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  • Articles  (1,341)
  • Springer  (1,341)
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  • 1992  (1,341)
  • Electrical Engineering, Measurement and Control Technology  (1,341)
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  • Articles  (1,341)
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  • 1990-1994  (1,341)
  • 1950-1954
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  • 1
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    Springer
    Circuits, systems and signal processing 11 (1992), S. 115-136 
    ISSN: 1531-5878
    Source: Springer Online Journal Archives 1860-2000
    Topics: Electrical Engineering, Measurement and Control Technology
    Notes: Abstract By considering all orderings of the input samples, which are discrete-time continuous-valued, it is shown here that a weighted median (WM) filter of spanN can be specified unambiguously by 2N−1 consistent linear inequalities relating the weights. This specification is identical to that of a self-dual threshold function with the same weights. It is also shown that WM filters with symmetric weights can be specified by ternary threshold functions. Based on these inequalities, properties of WM filters which can be used to check equivalence of some WM filters are derived.
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  • 2
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    Circuits, systems and signal processing 11 (1992), S. 137-151 
    ISSN: 1531-5878
    Source: Springer Online Journal Archives 1860-2000
    Topics: Electrical Engineering, Measurement and Control Technology
    Notes: Abstract Because binary mathematical morphology permits fast local neighborhood operations by flash conversion, it is used extensively in high-speed pattern-recognition computer systems. Further, since anyN-dimensional integer function may be represented by an (N + 1)-dimensional binary (bilevel) function, ordinary two-dimensional graylevel images become three-dimensional binary images. Thus these images may be processed by high-speed flash-conversion computers assuming that a sufficiently compact three-dimensional kernel can be devised. The tetradekahedron of the face-centered-cubic tessellation forms a perfect kernel in three-dimensions. Its neighborhood is compact. It has total symmetry with all 12 neighbors equidistant from the central element. Using this kernel a variety of useful three-dimensional morphological operations may be performed for target track detection, shaded graphics, data clustering, automated focusing, and spatial filtering.
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  • 3
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    Circuits, systems and signal processing 11 (1992), S. 153-169 
    ISSN: 1531-5878
    Source: Springer Online Journal Archives 1860-2000
    Topics: Electrical Engineering, Measurement and Control Technology
    Notes: Abstract Two techniques for image restoration are compared in this paper. One is a technique based on the theory of optimal adaptive stack filtering; the other is a recently developed vector detection approach to image restoration. The primary difference between these two techniques is that the optimal detection technique exploits multilevela priori information, while the stack filter uses only single level zero crossing information. The design constraints for stack filters and vector detection are similar. Both approaches rely on the existence of a training sequence for the image source in order to obtain optimal processing. Adaptive stack filters do, however, require a training set of the noise while the optimal detection approach only needs a multivariate parametric representation. The image-restoration performance of these two methods is compared in a signal dependent noise environment characterizing imaging systems with speckle, film-grain, and Poisson shot noise. Comparisons are made using the mean absolute error measure as well as a subjective measure.
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    Circuits, systems and signal processing 11 (1992), S. 325-352 
    ISSN: 1531-5878
    Source: Springer Online Journal Archives 1860-2000
    Topics: Electrical Engineering, Measurement and Control Technology
    Notes: Abstract The stability of digital ladder filters close in form, via the lossless discrete integrator (LDI) transformation, to doubly terminatedLC Cauer ladder low-pass filters is studied. The LDI transformation does not necessarily map stable analogue into stable digital filters. Necessary and sufficient conditions for these digital filter to be lossless and for a corresponding doubly terminated filter to be stable are given. LDIs are often used in the design of switched capacitor (SC) filters. For this case we provide a threshold sampling rate above which the SC LDI filter retains the stability of the analogue filter. In spite of the stability problem with the LDI mapping, it has been observed that when applied to simulate analogue filters the resulting filter is stable. It can now be argued that, in these cases, other factors in the determination of the sampling rate leads typically to a choice that is also sufficiently above the threshold rate for stability. The theory described is also useful to derive more general digital filters and to perform the design of stable LDI filters exclusively in the Z-plane without reference to analogue prototypes.
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  • 5
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    Circuits, systems and signal processing 11 (1992), S. 285-307 
    ISSN: 1531-5878
    Source: Springer Online Journal Archives 1860-2000
    Topics: Electrical Engineering, Measurement and Control Technology
    Notes: Abstract In this paper we describe a family of operators for constructing nontrivial left and right coprime factorizations under rather weak conditions for a large class of nonlinear feedback control systems that has a stabilizable or unstabilizable plant, using a common criterion of input-output stability. The proposed sufficiency and construction method are based on a generalization of the nonlinear Lipschitz operator theory formulated by us for such systems. This class of generalized nonlinear Lipschitz operators constitutes a very large family (an infinite-dimensional Banach space) of bounded nonlinear operators that describe (part of) the underlying systems. One of the main difficulties in constructing coprine factorizations for nonlinear feedback systems has been in taking care of the nonlinear composite and inverse operators that appear in the closed-loop configuration such that the overall feedback system is well defined in the sense of stability, causality, and uniqueness of the internal signals and such that the coprime factorizations can be achieved. In this paper we show how these difficult issues can be handled nicely under our framework of generalized nonlinear Lipschitz operator theory, at least for a very large class of nonlinear control systems. We give a simple illustrative example to show how these coprime factorizations can actually be characterized and constructed to yield explicit closed-form solutions.
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    Circuits, systems and signal processing 11 (1992), S. 387-398 
    ISSN: 1531-5878
    Source: Springer Online Journal Archives 1860-2000
    Topics: Electrical Engineering, Measurement and Control Technology
    Notes: Abstract In this paper we study the problem of designing a neural network that gives the correct binary representation of a given real number. Previously this problem has been studied by Tank and Hopfield. The network proposed by them exhibits “hysteresis” in the sense that the current vector of the network sometimes converges towards a binary vector that isnot the correct binary representation of the input current. The reason for this is that the network proposed by them has multiple asymptotically stable equilibria. In the present paper, we propose another neural network which has the property that it hasa single, globally attractive equilibrium for almost all values of the input current. Hence, irrespective of the initial conditions of the network, the current vector converges towards the correct binary representation of the input current.
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  • 7
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    Circuits, systems and signal processing 11 (1992), S. 421-430 
    ISSN: 1531-5878
    Source: Springer Online Journal Archives 1860-2000
    Topics: Electrical Engineering, Measurement and Control Technology
    Notes: Abstract Concepts of observability and strong observability for singular systems are introduced and characterized geometrically in terms of the system matrices without using the Weierstrass decomposition. Duality relations between observability and controllability and that between reachability and strong observability are established. A canonical form for the action of the output injection group on the set of observable systems is presented.
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    Circuits, systems and signal processing 11 (1992), S. 455-492 
    ISSN: 1531-5878
    Source: Springer Online Journal Archives 1860-2000
    Topics: Electrical Engineering, Measurement and Control Technology
    Notes: Abstract Mathematical morphology is becoming increasingly important in industrial vision applications for object recognition and defect inspection. In this paper we define a new function based on mathematical morphology, which we named the Rotationally Invariant Pecstrum (RIP). The RIP is proven to be invariant under rotation regardless of the shape of the structuring element. This paper also discusses how to use the RIP as an object descriptor and studies the effect of using different structuring elements on recognizing objects of different shapes.
