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  • Articles  (13,582)
  • Springer  (13,582)
  • 1990-1994  (6,770)
  • 1985-1989  (4,594)
  • 1960-1964  (2,054)
  • 1950-1954  (164)
  • Electrical Engineering, Measurement and Control Technology  (13,582)
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  • Articles  (13,582)
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  • 1
    Electronic Resource
    Electronic Resource
    Zero principles for implicit feedback systems (1994)
    Springer
    Circuits, systems and signal processing 13 (1994), S. 273-293 
    Details
    ISSN: 1531-5878
    Source: Springer Online Journal Archives 1860-2000
    Topics: Electrical Engineering, Measurement and Control Technology
    Notes: Abstract A basic control engineer's adage-the poles of a feedback compensator become zeros of the closed-loop system-admits difficulties of interpretation even in the most simple of cases; that of single-input, single-output. An earlier investigation has provided an analysis of this adage in a module-theoretic context for systems in state space form while avoiding restrictive assumptions on system minimality or squareness. The main result is expressed concisely in terms of an exact sequence of modules which include Ω-zero modules corresponding to the feedback system and the plant. Extended zero modules of Ω-type incorporate both finite invariant zero structure, and generic zero information which occurs when a system fails to be right-invertible. In the case of compensation in the feedback path, this main exact sequence reduces to a mathematically clear expression of the aforementioned adage: the Ω-zero module of the feedback system is precisely the direct sum of the Ω-zero module of the plant and the system pole module of the feedback compensator. This paper extends the previous work in order to avoid assumptions on causality in the plant. Implicit dynamical systems are employed, in lieu of systems in state space form. Once again, it is not assumed that the system is one-to-one or onto; and so the concepts of generic zeros and their modules are brought into the arena of implicit systems. The implicit system itself is assumed in this work to be regular; however, decoupling zeros are permitted. Moreover, input-decoupling zeros and system pole feedback relationships are considered.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF01188111
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  • 2
    Electronic Resource
    Electronic Resource
    Editorial (1994)
    Springer
    Circuits, systems and signal processing 13 (1994), S. 387-388 
    Details
    ISSN: 1531-5878
    Source: Springer Online Journal Archives 1860-2000
    Topics: Electrical Engineering, Measurement and Control Technology
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF01183735
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  • 3
    Electronic Resource
    Electronic Resource
    A polynomial approach to deriving a state-space model of a periodic process described by difference equations (1994)
    Springer
    Circuits, systems and signal processing 13 (1994), S. 373-384 
    Details
    ISSN: 1531-5878
    Source: Springer Online Journal Archives 1860-2000
    Topics: Electrical Engineering, Measurement and Control Technology
    Notes: Abstract When the problem is considered of obtaining a periodic description in state-space form of a linear process which can be modelled by linear difference equations with periodic coefficients, it is natural to ask whether it is possible to preliminarily derive a polynomial equivalent form of such equations, which in the periodic case plays a role similar to the Rosenbrock's polynomial matrix description of a linear time-invariant process. In this paper a polynomial time-invariant description of a linear periodic process is introduced. It is shown that such a polynomial description gives a simple characterization of the dimension of the space of the solutions corresponding to the null input function, i.e., of the order of the periodic model under consideration. In addition, it allows us to introduce a transfer matrix for the computation of the output responses corresponding to null initial conditions, and to deduce conditions for the periodic model to be causal. These results, as well as the possibility of defining strict system equivalence between two periodic models through their time-invariant polynomial descriptions, in a similar sense as in the time-invariant case, show the relevance of such a polynomial time-invariant description for the problem under consideration.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF01188117
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  • 4
    Electronic Resource
    Electronic Resource
    Feasibility study of parameter estimation of random sampling jitter using the bispectrum (1994)
    Springer
    Circuits, systems and signal processing 13 (1994), S. 435-453 
    Details
    ISSN: 1531-5878
    Source: Springer Online Journal Archives 1860-2000
    Topics: Electrical Engineering, Measurement and Control Technology
    Notes: Abstract An actual sampling process can be modeled as a random process, which consists of the regular (uniform) deterministic sampling process plus an error in the sampling times which constitutes a zero-mean noise (the jitter). In this paper we discuss the problem of estimating the jitter process. By assuming that the jitter process is an i.i.d. one, with standard deviation that is small compared to the regular sampling time, we show that the variance of the jitter process can be estimated from thenth order spectrum of the sampled data,n=2, 3, i.e., the jitter variance can be extracted from the 2nd-order spectrum or the 3rd-order spectrum (the bispectrum) of the sampled data, provided the continuous signal spectrum is known. However when the signal skewness exceeds a certain level, the potential performance of the bispectrum-based estimation is better than that of the spectrum-based estimation. Moreover, the former can also provide jitter variance estimates when the continuous signal spectrum is unknown while the latter cannot. This suggests that the bispectrum of the sampled data is potentially better for estimating any parameter of the sampling jitter process, once the signal skewness is sufficiently large.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF01183740
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  • 5
    Electronic Resource
    Electronic Resource
    Regularity and singularity in linear-quadratic control subject to implicit continuous-time systems (1994)
    Springer
    Circuits, systems and signal processing 13 (1994), S. 19-30 
    Details
    ISSN: 1531-5878
    Source: Springer Online Journal Archives 1860-2000
    Topics: Electrical Engineering, Measurement and Control Technology
    Notes: Abstract A linear-quadratic (LQ) control problem subject to a standard continuous-time system is called regular if the input weighting matrix is invertible, and singular if this is not the case. Consequently, optimal inputs for regular LQ problems are ordinary functions (state feedbacks), whereas optical controls for singular problems are in general distributions, e.g., impulses. We will show that regularity and singularity in LQ problems subject to ageneral (implicit) system depends not so much on the input weighting matrix, as on the property that the integrand of the cost criterion is a function only if inputs and state trajectories are, as is the case for LQ problems, subject to astandard system. In particular, we will provide a simple criterion for distinguishing between regularity and singularity in LQ problems subject to a general system. Our criterion is expressed in the system coefficients only and reduces to the classical one if the underlying system is standard.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF01183839
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  • 6
    Electronic Resource
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    Preface (1994)
    Springer
    Circuits, systems and signal processing 13 (1994), S. 119-119 
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    ISSN: 1531-5878
    Source: Springer Online Journal Archives 1860-2000
    Topics: Electrical Engineering, Measurement and Control Technology
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF01188100
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  • 7
    Electronic Resource
    Electronic Resource
    Explicit formulae for completions of linear time varying singular systems of differential equations (1994)
    Springer
    Circuits, systems and signal processing 13 (1994), S. 185-199 
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    ISSN: 1531-5878
    Source: Springer Online Journal Archives 1860-2000
    Topics: Electrical Engineering, Measurement and Control Technology
    Notes: Abstract Completions of linear time varying singular systems of the formE(t)x′(t)+F(t)x′(t)=f(t) are explicitly computed using recent results on rational matrix functions. The algorithm and the theory behind it are carefully described. Computational issues are discussed.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF01188105
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  • 8
    Electronic Resource
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    Spectral methods for the solution of linear descriptor systems using Fourier functions (1994)
    Springer
    Circuits, systems and signal processing 13 (1994), S. 225-239 
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    ISSN: 1531-5878
    Source: Springer Online Journal Archives 1860-2000
    Topics: Electrical Engineering, Measurement and Control Technology
    Notes: Abstract In this paper a spectral method using orthogonal periodic basis functions for the analysis of linear time invariant descriptor systems is discussed, and the case of the trigonometric Fourier functions is investigated in detail. The method is shown to be convergent, in the distributional sense. However, for any finite number of basis functions, the periodicity induced by the chosen basis can give rise to spurious impulsive components in the computed system response, even in the case of correct initial conditions.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF01188108
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  • 9
    Electronic Resource
    Electronic Resource
    Topological considerations for autoregressive systems with fixed Kronecker indices (1994)
    Springer
    Circuits, systems and signal processing 13 (1994), S. 295-308 
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    ISSN: 1531-5878
    Source: Springer Online Journal Archives 1860-2000
    Topics: Electrical Engineering, Measurement and Control Technology
    Notes: Abstract In this paper we will study topological properties of the class of proper and improperp×m transfer functions of a fixed McMillan degreen. A natural generalization of this class is all autoregressive systems of degreen under external system equivalence. The subset of irreducible systems has in a natural way the structure of a manifold and we show how to extend this topology to the set of all autoregressive systems of degree at mostn. We will describe the subset of systems with fixed Kronecker indicesv=(v1,...,v p ) as an orbit space, which will enable us to calculate the topological dimension for each collection of indicesv. Finally, we will describe the topological closure of those sets in the space of all autoregressive systems.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF01188112
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  • 10
    Electronic Resource
    Electronic Resource
    Output dynamics assignment for implicit descriptions (1994)
    Springer
    Circuits, systems and signal processing 13 (1994), S. 349-359 
    Details
    ISSN: 1531-5878
    Source: Springer Online Journal Archives 1860-2000
    Topics: Electrical Engineering, Measurement and Control Technology
    Notes: Abstract It has been shown in [B.M.90] that non-square implicit differential equations allow for the description of variable structure systems (variable order, variable sign, variable parameters). We combine here the possible control strategy developed in [L.91] for rectangular systems (insuring a unique output behavior for the system compensated with a proportional or proportional and derivative state feedback) with the detector and the observer introduced in [B.M.90] in order to obtain a closed-loop system where the initial structure variation disappears on the output. We also give necessary and sufficient conditions for the free assignment of the associated output dynamics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF01188115
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  • 11
    Electronic Resource
    Electronic Resource
    Higher order cumulants and cumulant spectra (1994)
    Springer
    Circuits, systems and signal processing 13 (1994), S. 391-402 
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    ISSN: 1531-5878
    Source: Springer Online Journal Archives 1860-2000
    Topics: Electrical Engineering, Measurement and Control Technology
    Notes: Abstract An exposition of joint cumulants and cumulant spectra is presented. A distinction is emphasized in this paper between the cumulant spectrum of a time series and its stationary version, here called apolyspectrum. The variance and covariance of the sample bispectrum is then derived using a relationship between cumulant spectra of the finite Fourier transform for the 2nd and 4th cumulant function, and the bispectrum and trispectrum of the time series.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF01183737
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  • 12
    Electronic Resource
    Electronic Resource
    On the detection of transient signals using spectral correlation (1994)
    Springer
    Circuits, systems and signal processing 13 (1994), S. 467-479 
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    ISSN: 1531-5878
    Source: Springer Online Journal Archives 1860-2000
    Topics: Electrical Engineering, Measurement and Control Technology
    Notes: Abstract The detection of a general class of transient (i.e., finite energy) signals in additive stationary interference using the spectral correlation function (second order cumulant spectrum) is presented. Observable features in the two-dimensional spectral correlation function due to properties of signals in the assumed class of transients are exploited to derive a detection statistic. The performance of the proposed detection statistic relative to a conventional power spectral detector is presented.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF01183742
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  • 13
    Electronic Resource
    Electronic Resource
    Development and application of a statistically based feature extraction algorithm for monitoring tool wear in Circuit Board Assembly (1994)
    Springer
    Circuits, systems and signal processing 13 (1994), S. 411-433 
    Details
    ISSN: 1531-5878
    Keywords: Statistics: Nonparametric time series estimation for pattern analysis ; Industries: Health monitoring and durability of rotating machinery ; Reliability: Incipient failure inspection/quality control/system safety
