Browsing by Author "Hwang, TM"

Now showing 1 - 9 of 9

A synchronization scheme using self-pulsating laser diodes in optical chaotic communication
(2000-03-01)
Juang, C
;
Hwang, TM
;
Juang, J
;
Lin, WW
;
應用數學系
A synchronization scheme using self-pulsating laser diodes in optical chaotic communication is proposed. Optical chaotic light can be obtained by injecting a sinusoidal electronic signal into a self-pulsating laser diode. To synchronize between two identical chaotic systems with different initial conditions, a drive and response system model is constructed according to Pecora and Carroll's theory. Synchronization can be achieved for optical simplex and duplex transmissions provided that the conditional Lyapunov exponents for the drive and response systems are all negative. This approach offers a key step toward realizing optical chaotic modulation and demodulation.
Chaotic behaviors of bistable laser diodes and its application in synchronization of optical communication
(2001-10-01)
Wang, WC
;
Hwang, TM
;
Juang, C
;
Juang, J
;
Liu, CY
Period-doubling routes to chaos behavior in bistable laser diodes is examined numerically, An external sinusoidal electronic drive is injected to generate chaotic light output. Phase portrait, Poincare map, bifurcation diagram, and Lyapunov exponent are then calculated to assert the existence of chaos. Furthermore, according to Pecora and Carroll's theory, a drive-response system is constructed by using the bistable laser diodes to mask the sinusoidal electronic signal with chaotic light. Synchronization can be achieved for optical simplex and duplex transmissions using bistable laser diodes. The proposed synchronization scheme between two separate chaotic systems provides a key step toward optical chaotic communication.
Fixed-point methods for a semiconductor quantum dot model
(2004-09-01)
Hwang, TM
;
Lin, WW
;
Liu, JL
;
Wang, WC
;
應用數學系
This paper presents various fixed-point methods for computing the ground state energy and its associated wave function of a semiconductor quantum dot model. The discretization of the three-dimensional Schrodinger equation leads to a large-scale cubic matrix polynomial eigenvalue problem for which the desired eigenvalue is embedded in the interior of the spectrum. The cubic problem is reformulated in several forms so that the desired eigenpair becomes a fixed point of the new formulations. Several algorithms are then proposed for solving the fixed-point problem. Numerical results show that the simple fixed-point method with acceleration schemes can be very efficient and stable. (C) 2004 Elsevier Ltd. All rights reserved.
FM detection from an optical chaotic carrier
(2001-07-01)
Huang, ST
;
Hwang, TM
;
Juang, C
;
Juang, J
;
Lin, WW
To synchronize two identical chaotic systems with different initial conditions, a drive and response system model is constructed according to Pecora and Carroll's theory. The drive and response systems become asymptotically synchronized if an FM signal is added to the drive system. The FM signal can be detected when the drive and response systems are strongly coupled.
Jacobi-Davidson methods for cubic eigenvalue problems
(2005-09-01)
Hwang, TM
;
Lin, WW
;
Liu, JL
;
Wang, WC
;
應用數學系
Several Jacobi-Davidson type methods are proposed for computing interior eigenpairs of large-scale cubic eigenvalue problems. To successively compute the eigenpairs, a novel explicit non-equivalence deflation method with low-rank updates is developed and analysed. Various techniques such as locking, search direction transformation, restarting, and preconditioning are incorporated into the methods to improve stability and efficiency. A semiconductor quantum dot model is given as an example to illustrate the cubic nature of the eigenvalue system resulting from the finite difference approximation. Numerical results of this model are given to demonstrate the convergence and effectiveness of the methods. Comparison results are also provided to indicate advantages and disadvantages among the various methods. Copyright (c) 2004 John Wiley & Sons, Ltd.
Numerical methods for semiconductor heterostructures with band nonparabolicity
(2003-09-01)
Wang, WC
;
Hwang, TM
;
Lin, WW
;
Liu, JL
;
應用數學系
This article presents numerical methods for computing bound state energies and associated wave functions of three-dimensional semiconductor heterostructures with special interest in the numerical treatment of the effect of band nonparabolicity. A nonuniform finite difference method is presented to approximate a model of a cylindrical-shaped semiconductor quantum dot embedded in another semiconductor matrix. A matrix reduction method is then proposed to dramatically reduce huge eigenvalue systems to relatively very small subsystems. Moreover, the nonparabolic band structure results in a cubic type of nonlinear eigenvalue problems for which a cubic Jacobi-Davidson method with an explicit nonequivalence deflation method are proposed to compute all the desired eigenpairs. Numerical results are given to illustrate the spectrum of energy levels and the corresponding wave functions in rather detail. (C) 2003 Elsevier B.V. All rights reserved.
Optical chaotic AM demodulation by asymptotic synchronization
(2000-02-01)
Juang, C
;
Hwang, TM
;
Juang, J
;
Lin, WW
;
應用數學系
Synchronization between two identical chaotic systems (drive and response) with different initial conditions can be achieved provided that the conditional Lyapunov exponents are all negative. Adding an AM signal to the drive system, the two systems become asymptotically synchronized. The AM signal can be recovered by utilizing the property of the asymptotic synchronization. Chaotic AM noise is present as a direct result of the chaotic AM demodulation. Signal-to-chaotic-AM-noise ratio is calculated as a function of the signal amplitude.
Optoelectronic delayed-feedback and chaos in quantum-well laser diodes
(2001-05-15)
Juang, C
;
Huang, CC
;
Hwang, TM
;
Juang, J
;
Lin, WW
Electronic-controlled route to chaos in a quantum-well laser diode is carried out by a delayed-feedback technique. By introducing an extra delayed-feedback control term cS(n)(t - tau), chaotic light output can be achieved at relatively low bias and small modulation depth. Bifurcation diagram, Poincare map, and Lyapunov exponents suggests quasi-periodicity route to chaos. (C) 2001 Elsevier Science B.V. All rights reserved.
Subcarrier multiplexing by chaotic multitone modulation
(2003-10-01)
Juang, C
;
Huang, ST
;
Liu, CY
;
Wang, WC
;
Hwang, TM
Subcarrier multiplexing by chaotic multitone modulation is investigated. Optical chaotic light can be achieved by injecting multiple subcarriers into a self-pulsating laser diode. Synchronization between two identical chaotic systems (drive and response) can be implemented provided that the conditional Lyapunov exponents are all negative. By adding amplitude modulation (AM) signals to each subcarrier, the two systems become asymptotically synchronized. The AM signals in each subcarrier can be recovered by the introduction of a filtering process where the Lyapunov exponent of the synchronized error function matches the cutoff frequency of a first order low pass filter.