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  • 9
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    Circuits, systems and signal processing 11 (1992), S. 493-508 
    ISSN: 1531-5878
    Source: Springer Online Journal Archives 1860-2000
    Topics: Electrical Engineering, Measurement and Control Technology
    Notes: Abstract This work presents close-form formulas for typical two-dimensional bandselect linear-phase FIR filters (e.g., band-pass, high-pass, and band-stop filters) optimal in the least-squares sense. Cases of both circular and elliptical symmetry are considered. The formulas refer to the coefficients of the frequency sampling form of the frequency response. Therefore they can either be directly used for filter implementation, if the frequency sampling structure is adopted, or used to obtain the impulse response coefficients via an inverse FFT.
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    Circuits, systems and signal processing 11 (1992), S. 3-4 
    ISSN: 1531-5878
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  • 11
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    Circuits, systems and signal processing 11 (1992), S. 5-6 
    ISSN: 1531-5878
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    Topics: Electrical Engineering, Measurement and Control Technology
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  • 12
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    Circuits, systems and signal processing 11 (1992), S. 431-439 
    ISSN: 1531-5878
    Source: Springer Online Journal Archives 1860-2000
    Topics: Electrical Engineering, Measurement and Control Technology
    Notes: Abstract An efficient design of digital differentiators (DD), with a variable frequency range of operation at low and midband frequencies, has been proposed. Implemented as a Taylor structure, a DD designed for orderN can be made to function as a universal configuration giving optimal transfer functions for all possible ordersN, without changing the coefficients.
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  • 13
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    Circuits, systems and signal processing 11 (1992), S. 443-454 
    ISSN: 1531-5878
    Source: Springer Online Journal Archives 1860-2000
    Topics: Electrical Engineering, Measurement and Control Technology
    Notes: Abstract For large-array processing problems there is a need for decentralized methods that are computationally efficient. A decentralized variant of the MUSIC algorithm, proposed in the literature, is here analysed from a statistical viewpoint, assuming that a large number of snapshots is available. As intuitively expected, the centralized MUSIC algorithm is more accurate than both the local and decentralized versions of MUSIC. More surprisingly, the decentralized variant of MUSIC is not always more accurate than the local MUSIC estimates. The theoretical analysis is supported by numerical examples.
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  • 14
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    Circuits, systems and signal processing 11 (1992), S. 7-45 
    ISSN: 1531-5878
    Source: Springer Online Journal Archives 1860-2000
    Topics: Electrical Engineering, Measurement and Control Technology
    Notes: Abstract Within the last two decades a small group of researchers has built a useful, nontrivial theory of nonlinear signal processing around the median-related filters known as rank-order filters, order-statistic filters, weighted median filters, and stack filters. This required significant effort to overcome the bias, both in education and research, toward linear theory, which has been dominant since the days of Fourier, Laplace, and “Convolute.” We trace the development of this theory of nonlinear filtering from its beginnings in the study of noise-removal properties and structural behavior of the median filter to the recently developed theory of optimal stack filtering. The theory of stack filtering provides a point of view which unifies many different filter classes, including morphological filters, so it is discussed in detail. Of particular importance is the way this theory has brought together, in a single analytical framework, both the estimation-based and the structural-based approaches to the design of these filters. Some recent applications of median and stack filters are provided to demonstrate the effectiveness of this approach to nonlinear filtering. They include: the design of an optimal stack filter for image restoration; the use of vector median filters to attenuate impulsive noise in color images and to eliminate cross luminance and cross color in TV images; and the use of median-based filters for image sequence coding, reconstruction, and scan rate conversion in normal TV and HDTV systems.
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  • 15
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    Circuits, systems and signal processing 11 (1992), S. 171-193 
    ISSN: 1531-5878
    Source: Springer Online Journal Archives 1860-2000
    Topics: Electrical Engineering, Measurement and Control Technology
    Notes: Abstract The four different types of stack filters, type-0 through type-3, are determined by four different shapes of the on-set of the positive Boolean function from which the stack filter is constructed. Under all three appending strategies commonly considered in the literature-first and last value carry-on strategy, constant value carry-on strategy, and the circular approach-stack filters of type-0 through type-2 possess the convergence property, while type-3 stack filters do not all share this property. Examples of cyclic behavior in type-3 stack filters are given. Conditions under which certain operations on stack filters which possess the convergence property produce other filters with this property are provided. In perhaps the most important result in this paper, it is shown that the root signal set of any type-3 stack filter is the intersection of the root sets of the type-1 and type-2 stack filters from which the type-3 filter is constructed. This should simplify the task of finding the set of roots of type-3 stack filters. The rates of convergence for stack filters of type-1 and type-2 are determined for each appending approach. The convergence behavior and rates of convergence of stack filters of type-1 and type-2 are then generalized to include type-1 and type-2 filters with indexi.
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    Circuits, systems and signal processing 11 (1992), S. 195-228 
    ISSN: 1531-5878
    Source: Springer Online Journal Archives 1860-2000
    Topics: Electrical Engineering, Measurement and Control Technology
    Notes: Abstract The present paper introduces a digital gray-scale morphological filtering technique that is based on postfiltering a given filter so the invariant class of the new filter is larger than the invariant class of the original filter. More specifically, the invariant class of the new filter contains the original invariant class together with all signals whose variation is below a chosen threshold. The postfiltering includes a single erosion and a single dilation by a one-parameter structuring element, the choice of parameter determining the resulting invariant class. While the methodology is quite general, the two applications considered pertain to moving averages with nonnegative weights and moving medians, both of which are morphological filters. Both suppress noise in a signal and each possesses specific advantages and disadvantages. In brief, means tend to give better noise suppression while blurring edges, whereas medians preserve edges, while at the same time flattening small background variation in the underlying signal. The new one-parameter family of filters derived from moving averages are called pseudomeans. The filters derived from medians are called pseudomedians. Both preserve uncorrupted low background variation, as well as steps. Because they preserve small variation while at the same time behaving like the original filters, both filters are especially effective when the noise occurs in bursts, rather than uniformly across the signal.
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  • 17
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    Circuits, systems and signal processing 11 (1992), S. 281-281 
    ISSN: 1531-5878
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    Topics: Electrical Engineering, Measurement and Control Technology
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    Circuits, systems and signal processing 11 (1992), S. ii 
    ISSN: 1531-5878
    Source: Springer Online Journal Archives 1860-2000
    Topics: Electrical Engineering, Measurement and Control Technology
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    Circuits, systems and signal processing 11 (1992), S. 229-252 
    ISSN: 1531-5878
    Source: Springer Online Journal Archives 1860-2000
    Topics: Electrical Engineering, Measurement and Control Technology
    Notes: Abstract A new class of morphological filters is proposed for image enhancement. The filter, known as the generalized morphological filter (GMF), uses multiple structuring elements and combines linear and morphological operations. The GMF can be designed to suppress various types of noise yet preserve geometrical structure in an image. A study of several aspects of the performance of the filter is presented. The study includes geometrical feature preservation, noise suppression, structuring element selection, and the root signal structure. For the sake of comparison, averaging and median filters are also used in the experiments and corresponding figures of merit of the performance of the filter. The empirical study shows that the generalized morphological filter possesses effective noise suppression with reduced geometrical feature blurring.