    Source: Springer Online Journal Archives 1860-2000
    Topics: Electrical Engineering, Measurement and Control Technology
    Notes: Abstract Vibroacoustic signals of rotating machinery are composed of sums of modulated periodicities, broadband random components, and occasionally a set of transient responses. These signals are not ergodic as the modulated periodicities are partially coherent. Progressive wear of the rotating machine causes the nonlinear structure of the received signal to intensify, and nonlinearity results in transfer of energy between harmonics of the signal's periodic components. Statistics developed from bispectrum and second-order cumulant spectrum estimates of the measured signal are combined with power spectrum amplitudes as feature inputs for standard multivariate classifiers. The higher-order statistics measure, respectively, the extent of nonlinearity and intermodulation of the received signal. Classification results of simulated and actual incipient wear data collected from a controlled experiment drilling circuit boards illustrate the potential of this novel statistical signal processing approach.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF01183739
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  • 14
    Electronic Resource
    Electronic Resource
    Geometric characterization of Lewis Structure Algorithm (1994)
    Springer
    Circuits, systems and signal processing 13 (1994), S. 255-272 
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    ISSN: 1531-5878
    Source: Springer Online Journal Archives 1860-2000
    Topics: Electrical Engineering, Measurement and Control Technology
    Notes: Abstract A geometric interpretation of the Lewis Structure Algorithm (LSA) is given in terms of precise projection maps directly defined from the (E, A, B, C) maps of the system. An extended version of LSA is offered which, in addition to this geometric information, also provides in a direct way, and within the same (E, A, B, C) class of models, a left inverse (if any) of the system. An example is given.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF01188110
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  • 15
    Electronic Resource
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    An intermediate algorithm for pole placement by output feedback in descriptor systems (1994)
    Springer
    Circuits, systems and signal processing 13 (1994), S. 329-345 
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    ISSN: 1531-5878
    Source: Springer Online Journal Archives 1860-2000
    Topics: Electrical Engineering, Measurement and Control Technology
    Notes: Abstract We consider the problem of control of linear, time-invariant, multivariable descriptor (implicit) systems. In particular we examine the effectiveness of an algorithm (which is a generalization of previous work in state space systems) for the design of an output feedback control giving pole placement in such systems. Conditions are presented which ensure that the algorithm produces the required control. We also address the important issue of uniqueness of solutions.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF01188114
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  • 16
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    Preface (1994)
    Springer
    Circuits, systems and signal processing 13 (1994), S. 389-390 
    Details
    ISSN: 1531-5878
    Source: Springer Online Journal Archives 1860-2000
    Topics: Electrical Engineering, Measurement and Control Technology
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF01183736
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  • 17
    Electronic Resource
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    Active sonar detection in multipath: A New bispectral analysis approach (1994)
    Springer
    Circuits, systems and signal processing 13 (1994), S. 455-466 
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    ISSN: 1531-5878
    Source: Springer Online Journal Archives 1860-2000
    Topics: Electrical Engineering, Measurement and Control Technology
    Notes: Abstract Detecting active sonar returns in multipath media is a central underwater signal processing problem. This paper studies a new approach to active sonar detection using bispectral analysis of sonar data. Its sensitivity to non-stationarities is used to develop a threshold detector that can be applied to broad classes of signals and noise. Precise statistical descriptions of the underwater medium and noise are not required. Theoretical analyses predicting its performance as a function of signal-to-noise ratio and time-bandwidth product are presented. Computer simulation experiments verify the results and show that its performance compares favorably to that of conventional detectors.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF01183741
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  • 18
    Electronic Resource
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    Signal detection using third-order moments (1994)
    Springer
    Circuits, systems and signal processing 13 (1994), S. 481-496 
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    ISSN: 1531-5878
    Source: Springer Online Journal Archives 1860-2000
    Topics: Electrical Engineering, Measurement and Control Technology
    Notes: Abstract The noise suppression capability of higher-order moments and spectra has made them attractive when the goal is to extract or reconstruct a signal that is contaminated by multivariate Gaussian noise or certain types of non-Gaussian noise. Two new detectors, one centralized and one distributed, which are based on the third-order moment of the data are proposed. The asymptotic performance of the centralized detector and the asymptotic distribution of the components of the distributed detector are analyzed. Further, the performance of these detectors is simulated and compared to that of the matched filter for three different types of interference: Gaussian noise, Gaussian noise corrupted by a sinusoid with random phase, and Arctic under-ice noise.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF01183743
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  • 19
    Electronic Resource
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    Control of linear systems under state-control constraints (1994)
    Springer
    Circuits, systems and signal processing 13 (1994), S. 361-372 
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    ISSN: 1531-5878
    Source: Springer Online Journal Archives 1860-2000
    Topics: Electrical Engineering, Measurement and Control Technology
    Notes: Abstract We investigate the controller design problem for linear systems in which the state and the controls are subject to static linear constraints. We give necessary and sufficient conditions for the existence, and present a complete parametrization of all stabilizing controllers. This parametrization allows us to transform the constrained control problem into a standard problem which can be solved using usualH 2 orH ∞ optimization methods. The approach is illustrated by a simple numerical example showing the various steps of the proposed algorithm.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF01188116
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  • 20
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    Limitations on the use of discrete linear models of continuous random processes (1994)
    Springer
    Circuits, systems and signal processing 13 (1994), S. 403-410 
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    ISSN: 1531-5878
    Source: Springer Online Journal Archives 1860-2000
    Topics: Electrical Engineering, Measurement and Control Technology
    Notes: Abstract A continuous stationary signal possessing non-Gaussian higher order statistics cannot be correctly modelled by any discrete process based on passing independently and identically distributed noise through a linear filter. In particular, it is shown that at third order there exists no discrete skewed linear model with a discrete bispectrum that is the same as that obtained from the Nyquist samples of any continuous stationary process. The nature of the problem is elucidated and an alternative method for modelling the third order statistics of continuous stationary processes is proposed.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF01183738
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  • 21
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    Design of 2D FIR digital filters with flatness constraints for the error function (1994)
    Springer
    Circuits, systems and signal processing 13 (1994), S. 65-75 
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    ISSN: 1531-5878
    Source: Springer Online Journal Archives 1860-2000
    Topics: Electrical Engineering, Measurement and Control Technology
    Notes: Abstract A method will be presented for the approximation of a desired two-dimensional frequency response by the frequency response of a two-dimensional finite-impulse-response digital filter. It is possible to match the functional values and an arbitrary number of derivatives of both responses for zero frequency, thus making the error flat up to a desired degree. Remaining degrees of freedom are used for anL 2-approximation. Closed form design formulae will be given.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF01183841
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  • 22
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    B-spline FIR filters (1994)
    Springer
    Circuits, systems and signal processing 13 (1994), S. 31-64 
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    ISSN: 1531-5878
    Source: Springer Online Journal Archives 1860-2000
    Topics: Electrical Engineering, Measurement and Control Technology
    Notes: Abstract This paper presents an efficient procedure for the design of interpolated FIR (IFIR) filters with linear phase. The algorithm uses the uniform B-spline function as an interpolator and solves the optimal Chebyshev approximation problem on the optimal subinterval. The technique can be used for the design of general lowpass, highpass and bandpass filters. While the number of multiplications of the IFIR filter is dependent on the bandwidth and the center frequency of the desired filter, it provides the minimum number of multiplications achievable and nearly always provides a substantial reduction when compared to Parks-McClellan designs.
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    URL: http://dx.doi.org/10.1007/BF01183840
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  • 23
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    Editorial (1994)
    Springer
    Circuits, systems and signal processing 13 (1994), S. 117-118 
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    ISSN: 1531-5878
    Source: Springer Online Journal Archives 1860-2000
    Topics: Electrical Engineering, Measurement and Control Technology
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF01188099
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  • 24
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    On the stability of solutions of autonomous index-I tractable and quasilinear index-2 tractable DAEs (1994)
    Springer
    Circuits, systems and signal processing 13 (1994), S. 139-154 
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    ISSN: 1531-5878
    Source: Springer Online Journal Archives 1860-2000
    Topics: Electrical Engineering, Measurement and Control Technology
    Notes: Conclusion We have seen that the stationary solutions of the regularized equations are asymptotically stable if the stationary solution of the original quasilinear index-2 tractable DAE is so. In other words, the given regularizations supply a solution sharing the stability properties of the solution of the unperturbed equation.
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    URL: http://dx.doi.org/10.1007/BF01188102
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  • 25
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    Progress on a general numerical method for nonlinear higher index DAEs II (1994)
    Springer
    Circuits, systems and signal processing 13 (1994), S. 123-138 
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    ISSN: 1531-5878
    Source: Springer Online Journal Archives 1860-2000
    Topics: Electrical Engineering, Measurement and Control Technology
    Notes: Abstract A method has been proposed for numerically solving lower dimensional, nonlinear, higher index differential algebraic equations for which more classical methods such as backward differentiation or implicit Runge-Kutta may not be appropriate. This method is based on solving nonlinear DAE derivative arrays. This paper discusses progress on the implementation of this method, resolves some of the issues involved, and lists some remaining problems. Computational experience on two prescribed path control problems is presented showing that the approach should prove practical for many applications.
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    URL: http://dx.doi.org/10.1007/BF01188101
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  • 26
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    Robust stability of systems with delayed feedback (1994)
    Springer
    Circuits, systems and signal processing 13 (1994), S. 213-222 
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    ISSN: 1531-5878
    Source: Springer Online Journal Archives 1860-2000
    Topics: Electrical Engineering, Measurement and Control Technology
    Notes: Abstract Some issues in the stability of differential delay systems in the linear and the nonlinear case are investigated. In particular, sufficient robustness conditions are derived under which a system remains stable, independent of the length of the delay(s). Applications in the design of delayed feedback systems are given. Two approaches are presented, one based on Lyapunov theory, the other on a transformation to Jordan form. In the former, sufficient conditions are obtained in the form of certain Riccati-type equations.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF01188107
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  • 27
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    Digital image coding using legendre transform (1994)
    Springer
    Circuits, systems and signal processing 13 (1994), S. 3-18 
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    ISSN: 1531-5878
    Source: Springer Online Journal Archives 1860-2000
    Topics: Electrical Engineering, Measurement and Control Technology
    Notes: Abstract Image coding can be implemented through DPCM, transform, hybrid, or segmentation coding techniques. Some transform coding techniques, such as cosine and Hadamard, have been exhaustively analyzed and evaluated, while others, such as Legendre, have not. This paper introduces the use of Legendre transform in image coding. The transform matrix for different block sizes is calculated, the fast algorithm is derived, and the performance is evaluated through both mean square error and subjective quality. The results obtained have indicated that the system performance is comparable with that of optimum KLT and cosine transforms; moreover, it is simpler in implementation.
