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Title: Control of spatio-temporal dynamics of bio and optoelectronics systems
Author: Gaciu, Nicoleta
ISNI:       0000 0001 3486 2432
Awarding Body: University of Surrey
Current Institution: University of Surrey
Date of Award: 2007
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Bio and optoelectronics systems are different systems in their composition and application but they have surprising similarities in terms of their spatio-temporal dynamics and dynamics control. Both systems are complex systems with many degrees of freedom that are spatially structured on micro and nano scales. Their behaviour can easily switch between stable regime to chaos by changing internal and external influencing factors. Historically, optoelectronics systems have been studied for more than 30 years. Due to novel biotechnological applications bio systems have more recently gained importance. Today, many natural and technological systems are composed of mesoscopic bio and optoelectronic devices or elements. In nature, many biological and chemical processes controlling the functioning of a system or a specific process (e.g. photosynthesis) occur in complex cellular and molecular ensembles. In technological systems, improvements in the development and design of novel materials on an atomic level have opened the way to efficient devices suitable for mass production. This work focuses on the control and analysis of two mesoscopic model examples: molecular motors and semiconductor lasers. In recent years they have been of particular importance due to their complex dynamics. These active systems have many features in common. Both are open systems which use an energy source to generate motion or light. Molecular motors are nanometer-scaled functional biomolecular structures that convert chemical energy into directed motion. Semiconductor lasers convert an electrical pump current into coherent light emission. Due to underlying complex interaction processes both systems show instabilities under the influence of parameters. In a molecular motor ensemble, external forces, diffusion of free and bound motors, and geometrical arrangement of the microtubule substrate tend to bring instabilities into the molecular motor system. In semiconductor lasers, the interplay of carrier diffusion, light diffraction and geometrical constraints given by the width of the laser (typically in the ?m regime) lead to complex interplay of longitudinal and transverse modes and to instabilities and chaos. The aim of this work is to fundamentally analyse the mechanism relevant for the complex dynamics of the two active systems and to derive schemes to control them. For this purpose I have performed complex numerical simulations. The theoretical description of the molecular motor systems is based on Fokker-Planck equations. Space-time simulations of the dynamics of molecular motors reveal the influence of the diffusion constant, arrangement of filaments, number and separation between filaments and external forces on the spatio-temporal dynamics of molecular ensemble. The theoretical analysis of semiconductor lasers is done on the basis of multi-mode Maxwell-Bloch equations. Simulations of the spatio-temporal dynamics in this system demonstrate that the application of a delayed optical feedback realised by a suitable external resonator configuration can lead to an efficient emission control. Various feedback configurations are discussed. The thesis is organised as follows. Chapter 1 gives a general introduction to molecular motors and semiconductor lasers. Chapter 2 focuses on molecular motors. This includes a review of theoretical models, molecular motor properties and simulation results on the complex spatio-temporal dynamics of molecular motor complexes. In Chapter 3 of this thesis, broad area semiconductor lasers with delayed optical feedback will be investigated. The analysis will concentrate on laser systems with unstructured and structured delayed optical feedback. Concluding remarks and future work are given in Chapter 4.
Supervisor: Not available Sponsor: Not available
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral
EThOS ID:  DOI: Not available