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  • Articles  (8,674)
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  • American Institute of Physics  (4,598)
  • Springer  (4,076)
  • 2000-2004  (8,674)
  • Electrical Engineering, Measurement and Control Technology  (8,674)
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  • Articles  (8,674)
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  • 1
    Electronic Resource
    Electronic Resource
    The recovery of distorted bandlimited almost-periodic signals (2000)
    Springer
    Circuits, systems and signal processing 19 (2000), S. 385-398 
    Details
    ISSN: 1531-5878
    Keywords: Recovery of distorted signals ; almost periodic signals ; bandlimited signals ; nonlinear systems ; nonlinear distortion
    Source: Springer Online Journal Archives 1860-2000
    Topics: Electrical Engineering, Measurement and Control Technology
    Notes: Abstract It is shown that thePQ theorem can be used to solve a certain signal recovery problem in which the transmitted and received signals are almost periodic functions. In this problem the signal to be recovered, which is bandlimited, is nonlinearly distorted and then bandlimited to the original band. Related signal recovery results are also given. These related results, unlike thePQ theorem, are applicable in settings in which the underlying signal space is not a Hilbert space or even a space that is complete.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF01196153
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  • 2
    Electronic Resource
    Electronic Resource
    Minimal realization for lifted periodic filters (2000)
    Springer
    Circuits, systems and signal processing 19 (2000), S. 411-421 
    Details
    ISSN: 1531-5878
    Keywords: Periodic filters ; lifted model ; minimal realization ; reachability ; observability
    Source: Springer Online Journal Archives 1860-2000
    Topics: Electrical Engineering, Measurement and Control Technology
    Notes: Abstract Practical applications in signals and systems often deal with lifted models of periodic digital filters, to which well-known methods and computing software for linear time-invariant (LTI) systems can be applied in the analysis and synthesis of periodic filters. When the design of a periodic filter is based on the lifted model, the resultant filter is usually in the lifted LTI form and needs to be further converted into the periodic form for implementational and computational purposes. In this paper, we present a computational procedure for obtaining a minimal realization of periodic digital filters from the fifted model.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF01196155
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  • 3
    Electronic Resource
    Electronic Resource
    Robust mixed-order root-music (2000)
    Springer
    Circuits, systems and signal processing 19 (2000), S. 451-466 
    Details
    ISSN: 1531-5878
    Keywords: Direction finding ; high-order statistics ; root-MUSIC ; robustness
    Source: Springer Online Journal Archives 1860-2000
    Topics: Electrical Engineering, Measurement and Control Technology
    Notes: Abstract Several typical situations unfavorable for second-order direction-finding methods are known to be easily overcome by means of higher-order techniques. In turn, in typical situations unfavorable for higher-order methods, second-order algorithms often perform quite well. Therefore, appropriately combining covariance- and cumulant-based techniques into one scheme, it is possible to obtain an algorithm with an improved robustness. In this paper, we propose two modifications of such combined methods, referred to asmixed-order root-MUSIC.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF01196158
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  • 4
    Electronic Resource
    Electronic Resource
    A quasi-parametric algorithm for synthetic aperture radar target feature extraction and imaging with angle diversity (2000)
    Springer
    Circuits, systems and signal processing 19 (2000), S. 301-319 
    Details
    ISSN: 1531-5878
    Keywords: Synthetic aperture radar (SAR) ; angle diversity ; feature extraction ; quasiparametric parameter estimation ; data missing ; image formation
    Source: Springer Online Journal Archives 1860-2000
    Topics: Electrical Engineering, Measurement and Control Technology
    Notes: Abstract We present synthetic aperture radar (SAR) target feature extraction and imaging techniques with angle divesity. We first establish a flexible data model that describes each target scatterer as a two-dimensional (2D) complex sequence with arbitrary amplitude and constant phase in range and cross-range. A new algorithm, referred to as the QUasiparametric ALgorithm for target feature Extraction (QUALE), is then presented for SAR target feature extraction via data fusion through angle diversity based on the flexible data model. QUALE first estimates the model parameters, which include, for each scatterer, a 2D arbitrary real-valued amplitude sequence, a constant phase, and scatterer locations in range and cross-reange. QUALE then averages the estimated 2D real-valued amplitude sequence over range by making the assumption that the scatterer radar cross section is approximately consant. QUALE next models the so-obtained 1D sequence with a simple sinc function by assuming that the scatterer is approximately a dihedral (a trihedral is approximated as a very short dihedral) and estimates the relevant sinc function parameters by minimizing a nonlinear least-squares fitting function. Finally, the approximate 2D SAR image is reconstructed by using the estimated features. Numerical examples are given to demonstrate the perfomance of the proposed algorithm.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF01200890
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  • 5
    Electronic Resource
    Electronic Resource
    A high performance architecture for computing the time-frequency spectrum (2000)
    Springer
    Circuits, systems and signal processing 19 (2000), S. 437-450 
    Details
    ISSN: 1531-5878
    Keywords: Time-frequency spectrum ; nonstationary signals ; time-varying correlogram ; parallel architecture ; systolic arrays
    Source: Springer Online Journal Archives 1860-2000
    Topics: Electrical Engineering, Measurement and Control Technology
    Notes: Abstract To solve the problem of detecting and displaying the changes in the spectra of nonstationary signals, there are two possible approaches. Either one uses the same estimators as for the stationary signals, but one approach uses shorter-length data blocks during which the signal is assumed to be stationary, and the other one uses the same length data and applies a time-varying spectrum estimator that accounts for the nonstationarity. A time-varying spectrum estimator called a time-varying correlogram (TVC) is a well-known estimator of the time-frequency spectrum of a nonstationary signal. In this paper, a high performance VLSI architecture for computing TVC is proposed.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF01196157
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  • 6
    Electronic Resource
    Electronic Resource
    On evaluating A class of frame-based nonstationary pattern recognition methods using bhattacharyya distance (2000)
    Springer
    Circuits, systems and signal processing 19 (2000), S. 467-485 
    Details
    ISSN: 1531-5878
    Keywords: Nonstationary pattern recognition ; frame-based methods ; Bhattacharyya distance ; Bayes error ; upper bound trajectory ; robust AR speech analysis
    Source: Springer Online Journal Archives 1860-2000
    Topics: Electrical Engineering, Measurement and Control Technology
    Notes: Abstract We consider a possible evaluation of frame-based nonstationary pattern recognition methods by using the upper bound trajectories of the Bayes error based on the Bhattacharrya distance. The experimental part of the work is based on natural speech processing, using isolated spoken Serbian vowels and digits as examples of nonstationary signals. The results obtained justify the use of the upper bound trajectories of the Bayes error expressed by the Bhattacharyya distance as a possible evaluation tool for the class of frame-based nonstationary pattern recognition systems.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF01196159
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  • 7
    Electronic Resource
    Electronic Resource
    Vector fitting by pole relocation for the state equation approximation of nonrational transfer matrices (2000)
    Springer
    Circuits, systems and signal processing 19 (2000), S. 549-566 
    Details
    ISSN: 1531-5878
    Keywords: Rational approximation ; rational fitting ; state equations ; transfer function ; transmission lines ; poles ; residues
    Source: Springer Online Journal Archives 1860-2000
    Topics: Electrical Engineering, Measurement and Control Technology
    Notes: Abstract Often the information available for a state equation description in the form $$\dot x = Ax + Bu$$ ,y=Cx+Du is via a transfer function matrixH(s) obtained by measurements or complicated computations for frequenciess=jω. ThusH(s) is nonrational or rational of high order. Its state equation approximation means obtainingA, B, C, D in the rational transfer matrixC(sI-A) −1 B+D≈H(s). This approximation problem is difficult because it is nonlinear and often ill conditioned. This paper describes a methodology for fitting the columnsh(s) ofH(s) by two linear procedures. First θ(s)h(s) is fitted with a set of prescribed poles, where θ(s) is an unknown rational function with the same poles as θ(s)h(s). Then the poles forh(s) are calculated as the zeros of θ(s). With the poles known, the unknown residues and constant terms are calculated forh(s). If necessary, the procedure is repeated with the new poles taken as prescribed poles. The procedure is accurate and robust, and uses only standard numerical linear algebra computations. Illustrative examples for the application of vector fitting are given for a power transformer, a transmission line, and a network of transmission lines.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF01271288
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  • 8
    Electronic Resource
    Electronic Resource
    Exact solution of a bandpass matching problem (2000)
    Springer
    Circuits, systems and signal processing 19 (2000), S. 59-69 
    Details
    ISSN: 1531-5878
    Keywords: Bandpass matching ; matching network design ; rf circuits
    Source: Springer Online Journal Archives 1860-2000
    Topics: Electrical Engineering, Measurement and Control Technology
    Notes: Abstract This paper discusses the exact design of a bandpass matching circuit for transmission of power from a source of internal resistanceR 1 to a load of resistanceR 2. The design is obtained in terms of an unknownQ factor, the value of which is to be determined by solving a cubic equation.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF01229992
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  • 9
    Electronic Resource
    Electronic Resource
    Polynomial ambiguity resistant precoders: Theory and applications in ISI/multipath cancellation (2000)
    Springer
    Circuits, systems and signal processing 19 (2000), S. 71-98 
    Details
    ISSN: 1531-5878
    Source: Springer Online Journal Archives 1860-2000
    Topics: Electrical Engineering, Measurement and Control Technology
    Notes: Abstract In this paper, precoding techniques are studied for combating the intersymbol interference (ISI)/multipath effects in communication systems. We introduce a new type-precoder which we term thepolynomial ambiguity resistant (PAR) precoder for its ability to resist signal distortion induced by finite impulse response (FIR) channels. In particular, the precoder allows a receiver to identify an input signal without knowing the channel characteristics at the expense of a minimum amount of bandwidth increase. A family of such precoders, which is linear (no modulo operations), channel independent, and modulation pattern preserving (except for some occasional 0 symbols), is presented. Also presented is a closed-form algorithm that can simultaneously identify the input signals and zero-forcing equalizers.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF01212464
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  • 10
    Electronic Resource
    Electronic Resource
    Combining Capon and APES for estimation of spectral lines (2000)
    Springer
    Circuits, systems and signal processing 19 (2000), S. 159-169 
    Details
    ISSN: 1531-5878
    Keywords: Spectral estimation ; matched filterbanks ; parameter estimation
    Source: Springer Online Journal Archives 1860-2000
    Topics: Electrical Engineering, Measurement and Control Technology
    Notes: Abstract We propose combining the Capon and the APES spectral estimators for estimation of both the amplitude and the frequency of spectral lines. The so-obtained estimator does not suffer from Capon's biased amplitude estimates nor from APES' biased frequency estimates or resolution problem. Furthermore, the combined estimator is computationally simpler than APES and has about the same complexity as Capon. Numerical simulations are presented illustrating the increased performance.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF01212468
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  • 11
    Electronic Resource
    Electronic Resource
    Stability of multidimensional nonnegative systems (2000)
    Springer
    Circuits, systems and signal processing 19 (2000), S. 197-204 
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    ISSN: 1531-5878
    Keywords: Discrete-time linear dynamics ; multidimensional systems ; nonnegative matrices in dynamical systems ; Lyapunov stability ; localized Lyapunov functions
    Source: Springer Online Journal Archives 1860-2000
    Topics: Electrical Engineering, Measurement and Control Technology
    Notes: Abstract The stability of discrete-time linear multidimensional dynamics is studied from the viewpoint of quadratic Lyapunov stability. The concept of a localized Lyapunov function is introduced to analyze the state behavior of multidimensional dynamics. It is shown that if the sum of the absolute-valued coefficient matrices of a multidimensional dynamics is stable in the sense that the spectral radius is less than unity, then any state transition of the multidimensional dynamics shows a step-by-step decrease with respect to an appropriately constructed localized diagonal Lyapunov function. The obtained result is a natural extension of an already-known result on the stability of nonnegative matrices.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF01204574
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  • 12
    Electronic Resource
    Electronic Resource
    Immittance-type tabular stability test for 2-D LSI systems based on a zero location test for 1-D complex polynomials (2000)
    Springer
    Circuits, systems and signal processing 19 (2000), S. 245-265 
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    ISSN: 1531-5878
    Source: Springer Online Journal Archives 1860-2000
    Topics: Electrical Engineering, Measurement and Control Technology
    Notes: Abstract A new algebraic test is developed to determine whether or not a two-variable (2-D) characteristic polynomial of a recursive linear shift invariant (LSI, discrete-time) system is “stable” (i.e., it does not vanish in the closed exterior of the unit bi-circle). The method is based on the original form of a unit-circle zero location test for one variable (1-D) polynomials with complex coefficients proposed by the author. The test requires the construction of a “table”, in the form of a sequence of centrosymmetric matrices or 2-D polynomials, that is obtained using a certain three-term recursion, and examination of the zero location with respect to the unit circle of a few associated 1-D polynomials. The minimal set necessary and sufficient conditions for 2-D stability involves one 1-D polynomial whose zeros must reside inside the unit circle (which may be examined before the table is constructed), and one symmetric 1-D polynomial (which becomes available after completing the table) that is required not to have zeros on the unit circle. A larger set of intermediate necessary conditions for stability (which may be examined during the table's construction) are also given. The test compares favorably with Jury's recently improved 2-D stability test in terms of complexity and munerical stability.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF01204577