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    Circuits, systems and signal processing 11 (1992), S. 253-280 
    ISSN: 1531-5878
    Source: Springer Online Journal Archives 1860-2000
    Topics: Electrical Engineering, Measurement and Control Technology
    Notes: Abstract This paper presents the analysis and the implementation algorithms of the morphological skeleton transform (MST) of binary images. A general MST algorithm is provided from which different subclasses of MSTs can be derived by choosing different structuring elements. Three subclasses of MSTs are discussed in this paper: the uniform-step-distance MST (USDMST), the periodically-uniform-step-distance MST (PUSDMST) and the pseudo-Euclidean MST (PEMST). A general discrete distance called morphological distance relates distance measures to the definitions of structuring elements. The PEMST is proposed which uses isotropic discrete structuring elements called quasi-circular structuring elements (QCSE). The QCSEs of all integer sizes are composed by a dilation interpolation method so that they can be decomposed into simplest elements in order to reduce computation. The PEMST has better performance in terms of rotation-invariance than any existing MSTs. The algorithm has an approximately linear computational complexity. Finally, the implementation of the three MSTs are discussed.
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    Circuits, systems and signal processing 11 (1992), S. 309-324 
    ISSN: 1531-5878
    Source: Springer Online Journal Archives 1860-2000
    Topics: Electrical Engineering, Measurement and Control Technology
    Notes: Abstract Dual time-scale sampling with intermediate discrete filtering, called moving-average skip sampling, is introduced to overcome the problem of unstable zeros of the sampled system. The new scheme proves easy to implement and efficiently recovers the minimum-phase property of the continuous system at major sampling intervals. An example illustrates the effect of moving-average skip sampling on the nonminimum-phase zeros.
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    Circuits, systems and signal processing 11 (1992), S. 47-108 
    ISSN: 1531-5878
    Source: Springer Online Journal Archives 1860-2000
    Topics: Electrical Engineering, Measurement and Control Technology
    Notes: Abstract This paper consists of a tutorial overview of morphological filtering, a theory introduced in 1988 in the context of mathematical morphology. Its first section is devoted to the presentation of the lattice framework. Emphasis is put on the lattices of numerical functions in digital and continuous spaces. The basic filters, namely the openings and the closings, are then described and their various versions are listed. In the third section morphological filters are defined as increasing idempotent operators, and their laws of composition are proved. The last sections are concerned with two special classes of filters and their derivations: first, the alternating sequential filters allow us to bring into play families of operators depending on a positive scale parameter. Finally, the center and the toggle mappings modify the function under study by comparing it, at each point, with a few reference transforms.
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    Circuits, systems and signal processing 11 (1992), S. 109-114 
    ISSN: 1531-5878
    Source: Springer Online Journal Archives 1860-2000
    Topics: Electrical Engineering, Measurement and Control Technology
    Notes: Abstract LetX 1,X 2,... be a stationary sequence of random variables with Pr{X t, ≤x}=F(x),t=1, 2,... Also let i ∶n,(t) ,i=1,...,n, denote the ith order statistic (OS) in the moving sample (X t−N ,...,X t,...,X t+N) of odd sizen=2N+1. ThenY t=∑a i X i ∶n(t) with ∑a i=1 is an order-statistics filter. In practicea i≥0,i=1,...,n. Fort〉N, the sequence {Y t} is also stationary. IfX 1 X 2, ... are independent, the autocorrelation function ρ(r)=corr(Y t,Y t+r) is zero forr 〉n − 1 and forr ≤n − 1 can be evaluated directly in terms of the means, variances, and covariances of the OS in random samples of sizen +r fromF(x). In special cases several authors have observed that the spectral density functionf(ω) of {Y t} is initially decreasing for ω 〉 0. This result is made more precise and shown to hold generally under white noise. The effect of outliers (impulses) is also discussed.
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    Circuits, systems and signal processing 11 (1992), S. 353-362 
    ISSN: 1531-5878
    Source: Springer Online Journal Archives 1860-2000
    Topics: Electrical Engineering, Measurement and Control Technology
    Notes: Abstract It is well known that the sequence ofs-numbers {sn},n=0, 1,..., of a compact operator, and particularly a compact Hankel operator Γ=[h j+k −1], converges monotonically to zero. Since the (n + 1)sts-number sn measures the error ofL ∞(¦z¦=1) approximation, modulo an additive H∞ function, by nth degree proper rational functions whose poles are restricted to ¦z¦ 〈 1, it is very important to study how fast {s n } converges to zero. It is not difficult to see that ifh n =O(n −α), for someα 〉 1, thens n =O(n −α). In this paper we construct, for any given sequenceɛ n ↓ 0, a compact Hankel operator Γ such thats n ≥ɛ n for alln.
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    Circuits, systems and signal processing 11 (1992), S. i 
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    Circuits, systems and signal processing 11 (1992), S. 365-376 
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    Topics: Electrical Engineering, Measurement and Control Technology
    Notes: Abstract This paper addresses the problem of robust linear estimations of systems perturbed by noise with a wide sense stationary (WSS) process, with its spectral density known only to be in a neighborhood of some specified spectral density. The asymptotic efficiency of the least-square (LS) estimator relative to the best linear unbiased estimator (BLUE) is known to depend upon the degree of the variance of the spread of the noise spectral density at the frequencies where the spectral mass of the system's impulse response function is concentrated. A signal estimator in the frequency domain is considered and it is demonstrated that where the Fourier transform is applied to the observed data, robust estimation occurs.
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    Circuits, systems and signal processing 11 (1992), S. 377-385 
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    Topics: Electrical Engineering, Measurement and Control Technology
    Notes: Abstract Fast progressive reconstruction (FPR) of images based on discrete Fourier transform (DFT) and Walsh-Hadamard transform (WHT) has been developed by Takikawa [3]. This technique is now extended to the discrete cosine transform (DCT). The quality of reconstructed images during the intermediate stages based on these transforms is analyzed. This comparison is both subjective and objective. The feasibility of the DCT in this FPR scheme is discussed.
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    Circuits, systems and signal processing 11 (1992), S. 399-419 
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    Topics: Electrical Engineering, Measurement and Control Technology
    Notes: Abstract In contrast to 1-D systems, the 2-D systems have no natural notion of “causality.” An artificial restriction traditionally imposed to allow recursive solution of these systems is that of “recursibility.” In this paper we study 2-Dsingular systems, taking advantage of the nonoriented or noncausal nature of these systems to provide a solution even if the requirement of recursibility does not hold. It is shown thatnonrecursible masks may be described using singular 2-D systems. The analysis approach relies on thefundamental matrix.
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    Mathematics of control, signals, and systems 5 (1992), S. 1-22 
    ISSN: 1435-568X
    Keywords: Distributed parameter system ; Strong stabilization ; Stable compensator ; Parity interlacing condition ; Callier-Desoer class
    Source: Springer Online Journal Archives 1860-2000
    Topics: Electrical Engineering, Measurement and Control Technology , Mathematics , Technology
    Notes: Abstract It is proved that a multivariable distributed system, that has no poles on the boundary of the half-plane of analyticity of its transfer function, can be stabilized with a stable strictly proper lumped compensator if and only if the standard parity interlacing condition is satisfied. The problem is formulated and solved in a Banach algebra of transfer functions that are Laplace transforms of measures having a finite total variation with respect to some given submultiplicative weight function. In particular, this result can be applied to transfer functions in the Callier-Desoer class, and it seems to be new even for this class. The proofs are closely related to and based on the scalar case solved previously.
