Recent progress in high-bit-rate applications of four-wave-mixing in SOAs

Non-linearities in semiconductor optical amplifiers have been used to demonstrate a wide range of functions applicable to future optical networks such as wavelength conversion and optical switching. Four-wave-mixing effects in SOAs have been studied extensively in many laboratories with respect to the underlying physical processes and system applications. At BT Labs an optimisation of SOAs for FWM has been achieved by altering the device active layer composition and by increasing the device length. We will review recent progress at BT Labs in dispersion compensation, wavelength conversion and demultiplexing at bit-rates of 40Gbit/s using these devices.

UEGO based measurement of EGR rate and residual gas fraction

A technique is presented for measuring the exhaust gas recirculation (EGR) and residual gas fraction (RGF) using a fast UEGO based O2 measurement of the manifold or in-cylinder gases, and of the exhaust gases. The technique has some advantages over the more common CO2-based method. In the case of an RGF measurement, fuel interference must be eliminated and special fuelling arrangements are is required. It is shown how a UEGO-based measurement, though sensitive to reactive species in the exhaust (such as H 2), as a system reports EGR/ RGF rates faithfully. Preliminary tests showed that EGR and RGF measurements using the O2 approach agreed well with CO2-based measurements. © 2011 SAE International.

A single-rate context-dependent learning process underlies rapid adaptation to familiar object dynamics.

Motor learning has been extensively studied using dynamic (force-field) perturbations. These induce movement errors that result in adaptive changes to the motor commands. Several state-space models have been developed to explain how trial-by-trial errors drive the progressive adaptation observed in such studies. These models have been applied to adaptation involving novel dynamics, which typically occurs over tens to hundreds of trials, and which appears to be mediated by a dual-rate adaptation process. In contrast, when manipulating objects with familiar dynamics, subjects adapt rapidly within a few trials. Here, we apply state-space models to familiar dynamics, asking whether adaptation is mediated by a single-rate or dual-rate process. Previously, we reported a task in which subjects rotate an object with known dynamics. By presenting the object at different visual orientations, adaptation was shown to be context-specific, with limited generalization to novel orientations. Here we show that a multiple-context state-space model, with a generalization function tuned to visual object orientation, can reproduce the time-course of adaptation and de-adaptation as well as the observed context-dependent behavior. In contrast to the dual-rate process associated with novel dynamics, we show that a single-rate process mediates adaptation to familiar object dynamics. The model predicts that during exposure to the object across multiple orientations, there will be a degree of independence for adaptation and de-adaptation within each context, and that the states associated with all contexts will slowly de-adapt during exposure in one particular context. We confirm these predictions in two new experiments. Results of the current study thus highlight similarities and differences in the processes engaged during exposure to novel versus familiar dynamics. In both cases, adaptation is mediated by multiple context-specific representations. In the case of familiar object dynamics, however, the representations can be engaged based on visual context, and are updated by a single-rate process.

Scalar dissipation rate approach

An improved understanding of lean fuel turbulent premixed flames must play a central role in the fundamental science of these new concepts.

Application of scalar dissipation rate modelling to industrial burners in partially premixed regimes

The objective of this paper is to test various available turbulent burning velocity models on an experimental version of Siemens small scale combustor using the commercial CFD code. Failure of burning velocity model with different expressions for turbulent burning velocity is observed with an unphysical flame flashback into the swirler. Eddy Dissipation Model/Finite Rate Chemistry is found to over-predict mean temperature and species concentrations. Solving for reaction progress equation with its variance using scalar dissipation rate modelling produced reasonably good agreement with the available experimental data. Two different turbulence models Shear Stress Transport (SST) and Scale Adaptive Simulation (SAS) SST are tested and results from transient SST simulations are observed to be predicting well. SAS-SST is found to under-predict with temperature and species distribution.

Scalar dissipation rate transport in the corrugated flamelets and thin reaction zones regime for turbulent premixed flames

The characteristics of the scalar dissipation rate transport in the corrugated flamelets and the thin reaction zones regimes are studied based on two three-dimensional Direct Numerical Simulation (DNS) databases for freely propagating statistically planar turbulent premixed flames. The turbulent flame parameters are so chosen that the database which represents the corrugated flamelets regime has a global Damköhler number Da>1 whereas the database representing the thin reaction zones regime has Da <1. It is demonstrated that the terms originating from the correlation between fluctuating velocity and scalar gradient T1 shows strong Da dependence. The terms originating from dilatation T2, the scalar inner product of gradients of velocity and scalar fields T3 and the correlation between reaction rate and scalar gradients T4 and the dissipation term D2 remain important for both the flames. However, T3 dissipates scalar dissipation rate in the Da > 1 flame while it produces scalar dissipation rate in the Da < 1 flame. This difference is because of the change in the alignment between scalar and velocity gradients

External-cavity mode-locked quantum-dot laser diodes for low repetition rate, sub-picosecond pulse generation

This paper presents an investigation of the mode-locking performance of a two-section external-cavity mode-locked InGaAs quantum-dot laser diode, focusing on repetition rate, pulse duration and pulse energy. The lowest repetition rate to-date of any passively mode-locked semiconductor laser diode is demonstrated (310 MHz) and a restriction on the pulse energy (at 0.4 pJ) for the shortest pulse durations is identified. Fundamental mode-locking from 310 MHz to 1.1 GHz was investigated, and harmonic mode-locking was achieved up to a repetition rate of 4.4 GHz. Fourier transform limited subpicosecond pulse generation was realized through implementation of an intra-cavity glass etalon, and pulse durations from 930fs to 8.3ps were demonstrated for a repetition rate of 1 GHz. For all investigations, mode-locking with the shortest pulse durations yielded constant pulse energies of ∼0.4 pJ, revealing an independence of the pulse energy on all the mode-locking parameters investigated (cavity configuration, driving conditions, pulse duration, repetition rate, and output power). © 2011 IEEE.