Now showing items 21-39 of 39
| Abstract: | Nonlinear dynamics of laser systems has become an interesting area of research in recent times. Lasers are good examples of nonlinear dissipative systems showing many kinds of nonlinear phenomena such as chaos, multistability and quasiperiodicity. The study of these phenomena in lasers has fundamental scientific importance since the investigations on these effects reveal many interesting features of nonlinear effects in practical systems. Further, the understanding of the instabilities in lasers is helpful in detecting and controlling such effects. Chaos is one of the most interesting phenomena shown by nonlinear deterministic systems. It is found that, like many nonlinear dissipative systems, lasers also show chaos for certain ranges of parameters. Many investigations on laser chaos have been done in the last two decades. The earlier studies in this field were concentrated on the dynamical aspects of laser chaos. However, recent developments in this area mainly belong to the control and synchronization of chaos. A number of attempts have been reported in controlling or suppressing chaos in lasers since lasers are the practical systems aimed to operated in stable or periodic mode. On the other hand, laser chaos has been found to be applicable in high speed secure communication based on synchronization of chaos. Thus, chaos in laser systems has technological importance also. Semiconductor lasers are most applicable in the fields of optical communications among various kinds of laser due to many reasons such as their compactness, reliability modest cost and the opportunity of direct current modulation. They show chaos and other instabilities under various physical conditions such as direct modulation and optical or optoelectronic feedback. It is desirable for semiconductor lasers to have stable and regular operation. Thus, the understanding of chaos and other instabilities in semiconductor lasers and their xi control is highly important in photonics. We address the problem of controlling chaos produced by direct modulation of laser diodes. We consider the delay feedback control methods for this purpose and study their performance using numerical simulation. Besides the control of chaos, control of other nonlinear effects such as quasiperiodicity and bistability using delay feedback methods are also investigated. A number of secure communication schemes based on synchronization of chaos semiconductor lasers have been successfully demonstrated theoretically and experimentally. The current investigations in these field include the study of practical issues on the implementations of such encryption schemes. We theoretically study the issues such as channel delay, phase mismatch and frequency detuning on the synchronization of chaos in directly modulated laser diodes. It would be helpful for designing and implementing chaotic encryption schemes using synchronization of chaos in modulated semiconductor laser |
| URI: | http://dyuthi.cusat.ac.in/purl/878 |
| Files | Size |
|---|---|
| Dyuthi-T0190.pdf | (4.782Mb) |
| Abstract: | Results of a numerical study of synchronisation of two directly modulated semiconductor lasers, using bi-directional coupling, are presented. The effect of stepwise increase in the coupling strength (C) on the synchronisation of the chaotic outputs of two such lasers is studied, with the help of parameter space plots, synchronisation error plots, phase diagrams and time series outputs. Numerical results indicate that as C increases, the system achieves synchronisation as well as stability together with an increase in the output power. The stability of the synchronised states is checked by applying a perturbation to the system after it becomes synchronised and then noting the time it takes to regain synchronisation. For lower values of C the system does not regain synchronisation. But, with higher values synchronisation is regained within a very short time. |
| URI: | http://dyuthi.cusat.ac.in/purl/2557 |
| Files | Size |
|---|---|
| Dyuthi-P0116.pdf | (729.4Kb) |
| Abstract: | We have numerically studied the behavior of a two-mode Nd-YAG laser with an intracavity KTP crystal. It is found that when the parameter, which is a measure of the relative orientations of the KTP crystal with respect to the Nd-YAG crystal, is varied continuously, the output intensity fluctuations change from chaotic to stable behavior through a sequence of reverse period doubling bifurcations. The graph of the intensity in the X-polarized mode against that in the Y-polarized mode shows a complex pattern in the chaotic regime. The Lyapunov exponent is calculated for the chaotic and periodic regions. |
