Creation of a complex butterfly attractor using a novel Lorenz-type system

A novel Lorenz-type system of nonlinear differential equations is proposed. Unlike the original Lorenz system, where the chaotic dynamics remain confined to the positive half-space with respect to the Z state variable due to a limiting threshold effect, the proposed system enables bipolar swing of this state variable. In addition, the classical set of parameters (a, b, c) controlling the behavior of the Lorenz system are reduced to a single parameter, namely a. Two possible modes of operation are admitted by the system; switching between these two modes results in the creation of a complex butterfly chaotic attractor. Numerical simulations and results from an experimental setup are presented

Use of semiconductor optical amplifiers in signal processing applications

We describe a 42.6 Gbit/s all-optical pattern recognition system which uses semiconductor optical amplifiers (SOAs). A circuit with three SOA-based logic gates is used to identify the presence of specific port numbers in an optical packet header.

On classical and other methods of discriminant analysis and estimation of log-odds

For two multinormal populations with equal covariance matrices the likelihood ratio discriminant function, an alternative allocation rule to the sample linear discriminant function when n1 ≠ n2 ,is studied analytically. With the assumption of a known covariance matrix its distribution is derived and the expectation of its actual and apparent error rates evaluated and compared with those of the sample linear discriminant function. This comparison indicates that the likelihood ratio allocation rule is robust to unequal sample sizes. The quadratic discriminant function is studied, its distribution reviewed and evaluation of its probabilities of misclassification discussed. For known covariance matrices the distribution of the sample quadratic discriminant function is derived. When the known covariance matrices are proportional exact expressions for the expectation of its actual and apparent error rates are obtained and evaluated. The effectiveness of the sample linear discriminant function for this case is also considered. Estimation of true log-odds for two multinormal populations with equal or unequal covariance matrices is studied. The estimative, Bayesian predictive and a kernel method are compared by evaluating their biases and mean square errors. Some algebraic expressions for these quantities are derived. With equal covariance matrices the predictive method is preferable. Where it derives this superiority is investigated by considering its performance for various levels of fixed true log-odds. It is also shown that the predictive method is sensitive to n1 ≠ n2. For unequal but proportional covariance matrices the unbiased estimative method is preferred. Product Normal kernel density estimates are used to give a kernel estimator of true log-odds. The effect of correlation in the variables with product kernels is considered. With equal covariance matrices the kernel and parametric estimators are compared by simulation. For moderately correlated variables and large dimension sizes the product kernel method is a good estimator of true log-odds.

Properties and applications of injection locking in 1.55 μm quantum-dash mode-locked semiconductor lasers

Mode-locked semiconductor lasers are compact pulsed sources with ultra-narrow pulse widths and high repetition-rates. In order to use these sources in real applications, their performance needs to be optimised in several aspects, usually by external control. We experimentally investigate the behaviour of recently-developed quantum-dash mode-locked lasers (QDMLLs) emitting at 1.55 μm under external optical injection. Single-section and two-section lasers with different repetition frequencies and active-region structures are studied. Particularly, we are interested in a regime which the laser remains mode-locked and the individual modes are simultaneously phase-locked to the external laser. Injection-locked self-mode-locked lasers demonstrate tunable microwave generation at first or second harmonic of the free-running repetition frequency with sub-MHz RF linewidth. For two-section mode-locked lasers, using dual-mode optical injection (injection of two coherent CW lines), narrowing the RF linewidth close to that of the electrical source, narrowing the optical linewidths and reduction in the time-bandwidth product is achieved. Under optimised bias conditions of the slave laser, a repetition frequency tuning ratio >2% is achieved, a record for a monolithic semiconductor mode-locked laser. In addition, we demonstrate a novel all-optical stabilisation technique for mode-locked semiconductor lasers by combination of CW optical injection and optical feedback to simultaneously improve the time-bandwidth product and timing-jitter of the laser. This scheme does not need an RF source and no optical to electrical conversion is required and thus is ideal for photonic integration. Finally, an application of injection-locked mode-locked lasers is introduced in a multichannel phase-sensitive amplifier (PSA). We show that with dual-mode injection-locking, simultaneous phase-synchronisation of two channels to local pump sources is realised through one injection-locking stage. An experimental proof of concept is demonstrated for two 10 Gbps phase-encoded (DPSK) channels showing more than 7 dB phase-sensitive gain and less than 1 dB penalty of the receiver sensitivity.