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    Mathematics of control, signals, and systems 5 (1992), S. 23-39 
    ISSN: 1435-568X
    Keywords: Adaptive algorithms ; Condition estimation ; Recursive least squares ; Signal processing ; Singular values
    Source: Springer Online Journal Archives 1860-2000
    Topics: Electrical Engineering, Measurement and Control Technology , Mathematics , Technology
    Notes: Abstract We apply a fast adaptive condition estimation scheme, calledACE, to recursive least squares (RLS) computations in signal processing.ACE is fast in the sense that onlyO(n) operations are required forn parameter problems, and is adaptive over time, i.e., estimates at timet are used to produce estimates at timet + 1. RLS algorithms for linear prediction of time series are applied in various fields of signal processing: identification, estimation, and control. However, RLS algorithms are known to suffer from numerical instability problems under finite word-length conditions, due to ill-conditioning. We apply adaptive procedures, linear in the order of the problem, for accurately tracking relevant extreme eigen-values or singular values and the associated condition numbers over timet. In this paper exponentially weighted data windows are considered. The sliding data window case, which involves downdating as well as updating, is considered else-where. Numerical experiments indicate thatACE yields an accurate, yet inexpensive, RLS condition estimator for signal processing applications.
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    Mathematics of control, signals, and systems 5 (1992), S. 117-149 
    ISSN: 1435-568X
    Keywords: Hankel matrices ; Manifolds ; Partial realization ; Cell decomposition ; Bruhat decomposition ; Principal minors
    Source: Springer Online Journal Archives 1860-2000
    Topics: Electrical Engineering, Measurement and Control Technology , Mathematics , Technology
    Notes: Abstract In this paper we study the topology of manifolds of rectangular Hankel matrices, motivated by the problem of partial realization. Following Fischer and Frobenius, we introduce a rank-preserving Gl(2, ℝ)-action on the space Hank(M × N) of all realM × N Hankel matrices. We derive an explicit formula for the firstn x n principal minor of transformed Hankel matrices. Extending the earlier work of Brockett, the formula is applied to introduce a manifold structure on the space Hank(n, M × N) of allM × N Hankels of rankn. We construct a cell decomposition of Hank(M × N) which induces a cellular subdivision on each of the manifolds Hank(n, M × N) wheren ≤ min (M, N). This new cell decomposition is applied to investigate the topology of partial realizations.
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    Mathematics of control, signals, and systems 5 (1992), S. 41-66 
    ISSN: 1435-568X
    Keywords: Local controllability ; Normal reachability ; Measurable controls ; Control approximations
    Source: Springer Online Journal Archives 1860-2000
    Topics: Electrical Engineering, Measurement and Control Technology , Mathematics , Technology
    Notes: Abstract We introduce a local property of nonlinear systems called the nontangency property and we show that, in the presence of this nontangency property, small-time local controllability by measurable controls implies small-time local controllability by piecewise-constant controls; furthermore, the initial state is normally reachable from itself in arbitrarily small time. The class of systems that are small-time locally controllable and satisfy the nontangency property is shown to contain all real-analytic systems, all smooth systems with the Lie-algebra rank condition, and all locally boundedC 1 systems. Some consequences of small-time normal self-reachability are also discussed.
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    Mathematics of control, signals, and systems 5 (1992), S. 67-79 
    ISSN: 1435-568X
    Keywords: Hankel norm ; Rational approximation ; Order of approximation ; Wiener class
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    Notes: Abstract The problem of approximating Hankel operators of infinite rank by finite-rank Hankel operators is considered. For efficiency, truncated infinite Hankel matrices Γn of Γ are utilized. In this paper for any compact Hankel operator Γ of the Wiener class, we derive the rate of l2-convergence of the Schmidt pairs of Γn to the corresponding Schmidt pairs of Γ. For a certain subclass of Hankel operators of the Wiener class, we also obtain the rate of l1-convergence. In addition, an upper bound for the rate of uniform convergence of the rational symbols of best rank-k Hankel approximants of Γn to the corresponding rational symbol of the best rank-k Hankel approximant to Γ asn → ∞ is derived.
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    Mathematics of control, signals, and systems 5 (1992), S. 81-91 
    ISSN: 1435-568X
    Keywords: Deflection ratio ; Generalized signal-to-noise ratio ; Quadratic detection ; Stochastic signal detection ; Reproducing kernel Hilbert space
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    Topics: Electrical Engineering, Measurement and Control Technology , Mathematics , Technology
    Notes: Abstract The generalized signal-to-noise ratio (GSNR) is a measure of performance often used in evaluating binary hypothesis testing procedures. In this paper, we investigate the properties of the GSNR as applied to the evaluation of quadratic detectors with Gaussian hypotheses. Appealing to reproducing kernel Hilbert space theory, we give a representation for the GSNR that is particularly useful for evaluating extremal properties. Finally, we discuss an alternative performance measure that is both intuitively appealing and superior to the GSNR in some respects.
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    Mathematics of control, signals, and systems 5 (1992), S. 93-114 
    ISSN: 1435-568X
    Keywords: Ergodic control ; Singular control ; Bounded variation control ; Diffusion process ; Dynamic programming ; Reflected diffusion
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    Notes: Abstract A multidimensional Wiener process is controlled by an additive process of bounded variation. A convex nonnegative function measures the cost associated with the position of the state process, and the cost of controlling is proportional to the displacement induced. We minimize a limiting time-average expected (ergodic) criterion. Under reasonable assumptions, we prove that the optimal discounted cost converges to the optimal ergodic cost. Moreover, under some additional conditions there exists a convex Lipschitz continuous function solution to the corresponding Hamilton-Jacobi-Bellman equation which provides an optimal stationary feedback control.
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    Mathematics of control, signals, and systems 5 (1992), S. 365-390 
    ISSN: 1435-568X
    Keywords: Automata ; Invertibility ; Observability ; Resiliency ; Error recovery ; Discrete-event dynamic systems
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    Topics: Electrical Engineering, Measurement and Control Technology , Mathematics , Technology
    Notes: Abstract In this paper we consider a class of Discrete-Event Dynamic Systems (DEDS) modeled as finite-state automata in which only some of the transition events are directly observed. An invertible DEDS is one for which it is possible to reconstruct the entire event string from the observation of the output string. The dynamics of invertibility are somewhat complex, as ambiguities in unobservable events are typically resolved only at discrete intervals and, perhaps, with finite delay. A notion of resiliency or error recovery is developed for invertibility, and polynomial-time tests for invertibility and for resilient invertibility, as well as a procedure for the construction of a resilient inverter, are discussed.
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    Optical and quantum electronics 24 (1992), S. 647-659 
    ISSN: 1572-817X
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    Notes: Abstract Usually, coupling coefficients of parallel weakly-guiding waveguides of arbitrary crosssectional shape with uniform infinite cladding are calculated via two-dimensional overlap integrals of the refractive-index distribution of the concerned waveguide core and the field distributions of the two coupling isolated-core modes. In this paper it is shown that, in the case of synchronous coupled modes, the calculation can be reduced to the evaluation of a line integral involving only the field functions. Convenient formulations are obtained for typical forms of the field representation.