| URI: | http://dyuthi.cusat.ac.in/purl/2533 |
| Files | Size |
|---|---|
| Dyuthi-P0108.pdf | (743.1Kb) |
| Abstract: | The role of acoustic plasmons in the recently discovered high Tc superconductors is discussed. It is shown that the exchange of acoustic plasmons together with the usual phonon exchange between electrons can give rise to a Tc - 100 K. |
| URI: | http://dyuthi.cusat.ac.in/purl/2570 |
| Files | Size |
|---|---|
| Dyuthi-P0129.pdf | (164.0Kb) |
| Abstract: | The chaotic dynamics of directly modulated semiconductor lasers with delayed optoelectronic feedback is studied numerically. The effects of positive and negative delayed optoelectronic feedback in producing chaotic outputs from such lasers with nonlinear gain reduction in its optimum value range is investigated using bifurcation diagrams. The results are confirmed by calculating the Lyapunov exponents. A negative delayed optoelectronic feedback configuration is found to be more effective in inducing chaotic dynamics to such systems with nonlinear gain reduction factor in the practical value range. |
| URI: | http://dyuthi.cusat.ac.in/purl/2529 |
| Files | Size |
|---|---|
| Dyuthi-P0104.pdf | (1.292Mb) |
| Abstract: | A dynamical system with a damping that is quadratic in velocity is converted into the Hamiltonian format using a nonlinear transformation. Its quantum mechanical behaviour is then analysed by invoking the Gaussian effective potential technique. The method is worked out explicitly for the Duffing oscillator potential. |
| URI: | http://dyuthi.cusat.ac.in/purl/2559 |
| Files | Size |
|---|---|
| Dyuthi-P0118.pdf | (338.5Kb) |
| Abstract: | We establish numerically the validity of Huberman-Rudnick scaling relation for Lyapunov exponents during the period doubling route to chaos in one dimensional maps. We extend our studies to the context of a combination map. where the scaling index is found to be different. |
| URI: | http://dyuthi.cusat.ac.in/purl/2560 |
| Files | Size |
|---|---|
| Dyuthi-P0119.pdf | (905.4Kb) |
| Abstract: | The phenomenon of two-soliton resonances of the Kadomtsev-Petviashvilli equation for the superfluid surface density fluctuation in He films is studied. The velocity of the resonant soliton is obtained. |
| URI: | http://dyuthi.cusat.ac.in/purl/2561 |
| Files | Size |
|---|---|
| Dyuthi-P0120.pdf | (384.2Kb) |
| Abstract: | The dynamics of saturated two-dimensional superfluid4He films is shown to be governed by the Kadomtsev-Petviashvili equation with negative dispersion. It is established that the phenomena of soliton resonance could be observed in such films. Under the lowest order nonlinearity, such resonance would happen only if two dimensional effects are taken into account. The amplitude and velocity of the resonant soliton are obtained. |
| URI: | http://dyuthi.cusat.ac.in/purl/2568 |
| Files | Size |
|---|---|
| Dyuthi-P0127.pdf | (427.3Kb) |
| Abstract: | Optical emission from TiO2 plasma, generated by a nanosecond laser is spectroscopically analysed. The main chemical species are identified and the spatio-temporal distribution of the plasma parameters such as electron temperature and density are characterized based on the study of spectral distribution of the line intensities and their broadening characteristics. The parameters of laser induced plasma vary quickly owing to its expansion at low background pressure and the possible deviations from local thermodynamic equilibrium conditions are tested to show its validity. |
| URI: | http://dyuthi.cusat.ac.in/purl/1821 |
| Files | Size |
|---|---|
| Spectral Charac ... from Titanium Dioxide.pdf | (296.3Kb) |
| Abstract: | Optical emission from TiO2 plasma, generated by a nanosecond laser is spectroscopically analysed. The main chemical species are identified and the spatio-temporal distribution of the plasma parameters such as electron temperature and density are characterized based on the study of spectral distribution of the line intensities and their broadening characteristics. The parameters of laser induced plasma vary quickly owing to its expansion at low background pressure and the possible deviations from local thermodynamic equilibrium conditions are tested to show its validity |
| URI: | http://dyuthi.cusat.ac.in/purl/1822 |
| Files | Size |
|---|---|
| Spectral Charac ... from Titanium Dioxide.pdf | (296.3Kb) |