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  • 13
    Electronic Resource
    Electronic Resource
    Observer-based digital control of sampled-data systems with input/output time delays (2000)
    Springer
    Circuits, systems and signal processing 19 (2000), S. 1-11 
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    ISSN: 1531-5878
    Keywords: Observer-based digital control ; time delays
    Source: Springer Online Journal Archives 1860-2000
    Topics: Electrical Engineering, Measurement and Control Technology
    Notes: Abstract Using asynchronous initial sampling with different sampling rates in the input and output terminals, a novel observer-based digital control law for sampled-data systems is proposed, which can cope with the presence of time delays in input acquisition and output sampling.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF01229988
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  • 14
    Electronic Resource
    Electronic Resource
    Optimal wavelet filter banks for regularized restoration of noisy images (2000)
    Springer
    Circuits, systems and signal processing 19 (2000), S. 99-119 
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    ISSN: 1531-5878
    Keywords: Filter banks ; wavelets ; image restoration ; regularization ; generalized cross validation
    Source: Springer Online Journal Archives 1860-2000
    Topics: Electrical Engineering, Measurement and Control Technology
    Notes: Abstract Regularized image restoration methods efficiently handle the ill-posed problem of image restoration. Nevertheless, the issue of selecting the regularization parameter as well as the smoothing filter still constitutes an open research topic. A model of regularized image restoration is introduced and analyzed in this paper. The proposed model assumes that wavelet filter banks replace the smoothing filter of conventional regularized restoration. Filter factorizations for the optimal design of wavelet filter banks using the generalized-cross-validation (GCV) criterion are presented, and novel expressions of the influence matrix, which is used to calculate the GCV error, are derived. The error of the GCV method is expressed in terms of the modulation matrix of the filter bank and the modulation vector of the degradation filter. The expressions are given in general form for optimal wavelet filter bank design upon arbitrary sampling lattices. The numerical examples of image restoration using the proposed method that are presented indicate significant signal-to-noise ratio improvement, Δ SNR , compared to image restoration methods that employ the Laplacian as the smoothing filter.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF01212465
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  • 15
    Electronic Resource
    Electronic Resource
    Applicability of phase-locked loop to tracking the rhythmic activity in EEGS (2000)
    Springer
    Circuits, systems and signal processing 19 (2000), S. 171-186 
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    ISSN: 1531-5878
    Keywords: EEG rhythmic bands ; PLL ; SSB modulation ; meditation EEG
    Source: Springer Online Journal Archives 1860-2000
    Topics: Electrical Engineering, Measurement and Control Technology
    Notes: Abstract Conventional methods of spectral analysis are based on mathematical or numerical algorithms applied to digitized signals. This paper discusses the applicability of the phase-locked loop (PLL) approach for tracking electroencephalogram (EEG) rhythmic bands (delta, theta, alpha, or beta). The use of the PLL for frequency tracking should also aid the development of online EEG interpretation and screening based on frequency characteristics when the PLL is realized by hardware. As a result, two factors in the applicability of the PLL are: (1) translation of the EEG spectrum to a higher-frequency band by a single-sideband (SSB) modulation scheme, and (2) the narrowband spectral feature of the EEG—a small difference between two major frequencies. The PLL output is further quantized according to the EEG rhythmic bands. Our analysis shows that the integrated system is capable of tracking the EEG rhythmic patterns.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF01204572
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  • 16
    Electronic Resource
    Electronic Resource
    Guest editorial (2000)
    Springer
    Circuits, systems and signal processing 19 (2000), S. iii 
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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/BF01200886
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  • 17
    Electronic Resource
    Electronic Resource
    Efficient backward selection ofk-space samples in MRI on a hexagonal grid (2000)
    Springer
    Circuits, systems and signal processing 19 (2000), S. 267-278 
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    ISSN: 1531-5878
    Keywords: MRI ; spectroscopic imaging ; sample selection ; k-space ; hexagonal sampling ; reconstruction
    Source: Springer Online Journal Archives 1860-2000
    Topics: Electrical Engineering, Measurement and Control Technology
    Notes: Abstract Certain types of magnetic resonance imaging (MRI) such as magnetic resonance spectroscopic imaging and three-dimensional (3D) MRI require a great deal of time to acquire the image data. The acquisition time can be reduced if the image has a limited region of support, such as when imaging the brain or a cross section of the chest. Hexagonal sampling of the spatial frequency-domain (k-space) yields a 13.4% sampling density reduction compared to rectangular sampling of thek-space for images with a circular region of support (ROS) without incurring spatial aliasing in the reconstructed image. However, certain nonuniform sampling patterns are more efficient than hexagonal sampling for the same ROS. Sequential backward selection (SBS) has been used in previous work to optimize a nonuniform set ofk-space samples selected from a rectangular grid. To reduce the selection time, we present SBS of samples from a hexagonal grid. A Smith normal decomposition is used to transform the nonrectangular 2D discrete Fourier transform to a standard rectangular 2D fast Fourier transform so that the spatial-domain samples are represented directly on a rectangular grid without interpolation. The hexagonal grid allows the SBS algorithm to begin with a smaller set of candidate samples so that fewer samples have to be eliminated. Simulation results show that a significantly reduced selection time can be achieved with the proposed method in comparison with SBS on a rectangular grid.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF01200888
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  • 18
    Electronic Resource
    Electronic Resource
    Adaptive frequency estimation of sinusoidal signals in colored non-Gaussian noises (2000)
    Springer
    Circuits, systems and signal processing 19 (2000), S. 517-533 
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    ISSN: 1531-5878
    Keywords: Frequency estimation ; adaptive algorithm ; higher-order statistics ; non-Gaussian noise
    Source: Springer Online Journal Archives 1860-2000
    Topics: Electrical Engineering, Measurement and Control Technology
    Notes: Abstract This paper studies the problem of sinusoidal frequency estimation in colored non-Gaussian ARMA noises. A new adaptive approach is proposed by using the second-and third-order statistics of the measurements. Because of the simultaneous establishment of the signal and noise models, the new approach is applicable for tracking the frequencies at each time instant for stationary and nonstationary signal and/or noise cases. The effectiveness of the new approach is demonstrated by extensive computer simulations. As expected, the approach proposed in this paper outperforms the correlation-based approaches in suppressing the effects of the colored non-Gaussian ARMA noises.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF01271286
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  • 19
    Electronic Resource
    Electronic Resource
    An enhanced technique for online discrete cosine transform-based time-varying delay estimation (2000)
    Springer
    Circuits, systems and signal processing 19 (2000), S. 501-515 
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    ISSN: 1531-5878
    Keywords: Time-delay estimation ; discrete cosine transform ; maximum likelihood estimation
    Source: Springer Online Journal Archives 1860-2000
    Topics: Electrical Engineering, Measurement and Control Technology
    Notes: Abstract Time-delay estimation is developed in the transform domain where discrete cosine transform (DCT) coefficients of time-varying delay signals are estimated. The DCT is very efficient in compacting the signal energy in a small number of coefficients. Hence, the estimation of time-varying delay is obtained through the calculation of a small number of the DCT coefficients. An online maximum likelihood estimator of time-varying delay is developed. The coefficients of the transformed delay signal are obtained by maximizing the likelihood function. When dealing with noisy signals, it is observed that increasing the number of estimated DCT coefficients beyond a certain level does not produce better estimates of the delay signal. This happens because the extra DCT coefficients accommodate the noise present in the received signals.
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    URL: http://dx.doi.org/10.1007/BF01271285
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  • 20
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    Call for papers (2000)
    Springer
    Circuits, systems and signal processing 19 (2000), S. 71-71 
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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/BF01229993
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  • 21
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    On hidden periodicities (2000)
    Springer
    Circuits, systems and signal processing 19 (2000), S. 27-42 
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    ISSN: 1531-5878
    Keywords: Spectral estimation ; hidden periodicities
    Source: Springer Online Journal Archives 1860-2000
    Topics: Electrical Engineering, Measurement and Control Technology
    Notes: Abstract Many spectral analysis techniques have been developed over the years. In this paper we develop a new method of spectral analysis and show that it performs well in situations where the noise signal is of short duration. With this method we can restore the spectrum with desired precision having at hand values of the observed signal only on the finite interval.
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    URL: http://dx.doi.org/10.1007/BF01229990
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  • 22
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    On singular equilibria of index-1 DAEs (2000)
    Springer
    Circuits, systems and signal processing 19 (2000), S. 131-157 
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    ISSN: 1531-5878
    Keywords: Linearly implicit differential equations ; semiexplicit differential-algebraic equations ; singular equilibria ; weak singularities ; nonlinear electrical circuits ; singular flow ; singularity induced bifurcation
    Source: Springer Online Journal Archives 1860-2000
    Topics: Electrical Engineering, Measurement and Control Technology
    Notes: Abstract Some qualitative properties of singular equilibria arising in semiexplicit index-1 differential-algebraic equations are discussed in this paper. We extend a taxonomy of singularities from index-0 problems to address situations not covered by the singularity induced bifurcation, singular flow, and associated theorems. Although some related phenomena may occur, different behavior can be expected when the assumptions supporting these results are not satisfied, as is illustrated by several examples. Special attention is paid to the effect that the singular nature of the underlying ordinary differential equation and, eventually, of the solution manifold, has on the behavior of the original singular index-1 problem.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF01212467
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  • 23
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    Matrix conditions for the stability of 2D dynamics (2000)
    Springer
    Circuits, systems and signal processing 19 (2000), S. 187-196 
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    ISSN: 1531-5878
    Keywords: Stability of 2D systems ; quadratic Lyapunov stability ; matrix inequalities ; parallel addition of positive definite matrices
    Source: Springer Online Journal Archives 1860-2000
    Topics: Electrical Engineering, Measurement and Control Technology
    Notes: Abstract The stability of two-dimensional (2D) dynamics is studied from the viewpoint of quadratic Lyapunov stability. An already-known simple sufficient condition for the stability of 2D dynamics is first reconsidered by introducing a new notion about the stability of a pair of matrices. It is interpreted as a condition for step-by-step contractive stability in a suitably selected state coordinate. In this direction, some necessary and sufficient conditions for the stability of 2D dynamics are shown in detail. The meaning of the original simple sufficient condition is further clarified in this extension. A condition for being free of overflow oscillations in saturation arithmetic is added as a special topic of the Lyapunov stability of 2D dynamics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF01204573
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  • 24
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    Stability analysis of discontinuous dynamical systems using vector Lyapunov functions (2000)
    Springer
    Circuits, systems and signal processing 19 (2000), S. 221-243 
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    ISSN: 1531-5878
    Keywords: Stability analysis ; (interconnected) discontinuous dynamical systems ; vector ; Lyapunov functions ; stability-preserving mappings
    Source: Springer Online Journal Archives 1860-2000
    Topics: Electrical Engineering, Measurement and Control Technology
    Notes: Abstract In this paper, we establish several stability results for discontinuous dynamical systems defined onR +=[0, ∞) which make use of vector Lyapunov functions. For the scalar case, these results yield in particular theprincipal Lyapunov stability results for discontinuous dynamical systems reported earlier. We demonstrate the applicability of our results by studying a class of interconnected discontinuous dynamical systems and several specific examples.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF01204576
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  • 25
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    A wavelet-based interpolation-restoration method for superresolution (wavelet superresolution) (2000)
    Springer
    Circuits, systems and signal processing 19 (2000), S. 321-338 
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    ISSN: 1531-5878
    Keywords: Superresolution ; wavelet interpolation ; interlaced sampling
    Source: Springer Online Journal Archives 1860-2000
    Topics: Electrical Engineering, Measurement and Control Technology
    Notes: Abstract Superresolution produces high-quality, high-resolution images from a set of degraded, low-resolution images where relative frame-to-frame motions provide different looks at the scene. Superresolution translates data temporal bandwith into enhanced spatial resolution. If considered together on a reference grid, given low-resolution data are nonuniformly sampled. However, data from each frame are sampled regularly on a rectangular grid. This special type of nonuniform sampling is called interlaced sampling. We propose a new wavelet-based interpolation-restoration algorithm for superresolution. Our efficient wavelet interpolation technique takes advantage of the regularity and structure inherent in interlaced data, thereby significantly reducing the computational burden. We present one- and two-dimensional superresolution experiments to demonstrate the effectiveness of our algorithm.
