Spurious roots in nonlinear waveguide calculations and a new formatfor nonlinear waveguide dispersion equations

The existence of spurious roots in the widely used nonlinear waveguide dispersion equations is demonstrated. The spurious roots exist even when the linear waveguide dispersion equations are written in terms of the sine and cosine functions. The authors compare the similarities between the linear and nonlinear dispersion equations and present a new format of the nonlinear dispersion equations that simplify the numerical calculations and avoid the appearance of spurious roots     

Efficient difference frequency oscillator based on a Ti:sapphirelaser

The problem of expanding the Ti:sapphire laser wavelength range by generating difference (sum) frequencies is discussed. The authors present a high-efficiency coherent radiation source, based on a Ti:sapphire laser and a nonlinear LiIO₃ crystal, operating in the spectral range from 0.34 to 2.3 μm. For this purpose a Ti:sapphire dual-wavelength laser has been developed where the process of self-synchronization of both channels has been realized. A difference frequency oscillator with 2w_s-2w_l and 2w_l-w _s, including the spectral range from 0.503 to 0.79 and from 0.83 to 2.3 μm, has been realized. A detailed study of the temporal characteristics of Ti:sapphire lasing is given, the development of methods for mixed pulse overlapping is discussed, and other subjects, such as configuration of widely tunable coherent radiation sources, are addressed     

Another language for describing motions of mechatronics systems: a nonlinear position-dependent circuit theory

Dynamics and control of nonlinear mechanical systems and advanced mechatronic systems can be investigated more vividly and efficiently by using corresponding nonlinear position-dependent circuits that describe Lagrange's equations of motions and interactions with objects or/and task environments. Such expressions of Lagrange's equations via nonlinear circuits are indebted to lumped-parameter discretization of mechanical systems as a set of rigid bodies through equations of motion due to Newton's second law. This observation is quite analogous to validity of electric circuits that can be derived as lumped parameter versions of Maxwell's equations of electromagnetic waves. Couplings of nonlinear mechanical circuits with electrical circuits through actuator dynamics are also discussed. In such electromechanical circuits the passivity should be a generalization of impedance concept in order to cope with general nonlinear position-dependent circuits and play a crucial role in their related motion control problems. In particular, it is shown that the passivity as an input-output property gives rise to a necessary and sufficient characterization of H/sub /spl infin//-tuning for disturbance attenuation of robotic systems, which can give another system theoretic interpretation of the energy conservation law.     

构造非线性演化方程精确解的一个新方法

基于辅助方程提出一种求解非线性演化方程的一个新方法,该方法简单易行且具有一定的普适性,根据不同的参数可给出各种形式的精确解,从而有助于探索非线性方程的新解及其性质。并以mkdv方程为例,得到了其多组精确解,包括Jacobi椭圆函数解及Weierstrass椭圆函数解等,除涵盖了以往结果,还给出一些新解。     

Three-level oscillator: a new form of transferred-electron device

Electron transfer between three appropriately coupled sets of conduction-band valleys produces transport properties peculiarly favourable for transferred-electron devices. The necessary conditions should obtain in InP and in InP-InAs and InSb-GaSb alloys. Monte Carlo calculations of the velocity/field characteristics for these materials are described.     

Rotary traveling-wave oscillator arrays: a new clock technology

Rotary traveling-wave oscillators (RTWOs) represent a new transmission-line approach to gigahertz-rate clock generation. Using the inherently stable LC characteristics of on-chip VLSI interconnect, the clock distribution network becomes a low-impedance distributed oscillator. The RTWO operates by creating a rotating traveling wave within a closed-loop differential transmission line. Distributed CMOS inverters serve as both transmission-line amplifiers and latches to power the oscillation and ensure rotational lock. Load capacitance is absorbed into the transmission-line constants whereby energy is recirculated giving an adiabatic quality. Unusually for an LC oscillator, multiphase (360°) square waves are produced directly. RTWO structures are compact and can be wired together to form rotary oscillator arrays (ROAs) to distribute a phase-locked clock over a large chip. The principle is scalable to very high clock frequencies. Issues related to interconnect and field coupling dominate the design process for RTWOs. Taking precautions to avoid unwanted signal couplings, the rise and fall times of 20 ps, suggested by simulation, may be realized at low power consumption. Experimental results of the 0.25-μm CMOS test chip with 950-MHz and 3.4-GHz rings are presented, indicating 5,5-ps jitter and 34-dB power supply rejection ratio (PSRR). Design errors in the test chip precluded meaningful rise and fall time measurements     

