Recent Advances on InAs/InP Quantum Dash Based Semiconductor Lasers and Optical Amplifiers Operating at 1.55 μm

This paper summarizes recent advances on InAs/InP quantum dash (QD) materials for lasers and amplifiers, and QD device performance with particular interest in optical communication. We investigate both InAs/InP dashes in a barrier and dashes in a well (DWELL) heterostructures operating at 1.5 mum. These two types of QDs can provide high gain and low losses. Continuous-wave (CW) room-temperature lasing operation on ground state of cavity length as short as 200 mum has been achieved, demonstrating the high modal gain of the active core. A threshold current density as low as 110 A/cm² per QD layer has been obtained for infinite-length DWELL laser. An optimized DWELL structure allows achieving of a T₀ larger than 100 K for broad-area (BA) lasers, and of 80 K for single-transverse-mode lasers in the temperature range between 25degC and 85degC. Buried ridge stripe (BRS)-type single-mode distributed feedback (DFB) lasers are also demonstrated for the first time, exhibiting a side-mode suppression ratio (SMSR) as high as 45 dB. Such DFB lasers allow the first floor-free 10-Gb/s direct modulation for back-to-back and transmission over 16-km standard optical fiber. In addition, novel results are given on gain, noise, and four-wave mixing of QD-based semiconductor optical amplifiers. Furthermore, we demonstrate that QD Fabry-Perot (FP) lasers, owing to the small confinement factor and the three-dimensional (3-D) quantification of electronic energy levels, exhibit a beating linewidth as narrow as 15 kHz. Such an extremely narrow linewidth, compared to their QW or bulk counterparts, leads to the excellent phase noise and time-jitter characteristics when QD lasers are actively mode-locked. These advances constitute a new step toward the application of QD lasers and amplifiers to the field of optical fiber communications     

Epitaxial and large area PLD ferroelectric thin film heterostructures on silicon substrates

Abstract

Epitaxial thin films of Bi₄Ti₃O₁₂ and SrBi₂Ta₂O₉ have been deposited by pulsed laser deposition (PLD) onto epitaxial thin film templates of CeO₂/YSZ as well as on epitaxial electrodes of (La_0.5Sr_0.5)CoO₃, in turn deposited onto CeO₂/YSZ template layers. These electrode and buffer layers have been deposited by PLD as well. The same heterostructures, namely ferroelectric Bilayered perovskite films on the same stack of epitaxial layers, have also been deposited by large area PLD. This technique allows deposition with a good uniformity onto entire silicon 3-inch wafers. Thickness and composition uniformity of the ferroelectric films, electrodes and buffer layers are important with regard to their possible application in microelectronics. Uniformities achieved are in the range of 5 to 15% of the mean thickness, depending on the material and deposition conditions.     

Functionalized liquid natural rubber and liquid epoxidized natural rubber: A promising green toughening agent for polyester

Toughened unsaturated polyester resins (UPRs) were prepared using two different reactive rubbers, namely, liquid natural rubber (LNR) and liquid epoxidized natural rubber (LENR). The effect of varying amounts of LNR and LENR on the morphology, thermal, and mechanical properties of UPR were evaluated. Fourier Transform Infrared spectroscopy was used to investigate the probable crosslinking reaction and changes in the functional groups on crosslinking. Field emission scanning electron microscopy and infinite focus microscopy were used to study the morphology of fracture surfaces. Tensile test showed that both the rubber‐modified resins (1.5 wt %) improved tensile strength. The viscoelastic properties and thermal stability of the toughened polyesters were evaluated using dynamic mechanical thermal analysis and thermogravimetric analysis, respectively. A slight reduction in the glass transition temperature (T_g) of the polyester was reported on the addition of both the rubbers. An increment in impact strength and fracture toughness was observed at 1.5 wt % for LNR and 4.5 wt % for LENR‐modified UPR. The results showed that both the liquid rubbers improved the mechanical properties of UPR. However, LENR‐modified UPR exhibited a more significant improvement in the mechanical properties compared to LNR‐modified UPR. © 2014 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2015 , 132, 41292.     

Nanomagnetism reveals the intracellular clustering of iron oxide nanoparticles in the organism

There are very few methods to investigate how nanoparticles (NPs) are taken up and processed by cells in the organism in the short and long terms. We propose a nanomagnetism approach, in combination with electron microscopy, to document the magnetic outcome of iron oxide-based P904 NPs injected intravenously into mice. The NP superparamagnetic properties are shown to be modified by cell internalization, due to magnetic interactions between NPs sequestered within intracellular organelles. These modifications of magnetic behaviour are observed in vivo after NP uptake by resident macrophages in spleen and liver or by inflammatory macrophages in adipose tissue as well as in vitro in monocyte-derived macrophages. The dynamical magnetic response of cell-internalized NPs is theoretically and experimentally evidenced as a global signature of their local organization in the intracellular compartments. The clustering of NPs and their magnetism become dependent on the targeted organ, on the dose administrated and on the time elapsed since their injection. Nanomagnetism probes the intracellular clustering of iron-oxide NPs and sheds light on the impact of cellular metabolism on their magnetic responsivity.     