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    URL: http://dx.doi.org/10.1007/BF01200891
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    On intermediate view estimation in computed tomography (2000)
    Springer
    Circuits, systems and signal processing 19 (2000), S. 279-299 
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    ISSN: 1531-5878
    Keywords: Computed tomography ; view aliasing artifacts ; intermediate views ; interpolation ; reprojection ; region of interest
    Source: Springer Online Journal Archives 1860-2000
    Topics: Electrical Engineering, Measurement and Control Technology
    Notes: Abstract In many applications in computed tomography, practical limitations in data acquisition restrict the number of projections (views). The use of the standard convolution backprojection algorithm for reconstruction from an inadequate number of projections results in view aliasing artifacts. One approach to alleviating the effects of such artifacts consists of artificially increasing the number of views, by estimating a set of intermediate views. Two possible methods of estimating the intermediate views are interpolation and reprojection. In this paper, a study of the two is considered. Based on the merits and demerits of the two methods, a combination of the two methods is investigated. Specifically, a reconstruction from the available sinogram augmented by intermediate view reprojections, and the projections interpolated from the original views and the reprojections, provide an additional improvement with respect to view aliasing artifacts. The advantage of computing reprojections over smaller regions of interest is discussed. When the number of available projections is reasonably high but not adequate to produce an artifact-free reconstruction, estimating the intermediate views by interpolation provides an improvement without much additional degradation, at minimal computational cost.
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    URL: http://dx.doi.org/10.1007/BF01200889
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    An adaptive multiscale inverse scattering approach to photothermal depth profilometry (2000)
    Springer
    Circuits, systems and signal processing 19 (2000), S. 339-363 
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    ISSN: 1531-5878
    Keywords: Adaptive signal representation ; multiscale methods ; B-splines ; nonlinear inverse scattering ; photothermal depth profiling
    Source: Springer Online Journal Archives 1860-2000
    Topics: Electrical Engineering, Measurement and Control Technology
    Notes: Abstract Photothermal depth profilometry is formulated as a nonlinear inverse scattering problem. Starting with the one-dimensional heat diffusion equation, we derive a mathematical model relating arbitrary variation in the depth-dependent thermal conductivity to observed thermal wavefields at the surface of a material sample. The form of the model is particularly convenient for incorporation into a nonlinear optimization framework for is particularly convenient for incorporation into a nonlinear optimization framework for recovering the conductivity based on thermal wave data obtained at multiple frequencies. We develop an adaptive, multiscale algorithm for solving this highly ill-posed inverse problem. The algorithm is designed to produce an accurate, low-order representation of the thermal conductivity by automatically controlling the level of detail in the reconstruction. This control is designed to reflect both (1) the nature of the underlying physics, which says that scale should decrease with depth, and (2) the particular structure of the conductivity profile, which may require a sparse collection of fine-scale components to adequately represent significant features such as a layering structure. The approach is demonstrated in a variety of synthetic examples representative of nondestructive evaluation problems seen in the steel industry.
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    URL: http://dx.doi.org/10.1007/BF01200892
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    Stabilization of smoothness priors time-varying autoregressive models (2000)
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    Circuits, systems and signal processing 19 (2000), S. 423-435 
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    ISSN: 1531-5878
    Keywords: Time-varying autoregressive models ; stability ; smoothness priors ; Tihkonov regularization ; constrained optimization
    Source: Springer Online Journal Archives 1860-2000
    Topics: Electrical Engineering, Measurement and Control Technology
    Notes: Abstract The stability of time-varying autoregressive (AR) models is an important issue in such applications as time-varying spectrum estimation and electroencephalography simulation and estimation. In some cases, such as time-varying spectrum estimation, the models that exhibit roots near unit moduli are difficult to use. Thus a tighter stability condition such as stability with a positive margin is needed. A time-varying AR model is stable with a positive margin if the moduli of the roots of the time-varying characteristic polynomial are somewhat less than unity for every time instant. Recently, a new method for the estimation of the time-varying AR models was introduced. This method is based on the interpretation of the underdetermined time-varying prediction equations as an ill-posed inverse problem that is solved by Tikhonov regularization. The method is referred to as the deterministic regression smoothness priors (DRSP) scheme. In this paper, a stabilization method in which the DRSP scheme is augmented with nonlinear stability constrainst is proposed. The problem is formulated so that stability with a positive margin can also be achieved. The problem is solved iteratively with an exterior point algorithm. The performance of the algorithm is studied with a simulation. It is shown that the proposed approach is well suited to stable modeling of signals containing narrowband transitions.
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    Miller's theorem revisited (2000)
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    Circuits, systems and signal processing 19 (2000), S. 487-499 
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    ISSN: 1531-5878
    Keywords: Miller's theorem ; dual of Miller's theorem ; general network analysis
    Source: Springer Online Journal Archives 1860-2000
    Topics: Electrical Engineering, Measurement and Control Technology
    Notes: Abstract Miller's theorem is generally used for approximate analysis of high-frequency amplifier circuits. That it can be used without much difficulty for the exact analysis of such circuits as well as others, including passive networks, does not appear to be widely recognized in the literature. Although formulated and proved in 1972, the dual of Miller's theorem has hardly ever been used. In this paper, we present the exact analysis of a number of circuits of practical interest with the help of either Miller's theorem or its dual or both, almost by inspection.
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    Stability of constant coefficient linear singular systems with delay (2000)
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    Circuits, systems and signal processing 19 (2000), S. 13-25 
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    ISSN: 1531-5878
    Keywords: Singular systems ; delay ; consistency condition ; stability ; instability
    Source: Springer Online Journal Archives 1860-2000
    Topics: Electrical Engineering, Measurement and Control Technology
    Notes: Abstract In this paper, the general class of singular systems with delay and linear constant coefficient singular systems with delay are discussed. First, several definitions of stability are presented for singular systems with delay, and general sufficient stability conditions and instability conditions are obtained. Second, stability and instability are analyzed for linear constant coefficient singular systems with delay.
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    New criteria for blind source separation using second-order cyclic statistics (2000)
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    Circuits, systems and signal processing 19 (2000), S. 43-58 
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    ISSN: 1531-5878
    Keywords: Blind source separation ; adaptive algorithm ; second-order cyclic statistics ; convergence analysis
    Source: Springer Online Journal Archives 1860-2000
    Topics: Electrical Engineering, Measurement and Control Technology
    Notes: Abstract This paper addresses the problem of blind separation of cyclostationary sources. By using the cyclostationarity property of the source signals, new criteria based on second-order cyclic statistics (SOCS) are established, from which two algorithms for blind source separation are proposed. Compared with the existing higher-order statistics-based approaches, our new approach requires few data samples and does not impose any restrictions on the probability distributions of the source signals. Simulation results are given to demonstrate the effectiveness of this new approach.
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    Radar beam sharpening using an optimum FIR filter (2000)
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    Circuits, systems and signal processing 19 (2000), S. 121-129 
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    ISSN: 1531-5878
    Source: Springer Online Journal Archives 1860-2000
    Topics: Electrical Engineering, Measurement and Control Technology
    Notes: Abstract Imagery that is obtained by noncoherent radar sensors suffers from a multitude of quality degradations. Among these, antenna-induced poor angular resolution is one of the most troublesome. We present a new approach to beam sharpening that improves the apparent resolution of the radar sensor several times depending on the signal-to-noise ratio. The technique consists of a compensating filter whose coefficients are obtained by minimizing the expected quadratic estimation error. This filter is then applied to sets of real 35 GHZ noncoherent radar imagery, and its performance is demonstrated. Results of the implementation of the technique on real-time digital signal processing hardware are also provided.
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    Envelope-constrained IIR filter design: An LMIH ∞ optimization approach (2000)
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    Circuits, systems and signal processing 19 (2000), S. 205-220 
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    ISSN: 1531-5878
    Keywords: H ∞ filtering ; envelope-constrained ; infinite impulse response ; linear matrix inequality
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    Topics: Electrical Engineering, Measurement and Control Technology
    Notes: Abstract In this paper, we consider envelope-constrained (EC) infinite impulse response (IIR) filtering problems. The aim is to design an IIR filter such that theH ∞ norm of the filtering error transfer function is minimized subject to the constraint that the estimation error with a given input to the linear dynamic system is contained or bounded in a prescribed envelope. The filter design problem is formulated as a standard optimization problem in linear matrix inequalities (LMIs).
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    Guest editors' biographies (2000)
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    Circuits, systems and signal processing 19 (2000), S. v 
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    ISSN: 1531-5878
    Source: Springer Online Journal Archives 1860-2000
    Topics: Electrical Engineering, Measurement and Control Technology
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    New results on the inverse-system/deconvolution problem for linear dynamical systems (2000)
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    Circuits, systems and signal processing 19 (2000), S. 365-383 
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    ISSN: 1531-5878
    Keywords: Inverse-system ; deconvolution ; input-identification ; transfer-function inversion
    Source: Springer Online Journal Archives 1860-2000
    Topics: Electrical Engineering, Measurement and Control Technology
    Notes: Abstract A new theory and realization methodology for the inverse-system/deconvolution problem associated with dynamical systems is developed. This new theory, based on the assumption of a finite-dimensional, linearized dynamical system and uncertain input signalss(t) that have a feature calledwaveform structure, effectively overcomes the longstanding difficulties of realizing inverse systems for linear systems that have “more poles than zeros” and/or have “zeros in the right half-plane”. The results obtained here are derived for both continuous and discrete-time linear systems, using either analog or digital signal processing, and includetime-varying systems with uncertainvector input signalss(t)=(s 1 (t)...sr(t)) and/orvector output measurementsy(t)=(y 1 (t)...y m (t)).
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    Enhanced localized computerized tomography employing the discrete wavelet transform (2000)
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    Circuits, systems and signal processing 19 (2000), S. 399-409 
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    ISSN: 1531-5878
    Keywords: Computed tomography ; Radon transform ; discrete wavelet transform ; multiresolution analysis ; localized tomography
    Source: Springer Online Journal Archives 1860-2000
    Topics: Electrical Engineering, Measurement and Control Technology
    Notes: Abstract A new localized computerized tomography technique based on the multiresolution analysis (MRA) implementation of the discrete wavelet transform is proposed. Our technique is based upon viewing the projection data as a set of one-dimensional functions of the space variablet and decomposing each one into an approximation signal and a set of detail signals using MRA. The approximation signal and detiil signals associated with each projection are filtered using the ramp filter |ω| of the standard reconstruction technique filtered back projection to generate the set of filtered projections. It is shown that only a very sparse set of projection data outside of the region of interest (ROI) is required to reconstruct a high-quality image of the ROI and a reasonable image outside of the ROI. Simulation results using the Shepp-Logan head phantom are presented to demonstrate the proposed technique.
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    Optimization of fixed-polarity Reed-Muller circuits using dual-polarity property (2000)
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    Circuits, systems and signal processing 19 (2000), S. 535-548 
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    ISSN: 1531-5878
    Keywords: Reed-Muller circuits ; dual-polarity ; optimization
    Source: Springer Online Journal Archives 1860-2000
    Topics: Electrical Engineering, Measurement and Control Technology
    Notes: Abstract In the optimization of canonical Reed-Muller (RM) circuits, RM polynomials with different polarities are usually derived directly from Boolean expressions. Time efficiency is thus not fully achieved because the information in finding RM expansion of one polarity is not utilized by others. We show in this paper that two fixed-polarity RM expansions that have the same number of variables and whose polarities are dual can be derived from each other without resorting to Boolean expressions. By repeated operations, RM expansions of all polarities can be derived. We consequently apply the result in conjunction with a hypercube traversal strategy to optimize RM expansions (i.e., to find the best polarity RM expansion). A recursive route is found among all possible polarities to derive RM expansion one by one. Simulation results are given to show that our optimization process, which is simpler, can perform exhaustive search as efficiently as other good exhaustive-search methods in the field.