Terahertz oscillator based on nonlinear frequency conversion in a double vertical cavity

The feasibility of producing a vertical-cavity laser that operates in the far IR region and is based on the three-wave mixing due to the lattice nonlinearity of a GaAs/AlGaAs system is analyzed. It is shown that the use of a double Bragg cavity with the parameters tuned both to high-frequency oscillations (sources of nonlinear polarization) and to the difference frequency allows one to raise the intensity of the radiation in the far IR region. The power density of the radiation at a wavelength of 49.5 μm equals approximately 5 × 10^?4 μW/μm² at a drive current density of 5 kA/cm². It is suggested that a drive current should be supplied with the use of intercavity contacts, to be located in the vicinity of a node in the difference mode; then, the absorption of radiation by free charge carriers will be reduced to a minimum.     

Explaining and eliminating latchup in a classical Wien oscillator via nonlinear design

A classical Wien-type sinusoidal oscillator is analyzed to explain the origin of its latchup behavior. Only when a correct nonlinear model of the oscillator is derived and the stability of all equilibrium points associated with each region of operation of the fundamentally nonlinear amplifier characteristics is studied can this phenomena be predicted. It is further shown how latchup can be eliminated. Ahmed S. Elwakil was born in Cairo, Egypt. He received his B.Sc. and M.Sc. degrees from Cairo University and his Ph.D. from the National University of Ireland, all in Electrical and Electronic Engineering. His main research interests are in the area of analog electronic circuit design with particular emphasis on nonlinear circuit analysis and design techniques, nonlinear dynamics and chaos theory. He is author and co-author of more than 70 publications in these areas. Dr. Elwakil is a senior member of IEEE, a member of the IEEE technical committee on nonlinear circuits and systems, a member of IEE, an associate member at the centre for chaos control at the City University of Hong Kong and an associate member at the International centre for Theoretical Physics. He has held several academic visiting positions and has acted as an instructor for two courses on VLSI organized by the United Nations University. He has served as a scientific committee member for many conferences and as a reviewer for numerous journals and conferences. Dr. Elwakil received the Government of Egypt first class medal for achievement in engineering sciences in 2003.     

Resolution of moment equations in a nonlinear optical amplifier

In the letter a new method for the resolution of the moment equations in a nonlinear optical amplifier is exposed. Results for the four first moments for the saturated and unsaturated absorption cases are presented. These results are in good agreement with those obtained by other authors.     

Multimode oscillations in a modified Van Der Pol oscillator containing a positive nonlinear conductance

This report indicates that an oscillation with a random waveform or a sinusoidal waveform is excited by a simple oscillator such as a modified Van Der Pol oscillator containing a positive non-linear conductance.     

Deuterated L-arginine phosphate: a new efficient nonlinear crystal

Deuterated L-arginine phosphate (d-LAP) is a highly transparent monoclinic crystal with attractive properties for efficient frequency conversion. It is grown easily from aqueous solution, and it is phase-matchable for all nonlinear processes where KDP is phase-matchable. Over most of its usable frequency range, it is substantially more efficient than KDP. Crystals grown in large sizes (100 cm³) have a high damage threshold, excellent optical quality, are less hygroscopic than KDP, and are easily fabricated into nonlinear devices. Deuterated LAP is attractive for harmonic generation of Nd lasers and for work in the ultraviolet down to about 250 nm     

A new approach for routing and wavelength assignment for permanent and reliable wavelength paths in wide all-optical WDM networks

This article proposes a new approach for routing and wavelength assignment (RWA) for permanent and reliable wavelength paths (WP) in wide all-optical WDM networks with wavelength continuity constraint. Given a number of available wavelengths on each optical fiber, for each simple link failure of the network, we seek to maximize the number of satisfied requests for connections. This is known as RWAP problem. In our algorithm, called RWA with Minimum Loaded Link for Permanent and Reliable wavelength paths (MLL-PR), routing is based on the search for the optimal path while trying to minimize the maximum load on the links of the network in order to minimize the maximum link capacity and then minimize the number of dropped lightpaths after any link failure. The wavelength assignment is based on a graph coloring method using tabu-search. A series of experiments using two well-known networks (ARPANET and NSFNET) have been carried out in order to evaluate the performance of our approach, in terms of the number of blocked demands, for different failure scenarios. Generally, our results are better than those provided by the current solving approaches taken as reference.