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    URL: http://dx.doi.org/10.1007/BF01183838
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  • 28
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    Design of FIR digital filters with flatness constraints for the error function (1994)
    Springer
    Circuits, systems and signal processing 13 (1994), S. 77-97 
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    ISSN: 1531-5878
    Source: Springer Online Journal Archives 1860-2000
    Topics: Electrical Engineering, Measurement and Control Technology
    Notes: Abstract A method will be presented for the approximation of a desired frequency response by the frequency response of a FIR filter. It is possible to match the functional values and an arbitrary number of derivatives of both responses for zero frequency, thus making the error flat up to a desired degree. Remaining degrees of freedom are used for a weightedL 2-approximation. Closed form design formulae will be given.
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    URL: http://dx.doi.org/10.1007/BF01183842
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  • 29
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    Solution of nonlinear kinematics of a parallel-link constrained Stewart platform manipulator (1994)
    Springer
    Circuits, systems and signal processing 13 (1994), S. 167-183 
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    ISSN: 1531-5878
    Source: Springer Online Journal Archives 1860-2000
    Topics: Electrical Engineering, Measurement and Control Technology
    Notes: Abstract The Stewart platform manipulator is a fully parallel kinematic linkage system that has great advantages over typical serial link robots. However, one major problem in controlling this kind of manipulator is that, due to its closed kinematic chain and parallel-link constrained structure, it is impossible to derive an explicit kinematic solution. This paper proposes a simplified algorithm to numerically solve the forward kinematics of a six-links Stewart platform. Taking advantage of some fundamental geometric operations, the proposed algorithm involves only 3 nonlinear simultaneous equations. The explicit expressions are derived for some special configurations which can directly give the geometric limitations to motion in terms of the geometric dimensions of the platforms and the legs.
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    URL: http://dx.doi.org/10.1007/BF01188104
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    Two mathematical models of unconfined detonation and their numerical solution (1994)
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    Circuits, systems and signal processing 13 (1994), S. 155-165 
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    ISSN: 1531-5878
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    Topics: Electrical Engineering, Measurement and Control Technology
    Notes: Abstract We consider the numerical solution of an unconfined detonation problem modelled by differential/algebraic equations in a boundary value format. The problem has index one throughout the interval of integration, except at a free boundary point, where it has index two. Moreover, a nonlinear constraint is active at the free boundary point. We consider a simple mathematical model, as well as a more realistic and functionally complex model. In both cases, the resulting boundary value problem is solved directly, using a collocation method. This approach compares favorably with the solution techniques proposed previously in the literature and enables us to examine some interesting properties of the solution to the detonation problem.
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    URL: http://dx.doi.org/10.1007/BF01188103
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    A relation of inclusion for implicit linear systems (1994)
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    Circuits, systems and signal processing 13 (1994), S. 241-254 
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    ISSN: 1531-5878
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    Topics: Electrical Engineering, Measurement and Control Technology
    Notes: Abstract In [2] a relation of covering for implicit systems has been introduced and studied. It has been shown that this notion is useful when studying the problems of minimal left inverse and minimal observer design. In the present paper we study a slightly more general notion: a relation of inclusion for implicit systems that enjoy the outputuniqueness property. We are chiefly interested in systems of a minimal size including a given system. A particular application we have in mind is a minimal order observer or a minimal left inverse construction. We show that study of including systems may allow us in some cases to reduce the size of an observer or an inverse beyond the one given by minimization under external equivalence. A similar approach has been applied in [2] to minimal covering systems. However, including systems have an important advantage over the covering ones: since they constitute a broader class, they offer us more freedom in picking a minimal one of a desired sort.
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    Structural solution of the disturbance decoupling problem for implicit linear discrete-time systems (1994)
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    Circuits, systems and signal processing 13 (1994), S. 311-327 
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    ISSN: 1531-5878
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    Topics: Electrical Engineering, Measurement and Control Technology
    Notes: Abstract The proportional canonical form and its complete orbital invariants, described by Loiseau and Lebret in [11] or [8], are used to obtain structural equivalent characterizations of the solutions to the Disturbance Decoupling Problems which have been defined and geometrically studied by Banaszuk, Kociecki and Przyluski in [3]. In addition, a new problem, based on deeper input-output consideration, is introduced. Necessary conditions for this last problem are given.
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    Nonlinear approximations using elliptic basis function networks (1994)
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    Circuits, systems and signal processing 13 (1994), S. 99-113 
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    ISSN: 1531-5878
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    Topics: Electrical Engineering, Measurement and Control Technology
    Notes: Abstract Sharp conditions are given under which real-valued functions of several real variables can be approximated arbitrarily well by finite linear combinations of elliptic basis functions. Also given is a related result concerning the representation of functions as a limit in the mean of integrals involving elliptic basis functions.
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    On the robust control of nonlinear systems (1994)
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    Circuits, systems and signal processing 13 (1994), S. 203-211 
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    ISSN: 1531-5878
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    Topics: Electrical Engineering, Measurement and Control Technology
    Notes: Abstract In this paper we consider robust stabilization of the class of nonlinear plants of the form $$\dot x = f(x) + \sum\limits_{i = 1}^m {g_i } (x)u_i (t),$$ which are equivalent, under smooth state space coordinate transformations and nonlinear state feedback, to controllable systems. This approach is very sensitive for unknown parameters' values. Parameter adaptation may be used as a technique to robustify minimum-phase systems [3]. We give an example of a locally stable adaptive tracking system in which the last assumption is weakened. The minimum-phase plant considered in the paper is a current-controlled squirrel cage induction motor.
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    Characterization of spectral correlation detector statistics useful in transient detection (1994)
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    Circuits, systems and signal processing 13 (1994), S. 497-511 
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    Topics: Electrical Engineering, Measurement and Control Technology
    Notes: Abstract The statistics of a class of transient signal detectors known as spectral correlative detectors (SCD) are investigated. Rather than use asymptotic statistics, which are not valid for the short sample sizes typically encountered in transient detection, finite sample statistics are developed. In particular, for the case of no frequency averaging, the statistics are characterized in terms of a magnitude-of-complex-Wishart (MOCW) density function, and a noncentral-MOCW (NMOCW) density function under the condition that the transient signal is absent and present, respectively. Subsequently, the statistics of the SCD for various coherent and incoherent averaging lengths are characterized in an analogous fashion. Finally some experimental verification of these densities is presented.
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    Feedback stabilization of a hybrid PDE-ODE system: Application to an overhead crane (1994)
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    Mathematics of control, signals, and systems 7 (1994), S. 1-22 
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    ISSN: 1435-568X
    Keywords: Asymptotic stabilization ; Boundary control ; Distributed parameter systems ; Hybrid system ; Lyapunov approach
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    Topics: Electrical Engineering, Measurement and Control Technology , Mathematics , Technology
    Notes: Abstract This paper deals with the feedback stabilization of a hybrid PDE-ODE system which models an overhead crane with a flexible cable. The well-posedness of the closed-loop system is established, and asymptotic stabilization is proved, using LaSalle's Invariance Principle, for a class of nonlinear feedback laws. Estimates of the rate of decay are provided for a simplified model. Illustrative simulations are displayed.
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    Nilpotent bases for a class of nonintegrable distributions with applications to trajectory generation for nonholonomic systems (1994)
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    Mathematics of control, signals, and systems 7 (1994), S. 58-75 
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    ISSN: 1435-568X
    Keywords: Nilpotent vector fields ; Nonholonomic control systems ; Trajectory generation
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    Topics: Electrical Engineering, Measurement and Control Technology , Mathematics , Technology
    Notes: Abstract This paper develops a constructive method for finding a nilpotent basis for a special class of smooth nonholonomic distributions. The main tool is the use of the Goursat normal form theorem which arises in the study of exterior differential systems. The results are applied to the problem of finding a set of nilpotent input vector fields for a nonholonomic control system, which can then be used to construct explicit trajectories to drive the system between any two points. A kinematic model of a rolling penny is used to illustrate this approach. The methods presented here extend previous work using the “chained form” and cast that work into a coordinate-free setting.
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    Small-gain theorem for ISS systems and applications (1994)
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    Mathematics of control, signals, and systems 7 (1994), S. 95-120 
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    ISSN: 1435-568X
    Keywords: Input-to-state stability ; Nonlinear systems ; Partial-state feedback ; Global stability
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    Topics: Electrical Engineering, Measurement and Control Technology , Mathematics , Technology
    Notes: Abstract We introduce a concept of input-to-output practical stability (IOpS) which is a natural generalization of input-to-state stability proposed by Sontag. It allows us to establish two important results. The first one states that the general interconnection of two IOpS systems is again an IOpS system if an appropriate composition of the gain functions is smaller than the identity function. The second one shows an example of gain function assignment by feedback. As an illustration of the interest of these results, we address the problem of global asymptotic stabilization via partial-state feedback for linear systems with nonlinear, stable dynamic perturbations and for systems which have a particular disturbed recurrent structure.
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    Interconnections and symmetries of linear differential systems (1994)
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    Mathematics of control, signals, and systems 7 (1994), S. 167-186 
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    Keywords: Feedback ; Interconnection ; Linear system ; Reductive group ; Symmetry
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    Topics: Electrical Engineering, Measurement and Control Technology , Mathematics , Technology
    Notes: Abstract In this paper we study the interplay between control problems and symmetries in the context of linear systems. In particular, we establish sufficient conditions under which it is possible to control a symmetric system in order to make it achieve control objectives, without “breaking” its symmetry.
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    Feedback linearization and driftless systems (1994)
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    Mathematics of control, signals, and systems 7 (1994), S. 235-254 
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    ISSN: 1435-568X
    Keywords: Nonlinear systems ; Feedback linearization ; Dynamic immersion ; Driftless systems ; Pfaffian systems
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    Topics: Electrical Engineering, Measurement and Control Technology , Mathematics , Technology
    Notes: Abstract The problem of dynamic feedback linearization is recast using the notion of dynamic immersion. We investigate here a “generic” property which holds at every point of a dense open subset, but may fail at some points of interest, such as equilibrium points. Linearizable systems are then systems that can be immersed into linear controllable ones. This setting is used to study the linearization of driftless systems: a geometric sufficient condition in terms of Lie brackets is given; this condition is also shown to be necessary when the number of inputs equals two. Though noninvertible feedbacks are nota priori excluded, it turns out that linearizable driftless systems with two inputs can be linearized using only invertible feedbacks, and can also be put into a chained form by (invertible) static feedback. Most of the developments are done within the framework of differential forms and Pfaffian systems.