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    Efficient linear-phase FIR, maximally flat error approximations for the amplitude response |1/ω r |,r,r=1, 2, 3,..., and a versatile realization (2000)
    Springer
    Circuits, systems and signal processing 19 (2000), S. 567-580 
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    ISSN: 1531-5878
    Keywords: Linear-phase digital filters ; FIR integrators
    Source: Springer Online Journal Archives 1860-2000
    Topics: Electrical Engineering, Measurement and Control Technology
    Notes: Abstract In this paper, designs of linear-phase finite impulse response (FIR) filters approximating the ideal frequency responseH (ω,r) Δ|1/ω r r=1, 2, 3,..., by using maximally flat error criteria have been proposed. Exact weights required for the realizations have been derived and are shown to be independent of the filter orderN. The suggested designs are particularly suitable for operation in the midband frequency range of 0.10π–0.90π radians.
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    Balanced Parametrizations of Stable SISO All-Pass Systems in Discrete Time (2000)
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    Mathematics of control, signals, and systems 13 (2000), S. 240-276 
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    ISSN: 1435-568X
    Keywords: Key words. Stable all-pass systems, Balanced realizations, Schur parameters, Stable AR systems, Topology.
    Source: Springer Online Journal Archives 1860-2000
    Topics: Electrical Engineering, Measurement and Control Technology , Mathematics , Technology
    Notes: Abstract. A balanced canonical form for discrete-time stable SISO all-pass systems is obtained by requiring the realization to be balanced and such that the reachability matrix is upper triangular with positive diagonal entries, in analogy to the continuous-time balanced canonical form of Ober [O1]. It is shown that the resulting balanced canonical form can be parametrized by Schur parameters. The relation with the Schur parameters for stable AR systems is established. Using the structure of the canonical form it is shown that, for the space of stable all-pass systems of order less than or equal to a fixed number n, the topology of pointwise convergence and the topology induced by H 2 coincide. The topological space thus obtained has the structure of a hypersphere. Model reduction procedures based on truncation, which respect the canonical form, are discussed.
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    Time-Varying and Adaptive Discrete-Time Low-Gain Control of Infinite-Dimensional Linear Systems with Input Nonlinearities (2000)
    Springer
    Mathematics of control, signals, and systems 13 (2000), S. 293-317 
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    ISSN: 1435-568X
    Keywords: Key words. Discrete-time systems, Infinite-dimensional systems, Integral control, Input nonlinearities, Regular systems, Robust tracking, Sampled-data control.
    Source: Springer Online Journal Archives 1860-2000
    Topics: Electrical Engineering, Measurement and Control Technology , Mathematics , Technology
    Notes: Abstract. Discrete-time low-gain control strategies are presented for tracking constant reference signals for infinite-dimensional, discrete-time, power-stable, linear systems subject to input nonlinearities. Both non-adaptive (but time-varying) and adaptive controls are considered. The discrete-time results are applied in the development of sampled-data integral control for infinite-dimensional, continuous-time, exponentially stable, regular, linear systems with input nonlinearities.
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    Continuous-Time Blind Channel Deconvolution Using Laguerre Shifts (2000)
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    Mathematics of control, signals, and systems 13 (2000), S. 333-346 
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    ISSN: 1435-568X
    Keywords: Key words. Blind identification, Deconvolution, Laguerre functions, Continuous-time, Matched filter, Equalizer, Inter-symbol interference.
    Source: Springer Online Journal Archives 1860-2000
    Topics: Electrical Engineering, Measurement and Control Technology , Mathematics , Technology
    Notes: Abstract. The objective of this paper is to study the problem of continuous-time blind deconvolution of a pulse amplitude modulated signal propagated over an unknown channel and perturbed by additive noise. The main idea is to use so-called Laguerre filters to estimate a continuous-time model of the channel. Laguerre-filter-based models can be viewed as an extension of finite-impulse-response (FIR) models to the continuous-time case, and lead to compact and parsimonious linear-in-the-parameters models.¶ Given an estimate of the channel, different symbol estimation techniques are possible. Here, the shift property of Laguerre filters is used to derive a minimum mean square error estimator to recover the transmitted symbols. This is done in a way that closely resembles recent FIR-based schemes for the corresponding discrete-time case.¶ The advantage of this concept is that physical a priori information can be incorporated in the model structure, like the transmitter pulse shape.
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    Robust Properties of Risk-Sensitive Control (2000)
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    Mathematics of control, signals, and systems 13 (2000), S. 318-332 
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    ISSN: 1435-568X
    Keywords: Key words. Risk-sensitive stochastic control, Robustness, Small gain theorem.
    Source: Springer Online Journal Archives 1860-2000
    Topics: Electrical Engineering, Measurement and Control Technology , Mathematics , Technology
    Notes: Abstract. The purpose of this paper is to characterize and prove robustness properties of risk-sensitive controllers precisely. In particular, we establish a stochastic version of the small gain theorem. This theorem is expressed in terms of an inequality which bounds the average output power in terms of the input power. Since this inequality is closely related to the risk-sensitive criterion, our stochastic small gain theorem can be expressed in terms of the risk-sensitive criterion. This provides a concrete motivation for the use of the risk-sensitive criterion stochastic robustness.
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    On Partial Order Characterizations of Information Structures (2000)
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    Mathematics of control, signals, and systems 13 (2000), S. 277-292 
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    ISSN: 1435-568X
    Keywords: Key words. Information structure, Concurrency, Nonsequential systems, Deadlock-freeness.
    Source: Springer Online Journal Archives 1860-2000
    Topics: Electrical Engineering, Measurement and Control Technology , Mathematics , Technology
    Notes: Abstract. The degree of concurrency possible in an informationally decentralized nonsequential system is determined by the precedence constraints imposed by the system's information structure on its controlled and uncontrolled inputs. One approach to characterizing these constraints is to attempt to associate each realization of the system's inputs with the strongest partial ordering of the system's decision-making agents that is consistent with the system's information structure. If such an association is possible, it leads to a partial order characterization of the corresponding information structure. In this paper we show that, in general, no such partial order characterization exists and we identify a sufficient (but not necessary) condition for existence. The condition has design implications that are important and intuitive and are discussed in the paper. Our results demonstrate that partial-order-based descriptions of concurrency, sometimes used in computer science, are not always correct.
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    Optimal Average Case Estimation in Hilbert Norms (2000)
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    Mathematics of control, signals, and systems 13 (2000), S. 347-359 
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    ISSN: 1435-568X
    Keywords: Key words. Identification algorithms, Average case setting, Local errors, Optimal algorithm, Optimal subspace.
    Source: Springer Online Journal Archives 1860-2000
    Topics: Electrical Engineering, Measurement and Control Technology , Mathematics , Technology
    Notes: Abstract. In contrast to the worst case approach, the average case setting provides less conservative insight into the quality of estimation algorithms. In this paper we consider two local average case error measures of algorithms based on noisy information, in Hilbert norms in the problem element and information spaces. We define the optimal algorithm and provide formulas for its two local errors, which explicitly exhibit the influence of factors such as information, information (measurement) errors, norms in the considered spaces, a subset where approximations are allowed, and “unmodeled dynamics.” Based on the error expression, we formulate in algebraic language the problem of selecting the optimal approximating subspace. The solution is given along with the specific formula for the error, which depends on the eigenvalues of a certain matrix defined by information and norms under consideration.
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    Influence of nonlinearly induced diffraction on spatial solitary waves (2000)
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    Optical and quantum electronics 32 (2000), S. 49-62 
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    ISSN: 1572-817X
    Keywords: Kerr-type of nonlinearity ; planar optical waveguides ; self-focussing of optical beams ; spatial solitary waves
    Source: Springer Online Journal Archives 1860-2000
    Topics: Electrical Engineering, Measurement and Control Technology , Physics
    Notes: Abstract Spatial solitary waves carried by a TE mode in planar optical waveguides with Kerr-type of nonlinearity are investigated based on a modified nonlinear (1 + 1) Schrödinger equation. Looking for effects instigated by the spatial inhomogeneity of the nonlinear polarization, the nonzero divE-term is taken into account in the nonlinear guided wave equation together with the nonparaxial approach and vector model. It is shown that, at self-focusing of beams in a (1 + 1) geometry, the effect coming out from the divergence term predominates over modifications related to the nonparaxial vector model. This term is interpreted as nonlinearly induced diffraction which plays the role of an effective saturation. Analytical solutions supported by numerical results are found.
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    Calculation of cutoff frequency of arbitrary weak guidance optical waveguides by extended boundary condition method (2000)
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    Optical and quantum electronics 32 (2000), S. 31-42 
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    ISSN: 1572-817X
    Keywords: elliptical optical waveguides ; extended boundary condition method ; mode cutoff ; moment method ; optical waveguide theory ; rectangular optical waveguides
    Source: Springer Online Journal Archives 1860-2000
    Topics: Electrical Engineering, Measurement and Control Technology , Physics
    Notes: Abstract The extended boundary condition method is applied to both circular and elliptical regions for calculating cutoff frequencies Vc of weakly guiding optical waveguides, which consist of a uniform cladding and a core with arbitrary shape and index profile. The frequency shift formula method is explained by means of the extended boundary condition method on circular regions. Comparing the method with analytic and other rigorous methods, we show that it is indeed a powerful tool. Numerical results confirm that the mode designation and arrangement order in elliptical and rectangular waveguides are, in general, dependent on the aspect ratio.
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    On the polarisation sensitivity and performance optimisation of a dual pump four wave mixing based wavelength converter (2000)
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    Optical and quantum electronics 32 (2000), S. 97-113 
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    ISSN: 1572-817X
    Keywords: four wave mixing ; optical communications ; semiconductor optical amplifier ; wavelength conversion
    Source: Springer Online Journal Archives 1860-2000
    Topics: Electrical Engineering, Measurement and Control Technology , Physics
    Notes: Abstract This paper presents a detailed investigation of the performance of a wavelength conversion scheme. The converter is based on four wave mixing in semiconductor optical amplifiers using two parallel polarised pumps. Measurements of the conversion efficiency and the signal to background noise ratio of the two replicas of the signal, for the cases of the signal polarisation being either parallel or orthogonal relative to the pump waves have been carried out. These measurements will reveal the polarisation sensitivity of this scheme which appears to be less than 1 dB when the wavelength spacing between the signal and its closest spaced pump is larger than 12 nm. The experimental results are supported in a satisfactory way by theoretical considerations. A simple theoretical expression describing the polarisation sensitivity have been derived and the theoretical results are in good agreement with those experimentally obtained. A performance comparison of the conversion scheme using semiconductor optical amplifiers with different lengths but the same structure is also performed. Through the following study the optimum operational conditions for this wavelength conversion scheme will be determined.
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    High spatial intensity 10 W-CuBr laser with hydrogen additives (2000)
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    Optical and quantum electronics 32 (2000), S. 1209-1217 
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    ISSN: 1572-817X
    Keywords: copper vapor lasers ; CuBr lasers ; beam divergence ; hydrogen
    Source: Springer Online Journal Archives 1860-2000
    Topics: Electrical Engineering, Measurement and Control Technology , Physics
    Notes: Abstract High beam quality output has been demonstrated from a single medium-scale (2 cm dia. × 50 cm) CuBr laser with hydrogen additives. The addition of hydrogen leads to beam divergence reduction and laser power lift-up finally yielding 5-fold increase in laser power spatial intensity compared with the case of no hydrogen added. With a simple positive-branch unstable resonator practical (pulse-average) divergence of ∼80 μrad is achieved. The easy-feasible sealed-off version of CuBr laser makes it an attractive source for many high-quality laser beam applications.