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    Notes: Abstract The large nonlinearities of the solutions of a new type of rare-earth complexes RE(TTA)4:HP, synthesized by ourselves, are experimentally demonstrated. The critical powers for the self-trapping of a laser beam in the solutions were measured. The dependence of the self-trapping critical powers on the absorptivity of the solutions and the type of solute complexes was found. The analysis for the experimental results shows that the effects of self-focusing and self-trapping of light in the solutions are not due to the change of molecular local density but the thermo-optical nonlinearities of the dissolved molecules themselves.
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    Optical and quantum electronics 24 (1992), S. 661-676 
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    Notes: Abstract A transfer function of the thermal FM response of laser diodes is theoretically derived that is in excellent agreement with the experimentally measured FM response and agrees in general with an empirical expression reported earlier in the literature. The characteristic dip in the overall sinewave FM response and the time-domain stepresponse of the laser diode are analysed theoretically as a function of a thermal cutoff frequency and the ratio of thermal FM at d.c. to the carrier FM at d.c. From the step response analysis, the lower bound on the bit rate for penalty-free Alternate Mark Inversion FSK (AMI-FSK) transmission is derived which tallies well with the experimental observations. A first-order equalization network to correct the drooping nature of the FSK output pulse response is analysed theoretically.
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    Optical and quantum electronics 24 (1992), S. 631-646 
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    Notes: Abstract The mutual intensity of the optical field in the Fraunhofer diffraction region produced from the end of an optical fibre under illumination of a coherent beam, is theoretically analysed by using an optical fibre-end source model. In this source model, the optical field at the end of the fibre is expressed as an aggregation of independent plane waves with random directions and phases, because the guided modes propagating through the fibre may be regarded as a stochastic process. It is found that the optical field in the diffraction region from the multimode optical fibre is not homogeneous butquasi homogeneous in a statistical sense. The spatial coherence properties in the field are discussed in connection with theV number (the normalized frequency) of the fibre and in comparison with those in the field produced from an incoherent source obeying the van Cittert-Zernike theorem.
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    Optical and quantum electronics 24 (1992), S. 677-690 
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    Notes: Abstract A numerical study of the state and degree of polarization along single-polarization fibres has been carried out on the basis of Müller-Stokes matrix approach and the mode coupling centre model. The general quasimonochromatic case is considered. Correspondence between polarization holdingh-parameter and the mode coupling centres' parameters has been established. The spectral average process has been considered and a novel criterion has been proposed. Expressions for the degree of polarization along the fibre have been derived for the cases of guided mode excitation and nonpolarized input. The degree of polarization has been shown to tend to a saturation level which depends on theh-parameter, the differential mode attenuation gDα and the coherence lengthL γ in the fibre.
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    Optical and quantum electronics 24 (1992), S. 703-703 
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    Optical and quantum electronics 24 (1992), S. 691-701 
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    Notes: Abstract For a nonlinear three-core fibre coupler an important subclass of solutions has been investigated analytically. These are the stationary solutions or nonlinear eigenmodes. Their stability is checked using an exact method as well as the linear perturbation method, and numerical tests.
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    Optical and quantum electronics 24 (1992), S. 704-704 
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    Optical and quantum electronics 24 (1992), S. 719-735 
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    Notes: Abstract Developments of narrow-linewidth distributed-Bragg-reflection (DBR) and distributed-feed-back (DFB) lasers are described. The design of a narrow-linewidth DBR laser is described in detail. Kl optimization from the viewpoint of narrow-linewidth operation and stable single mode operation is discussed. The linewidth dependences on cavity length, facet reflectivity and threshold current density are investigated. Some approaches to suppressing spatial hole burning in DFB lasers are described.
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    Optical and quantum electronics 24 (1992), S. 705-717 
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    Notes: Abstract Mode-locked diode-pumped solid state lasers have become important sources for efficient and reliable short pulse generation. We review techniques for active mode-locking of diode-pumped lasers, highlighting techniques which have produced much shorter pulse durations than previous technologies and extended operating repetition rates to the several gigahertz regime. To achieve even shorter pulse durations a series of nonlinear passive mode-locking techniques have been developed. Self-starting additive pulse mode-locking, resonant passive mode-locking and self-mode-locking of diode-pumped solid-state lasers are described.
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    Optical and quantum electronics 24 (1992), S. 737-743 
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    Optical and quantum electronics 24 (1992), S. 775-781 
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    Notes: Abstract This paper reports theoretical and experimental work on the dependence of semi-conductor laser operation on junction voltage saturation. The relation between junction voltage saturation and the reliability of semiconductor lasers is discussed.
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    Optical and quantum electronics 24 (1992), S. 755-773 
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    Notes: Abstract A simple and easily programmable approach based on the resonance method has been developed for analysing optical waves guided by complicated configurations such as multilayer dielectric structures with arbitrary nonlinear media. In this formulation both TE and TM polarizations are considered. In the present paper, as an example of the resonance technique application, the five-layer waveguiding configuration, including two arbitrary nonlinear media along with a linear film of arbitrary profile, is treated. Numerical results are presented in the form of guided power versus propagation constant for various parameters of the problem.
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    Optical and quantum electronics 24 (1992), S. 745-753 
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    Notes: Abstract Four-wave mixing equations in photorefractive media are approximated by different dynamical models and treated by different numerical methods. It is shown that the onset of instabilities and irregular behaviour in the same crystal, with a single wave mixing region, may be dependent both on the model used and the numerical method applied. Long-time irregular dynamics following from any finite-order difference schemes should be viewed with caution.
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    Optical and quantum electronics 24 (1992), S. 801-824 
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    Notes: Abstract The basic ideas and current state of the art of ultrashort pulse generation by injection lasers are reviewed. All developed techniques, including gain switching,Q-switching, and mode-locking are described and compared. A simple theoretical treatment of a diode laser which emits picosecond light pulses is discussed. Some fundamental limits of the pulse parameters are discussed. Finally, compression of chirped optical pulses by optical fibres and the soliton effect is considered.
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    Optical and quantum electronics 24 (1992), S. 825-832 
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    Notes: Abstract We report for the first time the determination of the real part of the third order nonlinear susceptibilitiesχ (3) (−ω, ω, 0, 0) in the isotropic phase of two nematic liquid crystalsp-(ethoxybenzylidine)-p-butylaniline (EBBA) andp-(methoxybenzylidene)-p-butylaniline (MBBA) from electrooptic Kerr effect experiments. The highest value ofχ (3) observed near nematic-to-isotropic transition temperature, at 632.8 nm is found to be 1.067×10−20 m2V−2 for EBBA and 6.602×10−20 m2V−2 for MBBA.
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    Optical and quantum electronics 24 (1992), S. 783-800 
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    Notes: Abstract Recent progress is reviewed in surface-normal optoelectronic devices primarily for use in optical switching and information processing. A type of optoelectronic integrated circuit (OEIC), the surface-normal two-dimensional array, is fabricated using these devices. This improves on first-generation OEICs by featuring large-scale integration in a small area, which results in a higher production yield. It also has structures which can easily be integrated with electronic circuits and can meet multichannel requirements. This approach supports optoelectronic progress towards optical information processing.
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    Optical and quantum electronics 24 (1992), S. 833-839 
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    Notes: Abstract The 5×5 coupler is of interest because of its application to coherent detection. The supermodes of the entire structure are determined by analysing the coupling of the component fibre modes through coupled-mode theory. The beating of the supermodes along the coupler determines the output power in each of the cores. Equal power splitting is a requirement for coherent detection. We show that this condition is not easily satisfied.