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    Liapunov functions and stability criteria for nonlinear systems with multiple critical eigenvalues (1994)
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    Mathematics of control, signals, and systems 7 (1994), S. 255-278 
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    ISSN: 1435-568X
    Keywords: Nonlinear control ; Liapunov ; Critical ; Relaxed ; D-stability
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    Topics: Electrical Engineering, Measurement and Control Technology , Mathematics , Technology
    Notes: Abstract Efficient criteria are derived via explicit construction of Liapunov functions for local asymptotic stability inference of nonlinear systems, whose linearizations possessc ≥ 2 critical modes at an equilibrium point. The stability criteria are obtained in the context of two novel notions, relaxed definiteness and relaxed stability. A real symmetricc×c matrixQ isrelaxed negative definite ifw TQw〈0 for any 0≠wεℜ + c , ℜ+=[0, ∞); a matrixR isrelaxed stable if there is aP〉0 such thatPR+R TP is relaxed negative definite. The construction leads to some characterizations of the nonlinear system's local structure,in the sense of Liapunov, and the so-called stability characteristic matrices and tensors. It is shown that a nonlinear system with multiple critical modes is locally asymptotically stable generically if the stability characteristic matrix is relaxed stable and less generically if the stability characteristic tensor is trivial or degenerate in certain way and the perturbed stability characteristic matrix is relaxed stable.
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    Decentralized sequential detection with sensors performing sequential tests (1994)
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    Mathematics of control, signals, and systems 7 (1994), S. 292-305 
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    ISSN: 1435-568X
    Keywords: Decentralized detection ; Sequential analysis ; Dynamic programming ; Distributed decision making ; Optimal stopping rules ; Stochastic teams
    Source: Springer Online Journal Archives 1860-2000
    Topics: Electrical Engineering, Measurement and Control Technology , Mathematics , Technology
    Notes: Abstract A decentralized sequential detection problem is considered where a set of sensors making independent observations must decide which of the given two hypotheses is true. Decision errors are penalized through a common cost function, and each time step taken by the sensors as a team is assigned a positive cost. It is shown that optimal sensor decision functions can be found in the class ofgeneralized sequential probability ratio tests (GSPRTs) with monotonically convergent thresholds. A technique is presented for obtaining the optimal thresholds. The performance of the optimal policy is compared with that of a policy which uses SPRTs at each of the sensors.
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    Approximation algorithm for an infinite-dimensional operator equation XL−BX=C (1994)
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    Mathematics of control, signals, and systems 7 (1994), S. 76-93 
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    ISSN: 1435-568X
    Keywords: Infinite-dimensional Sylvester equation ; Inverse problem ; Approximation algorithm ; Parabolic feedback systems
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    Topics: Electrical Engineering, Measurement and Control Technology , Mathematics , Technology
    Notes: Abstract We study an infinite-dimensional operator equation XL−BX=C in a separable Hilbert space. The equation arises in the stabilization study of general linear parabolic systems, where the operatorsL, B, and C are coefficient operators describing a feedback control system. The solution to the stabilization naturally leads to an approximation problem of the operator equation. In this paper we propose a concrete algorithm for the approximation with the prescribed convergence rate when the closed operatorL is self-adjoint or more generally a spectral operator with compact resolvent.
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    Stochastic averaging analysis of a steepest-descent-type adaptive time-delay estimation algorithm (1994)
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    Mathematics of control, signals, and systems 7 (1994), S. 121-147 
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    ISSN: 1435-568X
    Keywords: Averaging analysis ; Time-delay estimation ; Adaptive algorithm
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    Topics: Electrical Engineering, Measurement and Control Technology , Mathematics , Technology
    Notes: Abstract In this paper stochastic averaging analysis tools are used to study an adaptive time-delay estimation algorithm. Analyzing such an algorithm is very difficult because of its nonlinear, infinite-dimensional, and time-variant nature. By stochastic averaging analysis, we show that for the time-invariant delay case, the adaptive algorithm output converges weakly to the solution of an ordinary differential equation. Local convergence is demonstrated by showing that the solution of this differential equation converges exponentially to the true delay under reasonable initial conditions. Implementation of the algorithm is also discussed. Guided by the averaging results, a modified algorithm is proposed to eliminate the bias of the delay estimation. Second-order analysis is carried out and the results provide a theoretical justification of the observations made by other researchers with simulation and heuristic argument. Computer simulations are also included to support the analysis.
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    A time-varying Beurling-Lax theorem and a related interpolation problem (1994)
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    Mathematics of control, signals, and systems 7 (1994), S. 148-166 
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    ISSN: 1435-568X
    Keywords: Time-varying systems ; Beurling-Lax theorem ; Sarason interpolation ; Krein spaces ; Causality ; Interpolation
    Source: Springer Online Journal Archives 1860-2000
    Topics: Electrical Engineering, Measurement and Control Technology , Mathematics , Technology
    Notes: Abstract This article concerns linear time-varying interpretations of the Beurling-Lax-Ball-Helton theorem and of Sarason's interpolation problem. The former characterizes shift-invariantH 2 (Krein) subspaces. Unilateral shift invariance reflects both causality and time invariance. Removing the stationarity requirement, a generalized theorem provides a characterization of certain causal subspace families Mt ⊂L2(t, ∞), t ε ℝ. Sarason's interpolation problem is interpreted here as a search for a (close to) minimal induced norm system, given causal input-output specifications. The Beurling-Lax theorem helps in identifying admissible specification classes. The problem is then reduced to and solved in terms of a linear time-varying Nehari problem. Technically, developments are based on timedomain, state-space methods.
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    On the stabilization of controllable and observable systems by an output feedback law (1994)
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    Mathematics of control, signals, and systems 7 (1994), S. 187-216 
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    ISSN: 1435-568X
    Keywords: Nonlinear systems ; Stabilization ; Controllability ; Observability ; Output feedback
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    Topics: Electrical Engineering, Measurement and Control Technology , Mathematics , Technology
    Notes: Abstract For control systems which can be locally stabilized in small time by means of a dynamic periodic time-varyingstate feedback law, we give a sufficient condition on Lie derivatives of the output for local stabilization in small time by means of a dynamic periodic time-varyingoutput feedback law. If the system is analytic our sufficient condition is also necessary.
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    The computational complexity of approximating the minimal perturbation scaling to achieve instability in an interval matrix (1994)
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    Mathematics of control, signals, and systems 7 (1994), S. 279-291 
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    ISSN: 1435-568X
    Keywords: Computational complexity ; Approximation complexity ; Robust stability ; Interval matrix
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    Topics: Electrical Engineering, Measurement and Control Technology , Mathematics , Technology
    Notes: Abstract An interval matrix can be represented in terms of a “center” matrix and a nonnegative error matrix, specifying maximum elementwise perturbations from the center matrix. A commonly proposed robust stability (regularity) characterization for an interval matrix with a stable (nonsingular) center matrix identifies the minimum scaling of this error matrix for which instability (singularity) is achieved. In this paper it is shown that approximating this minimum scaling is a MAX-SNP-hard problem. This implies that in the general case, unless the class of deterministic polynomial-time decision problems, P, equals the class of nondeterministic polynomial-time decision problems, NP, thought to be highly unlikely, this minimum scaling cannot be approximated with a ratio arbitrarily close to unity in polynomial time.
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    Singular extremals on Lie groups (1994)
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    Mathematics of control, signals, and systems 7 (1994), S. 217-234 
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    ISSN: 1435-568X
    Keywords: Singular extremals ; Characteristics ; Lie group ; Nonholonomic distribution ; Differential forms ; Sub-Riemannian geometry
    Source: Springer Online Journal Archives 1860-2000
    Topics: Electrical Engineering, Measurement and Control Technology , Mathematics , Technology
    Notes: Abstract We investigate the space of singular curves associated to a distribution ofk-planes, or, what is the same thing, a nonlinear deterministic control system linear in controls. A singular curve is one for which the associated linearized system is not controllable. If a quadratic positive-definite cost function is introduced, then the corresponding optimal control problem is known as the sub-Riemannian geodesic problem. The original motivation for our work was the question “Are all sub-Riemannian minimizers smooth?” which is equivalent to the question “Are singular minimizers necessarily smooth?” Our main result concerns the singular curves for a class of homogeneous systems whose state spaces are compact Lie groups. We prove that for this class each singular curve lies in a lower-dimensional subgroup within which it is regular and we use this result to prove that all sub-Riemannian minimizers are smooth. A central ingredient of our proof is a symplectic-geometric characterization of singular curves formulated by Hsu. We extend this characterization to nonsmooth singular curves. We find that the symplectic point of view clarifies the situation and simplifies calculations.
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    Embedding of time-varying contractive systems in lossless realizations (1994)
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    Mathematics of control, signals, and systems 7 (1994), S. 306-330 
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    ISSN: 1435-568X
    Keywords: Lossless embedding ; Linear time-varying systems ; Riccati difference equation ; Bounded real lemma
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    Topics: Electrical Engineering, Measurement and Control Technology , Mathematics , Technology
    Notes: Abstract The lossless embedding problem, also known as the Darlington synthesis or unitary extension problem, considers the extension of a given contractive system to become the partial input-output operator of a lossless system. In this paper the embedding problem is solved for discrete-time time-varying systems with finite but possibly time-varying state dimensions, for the strictly contractive as well as the boundary case. The construction is done in a state space context and gives rise to a time-varying Riccati difference equation which is shown to have a closed-form solution. As a corollary, a discrete-time Bounded Real Lemma is formulated, linking contractiveness of an input-output operator to conditions on its state realization.
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    On the stability of slowly time-varying linear systems (1994)
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    Mathematics of control, signals, and systems 7 (1994), S. 331-350 
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    ISSN: 1435-568X
    Keywords: Time-varying systems ; Linear systems ; Stability ; Stochastic stability
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    Topics: Electrical Engineering, Measurement and Control Technology , Mathematics , Technology
    Notes: Abstract New conditions are given in both deterministic and stochastic settings for the stability of the system x=A(t)x when A(t) is slowly varying. Roughly speaking, the eigenvalues of A(t) are allowed to “wander” into the right half-plane as long as “on average” they are strictly in the left half-plane.
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    Overview of GSM: Philosophy and results (1994)
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    International journal of wireless information networks 1 (1994), S. 7-16 
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    ISSN: 1572-8129
    Keywords: Digital cellular ; network architecture ; radio interface ; wireless services
    Source: Springer Online Journal Archives 1860-2000
    Topics: Electrical Engineering, Measurement and Control Technology
    Notes: Abstract The work on GSM, a standardized European second-generation cellular system, was started in 1982 in order to prevent the fragmentation of the first-generation cellular market from continuing into the second generation. The goal was to define a system with open interfaces for Pan-European use that would offer the best compromise between a number of conflicting requirements, such as spectrum economy, high speech quality, low cost, and a large range of services. A broad outline of the novel features is presented, both concerning the architecture of the system and of the services offered, as well as the reasoning behind the more important choices. Finally, some views are presented concerning the future development of GSM and of the third-generation system, the co-called Future Public Land Mobile Telecommunication System, commonly referred to as FPLMTS.
