Highly monomode W1 waveguide square lattice photonic crystal lasers

Lasing of W1 square lattice-based photonic crystal lasers on the substrate approach is analyzed. A second-order distributed feedback highly monomode behavior is observed. A comprehensive two-dimensional and three-dimensional finite-difference time-domain computation analysis shows that this characteristic arises from the lattice geometry. Single-mode lasers can be obtained using this geometry, opening the way to the realization of monomode laser arrays.     

Microbubbles for optofluidics: controlled defects in bubble crystals

We use liquid–gas microfluidics as a low-cost, tunable microstructuring tool, for which applications can be envisioned in optics. In order to obtain relevant geometries for photonics, beyond simple self-assembled crystals, we propose an original approach that excludes bubbles from chosen zones thanks to tiny pillars. To assess the strength of the exclusion mechanism, we predict the behaviour of a single flattened bubble in front of a thin cylindrical pillar located in a rectangular microchannel. The model compares the hydrodynamic force F _fluid that pushes the bubble and the force F _s, due to surface tension, resulting from the surface augmentation when the bubble rises over the pillar. The resulting predictions have been confirmed by experimental results which showed that the bubble passes over the pillar if F _s < F _fluid and goes around it in other cases. Consistently with this model, dynamic bubble crystals with controlled lacuna defects of one, two, or a line of bubbles have been successfully produced. Defects can be switched on or off by changing the flow. Using a photosensitive polymer as a carrier liquid, static bubble crystals have also been produced.     

2.6 μm GaSB based photonic crystal coupled cavity lasers

Long wavelength GaInAsSb/AlGaAsSb quantum wells lasers have been grown by molecular beam epitaxy and processed into ridge cavities coupled by an intracavity photonic crystal mirror, to enhance the laser spectral properties. The devices operate in the continuous-wave regime at room temperature with a single frequency emission at 2.6 m.     

850 nm wavelength range nanoscale resonant optical filter fabrication using standard microelectronics techniques

The fabrication and characterization of a nanoscale resonant optical filter at wavelength around 850 nm is reported using standard C-MOS compatible microelectronics techniques. We discuss the different steps of the process and their impact on the final structure. We show that the use of these techniques gives an efficient filter on glass substrate with high transmission and a narrow bandwidth of 0.4 nm. We also demonstrate the same process on a silicon substrate for a potential integration with electronic functions.     

Diffusion of radiogenic helium in natural uranium oxides

The issue of nuclear waste management – and especially spent fuel disposal – demands further research on the long-term behavior of helium and its impact on physical changes in UO₂ and (U,Pu)O₂ matrices subjected to self-irradiation. Helium produced by radioactive decay of the actinides concentrates in the grains or is trapped at the grain boundaries. Various scenarios can be considered, and can have a significant effect on the radionuclide source terms that will be accessible to water after the canisters have been breached. Helium production and matrix damage is generally simulated by external irradiation or with actinide-doped materials. A natural uranium oxide sample was studied to acquire data on the behavior of radiogenic helium and its diffusion under self-irradiation in spent fuel. The sample from the Pen Ar Ran deposit in the Vendée region of France dated at 320 ± 9 million of years was selected for its simple geological history, making it a suitable natural analog of spent fuel under repository conditions during the initial period in a closed system not subject to mass transfer with the surrounding environment. Helium outgassing measured by mass spectrometry to determine the He diffusion coefficients through the ore shows that: (i) a maximum of 5% (2.1% on average) of the helium produced during the last 320 Ma in this natural analog was conserved, (ii) about 33% of the residual helium is occluded in the matrix and vacancy defects (about 10⁻⁵ mol g⁻¹) and 67% in bubbles that were analyzed by HRTEM. A similar distribution has been observed in spent fuel and in (U_0.9,Pu_0.1)O₂. The results obtained for the natural Pen Ar Ran sample can be applied by analogy to spent fuel, especially in terms of the apparent solubility limit and the formation, characteristics and behavior of the helium bubbles.     