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    Optical and quantum electronics 24 (1992), S. 841-849 
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    Notes: Abstract Extremely stable and self-starting operation of a self-mode-locked Ti:Al2O3 laser can be achieved by incorporating a jet of dilute saturable absorber in the laser resonator. We have demonstrated a laser which generates pulses as short as 47 fs, with 700 mW average power near 800 nm when pumped by 7 W from an all-lines argon laser. A mixture of saturable absorber dyes starts the mode-locking process but does not restrict the tuning range of the laser. Pulses less than 100 fs in duration are generated at wavelengths between 700 nm and 900 nm with two sets of optics. Pulses of 100 fs from this laser have been compressed to 26 fs with standard fibre-prism techniques.
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    Notes: Abstract Developments in ultrafast Ti:sapphire laser technology can be applied in the investigation of nonlinear optical processes. We describe the application of a self-sustaining femtosecond Ti:sapphire laser as an illumination source in the field of confocal laser scanning fluorescence microscopy (LSM). We present spectra for various fluorescent stains under two-photon excitation and present LSM images of stained samples under mode-locked illumination. The potential for such a system as a non-destructive technique for studying live cells in biomedical research is discussed.
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    Optical and quantum electronics 24 (1992), S. vii 
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    Optical and quantum electronics 24 (1992), S. S861 
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    Notes: Abstract A survey is given on the various algorithms to describe the propagation of radiation fields in the paraxial approximation, starting with the Kirchhoff-Fresnel-Collins-integral and ending with the intensity moments and the generalizedABCD-law. The importance of characterizing beam quality for technical applications by suitable parameters is pointed out. The two competing definitions of beam parameters, intensity moments and power content values are discussed.
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    Optical and quantum electronics 24 (1992), S. S865 
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    Notes: Abstract Description of the transformation properties of the beam waist parameters of an astigmatic Gaussian beam by a medium characterized by an ABCD matrix is presented. Transformations by thin and thick lenses are considered in detail. We conclude that both astigmatism and ellipticity of the beam can be corrected but not simultaneously. The corrections can be carried out by both proper selection of lens position and of the lens thickness as well; however, in the latter case limitations hold for possible lens positions.
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    Optical and quantum electronics 24 (1992), S. S903 
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    Notes: Abstract The properties of unstable resonators in on-axis and off-axis geometry were investigated both theoretically and experimentally. Diffraction loss, mode structure, beam quality and misalignment sensitivity were measured in single-shot operation with a gas-cooled Nd: YAG slab laser (4×12×100 mm3) and compared with theoretical results obtained by solving the Fresnel integral equation numerically. The excellent agreement allowed detailed resonator optimization. Furthermore, the resonator performance in high-power operation was investigated with two water-cooled Nd: YAG slab lasers (6×25×163 mm3 and 7×26×191 mm3) capable of 670 W of output power. Beam quality near the diffraction limit and a maximum output power of 475 W was achieved with an on-axis unstable resonator with variable-reflectivity mirror.
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    Optical and quantum electronics 24 (1992), S. S881 
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    Notes: Abstract An analytic and measurable beam parameter is defined for beams emerging from heterojunction monomode diode lasers with very thin active layers, which provides a joint description of their focusing capabilities and far field divergence behaviour. This parameter can be of use as a figure of merit to compare either the output responses of this type of laser or the different optical systems employed to modify the laser beam. The minimum value of this parameter is determined. Also, it is shown that the beams emitted by these lasers cannot be transformed into circularly symmetric ones by anyABCD optical system. Finally, the possibility of achieving circularly symmetric intensities (at least to second order) and/or beam collimation at some plane is investigated, and its connection with the coupling efficiency between a monomode diode laser and an optical fibre is pointed out.
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    Optical and quantum electronics 24 (1992), S. S889 
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    Notes: Abstract The output characteristics of several large-area multichannel unstable resonators are presented. The conventional unstable resonator and a novel toric unstable resonator, in both confocal and nonconfocal configurations, have been studied. Output beam profiles, optical energy extraction, beam focusability, resonator alignment properties and polarization states of the various resonators have been analysed in depth.
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    Optical and quantum electronics 24 (1992), S. S873 
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    Notes: Abstract The orientation of a general partially coherent beam is described by introducing two pairs of orthogonal axes defined in terms of the second-order coherence features of the field. A general classification scheme for light beams is presented, based on their rotational behaviour under free propagation. This behaviour could be inferred from the values of certain measurable parameters at some plane. As an example of interest, the above classification is applied to Gaussian (coherent) beams with general astigmatism.
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    Optical and quantum electronics 24 (1992), S. S927 
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    Notes: Abstract The properties of the phase space beam analyser (PSBA), first introduced by Nemes, were investigated theoretically and experimentally. This optical system enables one to measure far-field divergence and beam radius of a laser beam simultaneously. Experiments were performed with a pulsed Nd: YAG laser with stable and unstable resonators and with a HeNe laser in fundamental mode operation. The theoretical description was based on Fresnel integrals, which were solved numerically using a FFT algorithm. The results presented indicate that the PSBA provides a simple means to determine beam quality and to investigate the mode properties of optical resonators, if diffraction effects are properly compensated.
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    Optical and quantum electronics 24 (1992), S. S963 
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    Notes: Abstract We describe a novel apparatus which measures the waist, its position and the amplitudes of the transverse modes in a laser system starting from intensity measurements. The validity of our approach is confirmed by many numerical simulations and by preliminary experimental results.
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    Optical and quantum electronics 24 (1992), S. 31-40 
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    Notes: Abstract Nonlinear dual core couplers acting as switches and amplifiers can theoretically operate at arbitrarily low input power provided the device is sufficiently long. Two radically different strategies exist: one with touching cores and a device length many periods long and the other with cores well separated and a device length one or two periods long. We find that the many-period scheme is several times longer than the few-period scheme for switches and orders of magnitude longer for large amplification.
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    Optical and quantum electronics 24 (1992), S. 49-53 
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    Notes: Abstract The 4×4 ray transfer matrix method is extended to describe generalized multiple-prism dispersive systems of practical interest. Particular attention is given to the generalized optical path coefficient (B r )and the dispersion component (F r ).
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    Optical and quantum electronics 24 (1992), S. 41-48 
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    Notes: Abstract This paper presents a BER analysis for two types of optical FSK transmission systems using a Mach-Zehnder interferometer as a discriminator. In one case the discriminator is assumed to be kept on the transmitter side and in the second case, on the receiver side. The analysis takes into account the linewidth of the source and other noises in the system. The discriminator disperses the input pulse, and an optimum filter required to produce a raised cosine output pulse spectrum is proposed. Such an optimum filter gives the minimum noise bandwidth without causing any ISI at the decision instant. The values of the equivalent noise-bandwidth factorsI 2 andI 3 of the filter vary between 0.563 to 0.822 and 0.086 to 0.193, respectively, when the interferometer delay timeτ is varied from zero to bit time. BER curves are given for various conditions of the FSK systems. To avoid an error floor the linewidth of the source should be 〈0.01/τ.