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    Autonomous SIR-based power control for a TDMA radio system (1994)
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    International journal of wireless information networks 1 (1994), S. 187-198 
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    ISSN: 1572-8129
    Source: Springer Online Journal Archives 1860-2000
    Topics: Electrical Engineering, Measurement and Control Technology
    Notes: Abstract Power control based on signal-to-interference ratio (SIR) has been proposed as a technique for managing cochannel interference due to frequency reuse in a time-division multiple-access (TDMA) radio system. Early studies have focused on SIR balancing approaches that require centralized control for global power adjustment and/or associated channel reassignment or call admission control. This paper investigates the achievable performance of an autonomous power control technique which relies only on a simple fixed-step feedback adjustment algorithm. Simulation results, assuming no adaptation to Rayleigh fading, indicate that this simple power control technique can perform nearly as well as ideal SIR balancing/call removal, yielding a possible increase in spectrum efficiency of at least three times compared to a system without power control. Tracking of Rayleigh fading is found to provide an additional improvement in SIR of 4 to 4.5 dB for the range of fading rates expected in the pedestrian wireless access environments. This work is targeted toward understanding the traffic capacity and deployment implications of wireless technology alternatives that could provide access to local exchange networks.
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    Performance of cellular packet CDMA in an integrated voice/data network (1994)
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    International journal of wireless information networks 1 (1994), S. 199-222 
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    ISSN: 1572-8129
    Keywords: Cellular packet CDMA ; voice/data network ; spreading factor ; forward error correction ; propagation loss coefficient
    Source: Springer Online Journal Archives 1860-2000
    Topics: Electrical Engineering, Measurement and Control Technology
    Notes: Abstract This paper presents a simulation-based study of cellular packet CDMA systems operating in an integrated voice/data traffic scenario. Spread-spectrum CDMA provides a suitable framework for resource-shared packet transport capable of combining isochronous (voice, ISDN) and bursty data services. In this work, a general network model for cellular packet CDMA with mixed voice/data traffic is described and used to evaluate the capacity/performance impact of several key system parameters. First, the effect of spreading factor (N) and forward error correction (FEC) rate are studied, confirming earlier work indicating a weak dependence onN and a well-defined optimum code rate in the range of 0.5–0.7 (with BCH coding). Next, the effect of propagation loss coefficient (γ) on network capacity is investigated over a range of possible assumptions forγ, including both constant and distance-dependent models. The results show that system capacity depends strongly onγ, varying by as much as a factor of 2 over the range of parameters considered. For a given distance-dependentγ assumption, performance results are also obtained for different cell sizes in order to understand the overall spatial reuse efficiency achievable in different cellular and microcellular scenarios. This is followed by an investigation of traffic source model effects: first the capacity improvement from voice activity detection VAD) is presented, showing the expected ∼2∶1 gains. Results for varying proportions of voice and data traffic intensities indicate that the operating efficiency does not change significantly as the proportion of bursty data relative to voice is varied.
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    URL: http://dx.doi.org/10.1007/BF02107419
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    Error propagation in laser beam spatial parameters (1994)
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    Optical and quantum electronics 26 (1994), S. 25-34 
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    Topics: Electrical Engineering, Measurement and Control Technology , Physics
    Notes: Abstract We have performed a propagation-of-errors analysis on two methods used to determine the spatial parameters of a laser beam. We measured diameters of a diode laser beam focused by a 993 mm focal length lens. Measurement uncertainties of less than 1% can result in uncertainties greater than 200% in locating the beam waist of the laser. We compare the inherent uncertainties in the spatial parameters as obtained by the two methods. Longer focal length lenses and lens position can reduce this magnification of uncertainty, but would require large propagation distances.
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    URL: http://dx.doi.org/10.1007/BF00573898
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    Splice loss in single- and twin-core buried channel waveguide devices (1994)
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    Optical and quantum electronics 26 (1994), S. 45-62 
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    Topics: Electrical Engineering, Measurement and Control Technology , Physics
    Notes: Abstract We quantify the magnitude of the power loss incurred when a square-core buried channel waveguide (BCW) is spliced to a standard circular-core telecommunications fibre. With a view to minimizing the dissipated power, we show that a simple equal-core-area criterion provides an elegant means of determining the optimum core dimensions. This result is found to hold for more general BCW cross-sections that possess a reasonable degree of symmetry. The fundamental problems of waveguide misalignment and angular tilt are also investigated and their effect on splice loss is quantified. Our theoretical model is applied to both single- and twin-core waveguides.
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    URL: http://dx.doi.org/10.1007/BF00573900
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    Nonlinear optical interactions in dye-doped solids (1994)
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    Optical and quantum electronics 26 (1994), S. 1-23 
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    Topics: Electrical Engineering, Measurement and Control Technology , Physics
    Notes: Abstract We present a brief review of non-linear optical investigations on dye-doped solids using low-power CW lasers. After a brief introduction to the photophysics of the dye molecules, we discuss specific nonlinear processes such as self-diffraction, optical phase conjugation, two-beam coupling and polarization gratings in these systems. The application potential of dye-doped solid devices is discussed.
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    URL: http://dx.doi.org/10.1007/BF00573897
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    Book review (1994)
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    Optical and quantum electronics 26 (1994), S. 1041-1042 
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    Topics: Electrical Engineering, Measurement and Control Technology , Physics
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    URL: http://dx.doi.org/10.1007/BF00305004
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    Impact ionizing electroluminescence of a double barrier structure (1994)
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    Optical and quantum electronics 26 (1994), S. 1033-1040 
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    Notes: Abstract The impact ionizing electroluminescence model of a unipolar double barrier structure has been developed. The electron density in the quantum well and the hole density generated in the collector region are based on electron current. The electroluminescence results from direct radiative recombination between the electrons and holes in the quantum well. The results show that a light on-off ratio of the electroluminescence can be obtained.
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    URL: http://dx.doi.org/10.1007/BF00305003
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    Phase-conjugate bistability and multistability in moving-grating operated orthogonally polarized pump four-wave mixing in photorefractives (1994)
    Springer
    Optical and quantum electronics 26 (1994), S. 1019-1032 
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    Notes: Abstract We establish possible regions of bistability (BIST), multistability (MUST), hysteresis, self-oscillation (SO) and enhancement features of the phase-conjugate reflectivity (PCR) by use of moving-grating operation (MGO) in the orthogonally polarized pump four-wave mixing (OPP-FWM) geometry employing a photorefractive (PR) crystal (usually BaTiO3). Numerical evaluation of such PCR features has been presented as a function of parameters such as coupling strength (of complex gL and real g 0 L values), frequency-shift (Ω) owing to grating motion, the PR phase shift (øPR), and pump (r) and probe (q) intensity ratios. PCR results of this geometry are compared with those obtained from the regular (i.e. parallel-polarized pump) four-wave mixing (REG-FWM) geometry assuming the same set of parameters in both geometries. We find that the OPP geometry leads to a drastic PCR enhancement together with the appearance of a rich variety of multibranched solutions exhibiting BIST and MUST features of the PCR, particularly in the range 0.5 ≲ Ω ≲ 3 with values g 0L ∼ 10, r=1 and q ≲ 0.1 that are practically realizable. Nevertheless, this geometry sometimes offers the possibility of a PCR jump (from one stable state to the other), suggesting hysteresis caused by changing Ω only slightly. In the REG geometry, however, the PCR enhancement is less prominent, and also the BIST/MUST features rarely exist unless g 0 L becomes sufficiently large, say ∼ 20 or more.
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    Photoinduced dichroism and birefringence in films of Mordant Pure Yellow/poly(vinyl alcohol): simultaneous real-time investigations at two wavelengths (1994)
    Springer
    Optical and quantum electronics 26 (1994), S. 1013-1018 
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    Notes: Abstract Photoinduced anisotropy in films of azo-dye Mordant Pure Yellow (MPY) dissolved in a polyvinyl alcohol matrix, is investigated. The photodichroism and photoinduced birefringence are measured in real time for two wavelengths, 488 nm (in the absorption band) and 633 nm (outside it), on excitation with an Ar+ laser beam. It is shown that strong dichroism is induced without changing the average optical density of the film, and the kinetic curves of the birefringence and the dichroism are substantially different. The conclusion is made that the photoprocesses of the dye molecules cause a reconstruction of the matrix.
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    On the possibility of mode-locking a dye laser by a fast saturable absorber (1994)
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    Optical and quantum electronics 26 (1994), S. 79-85 
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    Topics: Electrical Engineering, Measurement and Control Technology , Physics
    Notes: Abstract The problem of mode-locking a fully relaxing saturable (dye) laser medium by an instantaneously saturating (fast) absorber is theoretically considered when group velocity dispersion and Kerr-type nonlinearity are present. Off-resonant chirped solutions are found whose minimum duration is determined by the relative losses (saturable and nonsaturable) and by the saturation depth of the absorber. The addition of nonlinear elements can only broaden the stability range of the solution with respect to the group velocity dispersion.
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    Review of numerical and approximate methods for the modal analysis of general optical dielectric waveguides (1994)
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    Optical and quantum electronics 26 (1994), S. S113 
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    Topics: Electrical Engineering, Measurement and Control Technology , Physics
    Notes: AbstactAbstact This paper reviews numerical and approximate methods for the modal analysis of general optical dielectric waveguides with emphasis on recent developments. Six groups of methods are reviewed, covering (1) the finite-element method, (2) the finite-difference method, (3) the integral-equation method, (4) methods based on series expansion, (5) approximate methods based on separation of variables, and (6) methods that do not fit into the above groups, ranging from the specialized ones for analysing restricted classes of waveguides to the most general ones for analysing inhomogeneous, arbitrarily-shaped, anisotropic waveguides. Some suggestions with regard to the selection of methods for particular applications are given.
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    Computation of higher-order waveguide modes by imaginary-distance beam propagation method (1994)
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    Optical and quantum electronics 26 (1994), S. S199 
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    Notes: Abstact Yevick and Hermansson presented an efficient numerical method for calculating fundamental modes of optical waveguides. We extend their technique to higher-order eigenmodes. Using a finite-difference beam propagation method, we obtain propagation constants and field profiles for the three lowest-order TE modes in an asymmetric rib waveguide.
