High-speed tandem of MQW modulators for coded pulse generation with 14-dB fiber-to-fiber gain

We report on a tandem of electroabsorption modulators integrated with an amplifier by the identical active layer (IAL) approach. A 14 dB fiber-to-fiber is obtained by the use of constant As-P ratio MQW active layer and operation at 10 Gb/s is demonstrated. A record modulator saturation power of 35 mW is also reported.     

Synthesis of self‐healing supramolecular rubbers from fatty acid derivatives,diethylene triamine,and urea

We describe the synthesis of supramolecular self‐healing elastomers from vegetable oil fatty acid derivatives, diethylene triamine, and urea. Our strategy to obtain materials that are self‐healing but do not flow relies on the use of a wide molecular distribution of randomly branched oligomers equipped with self‐complementary and complementary hydrogen bonding groups. We prepared such oligomers with a two steps procedure. In the first step, diethylene triamine was condensed with dimer acids. In the second step, the oligomers obtained were allowed to react with urea. The molecules were characterized by NMR and IR spectroscopies and Monte‐Carlo simulations were used to analyze the molecular size distribution. The sensitivity to small variations of the experimental conditions has been examined and the robustness of the synthetic procedure optimized. © 2008 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 46: 7925–7936, 2008     

Optimizing driving conditions of a MQW EA modulator for solitongeneration

A detailed analysis of the pulses generated with a multiple quantum well (MQW) electroabsorption (EA) modulator used as a soliton source is performed. The pulse temporal and spectral shape are simulated and a good agreement is obtained with the experimental results. An irregular holed spectrum shape is observed under certain operating conditions and its existence is attributed to parasitic phase modulation. This type of spectrum could be observed even for pulses having a time bandwidth τΔν product below 0.4 which makes them usually considered as nearly transform limited. However it is not the case. The influence of the pulse spectral shape on transmission performances is investigated by means of a realistic simulation of soliton pulse propagation at 10 Gb/s. It is shown that for 9000 km propagation distance and for pulses presenting this irregular spectral shape a signal degradation occurs as the timing jitter is above 10 ps and the quality factor Q is below 2, which results in an increase of the transmission bit error rate. In order to avoid the generation of this kind of pulses when operating a MQW modulator as a soliton source, a mapping is realized giving the adequate voltages to apply to the diode for acceptable soliton generation     

Rheological properties of suspensions of the green microalga Chlorella vulgaris at various volume fractions

A systematic study of the rheological properties of solutions of non-motile microalgae (Chlorella vulgaris CCAP 211-19) in a wide range of volume fractions is presented. As the volume fraction is gradually increased, several rheological regimes are observed. At low volume fractions (but yet beyond the Einstein diluted limit), the suspensions display a Newtonian rheological behaviour and the volume fraction dependence of the viscosity can be well described by the Quemada model (Quemada, Eur Phys J Appl Phys 1:119–127, 1997). For intermediate values of the volume fraction, a shear thinning behaviour is observed and the volume fraction dependence of the viscosity can be described by the Simha model (Simha, J Appl Phys 23:1020–1024, 1952). For the largest values of the volume fraction investigated, an apparent yield stress behaviour is observed. Increasing and decreasing stress ramps within this range of volume fractions indicate a thixotropic behaviour as well. The rheological behaviour observed within the high concentration regime bears similarities with the measurements performed by Heymann and Aksel (Phys Rev E 75:021505, 2007) on polymethyl methacrylate suspensions: irreversible flow behaviour (upon increasing/decreasing stresses) and dependence of the flow curve on the characteristic time of forcing (the averaging time per stress values). All these findings indicate a behaviour of the microalgae suspensions similar to that of suspensions of rigid particles. A deeper insight into the physical mechanisms underlying the shear thinning and the apparent yield stress regime is obtained by an in situ analysis of the microscopic flow of the suspension under shear. The shear thinning regime is associated to the formation of cell aggregates (flocs). Based on the Voronoi analysis of the correlation between the cell distribution and cell sizes, we suggest that the repulsive electrostatic interactions are responsible for this microscale organisation. The apparent yield stress regime originates in the formation of large-scale cell aggregates which behave as rigid plugs leading to a maximally random jammed state.     

20 Gbit/s high-performance integrated MQW TANDEM modulators andamplifier for soliton generation and coding

We report on the integration of two InGaAsP-InGaAsP MQW electroabsorption ridge modulators and an amplifier on the same active layer. The two modulators are separated by a 500-μm ridge waveguide optical amplifier, in order to prevent electrical crosstalk, and to compensate for optical losses. The first modulator is used as a soliton generator, and the second codes the generated pulses. The amplifier showed 8.2-dB gain for 120-mA injected current. This allowed a low fiber to fiber insertion loss of 9 dB for the tandem. We present here for the first time to our knowledge, a 20 Gbit/s operation for a tandem-amplifier device, together with transmission experiments     

Modelling and assessing local area differences in road casualties: a case study in England

The context of this research is the governmental targeting of road casualty reductions in England. Local authorities have a major role to play in achieving such targets and this research explores the relationships between road casualties and local authority characteristics such as population, road networks, traffic, and geography. Regression models are identified for types of road casualty to provide local area expectations against which observed numbers can be compared. A number of issues are identified that raise concerns about the current methods adopted for assessing road safety performances and about the implementation of this approach at local levels. These issues include the large impact on assessments of judgements of casualty severity and of estimates of starting point casualties when estimating reductions over time. This study leads to recommendations for ways in which current approaches to road casualty appraisal might be improved.     

Accurate determination of the band-offset of a quantum semiconductor structure from its capacitance-voltage profile: Application to an InP/Ga0.47In0.53As/InP single quantum well

We discuss the possible analysis of an electron distribution obtained by capacitance-voltage profiling for the determination of the conduction band offset of a single quantum well. We show that, for this method which requires only relatively light experimental equipment, a nonconsuming computational time interpretation can be set up within a quite satisfactory degree of accuracy. As an application, we report the study of a lattice matched InP/Ga_0.47In_0.53As/InP quantum well for which we get ΔE_c = (200±10) meV, in good agreement with other measurements upon this system.