopic investigation of such a triangular wedge, we observe the transition from the unperturbed cavity state to a strongly confined complex transversal mode. Such a structured silver layer can be utilized in future for charge carrier injection in an electrically driven organic solid state laser.

Due to their geometry, optical microcavities allow strong confinement of light between the mirrors and promise single mode operation at lowest possible lasing thresholds. Nevertheless, such devices suffer from losses not only due to parasitic absorption of the active or mirror layers, but especially via outcoupling of leaky and waveguided modes within the active layer. In this work, we present an organic microcavity sandwiched between high quality dielectric distributed Bragg reflectors. A highly conductive silver layer of 40nm thickness is added next to the active layer, leading to the formation of Tamm-Plasmon-Polaritons (TPP), one replacing the original cavity mode and shifting its resonance to the red, another one emerging from the long-wavelength sideband and moving to the blue. To avoid parasitic absorption introduced by such contacts, the silver layer is structured on the micrometer-scale using photolithography, yielding separated areas supporting either original cavity mode or red shifted TPP-resonances. This separation leads to a strong spatial trapping of the modes to only their resonant regions on the sample and can in turn be exploited to achieve complete three-dimensional confinement of photons. In elliptic holes produced in the metal layer, we observe the formation of Mathieu-Modes, leading to a reduction of the lasing threshold by six times. Facilitating triangular cuts in the silver layer, highly confined standing modes develop in the system, allowing a precise optimization of the spatial mode extension and reducing the threshold even further down to one order of magnitude below the threshold of an unstructured organic cavity. These results show that the introduction of absorptive metals, needed for the realization of an electrically driven laser, can in turn be harnessed to improve the characteristics of the device.

An organic microcavity is excited by blue and green pump lasers, showing bright coherent emission in the red. On page 746, A. Mischok et al. show how an additional plasmonic microstructure in the cavity leads to the formation of Tamm-Plasmon-Polariton states and an intricate far-field pattern, which enables the observation of photonic Bloch states. Photography by Juliane Schmidt.

We investigate the influence of the built-in voltage on the performance of organic bulk heterojuction solar cells that are based on a p-i-n structure. Electrical doping in the hole and the electron transport layer allows to tune their work function and hence to adjust the built-in voltage: Changing the doping concentration from 0.5 to 32 wt% induces a shift of the work function towards the transport levels and increases the built-in voltage. To determine the built-in voltage, we use electroabsorption spectroscopy which is based on an evaluation of the spectra caused by a change in absorption due to an electric field (Stark effect). For a model system with a bulk heterojunction of BF-DPB and C60, we show that higher doping concentrations in both the electron and the hole transport layer increase the built-in voltage, leading to an enhanced short circuit current and solar cell performance.

A one‐dimensional periodic rectangular potential, also known as the Kronig‐Penney (KP) potential, transforms the parabolic dispersion of a free particle into a set of bands separated by bandgaps. However, if the potential wells are deep enough, the lowest bands converge into a set of single discrete states, numbered from j = 1 to j = jmax, which can be even or odd, describing the number of extrema. Here, discrete and continuous KP states are experimentally observed within a periodically modulated metal–organic microcavity. Depending on the width of the photonic wires, the thickness of the cavity, and the added metal grating, the parity of the highest localized state jmax can be either even or odd, leading to a complementary parity of the first continuous mode. The apex of this Bloch‐like state in turn either starts at k = 0, or a π‐state at the edges of the Brillouin zone, formed by the periodic metallic wires. An easy analytical explanation and numerical confirmation of zero‐ or π‐phase locking for laser modes in spatially modulated microcavities are provided.

We investigate the built-in voltage in organic bulk heterojunction solar cells using electroabsorption spectroscopy based on the Stark effect, i.e. the variation of the absorption energies of a material caused by an electric field. Due to spectral contributions of permanent dipoles, a novel approach for evaluating the EA spectra is required. We use a fitting routine analyzing a broad spectral range instead of using only a single wavelength. A reliable quantitative determination of the built-in voltage is achieved.

We investigate the complex mode structure in microcavities with multidimensional optical confinement. Our active material is composed of the organic blend Alq3:DCM, embedded into a microcavity containing arrays of photonic wires, facilitating strong lateral confinement. We directly record the energy dispersion for one k→ vector component while the second lateral k→ component is scanned. Thereby, we obtain a detailed dispersion tomogram of the cavity resonances, showing excellent agreement with our optical model. We are able to exceed the lasing threshold and observe stimulated emission not only from the bottom of the cavity parabola, but also from higher order modes.

Organic microcavities offer tantalizing prospects for studying the interactions of light and matter. For electrical excitation of these processes, electrodes must be integrated. However, the large absorption properties of metals are generally considered fatal for optical coherence. With this in mind, we embedded a thin silver grating into an organic microcavity to generate periodic arrays of localized cavity modes and metal-based Tamm plasmon polaritons. These excited states are capable of phase coupling across the grating. At room temperature and under non-resonant pumping, we selectively stimulated coherent emission from in- and out-of-phase locked arrays. We show that an absorptive metal inside an optical cavity is compatible with coherent emission. Most importantly, the inherently low residual absorption of the organic layer enables coherence to spread over macroscopic distances, even at room temperature. Our strategy of embedding metal patterns into an organic microcavity yields a viable route towards electrically driven organic solid-state lasers.