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    Analysis of the eigenmodes of two coupled Ti: LiNbO3 optical waveguides and its application (1994)
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    Optical and quantum electronics 26 (1994), S. S173 
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    Notes: Abstact Two kinds of trial solutions for the symmetric and antisymmetric modes of the parallel Ti: LiNbO3 waveguide structure are proposed and their parameters are determined by use of the variational method. Comparison with the results of the finite-element method and reported experimental results shows that the solutions composed of Hermite-Gaussian functions might achieve better accuracy. It is shown that the formulae established here are suited for both single waveguide structures and coupled waveguide structures. In addition, we discuss the optimal electrode design for the symmetric directional coupler switches with a zero waveguide spacing. It is found that the required drive voltage can be lowered by choosing a small electrode gap and an appropriate electrode width.
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    Simple finite-difference algorithm for calculating waveguide modes (1994)
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    Optical and quantum electronics 26 (1994), S. S151 
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    Notes: Abstact A simple algorithm for solving the finite-difference (FD) equations for the mode eigenvalues and field distributions of a linear waveguide is presented. By applying the discretized Helmholtz operator column-by-column to an index distribution defined on an N x N grid, a matrix whose size is only a few times N x N is obtained. This yields a reduction in computation time and space compared with the other classical FD approaches which involve an N 2 x N 2 matrix. Our method is tested against problems for which the exact solutions are known, and we find a high degree of accuracy. Despite the existence of fast algorithms for the treatment of the classical N 2 x N 2 matrix, our new algorithm presents some advantages over existing FD methods of comparable speed, including: the ability to find all the modes and associated field profiles, very high numerical stability, and no numerical approximations in the procedure. In addition, some general optimum expressions for the domain size and density of grid points which are consistent with the desired precision are provided, and apply to any FD method including ours.
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    Semiconductor waveguide directional couplers for coherent receivers (1994)
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    Optical and quantum electronics 26 (1994), S. S529 
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    Notes: Abstract Optical waveguide 3-dB couplers integrated on semicondutors have been studied, designed and fabricated, using both bulk and diluted multi-quantum-well InGaAsP/InP-based materials, grown by MOCVD. The device structure is based on the two-mode interference (TMI) principle and is fully compatible for integration with the optoelectronic and electronic components of a coherent receiver. Bulk material couplers provide an output balanced within 0.05 dB per nanometer and an excess loss of 1.4 dB, compared to a straight guide, while coupling loss to a tapered-lensed single mode fibre is 4 dB. Improved coupling efficiency to single-mode fibres is achieved by use of moderately diluted multi-quantum-well waveguides, which include InGaAsP wells and InP barriers: coupling loss to a tapered-lensed single-mode fibre as low as 0.5 dB and excess loss of 1.8 dB are featured. Couplers fabricated with this waveguide structure have a balance sensitivity of 0.03 to 0.04 dB per nanometer. A moderately diluted multi-quantum-well 3-dB coupler has been permanently pigtailed and butt-coupled to a dual balanced PIN photoreceiver. This hybrid assembly was tested in a coherent transmission system at 155 and 622 Mbits-1 showing sensitivities, for 10-9 BER, of about-38.0 dBm and-28.8 dBm, respectively.
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    Design, modelling and implementation of the ATMOS project fibre delay line photonic switching matrix (1994)
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    Optical and quantum electronics 26 (1994), S. S497 
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    Notes: Abstract This paper presents the fibre delay line switching matrix, a high-performance photonic system consisting of an electrically controlled optical high-speed transport network. This photonic matrix adopts the asynchronous transfer mode (ATM) technique and an internal self-routing architecture based on wavelength encoding, for cell routing and multiplexing. A set of output queues provides the buffering function. An extensive performance evaluation is presented, with reference to both the traffic throughput and technology feasibility. Numerical results have been obtained to evaluate optical performance and the implementation of a 4×4 demonstrator, supporting a 2.5 Gbit s-1 input/output rate, shows the feasibility of the matrix with state-of-the-art optical technology. Its high performance makes the fibre delay line switching matrix a strong candidate for implementing the core of future high-speed broadband ATM switches.
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    Tuneable fibre source for picosecond pulses around 1.55 μm with repetition rates up to 20 GHz (1994)
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    Optical and quantum electronics 26 (1994), S. S547 
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    Notes: Abstract We report on the generation of picosecond optical pulses around 1.55 μm using a tuneable actively mode-locked erbium-doped fibre ring laser. Pulse widths of less than 10 ps have been achieved within the wavelength range 1518 to 1570 nm at a pulse repetition rate of 20 GHz. Pulse trains with lower repetition rates have been generated using electrical square-wave signals for driving the electrooptic modulator, resulting in 〈20 ps pulse widths. The implementation of an all polarization-preserving fibre ring cavity enabled stable and reproducible operation of the laser. Minimization of the overall ring dispersion offers tuneability at nearly constant repetition rate throughout the whole wavelength range. Simple analytic expressions are given that allow for optimization of the ring laser performance with respect to output power, relaxation oscillations and wavelength tuneability at constant repetition rate.
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    Space-charge-induced interband optical nonlinearities in asymmetric coupled quantum wells (1994)
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    Optical and quantum electronics 26 (1994), S. S565 
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    Notes: Abstract Space-charge-induced optical nonlinearities for asymmetric coupled quantum wells have been studied. Calculations for optimized AlGaAs structures show that a blue-shift of the band gap of 9 meV at a carrier density of 1012 cm-2 can be obtained. Experimental comparisons with a rectangular well show a large increase in room-temperature nonlinearities.
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    Erratum: ‘Succession of one-soliton pulses in the zero-dispersion region of silica optical fibres: the role of the phase difference between adjacent pulses’ (1994)
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    Optical and quantum electronics 26 (1994), S. S583 
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    Experimental determination of exponential parameters for multiphonon residual absorption in a ZBLAN: Er3+ fibre (1994)
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    Optical and quantum electronics 26 (1994), S. S559 
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    Notes: Abstract Determination of exponential parameters for both Stokes and anti-Stokes sidebands by excitation of a ZBLAN: Er3+ fibre and bulk samples gives values of 9.4×10-3 cm and 14.1×10-3 cm, respectively. Observed values are larger than equivalent parameters usually found for nonradiative transitions. As examples, the measured parameters are used to determine the multiphonon sideband absorption between the 4I11/2 and the 4I13/2 electronic transitions of Er3+ and also between 1G4 and 3F4 of Pr3+. Available energy ranges for sideband pumping of distributed amplifiers are given as well as the minimum multiphonon background losses intrinsic to the rare-earth plus pure glass base combination.
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    Corrigendum: ‘Output power limitations in CW single transverse mode Nd:YAG lasers with a rod of large cross-section’ (1994)
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    Optical and quantum electronics 26 (1994), S. S584 
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    Optical fibre amplifiers: physical model and design issues (1994)
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    Optical and quantum electronics 26 (1994), S. 585-608 
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    Notes: Abstract The development of optical fibre amplifiers has caused an impressive evolution in optical telecommunications systems since the end of the 1980s. The widespread application of active fibre amplifiers requires accurate tools to design and simulate these devices in very different operating conditions. The present work describes some physical aspects of active fibre amplifiers and a numerical model for the analysis of active optical fibres that can be applied to investigate spatial and spectral properties of amplifiers for the transmission windows of optical fibre telecommunications. Finally, various design issues relevant to the investigation of optimal fibre design of silica, fluoride erbium-doped and fluoride praseodymium-doped fibres are discussed and illustrated by means of examples.
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    Measurement of beam quality degradation due to spherical aberration in a simple lens (1994)
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    Optical and quantum electronics 26 (1994), S. 629-632 
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    Notes: Abstract We have measured the effect on laser beam quality factorM 2 of spherical aberration in a simple planoconvex lens. Theory predicts that the laser beam quality should remain essentially unchanged until the incident beam widthw exceeds a critical widthw q above which the beam quality will degrade rapidly, with theM 2 value increasing as (w/w q 4). We find good agreement between this theory and our experimental data.
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    Modelling and characterization of ferroelectric liquid crystal displays (1994)
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    Optical and quantum electronics 26 (1994), S. S571 
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    Notes: Abstract Modelling of liquid crystal displays is useful to predict their optical properties and dynamic behaviour. An integrated modelling system for ferroelectric liquid crystal displays has been developed. The system employs data from real FLC materials, polarizers, glasses, backlights, and colour filters, aiming to describe actual devices accurately. Optical transmission dependence on light wavelength and angle of incidence is obtained as a function of the liquid crystal director profile. This profile is in turn derived from energy minimization of bulk and glass surface conditioning contributions. The above static model has been extended to study sample switching in multiplexed displays. Usual slot times in actual displays are quite close to time response of FLC materials, hence no energy-minimized configurations are obtained upon switching. A dynamic model has been formulated to derive the director profile evolution with time, according to the employed driving scheme, and the rotational viscosity of the material. Predicted dynamic and optical results have been compared to experimental measurements on FLC test cells. It has been found that the behaviour of FLC cells depends on a large number of physical and optical parameters. Some of them may be obtained from FLC data sheets, and manufacturing conditions. Other parameters related to director profiles in relaxed states may be experimentally obtained by sample characterization through optical transmission measurements. A few little known parameters (e.g. specific elastic constants) remain; fortunately their influence on cell dynamics is low.
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    Influence of thermal fluctuation noise on two-wave mixing in saturable absorbers (1994)
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    Optical and quantum electronics 26 (1994), S. 633-640 
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    Notes: Abstract We have extended the description of nonlinear optical two-wave mixing in a three-level saturable absorbing medium to include a noise contribution from thermally driven fluctuations in the real part of the refractive index. An effective gain factor is introduced to describe this influence on the signal beam and numerical data are given for ruby. These data, which include saturation, show that the influence of noise on the signal beam near the saturation gain value is more than ten times larger than that calculated using the theory for a Kerr medium for the same gain value.
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    Optical document security (1994)
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    Optical and quantum electronics 26 (1994), S. 645-646 
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    Exact transcendental equation for scalar modes of rectangular dielectric waveguides (1994)
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    Optical and quantum electronics 26 (1994), S. 641-644 
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    Notes: Conclusion A Fourier operator method has been used to derive for the first time an exact closed-form eigenvalue equation for the scalar mode propagation constants of a buried rectangular dielectric waveguide. The new method has been implemented and the results used to determine the accuracy of the scalar finite-difference approach. It is hoped that the exact results obtained here may assist in the validation of the accuracy of the other numerical and semi-analytical methods.
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    Second-harmonic generation at periodic second-order susceptibility gratings with self-phase and cross-phase modulation (1994)
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    Optical and quantum electronics 26 (1994), S. 609-627 
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    Notes: Abstract Quasi-phase-matched second-harmonic generation at periodic quadratic susceptibility gratings with self-phase and cross-phase modulation owing to Kerr nonlinearities is investigated. A model of interaction of monochromatic plane travelling waves is considered. The solution assumes a nondepleted pump and results for a numerical computation of second-harmonic conversion efficiency for a highly efficient process are presented. It is shown that for high spatial-frequency gratings the efficiency of second-harmonic generation depends on the reduced detuning δ and the Kerr-nonlinearity coefficient κ only. In some cases, if the signs of δ and κ are opposite, the Kerr nonlinearity can enhance the second-harmonic conversion efficiency due to the compensation of the phase mismatch attained in the below-half-conversion stage by the reversed phase mismatch in the above-half-conversion stage of the process. The computed maximum conversion efficiencies for various values of δ and κ are plotted in a contour map on the δ-κ plane.