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    Modeling and interference-microscopy characterization of graded index transitions in ion-exchange waveguide integrated elements: transitions between annealed surfaces (2000)
    Springer
    Optical and quantum electronics 32 (2000), S. 1269-1281 
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    ISSN: 1572-817X
    Keywords: gradient index transitions ; interference microscopy ; waveguides
    Source: Springer Online Journal Archives 1860-2000
    Topics: Electrical Engineering, Measurement and Control Technology , Physics
    Notes: Abstract We employ interference microscopy to characterize in a direct and local way the graded index transitions at the boundaries of integrated optical elements fabricated by multistep ion-exchange processes, a task not yet possible by other technologies. A particular fabrication method based on purely thermal ion-exchange, which allows local single-mode propagation, is investigated. The refractive-index distribution is modeled on the basis of the linear theory of diffusion and adiabatic transitions of the refractive-index profile. Finally, its validity is analyzed by microinterferometry.
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    URL: http://dx.doi.org/10.1023/A:1007087817512
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    Quantum Dot Heterostructures (2000)
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    Optical and quantum electronics 32 (2000), S. 115-115 
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    ISSN: 1572-817X
    Source: Springer Online Journal Archives 1860-2000
    Topics: Electrical Engineering, Measurement and Control Technology , Physics
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    URL: http://dx.doi.org/10.1023/A:1007005725157
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    Electroluminescent device based on AlxGa1−xAs–GaAs quantum well nanostructures (2000)
    Springer
    Optical and quantum electronics 32 (2000), S. 1191-1199 
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    ISSN: 1572-817X
    Keywords: EL ; GaAs quantum well ; nanofabrication ; nanopillars ; SEM
    Source: Springer Online Journal Archives 1860-2000
    Topics: Electrical Engineering, Measurement and Control Technology , Physics
    Notes: Abstract AlGaAs–GaAs based quantum well nanopillar arrays are fabricated by using the UV lithography and the chlorine based reactive ion etching. The nanostructure is fabricated so as to get the confinement of carriers within the i-GaAs quantum well layer of 9 nm thick sandwiched between two barrier layers of Al0.33Ga0.67As of 11 nm thick in order to induce the possible light emission from the quantum well region. The size of pillars is obtained from SEM analysis. The number of pillars available within the 1 μm2 mesa size is found to be around 400 having the pillar size between 10 and 50 nm. Electroluminesence (EL) is detected from the nanopillars when applying a forward bias voltage of ≥1.3 V and the emitted light is observed at around 830 nm.
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    URL: http://dx.doi.org/10.1023/A:1007047415109
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    Spectral noise analysis of Er3+:Ti:LiNbO3 curved waveguide amplifiers (2000)
    Springer
    Optical and quantum electronics 32 (2000), S. 1-15 
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    ISSN: 1572-817X
    Keywords: Er:Ti:LiNbO3 curved waveguides ; noise figure and optical amplification ; spectral gain
    Source: Springer Online Journal Archives 1860-2000
    Topics: Electrical Engineering, Measurement and Control Technology , Physics
    Notes: Abstract We report simulations concerning optical amplification in Er:Ti:LiNbO3 curved waveguides. The derivation and the evaluation of the spectral optical gain, the spectral noise figure, the amplified spontaneous emission photon number, and the signal to noise ratio are performed under the small gain approximation. The simulations show the evolution of these parameters under various pump regimes, Er concentration profiles and waveguide lengths. The results obtained are of significant interest for the design of complex, rare earth-doped integrated optics structures involving bent waveguides.
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    URL: http://dx.doi.org/10.1023/A:1006992211635
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    Time-resolved spatial structure of TEA CO2 laser pulses (2000)
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    Optical and quantum electronics 32 (2000), S. 17-30 
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    ISSN: 1572-817X
    Keywords: bidimensional characterization ; electro-optical ; Hermite-Gauss modes ; laser pulse ; TEA CO2 laser
    Source: Springer Online Journal Archives 1860-2000
    Topics: Electrical Engineering, Measurement and Control Technology , Physics
    Notes: Abstract The evolution of the intensity profile of TEA CO2 laser pulses along the pulse length is investigated both analytically and experimentally. A simple scalar model of the pulse amplitude is introduced, which gives the loaded-cavity modes as a linear combination of bidimensional Hermite-Gauss functions. According to this model a number of equations are derived which link the time-varying spatial structure of the pulse to its time-resolved second-order intensity moments, namely, the beam width and the M2 parameter.
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    URL: http://dx.doi.org/10.1023/A:1007033113828
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    Fast and accurate reflectivity calculations for shaped core optical fibres (2000)
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    Optical and quantum electronics 32 (2000), S. 1245-1255 
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    ISSN: 1572-817X
    Keywords: facet reflectivity ; optical fibres ; analysis ; modelling
    Source: Springer Online Journal Archives 1860-2000
    Topics: Electrical Engineering, Measurement and Control Technology , Physics
    Notes: Abstract A novel scalar (i.e. paraxial) free space radiation mode method is presented for calculating the normal incidence facet reflectivity of the main guided mode of a step-index optical fibre with generally shaped smooth core. Numerical results are presented and discussed for several cases of the Nth order super-elliptical core shape, including the circular, elliptical, rectangular-type and slab limiting cases.
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    URL: http://dx.doi.org/10.1023/A:1007066020238
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    Instructions for Authors (2000)
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    Optical and quantum electronics 32 (2000), S. 1367-1372 
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    Source: Springer Online Journal Archives 1860-2000
    Topics: Electrical Engineering, Measurement and Control Technology , Physics
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    URL: http://dx.doi.org/10.1023/A:1026473015266
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    Crosstalks of two-waveguide and three-waveguide directional couplers (2000)
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    Optical and quantum electronics 32 (2000), S. 1257-1268 
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    ISSN: 1572-817X
    Keywords: waveguide directional couplers ; crosstalk ; normal mode theory ; coupled mode theory
    Source: Springer Online Journal Archives 1860-2000
    Topics: Electrical Engineering, Measurement and Control Technology , Physics
    Notes: Abstract Crosstalks of two-waveguide and three-waveguide directional couplers are analyzed mathematically based on the relationship between the coupled mode and the normal mode. Numerical techniques such as the finite-difference method and the beam propagation method are employed to confirm the validity of the derived expressions. The calculation results show that two-waveguide directional coupler is superior to any type of three-waveguide couplers from the practical viewpoint of the crosstalk and the coupling length.
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    Contents to Volume 32 (2000)
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    Optical and quantum electronics 32 (2000), S. 1359-1366 
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    Source: Springer Online Journal Archives 1860-2000
    Topics: Electrical Engineering, Measurement and Control Technology , Physics
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    URL: http://dx.doi.org/10.1023/A:1026413032104
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    Analysis of diffuse indoor infrared data links (2000)
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    Optical and quantum electronics 32 (2000), S. 1319-1323 
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    ISSN: 1572-817X
    Keywords: optical communication ; infrared ; indoor wireless communication
    Source: Springer Online Journal Archives 1860-2000
    Topics: Electrical Engineering, Measurement and Control Technology , Physics
    Notes: Abstract The authors present a simple channel model for diffuse infra-red indoor data communication systems. Based on the model, important trade-offs between the transmitted optical power, the bit-rate, and the receiver parameters are presented for the first time.
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    URL: http://dx.doi.org/10.1023/A:1026415911018
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    Chromaticity-tunable white light emission from organic multiple-quantum-well structure (2000)
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    Optical and quantum electronics 32 (2000), S. 1325-1331 
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    ISSN: 1572-817X
    Keywords: chromaticity ; multiple-quantum-well ; organic electroluminescence ; white-light emission
    Source: Springer Online Journal Archives 1860-2000
    Topics: Electrical Engineering, Measurement and Control Technology , Physics
    Notes: Abstract Organic multiple quantum wells (MQWs) white light emitting devices are fabricated in which blue fluorescent dye, a trimer of N-anylbenzimidazole (TPBI) and orange fluorescent rubrene doped tris (8-hydroxyquinoline) Aluminum act as quantum-well light emitting layers between triphenyldiamine derivative (TPD) potential barrier layers, and aluminium complex (Alq) act as an electron transporter and green emitter. The injected carriers are confined in different quantum wells and Alq layer. The white light emission comes from a combination of photons generated in different light emitting layers. The Commission Internationale de l' Eclairage (CIE) coordinates of the emitted light are tuned by increasing the number of TPBI wells due to its low fluorescent efficiency compared with rubrene.
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    Influence of neodymium concentration on the strength of thermal effects in continuous-wave diode-pumped Nd:YVO4 lasers at 1064 nm (2000)
    Springer
    Optical and quantum electronics 32 (2000), S. 1307-1317 
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    ISSN: 1572-817X
    Keywords: neodymium concentration ; Nd:YVO4 lasers ; continuous-wave power
    Source: Springer Online Journal Archives 1860-2000
    Topics: Electrical Engineering, Measurement and Control Technology , Physics
    Notes: Abstract The influence of neodymium ion concentration on the continuous-wave power performance of diode-pumped Nd:YVO4 lasers was experimentally investigated by using three crystals of approximately the same total absorption but different Nd concentrations of 0.5, 1, and 3 at.%. In situ measurements indicate that strong thermal lensing occurs in the highly doped sample (3 at.% Nd) and precludes scaling of the output power to large values. Results also show that undesirable thermal effects are dramatically reduced with decreasing active-ion concentration. The best power performance was obtained with a 10-mm-long Nd:YVO4 sample that had 0.5 at.% Nd. In this case, up to 6.5 W of continuous-wave output power was obtained at 1064 nm by using a 3% transmitting output coupler.
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    Three-dimensional photonic crystal structures achieved with self-organization of colloidal particles (2000)
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    Optical and quantum electronics 32 (2000), S. 1295-1300 
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    Keywords: photonic crystal ; self-organization ; transmission spectrum
    Source: Springer Online Journal Archives 1860-2000
    Topics: Electrical Engineering, Measurement and Control Technology , Physics
    Notes: Abstract Three-dimensional polystyrene/air photonic crystal structure with different particle diameters: 200, 270 and 340 nm was achieved. Strong photonic band gap effect reflected with transmission minimum down to −16 dB was observed. The central wavelengths of the valleys of spectra were well fitted with theoretical calculation. The augmentation of band gap effect versus particle diameter was attributed to an improved self-assembling of particles. An analysis of transmission spectra is also presented. The agreement between the results of experiment and numerical analysis is good.
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    Strong-interaction approximation in the theory of second harmonic generation of intense short laser pulses (2000)
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    Optical and quantum electronics 32 (2000), S. 1289-1294 
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    Keywords: laser pulse ; second harmonic generation
    Source: Springer Online Journal Archives 1860-2000
    Topics: Electrical Engineering, Measurement and Control Technology , Physics
    Notes: Abstract The method of strong interaction of nonlinear waves has been developed to analyse the second harmonic generation of intense laser radiation in the transient regime. Analytic solution for frequency conversion efficiency – taking into account the pump radiation depletion, influence of phase mismatch, dispersion of group velocities and higher nonlinearities – has been first obtained. A comparison of theoretically derived results and known experimental data has been conducted, and a general agreement of these results has been obtained. The optimal conditions of the second harmonic generation of neodymium laser radiation into femtosecond pulse duration range have been determined.
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    Power efficiency of a semiconductor laser with an external cavity (2000)
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    Optical and quantum electronics 32 (2000), S. 1343-1350 
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    Keywords: external cavity laser ; laser diode ; optical feedback ; power efficiency
    Source: Springer Online Journal Archives 1860-2000
    Topics: Electrical Engineering, Measurement and Control Technology , Physics
    Notes: Abstract Optical feedback modifies the power vs. current diagram of a laser diode as well as its spectrum. Though optimization of the spectral characteristics is usually the main goal in the design of an external cavity source, power efficiency is also important, especially with relatively high power devices, where temperature variations due to dissipation can have an impact on the wavelength stability and on the laser lifetime. A useful parameter to describe the total power efficiency of the stabilized laser, relative to that of the solitary laser, is proposed in this paper. The dependence of this parameter on the characteristics of the active device, and of the external cavity, is investigated.
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    Evaluation of Gb/s laser based fibre LAN links: Review of the Gigabit Ethernet model (2000)
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    Optical and quantum electronics 32 (2000), S. 169-192 
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    Keywords: Gigabit Ethernet ; modal bandwidth ; multimode fibre ; singlemode fibre
    Source: Springer Online Journal Archives 1860-2000
    Topics: Electrical Engineering, Measurement and Control Technology , Physics
    Notes: Abstract The theoretical model used by Gigabit Ethernet to develop the optical physical layer specifications is presented. The model calculates the penalties associated with using laser based transceivers on both multimode and singlemode fibre Gb/s links. Experimental verification of the model's predictions is also presented along with discussion on the use of the model to predict link performance. The model is generic to laser based fibre LAN links but specific details and examples relevant to Gigabit Ethernet are discussed.