All-optical signal processing using semiconductor optical amplifiers for next generation optical networks

This thesis details an experimental and simulation investigation of some novel all-optical signal processing techniques for future optical communication networks. These all-optical techniques include modulation format conversion, phase discrimination and clock recovery. The methods detailed in this thesis use the nonlinearities associated with semiconductor optical amplifiers (SOA) to manipulate signals in the optical domain. Chapter 1 provides an introduction into the work detailed in this thesis, discusses the increased demand for capacity in today’s optical fibre networks and finally explains why all-optical signal processing may be of interest for future optical networks. Chapter 2 discusses the relevant background information required to fully understand the all-optical techniques demonstrated in this thesis. Chapter 3 details some pump-probe measurement techniques used to calculate the gain and phase recovery times of a long SOA. A remarkably fast gain recovery is observed and the wavelength dependent nature of this recovery is investigated. Chapter 4 discusses the experimental demonstration of an all-optical modulation conversion technique which can convert on-off- keyed data into either duobinary or alternative mark inversion. In Chapter 5 a novel phase sensitive frequency conversion scheme capable of extracting the two orthogonal components of a quadrature phase modulated signal into two separate frequencies is demonstrated. Chapter 6 investigates a novel all-optical clock recovery technique for phase modulated optical orthogonal frequency division multiplexing superchannels and finally Chapter 7 provides a brief conclusion.

Multi-parametric metabolic assessment of cells under stress conditions

Glycolysis, glutaminolysis, the Krebs cycle and oxidative phosphorylation are the main metabolic pathways. Exposing cells to key metabolic substrates (glucose, glutamine and pyruvate); investigation of the contribution of substrates in stress conditions such as uncoupling and hypoxia was conducted. Glycolysis, O2 consumption, O2 and ATP levels and hypoxia inducible factor (HIF) signalling in PC12 cells were investigated. Upon uncoupling with FCCP mitochondria were depolarised similarly in all cases, but a strong increase in respiration was only seen in the cells fed on glutamine with either glucose or pyruvate. Inhibition of glutaminolysis reversed the glutamine dependant effect. Differential regulation of the respiratory response to FCCP by metabolic environment suggests mitochondrial uncoupling has a potential for substrate-specific inhibition of cell function. At reduced O2 availability (4 % and 0 % O2), cell bioenergetics and local oxygenation varied depending on the substrate composition. Results indicate that both supply and utilisation of key metabolic substrates can affect the pattern of HIF-1/2α accumulation by differentially regulating iO2¬, ATP levels and Akt/Erk/AMPK pathways. Inhibition of key metabolic pathways can modulate HIF regulatory pathways, metabolic responses and survival of cancer cells in hypoxia. Hypoxia leads to transcriptional activation, by HIF, of pyruvate dehydrogenase (PDH) kinase which phosphorylates and inhibits PDH, a mitochondrial enzyme that converts pyruvate into acetyl-CoA. The levels of PDH (total and phosphorylated), PDH kinase and HIF-1α were analysed in HCT116 and HCT116 SCO2-/- (deficient in complex IV of the respiratory chain) grown under 20.9 % and 3 % O2. Data indicate that regulation of PDH can occur in a manner independent of the HIF-1/PDH kinase 1 axis, mitochondrial respiration and the demand for acetyl-CoA. Collectively these results can be applied to many diseases; reduced nutrient supply and O2 during ischemia/stroke, hypoglycaemia in diabetes mellitus and cancer associated changes in uncoupling protein expression levels.