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    Carrier transport effects in quantum well lasers (1994)
    Springer
    Optical and quantum electronics 26 (1994), S. V 
    Details
    ISSN: 1572-817X
    Source: Springer Online Journal Archives 1860-2000
    Topics: Electrical Engineering, Measurement and Control Technology , Physics
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00326652
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    Experimental and theoretical study of the carrier capture time (1994)
    Springer
    Optical and quantum electronics 26 (1994), S. S667 
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    ISSN: 1572-817X
    Source: Springer Online Journal Archives 1860-2000
    Topics: Electrical Engineering, Measurement and Control Technology , Physics
    Notes: Abstract We present an experimental and theoretical study of the carrier capture time into a semiconductor quantum well. We observe for the first time the predicted oscillations of the phonon emission induced capture time experimentally and found good agreement with theory. Calculations show that not only does the LO phonon emission induced capture time (ph capture) oscillate as a function of well width, but also the carrier-carrier scattering induced capture time (c-c capture) oscillates by more than an order of magnitude as a function of the active layer design. Recently, it has been shown that the carrier capture time is directly related to the modulation bandwidth in a quantum well laser. As a result, it might be possible to tailor the modulation bandwidth by optimizing the capture efficiency using a proper design of the active layer in a quantum well laser.
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    URL: http://dx.doi.org/10.1007/BF00326654
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    Carrier transport effects in quantum well lasers: an overview (1994)
    Springer
    Optical and quantum electronics 26 (1994), S. S647 
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    ISSN: 1572-817X
    Source: Springer Online Journal Archives 1860-2000
    Topics: Electrical Engineering, Measurement and Control Technology , Physics
    Notes: Abstract Early theoretical predictions and later experimental work have shown that lasers with quantum well active areas have enhanced differential gain over bulk lasers. The resonance frequency in a semiconductor laser is proportional to the square root of the differential gain. The resonance frequency is directly related to the modulation bandwidth, and the enhancement in the intrinsic differential gain led to theoretical predictions of increased modulation bandwidth in quantum well lasers. This enhancement in the modulation bandwidth proved to be elusive initially, and later it was realized that other factors, namely carrier transport effects, played a more dominant role in the high-speed properties of quantum well lasers. Carrier transport effects, in addition to bandfilling, affect a wide range of static and dynamic properties of the quantum well lasers. This paper will present an overview of our present understanding of the carrier transport processes and their effects in quantum well lasers.
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    URL: http://dx.doi.org/10.1007/BF00326653
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    Ultrafast carrier dynamics in In1−x Ga x As/InP heterostructures (1994)
    Springer
    Optical and quantum electronics 26 (1994), S. S705 
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    ISSN: 1572-817X
    Source: Springer Online Journal Archives 1860-2000
    Topics: Electrical Engineering, Measurement and Control Technology , Physics
    Notes: Abstract We investigate carrier capture and carrier transport in the InGaAs/InP material system by luminescence spectroscopy with femtosecond time resolution. Comparative studies are performed on samples of different well width, barrier width and gallium mole fraction of the InGaAs layers. The investigations focus on excitation conditions that are comparable to those for semiconductor laser operation. Firm data on carrier dynamics are presented for these conditions. We find that the overall transfer rates of electrons and holes are similar and independent of well width. Furthermore, the transfer times show a linear dependence on barrier width. From experimental and model calculation results we derive some guidelines for the design of high-frequency laser devices.
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    URL: http://dx.doi.org/10.1007/BF00326657
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    The role of vertical transport and capture of electrons and holes for the transient optical response in quantum-well heterostructures (1994)
    Springer
    Optical and quantum electronics 26 (1994), S. S691 
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    ISSN: 1572-817X
    Source: Springer Online Journal Archives 1860-2000
    Topics: Electrical Engineering, Measurement and Control Technology , Physics
    Notes: Abstract The transient optical response of quantum wells (QWs) after optical and electrical carrier injection into the barrier layers is studied experimentally and theoretically. We have varied the transport geometry in GaAs/AlGaAs and InGaAs/InAlGaAs heterostructures and emphasize the basic principles for a theoretical treatment of electron and hole capture into QWs for a proper description of vertical carrier transport in the barriers of QW heterostructures. Comparing our experimental data with the results of theoretical model calculations, we determine the capture, reflection and transmission probabilities, the ambipolar diffusivities and the ambipolar mobilities in the barriers of GaAs/AlGaAs, as a model system. The temporal evolution of the electron and the hole capture current densities at the QWs are studied in detail for a wide variation of the injected carrier densities. Amplitude modulation experiments are performed for InGaAs/InAlGaAs QW laser devices providing increasing 3 dB frequencies for decreasing confinement layer thickness, indicating the influence of carrier transport in the barriers.
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    URL: http://dx.doi.org/10.1007/BF00326656
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    Quantum-mechanical versus semiclassical capture and transport properties in quantum well laser structures (1994)
    Springer
    Optical and quantum electronics 26 (1994), S. S679 
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    ISSN: 1572-817X
    Source: Springer Online Journal Archives 1860-2000
    Topics: Electrical Engineering, Measurement and Control Technology , Physics
    Notes: Abstract We have studied experimentally and modelled theoretically the capture properties and transport mechanisms of electrons and holes in laser structures. We describe first the extreme case where the barrier thickness is very large: then semiclassical drift-diffusion equations may be applied and quantum-mechanical effects at the edge of the well are negligible. A second extreme case occurs when the barrier is narrow enough for quantum mechanics to apply fully. There, strong variations of the capture time with the well width are expected and observed. In real laser structures, dimensions are such that we are in an intermediate case and both aspects have to be taken into account. We give some typical values for diffusion/capture mechanism induced delay times in such a case.
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    Hole capture rate of GaInAs/InP strained quantum-well lasers (1994)
    Springer
    Optical and quantum electronics 26 (1994), S. S719 
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    ISSN: 1572-817X
    Source: Springer Online Journal Archives 1860-2000
    Topics: Electrical Engineering, Measurement and Control Technology , Physics
    Notes: Abstract The property of hole capture of quantum wells is important in the static properties of lasers above threshold, such as the differential efficiency and light output power. We investigate experimentally the hole capture rate and its influence on the carrier overflow in the optical confinement layers for compressive-strained, tensile-strained and unstrained GaInAs/GaInAsP/InP quantum-well lasers emitting at 1.5 μm by measuring the spontaneous emission from the optical confinement layers above threshold. The carrier density in the optical confinement layers increases with current owing to finite hole capture rates. This increase is dependent on well thickness and barrier height determined by the strain. This increase is comparable in the tensile-strained and unstrained lasers with relatively low threshold, while in the compressive-strained laser it is about double that in the other two types. The dependence of this increase on threshold carrier density is also observed, that is the carrier density in the optical confinement layers increases rapidly in high-threshold samples, in particular, in the tensile-strained laser with large hole barrier height. From these results, laser operation with high output power and high efficiency is expected by reducing threshold carrier density in the tensile-strained laser and by increasing well numbers in the compressive-strained laser as long as the inhomogeneous injection between wells is not severe. By fitting measurements with theory, the hole capture time is estimated as 0.1 to 0.25 ps in these strained and unstrained lasers.
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    URL: http://dx.doi.org/10.1007/BF00326658
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    Carrier transport effects and dynamics in multiple quantum well optical amplifiers (1994)
    Springer
    Optical and quantum electronics 26 (1994), S. S731 
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    ISSN: 1572-817X
    Source: Springer Online Journal Archives 1860-2000
    Topics: Electrical Engineering, Measurement and Control Technology , Physics
    Notes: Abstract The gain recovery dynamics of multiple quantum well semiconductor optical amplifiers, following gain compression caused by ultrashort optical pulse excitation, have been studied for several devices of different structures. Fast, slow, and intermediate time constants are identified. The fast component (0.6 to 0.9 ps) corresponds to cooling of the dense, inverted electron-hole plasma. The slow component (150 to 300 ps) corresponds to replenishment of carriers from the external bias supply, with the dynamics dominated by spontaneous recombination (primarily Auger) of the electron-hole plasma. The intermediate time constant (2 to 14 ps) is caused by carrier capture by the quantum wells and is structure-dependent. For most of the devices, the capture process is dominated by diffusion-limited transport in the cladding/barrier region. The variation of carrier density and temperature also affects the refractive index profile of the devices and, hence, affects the waveguiding properties. Dynamical variation of the mode confinement factor is observed on the fast and slow timescales defined above.
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    URL: http://dx.doi.org/10.1007/BF00326659
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    Carrier dynamics and gain saturation in quantum-well lasers (1994)
    Springer
    Optical and quantum electronics 26 (1994), S. S757 
    Details
    ISSN: 1572-817X
    Source: Springer Online Journal Archives 1860-2000
    Topics: Electrical Engineering, Measurement and Control Technology , Physics
    Notes: Abstract A Monte Carlo technique has been developed to investigate the carrier dynamics and static gain saturation in graded-index separate confinement heterostructure quantumwell laser structures. The calculated electron relaxation times and gain compression coefficient show good agreement with published experiments.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00326660
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    Analysis of the effects of doping and barrier design on the small-signal modulation characteristics of long-wavelength multiple quantum well lasers (1994)
    Springer
    Optical and quantum electronics 26 (1994), S. S805 
    Details
    ISSN: 1572-817X
    Source: Springer Online Journal Archives 1860-2000
    Topics: Electrical Engineering, Measurement and Control Technology , Physics
    Notes: Abstract This theoretical work has modelled the small signal response of InGaAsP and InGaAlAs multiple quantum well (MQW) lasers based on an ambipolar carrier transport model. The MQW parameters such as barrier bandgap, barrier width and the number of quantum wells have been optimized for high-speed modulation. The effect of the p-type doping and the strain of the InGaAs well have also been investigated. For the InGaAsP-based system, the optimization for maximum 3 dB bandwitdth shows that the optimum width is about 5 nm for 1.1 μm barriers and 7 nm for 1.2 μm barriers. The optimum barrier bandgap wavelength is about 1.1 μm for the barrier width of 6 nm, about 1.15 μm for 8 nm and 10 nm barriers. The p-doped MQW exhibits a higher modulation bandwidth because of its high differential gain and improved carrier distribution among the MQWs. The compressively strained InGaAs quantum well system has the potential for a higher modulation bandwidth. For the InGaAlAs-based system, the optimization for maximum 3 dB bandwidth shows that the optimum width is about 4 nm for a barrier wavelength of 1.10 μm, and 6 nm for 1.2 μm. The optimum barrier bandgap wavelength is about 1.1 μm for a barrier width of 4 nm, and about 1.2 μm for 6, 8 and 10 nm.