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    A GaAs–InGaAs optoelectronic switch with multiple operation states (2000)
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    Optical and quantum electronics 32 (2000), S. 1301-1306 
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    Keywords: δ-doped ; negative differential resistance ; optoelectronic switch
    Source: Springer Online Journal Archives 1860-2000
    Topics: Electrical Engineering, Measurement and Control Technology , Physics
    Notes: Abstract An optoelectronic switch with both n- and p-type delta-doped (δ-doped) quantum wells was investigated. The δ-doped structures formed potential wells for the carrier accumulation and potential barriers for the carrier injection. Being possessed of δ-doped sheets with different doping levels, the potential barriers were sequentially collapsed to produce a double negative-differential-resistance (NDR) phenomenon in the current–voltage (I–V) characteristics of the device, due to the carrier accumulation in the potential wells. The device also showed an optical function related to the barrier heights controllable by incident light.
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    Spatial filtering using poled polymer etalon light modulators (2000)
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    Optical and quantum electronics 32 (2000), S. 1351-1358 
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    Keywords: electro-optic effect ; etalon ; light modulator ; organic material ; polymeric material ; spatial filter
    Source: Springer Online Journal Archives 1860-2000
    Topics: Electrical Engineering, Measurement and Control Technology , Physics
    Notes: Abstract Spatial filtering using poled polymer light modulators is studied. The use of a resonator structure is proposed to minimize the driving voltage. Side-chain polymer poly-orange tom-1 isophoronedisocyanate is used as a material. The measured electro-optic coefficient r 33 is 23 pm/V at the wavelength of 633 nm. Spatial filtering of the input images are realized with 30 V applied voltage.
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    On the measurement of the generalized degree of polarization (2000)
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    Optical and quantum electronics 32 (2000), S. 1333-1342 
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    Keywords: laser beams ; polarization ; beam characterization ; non-uniformely totally polarized beams
    Source: Springer Online Journal Archives 1860-2000
    Topics: Electrical Engineering, Measurement and Control Technology , Physics
    Notes: Abstract On the basis of well-known methods to obtain the standard Stokes parameters, two simple experimental procedures are analysed to measure the so-called generalized degree of polarization, P, defined elsewhere [Opt. Commun., 149 (1998) 230]. After discussing the accuracy of the methods, the generalized degree of polarization of a non-uniformly polarized beam emerging from an optically pumped birefringent Nd:YAG rod optically pumped is experimentally investigated in terms of the pumped power.
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    Analysis of twisted nematic liquid crystal Fabry–Perot interferometer (TN-FPI) filter based on the coupled mode theory (2000)
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    Optical and quantum electronics 32 (2000), S. 147-167 
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    ISSN: 1572-817X
    Keywords: Coupled mode theory ; liquid crystal ; tunable wavelength filter ; WDM
    Source: Springer Online Journal Archives 1860-2000
    Topics: Electrical Engineering, Measurement and Control Technology , Physics
    Notes: Abstract The tuning characteristics of a twisted nematic (TN) liquid crystal (LC) Fabry–Perot interferometer (FPI) wavelength filter, which is a basic component of wavelength division multiplexed transmission systems, is analyzed using coupled mode theory. First, a simplified modeling of the refractive index change in the LC layer is presented. Next, various characteristics of the eigen polarization modes of the LC medium and the cavity are derived analytically. Finally, the qualitative interpretation of the behavior of the FPI's resonance spectrum are given.
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    New biochemical material laser emission in microdroplets using ribo-flavin and its enhancement by mixing highly scattering intralipid medium (2000)
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    Optical and quantum electronics 32 (2000), S. 137-145 
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    ISSN: 1572-817X
    Keywords: highly scattering medium ; intralipid-10% suspension ; microdroplet laser ; new laser emission ; ribo-flavin
    Source: Springer Online Journal Archives 1860-2000
    Topics: Electrical Engineering, Measurement and Control Technology , Physics
    Notes: Abstract New laser emission from a biochemical material, ribo-flavin (vitamin B2), at 570 nm was observed for the first time in liquid microdroplets pumped at 475 nm using a pulsed optical parametric oscillator. Laser emission spectra from microdroplets containing ribo-flavin in water and glycerol solution exhibit periodic mode structures depending on the microdroplet diameter demonstrating the morphology-dependent resonances. Magnitude enhancement of lasing emission is confirmed experimentally from liquid microdroplets of ribo-flavin solution with appropriate mixture of the fat emulsion Intralipid-10% suspension as highly scattering medium. We believe that such biochemical-soft multiple light scatterer systems may allow a wide range lasing of other bio-materials and even lead to the discovery of some novel species as well as highly sensitive analysis and diagnosis for future applications.
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    Fibre mopfa source of femtosecond pulses with wavelength tunability from 790 to 830 nm (2000)
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    Optical and quantum electronics 32 (2000), S. 193-196 
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    ISSN: 1572-817X
    Keywords: frequency doubling ; optical fibre ; Raman scattering
    Source: Springer Online Journal Archives 1860-2000
    Topics: Electrical Engineering, Measurement and Control Technology , Physics
    Notes: Abstract A fibre-optic of sub-150 fs pulse with wavelength tunability from 790 to 830 nm is demonstrated. The output from a gain-switched DFB laser diode at 1552 nm is amplified and compressed in an EDFA generating a soliton-Raman continuum which was then frequency doubled. The output wavelength was tuned over a 40 nm range with very little variation in the pulse duration and output power.
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    Organic single-quantum-well electroluminescent device (2000)
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    Optical and quantum electronics 32 (2000), S. 117-123 
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    Keywords: electroluminescence ; organic ; quantum-well
    Source: Springer Online Journal Archives 1860-2000
    Topics: Electrical Engineering, Measurement and Control Technology , Physics
    Notes: Abstract A new kind of single-quantum-well electroluminescent (EL) device consists of a hole transport N,N-Bis(3-methyphenyl)-N,N-diphenylbenzidine(TPD) layer, and electron transport 8-(quinolinolate)-aluminum(Alq) layer and a light emitting layer of Alq doped with 5,6,11,12-tetraphenylnaphthacene (rubrene) has been fabricated by the multisource-type high-vaccum organic molecular deposition. The dopant rubrene is as a potential well, and the undoped Alq layer is as a barrier layer. The EL spectra shows the spectral narrowing and the emission peak energy blue-shift, and the efficiency and luminance of the device have been significantly improved. The experimental phenomena is explained as the result of recombination of carriers from the quantized energy state.
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    Lasing action of active-particles dispersed in microdroplets and its enhanced characteristics by highly scattering intralipid-10% mixture (2000)
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    Optical and quantum electronics 32 (2000), S. 125-135 
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    ISSN: 1572-817X
    Keywords: active particle ; fluorescent powder ; highly scattering medium ; intralipid-10% solution ; microdroplet laser ; new microdroplet-configuration
    Source: Springer Online Journal Archives 1860-2000
    Topics: Electrical Engineering, Measurement and Control Technology , Physics
    Notes: Abstract The first laser action of active-particles of 1–2 μm in diameter, red fluorescent-powder (FP), dispersed in nonactive (nonlasing) ∼100 μm-sized liquid microdroplets is reported. Lasing characteristics of FP-containing microdroplets by mixing Intralipid-10% as highly scattering turbid media are also described. Well-defined lasing thresholds can be confirmed from the FP-dispersed pure microdroplets, and lowered lasing threshold along with enhanced lasing emission is achieved by appropriately mixing the Intralipid-10% solution. Lasing threshold in these microdroplets can be determined not through the spectral narrowing features but through the input–output data. We believe that these new microdroplet configurations offer one of the new categories of lasing media and they seem also to simulate to some biological pigments or organelles contained in cells and small tissues.
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    Efficient coupling of a laser to a waveguide using a taper designed by conformal mapping (2000)
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    Optical and quantum electronics 32 (2000), S. 197-208 
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    ISSN: 1572-817X
    Keywords: lasers ; pigtailing ; waveguides
    Source: Springer Online Journal Archives 1860-2000
    Topics: Electrical Engineering, Measurement and Control Technology , Physics
    Notes: Abstract Maximising the optical power collected in a waveguide from the diffracting field of a semiconductor laser is desirable in optical fibre communication systems. However, the spot size and phase front curvature of the laser field usually makes a poor overlap with the mode of the receiving waveguide. Various proposals have been made to improve this coupling. This paper presents the design of a tapered waveguide section, having the correct geometry and refractive index profile, to efficiently capture and transform the rapidly diffracting light from a semiconductor laser to a planar wavefront in a straight waveguide. Experimentally, such an approach requires the refining of available techniques (UV exposure, ion implantation or diffusion) to obtain the required grading of the refractive index profile within the tapered input section of the receiving waveguide.
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    Solutions for heteroepitaxial growth of GaN and their impact on devices (2000)
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    Optical and quantum electronics 32 (2000), S. 227-248 
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    Keywords: dislocations ; GaN ; heteroepitaxy ; laser ; LEDs
    Source: Springer Online Journal Archives 1860-2000
    Topics: Electrical Engineering, Measurement and Control Technology , Physics
    Notes: Abstract GaN technology relies on highly mismatched heteroepitaxial growth, mainly on sapphire or SiC substrates, and therefore suffers from 109 to 1010 threading dislocations per cm2. The origin and the deteriorating influence of the extremely high dislocation densities are analyzed with regard to the specific circumstances of GaN technology. Various attempts to cope with heteroepitaxial growth are discussed, from the use of nucleation layers to the growth on GaN single bulk crystals. Special focus is put on the impact of the approaches on the device performance.
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    Quantum well and quantum dot lasers: From strained-layer and self-organized epitaxy to high-performance devices (2000)
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    Optical and quantum electronics 32 (2000), S. 211-225 
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    ISSN: 1572-817X
    Keywords: electron-hole scattering ; hot-carrier effects ; performance ; quantum dot laser ; quantum well laser ; tunneling injection
    Source: Springer Online Journal Archives 1860-2000
    Topics: Electrical Engineering, Measurement and Control Technology , Physics
    Notes: Abstract Strained heterostructures are now widely used to realize high-performance lasers. Highly mismatched epitaxy also produces defect-free quantum dots via an island growth mode. The characteristics of high-speed strained quantum well and quantum dot lasers are described. It is seen that substantial improvements in small-signal modulation bandwidth are obtained in both 1 μm (48 GHz) and 1.55 μm (26 GHz) by tunneling electrons directly into the lasing sub-band. In quantum dots the small-signal modulation bandwidth is limited by electron-hole scattering to ∼7 GHz at room temperature and 23 GHz at 80 K. The properties of these devices are described.