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    Optical and quantum electronics 24 (1992), S. 1-30 
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    Notes: Abstract We review dispersion relations, which relate the real part of the optical susceptibility (refraction) to the imaginary part (absorption). We derive and discuss these relations as applied to nonlinear optical systems. It is shown that in the nonlinear case, for self-action effects the correct form for such dispersion relations is nondegenerate, i.e. it is necessary to use multiple frequency arguments. Nonlinear dispersion relations have been shown to be very useful as they usually only require integration over a limited frequency range (corresponding to frequencies at which the absorption changes), unlike the conventional linear Kramers-Krönig relation which requires integration over all absorbing frequencies. Furthermore, calculation of refractive index changes using dispersion relations is easier than a direct calculation of the susceptibility, as transition rates (which give absorption coefficients) are, in general, far easier to calculate than the expectation value of the optical polarization. Both resonant (generation of some excitation that is long lived compared with an optical period) and nonresonant ‘instantaneous’ optical nonlinearities are discussed, and it is shown that the nonlinear dispersion relation has a common form and can be understood in terms of the linear Kramers-Krönig relation applied to a new system consisting of the material plus some ‘perturbation’. We present several examples of the form of this external perturbation, which can be viewed as the pump in a pump-probe experiment. We discuss the two-level saturated atom model and bandfilling in semiconductors among others for the resonant case. For the nonresonant case some recent work is included where the electronic nonlinear refractive coefficient,n 2, is determined from the nonlinear absorption processes of two-photon absorption, Raman transitions and the a.c. Stark effect. We also review how the dispersion relations can be extended to give alternative forms for frequency summation which, for example, allows the real and imaginary parts ofχ (2) to be related.
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    Optical and quantum electronics 24 (1992), S. 55-66 
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    Notes: Abstract Two mechanisms of self-confinement of wave packets on different carrying frequencies in monomode optical fibre are investigated. It is shown that the equations describing the processes possess a Hamiltonian structure. A new class of asymptotically free soliton solutions are found. Two spectral bandwidths for self-confinement of the optical pulses are determined.
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    Optical and quantum electronics 24 (1992), S. 67-72 
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    Notes: Abstract A self-heated multikilohertz laser is reported which operates on the 452.9 nm cyclic transition of atomic iron. The iron atoms are provided by dissociation of iron bromide donor molecules, formedin situ by passing Ne-HBr buffer gas over iron pieces in the laser-discharge active region. The output characteristics of the laser are described. Laser oscillation predicted by Walteret al. (IEEE J. Quantum Electron. QE-2 (1966) 474) for the 583.4 nm transition of rhenium was searched for using the same laser device, but was not realized.
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    Optical and quantum electronics 24 (1992), S. 83-87 
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    Optical and quantum electronics 24 (1992), S. 73-82 
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    Notes: Abstract The operating characteristics of a small self-heated copper halide laser (λ=510.6 and 578.2 nm) are described, where the copper lasant atoms are produced by electric-discharge dissociation of copper bromide that is generatedin situ by flowing Ne-HBr gas mixture over copper pieces in the laser tube. The excitation technique permits fast startup (〈1 min to laser oscillation from cold), and rapid and simple control of the CuBr vapour pressure, simultaneously introducing H2 to increase the efficiency. Specific laser output energies and average powers of 12μJ cm−3 and 195 mW cm−3, respectively, are almost a factor of 2 higher than those previously reported in the literature for multi-kilohertz copper bromide lasers. A maximum power of 7.8 W was obtained from the 40 cm3 active region. At its highest efficiency (0.8%) the laser produced 6.1 W.
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    Optical and quantum electronics 24 (1992), S. 89-92 
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    Optical and quantum electronics 24 (1992), S. 93-94 
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    Optical and quantum electronics 24 (1992), S. 1137-1150 
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    Notes: Abstract Principles and applications of time-domain optical data storage using stimulated photon echo are briefly reviewed. Special emphasis is laid upon the comparison of this memory with holography; both memories use the interference between two optical waves. Some new experimental developments are introduced using samples of europium-ion-doped crystals, one of the most promising candidates in time-domain data storage. Some other topics, such as ultrafast data storage, time-domain data processing, and time- and spatial-image storage using photon echo, are also discussed.
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    Optical and quantum electronics 24 (1992), S. 1151-1163 
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    Notes: Abstract Basic structures and functions of optically addressed spatial light modulators (SLMs) are discussed in the context of system applications. The most important functions imposed on spatial light modulators are those of image acceptance and transducers. SLMs using ferroelectric liquid crystal (FLC) satisfy essential requirements for high levels of resolution, sensitivity and response speed. We specifically surveyed the current performance of bipolar-operational spatial light modulators (BSLMs) that sufficiently exploit the bistability of FLC to output reversibly positive and negative images and to store them. The high performance of BSLMs makes them useful for many optical applications including image processing and real-time holography.
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    Optical and quantum electronics 24 (1992), S. 1165-1172 
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    Notes: Abstract Based on the two-level model of recording and read-out of dynamic holographic gratings, precise expressions for wave amplitudes, diffraction efficiency and the gain coefficient representing the generalization of the corresponding formula by Kukhtarevet al. have been obtained. This model allows one to take into account the effect of the read-out beam on the holographic grating and to solve a problem of four-wave mixing in transmission geometry with wave depletion and arbitrary value of the spatial phase shift between the holographic grating and the interference pattern.
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    Optical and quantum electronics 24 (1992), S. 1173-1179 
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    Notes: Abstract A long train of actively mode-locked pulses is obtained from a negative feedback controlled Nd:YAG laser. The 70μs pulse train contains up to 0.1 J energy and the duration of the picosecond pulses is 120 ps. The laser is operated at a repetition rate of 20 Hz. ActiveQ-control of the cavity generates a short pulse train of duration 50 to 70 ns. An excellent peak-to-background intensity ratio of the correlation function for the picosecond pulses in the train of 5×103 is reported.
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    Optical and quantum electronics 24 (1992), S. 1181-1189 
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    Notes: Abstract New optoelectronic techniques for measuring semiconductor laser turn-on delay times and jitter with a picosecond temporal resolution are proposed and were employed for both conventional, homogeneous cavity and ion-bombarded picosecond diode laser characterization. Distinct differences in the characteristics of those lasers were found.
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    Optical and quantum electronics 24 (1992), S. 1191-1201 
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    Notes: Abstract An alternative theoretical analysis directed to obtaining a more accurate expression for the critical power in the symmetric nonlinear directional coupler, or other nonlinear, five-layer waveguiding structures, is reported. Our analysis works with the nonlinear supermodes of the waveguide, and it is presented as an improvement of the preceding study by Silberberg and Stegeman [1]. Numerical simulations comparing both techniques, and by means of the beam propagation method, are reported for a few cases. A set of three representative, power dependent parameters is proposed, in order to give a comprehensive view of the power flow between both branches in the device as a function of the excitation conditions.