Synthesis and radioprotective properties of pulvinic acid derivatives

A high-throughput screening method has highlighted the marked antioxidant activity of some pulvinic acid derivatives (PADs) towards oxidation of thymidine, under γ and UV irradiation, and Fenton-like conditions. Here, we report the synthesis of a series of new hydrophilic PADs and the evaluation of their radioprotective efficacy in cell culture. Using a cell-based fluorescent assay, we show that some of these compounds have a pronounced ability to prevent cell death caused by radiation and to allow the subsequent resumption of proliferation. Thus, PADs may be considered as a novel class of radioprotective agents.     

Processing and Characterization of Bulk Chalcogenide Glasses Used for Waveguide Applications

Chalcogenide glasses (ChG) are of interest due to their optical and electronic properties for use in waveguide applications. To assess expected uniformity in films deposited from bulk glass starting materials, the extent of parent bulk glass property variation was evaluated. Resulting structural and optical properties of melt-derived ChG's were investigated using X-ray diffraction (XRD), Raman spectroscopy, differential thermal analysis and spectrophotometric analysis. The influence of melt size, purification, and other melting conditions on sample homogeneity were quantified and within-melt property variation of bulk glass samples was found to be less than 5% for all parameters examined.     

Evaluation of the termination mode in the radical polymerization of 2,2,2‐trifluoroethyl α‐fluoroacrylate

The mode of termination of 2,2,2‐trifluoroethyl α‐fluoroacrylate (FATRIFE) in radical polymerization was studied, and only termination by recombination occurred, which led to telechelic macromolecular structures. The radical polymerization in acetonitrile was carried out to synthesize oligomers with a low number average degree of polymerization ( )_cum (about 20), using tert‐butylcyclohexyl peroxydicarbonate (TBCPC) as initiator at 75 °C. The initial [TBCPC]₀/[FATRIFE]₀ molar ratio was monitored to evaluate its influence on the ( )_cum of α‐fluoroacrylic oligomers. The ¹H NMR analysis of the polymers showed that the ( )_cum values obtained were higher than 40, in spite of a high C₀ value. To explain these results, the mode of termination was evaluated using the following kinetic law: . The development of kinetic relationships allowed us to calculate the ratio k_prt/k_i·k_p as about 17–30 mol s l^?1, and to confirm that primary radical termination (PRT) was in competition with bimolecular macromolecular termination (BMT). © 2002 Society of Chemical Industry     

Sequenced aeration in a membrane bioreactor: Specific nitrogen removal rates

The aim of this work was to quantify the activity of autotrophic and heterotrophic populations present in a submerged membrane bioreactor submitted to a sequenced aeration, ensuring alternate nitrification and denitrification (BIOSEP® process). Specific nitrification and denitrification rates were determined over a fifteen‐month running period, with and without physico‐chemical phosphorus removal. The results show (i) zero‐order kinetics; (ii) a specific activity independent of MLVSS concentration; and (iii) an evolution of the nitrification kinetics directly linked to an evolution of the nitrifying population within the unit. The study confirmed that denitrification kinetics depend on the concentration and on the nature of wastewater organic matter.     

Electrosynthesis of pyrrole 3-carboxylic acid copolymer films and nanotubes with tunable degree of functionalization for biomedical applications

Tailoring polypyrrole (PPy), an electroactive polymer, with functional groups to which a variety of bioactive molecules can be tethered is highly attractive for building biological structures on conducting surfaces for a range of biomedical applications. In this respect, we investigate the effects of three independent electrosynthesis parameters, namely the applied potential, the composition of the comonomer solution and the film thickness on the incorporation of carboxylic acid-functionalized pyrrole units (Py-COOH) into polypyrrole/Py-COOH copolymer films. FT-IR, XPS and fluorescence microscopy results show that a larger Py-COOH content is inserted in films electrosynthesized at low potential, that the surface functionality of the copolymer films increases with the molar percentage of Py-COOH in the comonomer solution, and that Py-COOH units are preferentially incorporated in the earlier stage of the electrosynthesis process. The method is further adapted for preparing functionalized PPy copolymer nanotubes with potential application in drug delivery. Specifically, functionalized copolymer nanotubes are electrosynthesized through the template method in polycarbonate membrane. Carboxylic acid groups available at the outer surface of these nanostructures are then derivatized to covalently immobilize poly(ethylene glycol) chains, a protein-repellent polymer, so as to enhance the antifouling properties of these promising delivery vehicles.     

Effect of Zr content on friction and wear behavior of Cr‐Zr‐N coating system

Nanostructured Cr‐Zr‐N thin film with different Zr content (0 to 48.8 at.%) was deposited, using an RF magnetron‐sputtering technique. The structural evolution and morphological changes were performed. The tribological performances were evaluated, using a ball‐on‐disk type Oscillating tribometer. The tests were carried out under normal loads of 2, 4 and 6 N, respectively, with an alumina ball (Al₂O₃) as a counter face. The results showed that the crystallite size of the Cr‐Zr‐N system was reduced to 10.8 nm at 31.8 at.% Zr content. Morphological studies of the films showed that the roughness continuously decreased with increasing Zr content, exhibiting a value of 11.2 nm at 31.8 at.% Zr. The wear rate tends to decrease with the increasing of Zr content to reach a lowest value of 1.95 × 10‐2 μm3.N.μm‐1 at 31.8 at.% Zr. The wear rate and friction coefficient were lower in the samples with 31.8 at.% Zr content. The improved friction and wear resistance were attributed to the grain refinement strengthening mechanism at 31.8 at.% of Zr.