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    Super high-power laser systems and their application (2000)
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    Optical and quantum electronics 32 (2000), S. 263-297 
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    ISSN: 1572-817X
    Keywords: AVLIS ; diode-pumped solid state laser ; laser fusion ; laser induced lightning ; material processing ; PW cpa laser ; X-ray
    Source: Springer Online Journal Archives 1860-2000
    Topics: Electrical Engineering, Measurement and Control Technology , Physics
    Notes: Abstract Super high-power laser systems have been studied. GEKKO XII glass laser, LEKKO VIII CO2 laser, diode-pumped solid-state laser and PW cpa Nd glass laser have been developed at Osaka University. They have proved to be very effective for laser fusion research. Various applications in the wide fields are presented.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1023/A:1007081622478
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    Study on the optoelectronic properties of amorphous selenium-based photoreceptors (2000)
    Springer
    Optical and quantum electronics 32 (2000), S. 249-261 
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    ISSN: 1572-817X
    Keywords: initial surface potential ; isothermal annealing ; photosensitivity ; photoinduced discharge curve ; residual potential
    Source: Springer Online Journal Archives 1860-2000
    Topics: Electrical Engineering, Measurement and Control Technology , Physics
    Notes: Abstract Due to its superior photosensitivity in the visible wavelength region, amorphous selenium-based material is widely used as the basic photoreceptor material in xerography. The optoelectronic properties of the samples were measured and calculated with photoinduced discharge curve (PIDC) by using Electrostatic Paper Analyzer, and the initial surface potential (V so), dark decay time (t d), photosensitivity (E 1/2) and residual potential (V r) could be obtained. It is found that the contrast voltage which affects directly the resolution of image can be improved by the blocking layer between the bulk (such as a-Se, a-As2Se3) and substrate (Al). Furthermore, the relations between thickness and optoelectronic properties of photoreceptor could be identified, and compared with different blocking layers and isothermal annealing effect for the photoreceptors.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1023/A:1007029605640
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    Frequency stabilization and measurements of 543 nm HeNe lasers (2000)
    Springer
    Optical and quantum electronics 32 (2000), S. 299-311 
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    ISSN: 1572-817X
    Keywords: frequency stabilization ; frequency measurement ; 543 nm HeNe laser ; iodine stabilization ; lamb-dip stabilization ; two-mode stabilization
    Source: Springer Online Journal Archives 1860-2000
    Topics: Electrical Engineering, Measurement and Control Technology , Physics
    Notes: Abstract In this paper we report our investigations on the frequency stabilization and frequency measurements of 543 nm HeNe laser. It contains following four different works. (1) Using a metal laser tube we have built an iodine-stabilized 543 nm HeNe laser by the Frequency-Modulation (FM) spectroscopy. The signal-to-noise ratio of the hyperfine spectrum reached 2 × 10−12 at 1 s sampling time. (2) We have built a compact iodine-stabilized 543 nm HeNe laser system using the third-harmonic locking technique. Stability better than 1 × 10−12 for sampling time 〉1 s is obtained. We also suggest the b10 line for the future recommendation. (3) We constructed the Lamb-dip stabilized He-20Ne and He-22Ne lasers and measured their frequency stability, reproducibility, and absolute frequencies. The results suggest that the Lamb-dip stabilized lasers are appropriate for secondary wavelength standards. We have also deduced the isotope shift of Ne atom at 543 nm. (4) We have developed two two-mode stabilized 543 nm HeNe lasers using the bang-bang control method. The Allan variance is 1 × 10−11 at 1 s sampling time.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1023/A:1007033709274
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    Bent waveguide with a high index reflector on LiNbO3 (2000)
    Springer
    Optical and quantum electronics 32 (2000), S. 313-325 
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    ISSN: 1572-817X
    Keywords: high index reflector ; LiNbO3 ; radiation loss ; waveguide bends
    Source: Springer Online Journal Archives 1860-2000
    Topics: Electrical Engineering, Measurement and Control Technology , Physics
    Notes: Abstract An abrupt bend structure with a corner reflector on LiNbO3 is proposed. In the proposed structure, a region whose refractive index is higher than that of the substrate is placed at the corner of the bend. The interface between the substrate and the high index region is used as a reflector for the guided wave. The calculated normalized transmission power is about 94% even when the bend angle is 10∘.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1023/A:1007098126113
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    Low loss niobium oxides film deposited by ion beam sputter deposition (2000)
    Springer
    Optical and quantum electronics 32 (2000), S. 327-337 
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    ISSN: 1572-817X
    Keywords: deposition rate ; homogeneity ; ion beam sputtering ; oxygen partial pressure ; surface roughness
    Source: Springer Online Journal Archives 1860-2000
    Topics: Electrical Engineering, Measurement and Control Technology , Physics
    Notes: Abstract Thin films of niobium oxides are deposited by ion beam sputtering with a Kaufman-type ion source. The deposition rate is function of the oxygen partial pressure. There is an optimum oxygen pressure at 7 × 10−5 Torr to deposite a stoichiometric film. The as-deposited films are amorphous. The optical parameters, including refractive index, extinction coefficient, and homogeneity, of the oxide films are influenced by post-baking temperature. The surface morphology measured by an atomic force microscope (AFM) shows that there is a certain range of optimum baking temperature which yields a smooth film and a good optical quality.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1023/A:1007050204074
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    Self-enhanced diffraction properties of a nominally undoped barium titanate crystal with a thermally fixed grating (2000)
    Springer
    Optical and quantum electronics 32 (2000), S. 349-365 
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    ISSN: 1572-817X
    Keywords: barium titanate ; beam coupling ; diffraction efficiency ; photorefractive effect ; thermal fixing
    Source: Springer Online Journal Archives 1860-2000
    Topics: Electrical Engineering, Measurement and Control Technology , Physics
    Notes: Abstract We describe recent studies on diffraction properties of a photorefractive barium titanate crystal having a thermally fixed grating. Buildup dynamics of diffracted signals are measured to analyze the contributions of ionic and re-created photocarrier (hole) gratings to the temperature-dependent diffraction efficiency in self-enhanced readout. An activation energy of mobile ions as nonphotoactive secondary carriers for fixing volume holograms is determined holographically. This value is compared with that of hydrogen ions estimated from polarization-dependent infrared absorption spectra in order to indentify the fixing species.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1023/A:1007096304983
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    Performances of an all-optical subtracted joint transform correlator that uses a photorefractive crystal (2000)
    Springer
    Optical and quantum electronics 32 (2000), S. 367-382 
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    ISSN: 1572-817X
    Keywords: pattern recognition ; photorefractive crystal ; volume hologram
    Source: Springer Online Journal Archives 1860-2000
    Topics: Electrical Engineering, Measurement and Control Technology , Physics
    Notes: Abstract An all-optical subtracted joint transform correlator (JTC) was proposed and it was experimentally shown that the correlator successfully performs the pattern recognition with the number of reference patterns. In the correlator, an optical interferometer was introduced to remove the additional correlation signals between the reference patterns themselves from the output plane and a photorefractive crystal was also introduced to record the joint power spectra as volume holograms. The processing for removing the additional correlation signals was performed by the parallel computations in the interferometer in real time. In this study it has been found that the correlator yields significantly better correlation results than the classical joint transform correlator does and the recording of the volume hologram corresponds to a nonlinear processing of the joint power spectrum in the fringe-adjusted joint transform correlator. However the volume hologram has angular selectivity for matching the Bragg condition. It would restrict the shift-invariant area of the input image plane. This restriction has been investigated experimentally.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1023/A:1007048421821
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    Spectral characteristics for a fiber grating external cavity laser (2000)
    Springer
    Optical and quantum electronics 32 (2000), S. 339-348 
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    ISSN: 1572-817X
    Keywords: antireflection coating ; external cavity laser ; fiber grating
    Source: Springer Online Journal Archives 1860-2000
    Topics: Electrical Engineering, Measurement and Control Technology , Physics
    Notes: Abstract A numerical investigation has been carried out on the influence of the antireflection (AR) coating of laser, the coupling efficiency of laser and fiber (η), and the reflectivity of fiber grating (R g) on the side-mode suppression ratio (SMSR) of the fiber grating external cavity laser (FGECL). The FGECL was fabricated by the assembly of the multimode Fabry–Perot (FP) laser chip and fiber grating. The results showed that the FGECL with a lower AR coating, higher η and R g exhibited a better SMSR. A comparison of the SMSR dependence on the η and R g showed that SMSR increased more rapidly with increasing η than SMSR for R g. These spectral characteristic studies of the SMSR dependence on the device parameters of the AR coating, η, and R g may provide useful device designs for the practical fabrication of a FGECL for use in dense wavelength division multiplexing (DWDM) applications.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1023/A:1007044320912
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    High density, high performance optical data storage via volume holography: Viability at last? (2000)
    Springer
    Optical and quantum electronics 32 (2000), S. 393-404 
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    ISSN: 1572-817X
    Keywords: holographic storage ; holography ; optical storage
    Source: Springer Online Journal Archives 1860-2000
    Topics: Electrical Engineering, Measurement and Control Technology , Physics
    Notes: Abstract The long held promise of using volume holography to deliver high performance optical storage is reviewed. The problems, which limited the development for many years, are accessed. Finally, we describe a series of innovations, which may make the technology viable at last.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1023/A:1007052522730
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    Ruggedized digital holographic data storage with fast access (2000)
    Springer
    Optical and quantum electronics 32 (2000), S. 383-392 
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    ISSN: 1572-817X
    Keywords: fast access memory ; holographic data storage ; photorefractive crystal ; solid-state memory
    Source: Springer Online Journal Archives 1860-2000
    Topics: Electrical Engineering, Measurement and Control Technology , Physics
    Notes: Abstract Recent investigations in holographic mass memory systems have produced proof-of-concept demonstrations that have highlighted their potential for providing unprecedented capacity, data transfer rates and fast random access performance (Heanue et al. 1994; Hong et al. 1995; Psaltis and Mok 1995; Bernal et al. 1996; McMichael et al. 1996). The exploratory nature of most such investigations has been largely confined to benchtop experiments which have ignored the practical constraints of packaging and environmental concerns. We have embarked on an effort to demonstrate the holographic mass memory concept by developing a compact prototype system geared for avionics and similar applications which demand the following features (mostly interdependent factors): (1) solid state design (no moving parts), (2) fast data seek time, (3) robust with respect to environmental factors (temperature, vibration, shock). In this paper, we report on the development and demonstration of two systems, one with 100 MB and the other with more than 1 GB of storage capacity. Both systems feature solid state design with the addressing mechanism realized with acoustooptic deflectors that are capable of better than 50 μsec data seek time. Since the basic designs for the two systems are similar, we describe only the larger system in detail. The operation of the smaller system has been demonstrated in various environments including hand-held operation and thermal/mechanical shock; a photograph of the smaller system is provided, as well as actual digital data retrieved from the same system.
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    URL: http://dx.doi.org/10.1023/A:1007000505891
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    Holographic read-only memory (2000)
    Springer
    Optical and quantum electronics 32 (2000), S. 405-417 
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    ISSN: 1572-817X
    Keywords: holographic storage ; read-only memory ; readout ; storage density
    Source: Springer Online Journal Archives 1860-2000
    Topics: Electrical Engineering, Measurement and Control Technology , Physics
    Notes: Abstract We describe the three-dimensional holographic optical disc system for application as read-only memory. Several systems design issues are discussed including imaging optics, storage density, readout rate, and the alignment servo system. We demonstrate 40 bits/m2 surface density and pixel-matched holographic data readout from a 12 cm disc spinning at 600 RPM.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1023/A:1007004622188
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    Special Issues on The 1998 International Photonics Conference (IPC '98) (2000)
    Springer
    Optical and quantum electronics 32 (2000), S. 209-209 
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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/10.1023/A:1017284122752
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    New approach of semiconductor laser related technologies for ultrafast photonics (2000)
    Springer
    Optical and quantum electronics 32 (2000), S. 443-452 
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    ISSN: 1572-817X
    Keywords: semiconductor laser ; ultrafast photonics ; ultrashort optical pulse
    Source: Springer Online Journal Archives 1860-2000
    Topics: Electrical Engineering, Measurement and Control Technology , Physics
    Notes: Abstract Ultrashort laser pulses offer new jump in information and communication technology. Especially semiconductor laser based ultrafast photonic devices and systems are promising. We review our new approaches for femtosecond pulse generation, and thin film technology for broad band semiconductor optical amplifiers.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1023/A:1007061222228
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    Diffraction patterns for a transmission volume hologram under Bragg mismatch (2000)
    Springer
    Optical and quantum electronics 32 (2000), S. 431-442 
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    ISSN: 1572-817X
    Keywords: Bragg degeneracy ; holographic storage ; photorefractive nonlinear optics ; volume holographic grating
    Source: Springer Online Journal Archives 1860-2000
    Topics: Electrical Engineering, Measurement and Control Technology , Physics
    Notes: Abstract We have presented simulations and experiments for 2-dimensional diffraction distributions of a transmission volume hologram. We sample the input pattern with a few elementary points and calculate the diffraction of the corresponding elementary grating. The simulations can describe well the diffraction pattern obtained in the experiment and can be used to predict the tolerance for angular deviation of the reading beam. The tolerance for angular deviation depends on its direction. It is affected by the Bragg degeneracy. The simulation results provide a clear picture of the spatial tolerance for reading a transmission volume hologram.