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    Optical and quantum electronics 24 (1992), S. 1203-1207 
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    Optical and quantum electronics 24 (1992), S. 1213-1214 
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    Optical and quantum electronics 24 (1992), S. iii 
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    Optical and quantum electronics 24 (1992), S. S1215 
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    Notes: Abstract We demonstrate all-optical fibre switches, including soliton-dragging logic gates, soliton-interaction gates and soliton-trapping AND-gates, that have the potential of operating up to speeds of 0.2 Tbps. Solitons in fibres are attractive for ultrafast timedomain switching because they avoid pulse distortion during propagation and because they exhibit particle-like properties. Soliton-dragging logic gates satisfy all requirements for a digital optical processor and having switching energies approaching 1 pJ. In addition, soliton-dragging logic gates are one example of a more general timedomain chirp switch architecture in which a dispersive delay line acts as a ‘lever-arm’ to reduce the switching energy. Soliton-interaction gates are based on elastic collisions between solitons and illustrate that solitons can be used to implement conservative, billiard-ball logic operations. Soliton-trapping AND-gates are sensitive to the timing of the input pulses and display on/off contrast ratios greater than 20∶1. The soliton-trapping AND-gate can serve as the final stage in an all-optical system and as the interface to electronics. These ultrafast gates may prove advantageous in applications where the switch bandwidth limits the performance of the system
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    Optical and quantum electronics 24 (1992), S. S1237 
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    Notes: Abstract We present a theoretical overview of soliton switching phenomena in two-mode nonlinear couplers. By complementing numerical studies with perturbative or exact solitary wave solutions, one finds that nonlinear Schrödinger or sine-Gordon solitons tend to maintain their identity in the coupled systems. Moreover, the coupling itself may originate novel vector solitary waves, such as gap solitons in periodic media. The switching dynamics in the presence of dissipative perturbations such as linear gain or intrapulse Raman scattering is also discussed.
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    Optical and quantum electronics 24 (1992), S. S1269 
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    Notes: Abstract The spatial soliton plays a fundamental role as a robust, particle-like object which can be manipulated to switch or spatially scan collimated light channels or optical pulses which are incident at an oblique angle to an interface separating two or more selffocusing Kerr slab dielectrics. The underlying equivalent particle/multiparticle theory can also be employed to predict stability properties of nonlinear surface or guided waves, to derive an analytic expression for the nonlinear Goos-Hanchen shift at a nonlinear interface and to quantify the effect of material diffusion, linear and twophoton absorption on the switching behaviour of the light beam. Pulsed spatial switching effects are studied in order to illustrate the general predictive power of the equivalent particle theory.
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    Optical and quantum electronics 24 (1992), S. S1337 
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    Optical and quantum electronics 24 (1992), S. S1315 
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    Notes: Abstract A numerical study of continuous-wave and pulse propagation in three-core fibre nonlinear directional couplers is presented. Intensity dependent demultiplexing is illustrated; in particular, novel nonlinear behaviour where a very small change in peak input intensity alters the core from which a pulse emerges.
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    Optical and quantum electronics 24 (1992), S. S1325 
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    Notes: Abstract A numerical study of the all-optical switching properties of an active nonlinear directional coupler is presented. The switching power is reduced for both CW and soliton inputs because of the gain. The switching properties of the coupler are enhanced for solitons, which switch nearly completely. For ultrashort pulses, the effects of the bandwidth of the gain medium are considered by using a general form for the gain band. The gain spectrum of erbium is also considered as a specific example.
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    Optical and quantum electronics 24 (1992), S. S1295 
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    Notes: Abstract In this paper we summarize what is currently known about optical switching between bright bistable soliton states in one and higher dimensions. A guideline to selecting media with appropriate intensity-dependent refractive indices to support bistable solitary waves is presented. The stability criterion for robustness of the solitary waves is discussed. Finally, some methods and numerical examples of optical switching are presented.
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    Optical and quantum electronics 24 (1992), S. 1339-1341 
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    Notes: Abstract A new resonator geometry for optically pumped far-infrared lasers is suggested. First experimental results of a transversely pumped CW laser are reported.
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    Optical and quantum electronics 24 (1992), S. 1343-1350 
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    Notes: Abstract A resonantly photo-pumped soft x-ray laser process is studied for neon-like iron ions with an automatic line match scheme. The special advantages of this scheme are shown. The temporal characteristics of lasing gains and their dependences on the pump strength and electron density are investigated. Unlike the electron-collisional excitation and some other photo-pumped excitation schemes, it is demonstrated that main photopumped gains come from 2p-4d-3p-3s transition channels. Using the experimental data of pump strengths from a non-LTE plasma produced in our experiment as input data, our model yields a peak gain of 5.6 cm−1, 2.8 cm−1 and 1.9 cm−1 on the dominant lasing transitions at 38.74 nm, 25.47 nm and 20.46 nm.
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    Optical and quantum electronics 24 (1992), S. 1351-1358 
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    Notes: Abstract The concept of Fresnel number is discussed and expressions are derived for misaligned optical systems. For the case of perfectly aligned optical elements, the usual number,N, based on a Fresnel zone concept is found to be given byN = (a 2/λ)(D 1/B 1 +A 2/B 2), whereB 1,D 1 andB 2,A 2 are the transfer matrix elements of the optical systems before and after a circular aperture of radiusa respectively. A modified definition of the Fresnel number is proposed for Gaussian beam propagation. This parameterN′ G, is related to the complex beam parameter and may be represented by the angleθ = tan−1 N′ G, found in the familiar Collins chart and its dual representation. A general relation for the transformation of this Fresnel number is found. The expressions for Gaussian beam transformation are thus simplified, since the waist-waist transform is given byN′ G1 =N′ G2 = 0. Finally, these two kinds of Fresnel numbers are written as tensors when applied to cases involving elliptical apertures, astigmatic beams and nonsymmetrical systems.
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    Optical and quantum electronics 24 (1992), S. 1373-1379 
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    Notes: Abstract The excess loss across an acute-angle symmetric X-junction composed of two weakly guiding single-mode buried channel waveguides of square core cross-section is shown to be very small provided the junction angle is greater than a few degrees. Numerical and approximate analytical results are presented, as well as a simple criterion for the onset of cross-talk as the junction angle decreases.
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    Optical and quantum electronics 24 (1992), S. 1359-1371 
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    Notes: Abstract We present a procedure based on the variational principle to obtain the modal propagation characteristics of single-mode diffused channel waveguides with arbitrary index profiles. The only assumption in our method, in addition to the scalar approximation, is that the trial field is separable along the depth and the width directions. The method is iterative, with each cycle of iteration requiring the solution of two planar waveguide propagation problems. The convergence is usually achieved within 2–3 cycles of iteration. Comparisons with other methods show that our method gives much better accuracy.
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    Optical and quantum electronics 24 (1992), S. 1401-1411 
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    Notes: Abstract It is shown that the full time-dependent problem of four-photon parametric interaction has a large set of exact wave solutions. This set includes normal and symbiotic periodic waves as well as solitary ones. Periodic solutions are given in terms of Jacobian elliptic functions.
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    Optical and quantum electronics 24 (1992), S. iii 
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    Optical and quantum electronics 24 (1992), S. 1381-1399 
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    Notes: Abstract The possibility of generation of short high-power pulses by pulse electroopticQ-switching in a high-gain excimer system was investigated numerically. Two methods of short-pulse generation were considered. In the first the electroopticQ-switch is controlled by two half-wave voltage gates. The method normally enables pulses from several hundreds of picoseconds to a few nanoseconds duration to be obtained. In the second method the Q-switch is controlled by a train of voltage gates of amplitude equal to the double half-wave voltage. In this case, even at short times of laser pumping (≈ 50 ns), it is possible to generate high-power pulses of duration from tens to several hundreds of picoseconds. The influence of various system parameters on the generation process and the parameters of the generated pulses was analysed in detail.
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