| Abstract: | Optical emission from TiO2 plasma, generated by a nanosecond laser is spectroscopically analysed. The main chemical species are identified and the spatio-temporal distribution of the plasma parameters such as electron temperature and density are characterized based on the study of spectral distribution of the line intensities and their broadening characteristics. The parameters of laser induced plasma vary quickly owing to its expansion at low background pressure and the possible deviations from local thermodynamic equilibrium conditions are tested to show its validity. |
| URI: | http://dyuthi.cusat.ac.in/purl/1823 |
| Files | Size |
|---|---|
| Spectral Charac ... from Titanium Dioxide.pdf | (296.3Kb) |
| Abstract: | Optical emission from TiO2 plasma, generated by a nanosecond laser is spectroscopically analysed. The main chemical species are identified and the spatio-temporal distribution of the plasma parameters such as electron temperature and density are characterized based on the study of spectral distribution of the line intensities and their broadening characteristics. The parameters of laser induced plasma vary quickly owing to its expansion at low background pressure and the possible deviations from local thermodynamic equilibrium conditions are tested to show its validity. |
| URI: | http://dyuthi.cusat.ac.in/purl/1820 |
| Files | Size |
|---|---|
| Spectral Charac ... from Titanium Dioxide.pdf | (296.3Kb) |
| Abstract: | We consider the stability properties of spatial and temporal periodic orbits of one-dimensional coupled-map lattices. The stability matrices for them are of the block-circulant form. This helps us to reduce the problem of stability of spatially periodic orbits to the smaller orbits corresponding to the building blocks of spatial periodicity, enabling us to obtain the conditions for stability in terms of those for smaller orbits. |
| URI: | http://dyuthi.cusat.ac.in/purl/2537 |
| Files | Size |
|---|---|
| Dyuthi-P0112.pdf | (184.9Kb) |
| Abstract: | The effect of coupling on two high frequency modulated semiconductor lasers is numerically studied. The phase diagrams and bifurcatio.n diagrams are drawn. As the coupling constant is increased the system goes from chaotic to periodic behavior through a reverse period doubling sequence. The Lyapunov exponent is calculated to characterize chaotic and periodic regions. |
| URI: | http://dyuthi.cusat.ac.in/purl/2534 |
| Files | Size |
|---|---|
| Dyuthi-P0109.pdf | (272.8Kb) |
| Abstract: | In this Letter we numerically investigate the dynamics of a system of two coupled chaotic multimode Nd:YAG lasers with two mode and three mode outputs. Unidirectional and bidirectional coupling schemes are adopted; intensity time series plots, phase space plots and synchronization plots are used for studying the dynamics. Quality of synchronization is measured using correlation index plots. It is found that for laser with two mode output bidirectional direct coupling scheme is found to be effective in achieving complete synchronization, control of chaos and amplification in output intensity. For laser with three mode output, bidirectional difference coupling scheme gives much better chaotic synchronization as compared to unidirectional difference coupling but at the cost of higher coupling strength. We also conclude that the coupling scheme and system properties play an important role in determining the type of synchronization exhibited by the system. |
| URI: | http://dyuthi.cusat.ac.in/purl/2530 |
| Files | Size |
|---|---|
| Dyuthi-P0105.pdf | (451.1Kb) |
| URI: | http://dyuthi.cusat.ac.in/purl/1706 |
| Files | Size |
|---|---|
| Dyuthi-T0298.pdf | (1.936Mb) |
| Abstract: | Large amplitude local density fluctuations in a thin superfluid He film is considered. It is shown that these large amplitude fluctuations travel and behave like "quasi-solitons" under collision, even when the full nonlinearity arising from the Van der Waals potential is taken into account. |
| URI: | http://dyuthi.cusat.ac.in/purl/2566 |
| Files | Size |
|---|---|
| Dyuthi-P0125.pdf | (299.5Kb) |
| Abstract: | We study the period-doubling bifurcations to chaos in a logistic map with a nonlinearly modulated parameter and show that the bifurcation structure is modified significantly. Using the renormalisation method due to Derrida et al. we establish the universal behaviour of the system at the onset of chaos. |
| URI: | http://dyuthi.cusat.ac.in/purl/2571 |
| Files | Size |
|---|---|
| Dyuthi-P0130.pdf | (215.1Kb) |
Now showing items 21-39 of 39
Dyuthi Digital Repository Copyright © 2007-2011 Cochin University of Science and Technology. Items in Dyuthi are protected by copyright, with all rights reserved, unless otherwise indicated.