Compact grating coupler using asymmetric waveguide scatterers

We demonstrate a novel grating coupler design based on double asymmetric and vertically oriented waveguide scatterers to efficiently couple normally incident light to a fundamental mode silicon waveguide laying on a buried oxide layer.Comment: 4 pages, 1 figur

Recent advances in solid-state organic lasers

Organic solid-state lasers are reviewed, with a special emphasis on works published during the last decade. Referring originally to dyes in solid-state polymeric matrices, organic lasers also include the rich family of organic semiconductors, paced by the rapid development of organic light emitting diodes. Organic lasers are broadly tunable coherent sources are potentially compact, convenient and manufactured at low-costs. In this review, we describe the basic photophysics of the materials used as gain media in organic lasers with a specific look at the distinctive feature of dyes and semiconductors. We also outline the laser architectures used in state-of-the-art organic lasers and the performances of these devices with regard to output power, lifetime, and beam quality. A survey of the recent trends in the field is given, highlighting the latest developments in terms of wavelength coverage, wavelength agility, efficiency and compactness, or towards integrated low-cost sources, with a special focus on the great challenges remaining for achieving direct electrical pumping. Finally, we discuss the very recent demonstration of new kinds of organic lasers based on polaritons or surface plasmons, which open new and very promising routes in the field of organic nanophotonics

Current induced anisotropic magnetoresistance in topological insulator films

Topological insulators are insulating in the bulk but possess spin-momentum locked metallic surface states protected by time-reversal symmetry. The existence of these surface states has been confirmed by angle-resolved photoemission spectroscopy (ARPES) and scanning tunneling microscopy (STM). Detecting these surface states by transport measurement, which might at first appear to be the most direct avenue, was shown to be much more challenging than expected. Here, we report a detailed electronic transport study in high quality Bi2Se3 topological insulator thin films. Measurements under in-plane magnetic field, along and perpendicular to the bias current show opposite magnetoresistance. We argue that this contrasting behavior is related to the locking of the spin and current direction providing evidence for helical spin structure of the topological surface states

Large-Angle, Broadband and Multifunctional Gratings Based on Directively Radiating Waveguide Scatterers

Conventional surface-relief gratings are inefficient at deflecting normally-incident light by large angles. This constrains their use in many applications and limits the overall efficiency of any optical instrument integrating gratings. Here, we demonstrate a simple approach for the design of diffraction gratings that can be highly efficient for large deflection angles, while also offering additional functionality. The gratings are composed of a unit cell comprising a vertically-oriented asymmetric slot-waveguide. The unit cell shows oscillating unidirectional scattering behavior that can be precisely tuned as a function of the waveguide length. This occurs due to interference between multiple modes excited by the incident light. In contrast to metasurface-based gratings with multiple resonant sub-elements, a periodic arrangement of such non-resonant diffracting elements allows for broadband operation and a strong tolerance for variations in angle of incidence. Full-wave simulations show that our grating designs can exhibit diffraction efficiencies ranging from 94% for a deflection angle of 47$^\circ$ to 80% for deflection angle of 80$^\circ$. To demonstrate the multifunctionality of our grating design technique, we have also proposed a flat polarization beamsplitter, which allows for the separation of the two orthogonal polarizations by 80$^\circ$, with an efficiency of 80%

Defining a Model of Classical Activation in Microglia

Microglia, the resident immune cells of the central nervous system, can become activated following injury, disease, or infection. In vitro, they can be activated by stimuli, which determine the inflammatory phenotype they will develop. In this thesis, stimulating microglia with tumor necrosis factor- and interferon- resulted in classical activation, characterized by proliferation, increased transcription of complement receptor 3 and major histocompatibility class II molecules, and elevated production and transcription of interleukin-1 and nitric oxide. Stimulation with TNF and IFN also changed the intensity of phosphorylated (activated) cyclic adenosine monophosphate response element binding protein immunoreactivity in microglia. Specifically, cells differentiated into populations with high or low pCREB intensity. This was the first example of such a response in microglia and was representative of what occurred in vivo, after ICH. Thus, the characterization of this model will be useful for future studies of this and other intracellular pathways of classically activated microglia.MAS

Nonlinear interactions in an organic polariton condensate

Under the right conditions, cavity polaritons form a macroscopic condensate in the ground state. The fascinating nonlinear behaviour of this condensate is largely dictated by the strength of polariton–polariton interactions. In inorganic semiconductors, these result principally from the Coulomb interaction between Wannier–Mott excitons. Such interactions are considerably weaker for the tightly bound Frenkel excitons characteristic of organic semiconductors and were notably absent in the first reported demonstration of organic polariton lasing. In this work, we demonstrate the realization of an organic polariton condensate, at room temperature, in a microcavity containing a thin film of 2,7-bis[9,9-di(4-methylphenyl)-fluoren-2-yl]-9,9-di(4-methylphenyl)fluorene. On reaching threshold, we observe the spontaneous formation of a linearly polarized condensate, which exhibits a superlinear power dependence, long-range order and a power-dependent blueshift: a clear signature of Frenkel polariton interactions