JNOG 33 - 2013

National audienceRecueil JNOG 3

Electrical and optical impulse response of High Speed Micro-OLEDs under ultra-short pulse excitation

International audienceThe electric and optical impulse response of two types of high-speed OLED (HSOLED) driven by ultrashort electrical pulses is investigated. The two HSOLED were designed and manufactured to be characterized in the presence of electrical pulses ranging from 10 to 100 ns in duration and a repetition rate of 10 Hz. The impact of the OLED geometry and the fabrication process on the time response is investigated. This is the first time that an optimized HSOLED exhibits an electrical time response as low as 2.1 ± 0.6 ns and also shorter than the device optical decay time (9.8 ± 0.2 ns). Moreover, the HSOLED measured current density reaches 3.0 kA/cm 2 , the highest value reported in the literature, with state-of-the-art electroluminescence of 12 W/cm

Observation of rogue waves in a 980nm-laser diode subject to filtered optical feedback

International audienceIn this work, rogue waves are observed in a 980 nm laser diode subject to filtered optical feedback via an fibre Bragg grating. A rogue-wave map is established for the first time experimentally as functions of optical feedback ratio and laser current. Rogue waves in our laser system are identified as a part of low frequency fluctuation jump-ups

Laser Chemosensor with Rapid Responsivity and Inherent Memory Based on a Polymer of Intrinsic Microporosity

This work explores the use of a polymer of intrinsic microporosity (PIM-1) as the active layer within a laser sensor to detect nitroaromatic-based explosive vapors. We show successful detection of dinitrobenzene (DNB) by monitoring the real-time photoluminescence. We also show that PIM-1 has an inherent memory, so that it accumulates the analyte during exposure. In addition, the optical gain and refractive index of the polymer were studied by amplified spontaneous emission and variable-angle ellipsometry, respectively. A second-order distributed feedback PIM-1 laser sensor was fabricated and found to show an increase in laser threshold of 2.5 times and a reduction of the laser slope efficiency by 4.4 times after a 5-min exposure to the DNB vapor. For pumping at 2 times threshold, the lasing action was stopped within 30 s indicating that PIM-1 has a very fast responsivity and as such has a potential sensing ability for ultra-low-concentration explosives

Analysis and optimization of propagation losses in LiNbO3 optical waveguides produced by swift heavy-ion irradiation

The propagation losses (PL) of lithium niobate optical planar waveguides fabricated by swift heavy-ion irradiation (SHI), an alternative to conventional ion implantation, have been investigated and optimized. For waveguide fabrication, congruently melting LiNbO3 substrates were irradiated with F ions at 20 MeV or 30 MeV and fluences in the range 1013–1014 cm−2. The influence of the temperature and time of post-irradiation annealing treatments has been systematically studied. Optimum propagation losses lower than 0.5 dB/cm have been obtained for both TE and TM modes, after a two-stage annealing treatment at 350 and 375∘C. Possible loss mechanisms are discussed

Photonic mode dispersion of a two-dimensional distributed feedback polymer laser

G. A. Turnbull, P. Andrew, William L. Barnes, and I. D. W. Samuel, Physical Review B, Vol. 67, article 165107 (2003). "Copyright © 2003 by the American Physical Society."We present an analysis of the photonic mode dispersion of a two-dimensional (2D) distributed feedback polymer laser based on the conjugated polymer poly[2-methoxy-5-(2′-ethylhexyloxy)-1,4-phenylene vinylene]. We use a combination of a simple model, together with experimental measurements of the photonic mode dispersion in transmission and emission, to explain the operating characteristics of the laser. The laser was found to oscillate at 636 nm on one edge of a photonic stop band in the photonic dispersion. A 2D coupling of modes traveling perpendicular to the orthogonal gratings was found to lead to a low divergence laser emission normal to the waveguide. At pump energies well above the oscillation threshold for this mode, a divergent, cross-shaped far-field emission was observed, resulting from a distributed feedback occurring over a wide range of wave vectors in one band of the photonic dispersion

Efficiency of radiative emission from thin films of a light-emitting conjugated polymer

J. A. E. Wasey, A. Safonov, I. D. W. Samuel, and William L. Barnes, Physical Review B, Vol. 64, article 205201 (2001). "Copyright © 2001 by the American Physical Society."We examine the efficiency of radiative emission from thin layers of light-emitting conjugated polymers. We compare our experimental results for photoluminescence of the conjugated polymer poly(2-methoxy, 5-(2′-ethyl-hexyloxy) 1,4 phenylenevinylene) (MEH-PPV) with those of a theoretical model, finding good agreement between the two. The specially developed model takes into account several factors including absorption in the emissive layer, a spread of emitter sites within the layer, and the broad emission spectrum of the polymer. We find that the photoluminescence quantum efficiency for radiative emission of a bare MEH-PPV film on a glass substrate is ∼25%. We then apply our model to study electroluminescent devices. We show that for these structures the efficiency of radiative emission is ∼10%. There is thus potential for considerable improvement in efficiency for both systems through recovery of some of the wasted waveguided light. Finally we use our model to reexamine some controversial results that indicate the probability of singlet exciton formation to be 0.4±0.05, and thus greater than the 0.25 expected from spin statistics. Our reanalysis supports a probability >0.25. We conclude by discussing the limitations of present models, including our own, in predicting the performance of realistic light-emitting diodes

Analysis of polarization mode dispersion fluctuations in single mode fibres due to temperature

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