The effects of composition and doping on the response of GeC-Siphotodiodes

The spectral responses of a series of heterojunction diodes of p-type Ge_1-yC_y on n-type Si (100) substrates were measured by Fourier transform infrared (IR) spectroscopy. Alloy layers 0.5 μm thick were grown by molecular beam epitaxy at a substrate temperature of 400°C and were doped p-type with different C concentrations. With increasing C content, the diode dark current decreased, and the optical absorption band edge shifted toward higher energy by 70 meV for 0.12 at% of C. The increase in energy was attributed to the composition dependence of the bandgap rather than to strain relaxation, because the GeC layers were nearly relaxed with the same strain. The photoresponsivity was 0.07 A/W at a wavelength of 1.55 μm, and 0.2 A/W at a wavelength of 1.3 μm. These measurements show that GeC photodetectors have good properties and reasonable response at technologically important near-IR wavelengths and can be fabricated by heteroepitaxy for compatibility with Si integrated circuits     

Tracing of industrial aerosol sources in an urban environment using Pb, Sr, and Nd isotopes

A comprehensive Pb-Sr-Nd isotope tracer study of atmospheric trace metal pollution has been performed in the urban environment of Strasbourg-Kehl. Filter dust of the principal pollutant sources (waste incinerators, thermal power plant and steel plant) and soot of car and ship exhausts have been analyzed. In addition tree barks (as biomonitors) and PM10 have been analyzed to trace and determine the distribution of the pollution in the environment. The industrial sources have highly variable epsilonNd values (-9.7 and -12.5 for incinerators and -17.5 for steel plant). Much higher epsilonNd values have been found for soot of car exhausts (-6 and -6.9). These high values make the Nd isotope system a powerful tool for the discrimination of traffic emissions but especially for the identification of diesel derived particles in the urban environment. The 206Pb/207Pb isotope ratios of gasoline are low (1.089) compared to diesel soot (1.159). The 26Pb/207Pb ratios of 1.151-1.152 for the steel plant and 1.152 for the solid waste incinerator are close to the Pb isotope ratio of diesel. The 87Sr/ 8Sr isotope ratios of the principal industrial sources vary significantly: 0.7095 for the domestic solid waste incinerator, 0.709 for the steel plant, and 0.7087 for car exhaust soot. PM10 aerosols collected in the urban center of Strasbourg show the influence of the pollutant sources at 3-7 km distance from the center. Most of the aerosols Pb isotopic compositions suggest Pb admixtures from at least three sources: a natural background and in function of the wind direction the domestic waste incinerator (S-wind) or the steel plant and the chemical waste incinerator (NE-wind). The traffic contribution can only be estimated with help of Nd isotopes. Therefore the clear identification of different pollutant sources in the urban environment is only possible by combining the three different isotope systems and is based on the fact that significant differences exist between the Pb, Sr, and Nd isotope ratios of the natural atmospheric background and pollutants containing Pb, Sr, and Nd of industrial origin with similar variable 206Pb/207Pb, 87Sr/ 86Sr, and 143Nd/144Nd.     

Strong electron irradiation hardness of 852 nm Al-free laser diodes

We have step-irradiated Al-free laser diodes with 1 MeV electrons at fluences from 10¹⁴ up to 10¹⁶ electrons/cm². We measure at each step their L-I and I-V characteristics to evaluate the impact of irradiation on optical and electrical properties. We also irradiated a test structure incorporating 3 GaInAsP quantum wells and a thick GaInP cladding. Quantum wells photoluminescence measurements show a strong degradation of its intensity. However laser diodes properties remain essentially unchanged, due to a strong forward bias annealing effect.     

Soft mold NanoImprint Lithography: a versatile tool for sub-wavelength grating applications

Microsystem Technologies - Due to its independency to the substrate used, Soft mold NanoImprint Lithography (S-NIL) is a technique of great interest in particular for the fabrication of optical...     

High temperature 10 Gbit/s directly modulated 1.3 μm DFB lasersusing InAsP/InGaAsP materials

Uncooled 10 Gbit/s direct modulation of high-power 1.3 μm InAsP/InGaAsP directly modulated multiple quantum well distributed feedback (DFB) lasers is demonstrated. High resonant frequencies and high efficiency at 85°C are obtained due to the high epitaxial quality of ternary, aluminium-free, quantum wells. Floor-free transmission on 90 and 140 ps/nm within ITU recommendations are demonstrated