Pulse compression dynamics in a nonlinear longitudinally inhomogeneous optical fiber

The output characteristics of a Gaussian frequency-modulated pulse in a longitudinally inhomogeneous single-mode active nonlinear optical fiber are investigated. On the basis of the numerical analysis of the obtained dynamic equations, it is shown that, by means of varying the input pulse parameters and the type of the longitudinal inhomogeneity of the group-velocity dispersion, it is possible to effectively control not only the length and degree of the compression of the propagating pulse but also the number of maximum-compression points along the length of the optical fiber.     

光网中路由与波长分配问题的一种新模型

路由与波长分配问题是波分复用光网中的一个关键问题.文章从经济学的角度出发提出了路由与波长分配问题的一种数学模型,并且进行了分析和仿真.结果表明,模型较大程度地反应了现实,对网络运营商而言很有参考价值.     

Chaotic dynamics of mode competition in a vertical-cavity surfaceemitting laser diode under DC excitation

We discuss the dynamics of transverse mode competition in an etched air-post vertical-cavity laser diode under dc excitation using an annular ring contact as a spatial filter. Distinct regions of operation are found for various ranges of fixed bias currents. At 1.5 times threshold, the device enters a region which exhibits chaotic fluctuations between the fundamental and a higher order lasing mode. The dynamics of these fluctuations are studied using the method of delays, and a calculation of the power spectrum and the correlation dimension are reported. It is found that the dynamics of the chaotic fluctuations have a correlation dimension of approximately 2.8. The results are indicative of a low-dimensional strange attractor underlying the modal competition noise     

Variable structure control of nonlinear systems: a new approach

A new approach for the design of variable structure control (VSC) of nonlinear systems is presented. It is based on a new method called the reaching law method, and is complemented by a sliding-mode equivalence technique. They facilitate the design of the system dynamics in all three modes of a VSC system including the sliding, reaching, and steady-state modes. Invariance and robustness properties are discussed. The approach is applied to a robot manipulator to demonstrate its effectiveness     

MCMP: a transport/session level distributed protocol for desktopconference setup

The multiparty conference management protocol (MCMP) is an end-to-end distributed session/transport level protocol intended for group management of desktop conferencing applications. This paper describes the MCMP conference setup algorithms and proves that they meet specified correctness properties. MCMP sets up control channels for use in exchanging control information while the conference is in progress. The logical topology used is a completely interconnected mesh, MCMP always provides best effort services in cases of failures. Correctness properties guaranteed upon termination of the protocol include connectivity, validity, uniqueness, and consistency of local views. Application control information that can be exchanged using the control channels include resource negotiation and subconferencing     

An iterative finite difference beam propagation method for modelingsecond-order nonlinear effects in optical waveguides

An iterative finite difference beam propagation method based on the Crank-Nicholson scheme is presented to simulate continuous wave (CW) second-order nonlinear effects in optical waveguides with the depletion of the pump wave taken into account. This method is an extension of the linear finite difference beam propagation method and preserves the same order of accuracy. Comparisons with the previously published explicit finite difference beam propagation method and the rectangular approximation method are presented. Quasi-phase matched difference frequency generation in AlGaAs and quasi-phase-matched second harmonic generation in LiNbO₃ are considered in the evaluation, showing that one iteration for the IFD-BPM is sufficient for the simulation with good accuracy and without increasing much computation time     

Time-frequency transforms: a new approach to first heart soundfrequency dynamics

This study employed a new analytical tool, the Binomial joint time-frequency transform, to test the hypothesis that first heart sound frequency rises during the isovolumic contraction period. Cardiac vibrations were recorded from eight open chest dogs using an ultralight accelerometer cemented directly to the epicardium of the anterior left ventricle. The frequency response of the recording system was flat +/- 3 dB from 0.1 to 400 Hz. Three characteristic time-frequency spectral patterns were evident in the animals investigated: 1) A frequency component that rose from approximately 40-140 Hz in a 30-50 ms interval immediately following the ECG R-wave. 2) A slowly varying or static frequency of 60-100 Hz beginning midway through the isovolumic contraction period. 3) Broad-band peaks occurring at the time of the Ia and Ib high frequency components. The presence of rapid frequency dynamics limits the usefulness of stationary analysis techniques for the first heart sound. The Binomial transform provided much better resolution than the spectrograph or spectrogram, the two most common non-stationary signal analysis techniques. By revealing the onset and dynamics of first heart sound frequencies, time-frequency transforms may allow mechanical assessment of individual cardiac structures.