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    URL: http://dx.doi.org/10.1007/BF00326663
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    A frequency response model in multiquantum well lasers with unequilibrium carrier transport (1994)
    Springer
    Optical and quantum electronics 26 (1994), S. S789 
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    ISSN: 1572-817X
    Source: Springer Online Journal Archives 1860-2000
    Topics: Electrical Engineering, Measurement and Control Technology , Physics
    Notes: Abstract A carrier transport model to explain the high-frequency response in high-speed MQW lasers is described. The ambipolar approximation, which is unsuitable for dealing with the high-speed carrier dynamics in MQW structures, was not adopted for small-signal analysis. The carrier transport effect can be characterized by four time constants: the electron transport time, τbmn; the hole transport time, τbmp; the electron escape time, τwbn; and the hole escape time, τwbp. The frequency response was interpreted as the sum of the constant response term due to the fast electron current and the roll-off term due to the slow hole transport time. The ratio of the electron contribution to the total response was proportional to the ratio of electron contribution to the total differential gain, ξ, and reciprocally proportional to χn0 = 1 + τbmn/τwbn. The value of ξ was calculated to be about 0.5 for typical MQW lasers. The roll-off frequency is mainly determined by . The ratio χp0 = 1 + τbmp/τwbp affects the resonant frequency and the damping rate in the high-bias condition.
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    URL: http://dx.doi.org/10.1007/BF00326662
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    Modelling carrier dynamics and small-signal modulation response in quantum-well lasers (1994)
    Springer
    Optical and quantum electronics 26 (1994), S. S767 
    Details
    ISSN: 1572-817X
    Source: Springer Online Journal Archives 1860-2000
    Topics: Electrical Engineering, Measurement and Control Technology , Physics
    Notes: Abstract This paper discusses models of carrier dynamics and modulation response in quantum-well lasers. We present a detailed carrier dynamics model that takes into account the different roles played by holes and electrons in such quantum-well lasers, the internal Coulomb field resulting from the mutual interaction of electrons and holes, and the effect of that field on the energy bands. We further address the ability to construct a simpler model that in the limited context of small-signal excitations yields results that are reasonably consistent with those of the detailed model. We compare that simple model to other common simple models and demonstrate the significance of identifying the important parameters in a simple model via self-consistent extraction from detailed calculations. We identify the equilibrium ratio of confined carriers to confinement region carriers, the local capture time and the transport time as the crucial parameters of any simple model.
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    URL: http://dx.doi.org/10.1007/BF00326661
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    Hybrid surface plasmon polaritons guided by ultrathin metal films (1994)
    Springer
    Optical and quantum electronics 26 (1994), S. 857-863 
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    ISSN: 1572-817X
    Source: Springer Online Journal Archives 1860-2000
    Topics: Electrical Engineering, Measurement and Control Technology , Physics
    Notes: Abstract Hybrid surface plasmon polaritons propagating in a new configuration comprising an ultrathin metal film bounded by a positive birefringent crystal on one side and a glass material on the other side are investigated. The results show that the conditions for existence of such hybrid surface plasmon polaritons have a strong dependence on the structure parameters. This feature opens the way for a new type of optical sensor with directional sensitivity.
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    URL: http://dx.doi.org/10.1007/BF00435090
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    Carrier transport and its effect on the turn-on delay time in strained GalnAsP/InP multiple quantum well lasers (1994)
    Springer
    Optical and quantum electronics 26 (1994), S. S843 
    Details
    ISSN: 1572-817X
    Source: Springer Online Journal Archives 1860-2000
    Topics: Electrical Engineering, Measurement and Control Technology , Physics
    Notes: Abstract The effects of carrier transport on turn-on delay time in multiple quantum well lasers were investigated both theoretically and experimentally. By using rate equation analysis with two components of the carrier density inside and outside of the quantum wells, we found that carrier transport caused two important effects: one is the stationary effect of a significant reduction in carrier density in quantum wells; the other is an increase in differential carrier lifetime. As an experimental investigation, compressively strained 1.3 μm GalnAsP/InP multiple quantum well (MQW) lasers were fabricated and their turn-on delay times were measured and investigated. The short-cavity buried-heterostructure lasers showed low-threshold current (2 to 3 mA) and small turn-on delay time (〈200 ps) at biasless 30 mA pulse current. Although these performances are suitable for high-speed digital transmission, it was found that the carrier lifetimes derived from the turn-on delay measurement were larger for strained quantum well lasers than for conventional quantum well lasers and double heterostructure lasers. These phenomena are explained using the carrier transport model and are discussed. The solutions for further reduction in carrier lifetime and turn-on delay are discussed.
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    URL: http://dx.doi.org/10.1007/BF00326665
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    Detailed large-signal dynamic modelling of DFB laser structures and comparison with experiment (1994)
    Springer
    Optical and quantum electronics 26 (1994), S. S817 
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    ISSN: 1572-817X
    Source: Springer Online Journal Archives 1860-2000
    Topics: Electrical Engineering, Measurement and Control Technology , Physics
    Notes: Abstract This paper describes the first general large-signal dynamic multiple-mode laser model that incorporates all the main mechanisms known to influence the dynamic behaviour of DFB laser structures with the exception of thermal effects: longitudinal mode spatial hole burning, carrier transport effects, nonlinear gain, and laser and submount parasitics. The time evolution of the output power and wavelength of all modes is predicted, and full spectra can be plotted as a function of time. The model has been extended to include an approximation to the effects of propagation down dispersive fibre, thereby allowing the simulation of filtered received eye diagrams. Detailed comparison of the model with the experimental performance of 2×λ/8 DFB lasers has shown good agreement, allowing the performance to be optimized, particularly with respect to longitudinal hole burning and carrier transport. The model is also applied to gain-switched operation of 2×λ/8 DFB structures, fast pulsing of three-section λ/4 DFB lasers, and the dynamic behaviour of complex coupling coefficient DFB laser structures.
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    URL: http://dx.doi.org/10.1007/BF00326664
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    TM mode optical characteristics of five-layer MOS optical waveguides (1994)
    Springer
    Optical and quantum electronics 26 (1994), S. 877-884 
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    ISSN: 1572-817X
    Source: Springer Online Journal Archives 1860-2000
    Topics: Electrical Engineering, Measurement and Control Technology , Physics
    Notes: Abstract The field distribution and complex eigenvalue equation of the TM mode are solved from the wave equation for a five-layer optical waveguide with finite metal cladding and a dielectric buffer layer. For air−Au−SiO2−GaAs−AlGaAs MOS waveguides, numerical results for the propagation constant and absorption loss of the TM mode are computed in the complex plane from the eigenvalue equation. The effects of some guided structural parameters on the mode propagation and absorption loss are analysed and discussed.
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    URL: http://dx.doi.org/10.1007/BF00435092
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    Numerical model of a proposed double heterostructure light-emitting diode for mid-infrared applications (1994)
    Springer
    Optical and quantum electronics 26 (1994), S. 885-897 
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    ISSN: 1572-817X
    Source: Springer Online Journal Archives 1860-2000
    Topics: Electrical Engineering, Measurement and Control Technology , Physics
    Notes: Abstract A numerical model of a proposed InAs/InAs0.88Sb0.12 double heterostructure lightemitting diode (DH-LED) has been developed for its d.c. and transient characterization in the 3 to 5 μm wavelength region. The dependence of the optical power and bandwidth on interfacial recombination and self-absorption have been studied. The active layer width has been optimized against interfacial recombination and self-absorption for maximum optical power, bandwidth and power-bandwidth products. The dependence of the power-bandwidth product of the DH-LED on the drive current for different active layer doping concentrations has also been studied. The electrical confinement in the proposed heterostructure has been estimated and its variation with the active layer thickness has been studied. The rise time of the proposed LED has been calculated by using the results of the transient analysis. On the basis of the proposed model, the device is expected to find useful applications as an optical source in future generations of fibre-optic communication systems in the 3 to 5 μm wavelength region.
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    URL: http://dx.doi.org/10.1007/BF00435093
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    A new approach to phase-shifting for moiré: simultaneous retrieval of information corresponding to the difference-beat and sum-beat patterns (1994)
    Springer
    Optical and quantum electronics 26 (1994), S. 899-901 
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    ISSN: 1572-817X
    Source: Springer Online Journal Archives 1860-2000
    Topics: Electrical Engineering, Measurement and Control Technology , Physics
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00435094
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    Symmetrizing transformation of general astigmatic Gaussian beams (1994)
    Springer
    Optical and quantum electronics 26 (1994), S. 903-910 
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    ISSN: 1572-817X
    Source: Springer Online Journal Archives 1860-2000
    Topics: Electrical Engineering, Measurement and Control Technology , Physics
    Notes: Abstract The symmetrizing transformation of coherent general astigmatic Gaussian beams is analysed by the tensor ABCD law. It is shown in this paper that a nonorthogonal astigmatic Gaussian beam (with rotation) can be transformed into a rotationally symmetric one by the combination of four cylindrical lenses. A simple example is given.
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    URL: http://dx.doi.org/10.1007/BF00340557
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    Beam quality of high-power broad-area visible diode lasers (1994)
    Springer
    Optical and quantum electronics 26 (1994), S. 911-928 
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    ISSN: 1572-817X
    Source: Springer Online Journal Archives 1860-2000
    Topics: Electrical Engineering, Measurement and Control Technology , Physics
    Notes: Abstract We characterize the beam quality of visible-wavelength GRIN-SCH-SQW lasers in terms of geometry and driving current. A second-moment-based, free beam measurement of M 2 yields values ranging from near unity on the plane parallel to the junction, to near 10 in the perpendicular plane. The M 2 values exhibit a dependence on the shape of the L-I characteristic. Higher-order moments are uso quantitatively describe the changes in beam shape as a function of current, and a correlation between the kurtosis and M 2 is observed.
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    URL: http://dx.doi.org/10.1007/BF00340558
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    A representation of Kerr-like nonlinearity for the analytical TM surface polariton solution (1994)
    Springer
    Optical and quantum electronics 26 (1994), S. 865-876 
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    ISSN: 1572-817X
    Source: Springer Online Journal Archives 1860-2000
    Topics: Electrical Engineering, Measurement and Control Technology , Physics
    Notes: Abstract The TM-polarized waves propagating along the interface between a nonlinear Kerr-like material and linear cladding are investigated. We analyse the nonlinear dielectric permittivity as a function of the electromagnetic field. It is shown that an exact analytical solution of Maxwell's equations corresponding to the TM surface polariton in the form described by sech function do exist in a Kerr-like nonlinear medium with the permittivity profile given by a hypergeometric function. We compare our analytical solution and analogous exact numerical solution in a Kerr medium. The power flow down the interface between two media is also discussed.
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    URL: http://dx.doi.org/10.1007/BF00435091
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