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    URL: http://dx.doi.org/10.1023/A:1007087101232
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    Angular multiplexed holographic memory system based on moving window on liquid crystal display and its crosstalk analysis (2000)
    Springer
    Optical and quantum electronics 32 (2000), S. 419-430 
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    ISSN: 1572-817X
    Keywords: crosstalk ; holographic memory ; LCD ; moving window ; multiplexing ; photorefractive material
    Source: Springer Online Journal Archives 1860-2000
    Topics: Electrical Engineering, Measurement and Control Technology , Physics
    Notes: Abstract We suggested a new non-mechanical angular multiplexed holographic memory system using a moving window, which was fabricated by controlling the pixels of a liquid crystal display (LCD) electronically. If we use light passed through the window left and right, and up and down, each window makes a reference wave with a different incidence angle and we can store angular-multiplexed holograms. The feasibility of the proposed method was demonstrated through optical experiments and its crosstalk noise analysis was also presented.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1023/A:1007074824914
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    Femtosecond semiconductor-based optoelectronic devices for optical-communication systems (2000)
    Springer
    Optical and quantum electronics 32 (2000), S. 453-471 
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    ISSN: 1572-817X
    Keywords: optical communication ; semiconductors ; ultrafast optics
    Source: Springer Online Journal Archives 1860-2000
    Topics: Electrical Engineering, Measurement and Control Technology , Physics
    Notes: Abstract Compact semiconductor-based ultrafast optoelectronic devices are crucial for networks with a throughput in the 1–10 Tb/s range. A variety of ultrafast phenomena in semiconductors are attractive for developing such new optoelectronic devices. This paper discusses the requirements of ultrafast optical-communication systems and necessary optoelectronic devices. Recent progress of ultrafast semiconductor-based optoelectronic devices are described with a focus on all-optical switching devices, including novel devices using electron spin polarization relaxation and intersubband transition both in multiple quantum well structures.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1023/A:1007002408115
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    Femtosecond pulse processing (2000)
    Springer
    Optical and quantum electronics 32 (2000), S. 473-487 
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    ISSN: 1572-817X
    Keywords: optical communications ; pulse shaping ; terahertz radiation ; ultrafast optics
    Source: Springer Online Journal Archives 1860-2000
    Topics: Electrical Engineering, Measurement and Control Technology , Physics
    Notes: Abstract We discuss Fourier methods for shaping and processing femtosecond optical signals. Examples of applications in optical communications and in generation of terahertz radiation are presented.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1023/A:1007062709024
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    Sampling of free-space magnetic pulses (2000)
    Springer
    Optical and quantum electronics 32 (2000), S. 489-502 
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    ISSN: 1572-817X
    Keywords: magneto-optic ; THz radiation
    Source: Springer Online Journal Archives 1860-2000
    Topics: Electrical Engineering, Measurement and Control Technology , Physics
    Notes: Abstract We report free-space detection of magnetic pulses via the Faraday effect with shot-noise limited detection. This allows a 10−8 T / √Hz magnetic field resolution. The orthogonal propagation of the optical probe beam and the THz waves demonstrate a 1.3 ps risetime with a 400 GHz frequency bandwidth. The temporal and frequency responses of several crystals are reported with a theoretical response function analysis presented. The dispersion of the magnetic pulse into the sensor crystal is illustrated with a theoretical simulation for comparison. We also contrast the properties of electro-optic sampling with this magneto-optic sampling technique.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1023/A:1007066809933
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    Intense THz-radiation from semiconductors under magnetic field irradiated with femtosecond laser pulses (2000)
    Springer
    Optical and quantum electronics 32 (2000), S. 521-529 
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    ISSN: 1572-817X
    Keywords: femtosecond laser pulses ; semiconductors ; THz-radiation
    Source: Springer Online Journal Archives 1860-2000
    Topics: Electrical Engineering, Measurement and Control Technology , Physics
    Notes: Abstract The THz-radiation power from InAs reaches sub-mW level in a 1.7-T magnetic field irradiated with femtosecond laser pulses of 1.5-W average power. The THz-radiation power is related almost quadratically both to the magnetic field and to the excitation laser power. Furthermore, the THz-radiation spectrum is found to be controlled by the excitation pulsewidth, chirp direction of the excitation pulse, and the magnetic field.
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    URL: http://dx.doi.org/10.1023/A:1007043616293
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    Generation of coherent terahertz radiation by photomixing of dual-mode lasers (2000)
    Springer
    Optical and quantum electronics 32 (2000), S. 503-520 
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    ISSN: 1572-817X
    Keywords: dual-mode lasers ; LTG-GaAs ; photomixing ; terahertz radiation
    Source: Springer Online Journal Archives 1860-2000
    Topics: Electrical Engineering, Measurement and Control Technology , Physics
    Notes: Abstract We have reviewed and discussed the generation of continuous-wave terahertz radiation by the photomixing of dual-mode lasers, which includes a multi-mode laser diode (LD), a dual-mode microchip laser, a monolithic dual-mode DBR LD, and a widely tunable dual-mode external cavity LD. It is demonstrated by several experiments that the beat frequency of a dual-mode laser is more stable than the original laser modes because of the common-mode rejection effect. We also suggest a novel scheme by which the optical beat is stabilized to less than 1 kHz and its frequency can be precisely determined as well.
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    URL: http://dx.doi.org/10.1023/A:1007070931314
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    Ultrafast response of multi-energy proton-bombarded GaAs photoconductors (2000)
    Springer
    Optical and quantum electronics 32 (2000), S. 553-571 
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    ISSN: 1572-817X
    Keywords: carrier lifetime ; electro-optic sampling ; photoconductor ; proton-bombarded GaAs ; THz radiation
    Source: Springer Online Journal Archives 1860-2000
    Topics: Electrical Engineering, Measurement and Control Technology , Physics
    Notes: Abstract We have investigated the ultrafast optical and optoelectronic characteristics of multi-energy proton-bombarded GaAs (GaAs:H+) material and devices in some detail. Photo-excited carrier lifetimes of GaAs:H+ were observed to be as low as 350 ± 50 fs. Photoconductive switches (PCS) fabricated on GaAs:H+ were found to exhibit lower dark currents (15 nA at a bias of 10 V) and higher breakdown voltage (〉 100 kV/cm) than PCS's fabricated on semi-insulating (S.I.) GaAs. The temporal response of the GaAs:H+ PCS was about 2 ps at full-wave half minimum. Optically excited terahertz (THz) radiation from GaAs:H+ was reported for the first time to our knowledge. The temporal response and spectral bandwidth of the emitted THz radiation were 0.7 ps and 1.25 THz, respectively. The field strength of the THz signal was about 20 mV/cm. From the THz data, we are able to deduce that the effective carrier mobility of GaAs:H+ was less than 1 cm2/V-sec.
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    URL: http://dx.doi.org/10.1023/A:1007055918110
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    Second-order nonlinear optical materials for efficient generation and amplification of temporally-coherent and narrow-linewidth terahertz waves (2000)
    Springer
    Optical and quantum electronics 32 (2000), S. 531-552 
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    ISSN: 1572-817X
    Keywords: backward configuration ; CdSe ; coherent THz waves ; difference-frequence generation ; forward configuration ; GaAs ; GaP ; GaSe ; LiNbO3 ; LiTaO3 ; optical parametric oscillation and amplification
    Source: Springer Online Journal Archives 1860-2000
    Topics: Electrical Engineering, Measurement and Control Technology , Physics
    Notes: Abstract We have considered forward and backward optical parametric oscillation and amplification, and difference-frequency generation for efficiently generating and amplifying terahertz waves in several second-order nonlinear optical materials. We have used a single crystal of CdSe as an example. We have also investigated GaSe, periodically-poled LiNbO3 and LiTaO3, and diffusion-bonded-stacked GaAs and GaP plates. The advantage of using birefringence in CdSe and GaSe is tunability of the output terahertz frequency. Furthermore, both CdSe and GaSe can be used to achieve the backward parametric oscillation without any cavity. On the other hand, in periodically-poled LiNbO3 and LiTaO3, one can take advantage of large diagonal elements of second-order nonlinear susceptibility tensor. In the diffusion-bonded-stacked GaAs and GaP plates, quasi-phase matching can be achieved by alternatively rotating the plates. We have shown that it is feasible to achieve forward optical parametric oscillation in the THz domain using these plates. The advantage of using coherent parametric processes is possibility of efficiently generating and amplifying temporally-coherent and narrow-linewidth terahertz waves. Compared with a noncollinear configuration, by using the parallel wave propagation configurations, the conversion efficiency can be higher because of longer effective interaction length among all the waves.
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    URL: http://dx.doi.org/10.1023/A:1007099701272
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    Comparison of optical pump-probe characterization of low-temperature-grown GaAs at well-above-bandgap and near-bandedge wavelengths (2000)
    Springer
    Optical and quantum electronics 32 (2000), S. 573-584 
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    ISSN: 1572-817X
    Keywords: low-temperature-grown GaAs ; photo-carrier lifetime ; time-resolved photoreflectance
    Source: Springer Online Journal Archives 1860-2000
    Topics: Electrical Engineering, Measurement and Control Technology , Physics
    Notes: Abstract Annealed low-temperature-grown GaAs was studied by time-resolved photoreflectance measurement at well-above-bandgap photon energies and by photoreflectance as well as transmission measurements at near-bandedge wavelength. At near-bandedge wavelength, the initial changes in reflectivity and transmission were observed to relax at identical relaxation rate, which was attributed to the absence of carrier cooling and the domination of carrier trapping. All the measured photoreflectance traces were found to be well fitted by the previously proposed three-component decomposition procedure. Among the three components, the fast positive peak was attributed to absorption bleaching and its relaxation, that is, the scattering of the photo-carrier out of their initially excited states by carrier cooling and trapping. The decay times of the positive peak, combined with the carrier cooling times extracted from photoreflectance measurement on semi-insulating GaAs, give consistent estimate of carrier trapping time at all wavelengths within the spectral range. Our results verify that well-above-bandgap photoreflectance measurement combined with the three-component fitting procedure can be used to estimate the photo-carrier trapping time which are consistent with that obtained by near-bandedge photoreflectance and transmission techniques.
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    URL: http://dx.doi.org/10.1023/A:1007008003089
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    Diode-laser pumped high-power and actively mode-locked Nd:YLF laser with fast switching (2000)
    Springer
    Optical and quantum electronics 32 (2000), S. 609-617 
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    ISSN: 1572-817X
    Keywords: mode-locked laser ; self-phase modulation
    Source: Springer Online Journal Archives 1860-2000
    Topics: Electrical Engineering, Measurement and Control Technology , Physics
    Notes: Abstract In an actively mode-locked laser, self-phase modulation can make pulse shorter at the expanse of causing instability at high pumping power. Using fast switching on the acousto-optic modulator, we can generate an actively mode-locked pulse train with shorter pulse width and higher average power than that driven by a sinusoidal signal. A 9-ps pulse train was generated in a mode-locked laser with an average power of 600 mW whose power level, to our knowledge, is the highest for diode-pumped and mode-locked Nd:YLF lasers.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1023/A:1007068205815
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    Large near resonance third order nonlinearity in GaN (2000)
    Springer
    Optical and quantum electronics 32 (2000), S. 619-640 
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    ISSN: 1572-817X
    Keywords: GaN ; nonlinear refractive index ; third-order nonlinearity ; two-photon absorption ; two-photon confocal microscopy
    Source: Springer Online Journal Archives 1860-2000
    Topics: Electrical Engineering, Measurement and Control Technology , Physics
    Notes: Abstract We have studied third order nonlinearities, including two-photon absorption coefficient β and nonlinear refractive index n 2, of GaN in below bandgap ultraviolet (UV) wavelength regime by using UV femtosecond pulses. Two-photon absorption was investigated by demonstrating femtosecond UV pulsewidth autocorrelation in a GaN thin film while femtosecond Z-scan measurements revealed information for both n 2 and β. The distribution of n 2 versus wavelength was found to be consistent with a model described by the quadratic Stark effect, which is the dominant factor contributed to the nonlinear refractive index near the bandgap. Large β on the order of 10 cm/GW and large negative n 2 with a magnitude on the order of several 10−12 cm2/W were obtained. The β at near mid-gap infrared (IR) wavelength was also found to be on the order of several cm/GW by using two-photon-type autocorrelations in a GaN thin film. Taking advantage of the large two-photon absorption at mid-gap wavelengths, we have demonstrated excellent image quality on two-photon confocal microscopy, including two-photon-scanning-photoluminescence imaging and two-photon optical-beam-induced current microscopy, on a GaN Hall measurement sample and an InGaN green light emitting diode.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1023/A:1007076506723
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