We demonstrate an electrooptic synthesis technique for generating arbitrarily shaped short optical pulses from a CW narrow linewidth laser. For the optical pulse shaping, a large-amplitude electrooptic phase modulator is specially fabricated by employing the quasi-velocity-matching. The phase modulated light having sidebands as wide as 1 THz is separated and phase-only-controlled spatially by a liquid crystal modulator array. After composing the light by using a grating, nearly 1. 2 ps of Fourier-transform-limited optical pulses is obtained.

It is shown from the Hilberts theory that if the real function Π(θ) has no zeros over the interval [0, 2π], it can be factorized into a product of the factor π+(θ) and its complex conjugate π-(θ)(=). This factorization is tested to decompose a real far-zone field pattern having zeros. To this end, the factorized factors are described in terms of bicomplex mathematics. In our bicomplex mathematics, the temporal imaginary unit "j" is newly defined to distinguish from the spatial imaginary unit i, both of which satisfy i2=-1 and j2=-1.

In this paper, we develop a novel method for tuning parameters known as the sensitivity parameters of membership functions used in a fuzzy classifier. The proposed method performs tuning by solving a set of inequalities. Each inequality represents a range of the ratio of the sensitivity parameters between the corresponding pair of classes. The range ensures the maximum classification rate for data of the two corresponding classes used for tuning. First, we discuss how such a set of inequalities is derived. We then propose an algorithm to solve the derived set of inequalities. We demonstrate the effectiveness of the proposed tuning method using two classification problems, namely, classification of commonly used iris data, and recognition of vehicle licence plates. The results are compared with those obtained by using the existing tuning method and with those by neural networks.

In this paper, we propose an extension of finite state tree automaton, called tree automaton with tree memory (TTA), and also define structure composing TTA (SC-TTA) and backward deterministic TTA (BD-TTA) as subclasses of TTA. We show that the classes of yield languages accepted by TTAs, SC-TTAs and BD-TTAs are equal to the class of recursively enumerable languages, the class of languages generated by tree-to-string finite state translation systems (TSFSTSs) and the class of languages generated by deterministic TSFSTSs, respectively. As a corollary, it is shown that the yield language accepted by an SC-TTA (resp. a BD-TTA) is linear space (resp. polynomial time) recognizable.

Requirements engineering refers to activities of gathering and organizing customer requirements and system specifications, making explicit representations of them, and making sure that they are valid and accounted for during the course of the design lifecycle of software. One very popular software development practice is the incremental development practice. The incremental development refers to practices that allow a program, or similarly specifications, to be developed, validated, and delivered in stages. The incremental practice is characterized by its depth-first process where focuses are given to small parts of the system in sequence to fair amounts of detail. In this paper, we present a development and validation of specifications in such an incremental style using a tool called ASADAL, a comprehensive CASE tool for real-time systems. ASADAL supports incremental and hierarchical refinements of specifications using multiple representational constructs and the evolving incomplete specifications can be formally tested with respect to critical real time properties or be simulated to determine whether the specifications capture the intended system behavior. In particular, we highlight features of ASADAL's specification simulator, called ASADAL/SIM, that plays a critical role in the incremental validation and helps users gain insights into the validity of evolving specifications. Such features include the multiple and mixed level simulation, real-value simulation, presentation and analysis of simulation data, and variety of flexible simulation control schemes. We illustrate the overall process using an example of an incremental specification development of an elevator control system.

When a set of objects is shared among several applications, multiple implementations for the set are required in order to suit each application as much as possible. Furthermore, if a set of objects could have multiple implementations, the following issues arise: (1) how to select the best implementation when processing queries on the set, and (2) how to propagate updates on an implementation of the set to the others. In this paper we propose a mechanism of multiple implementations for a set, and also give a solution for the latter issue. In the proposal a set can be of multiple types, and each of the types corresponds to an implementation already contained within the set. Update propagation can be achieved by a rewriting technique at compilation time. We also present a performance study in which the feasibility and effectiveness of our proposal were examined.

In this papers, we will discuss the different percentages of embedding certain subsystems successfully into a n-cube according to the fault model used. We will discuss two fault models: the first one assumes that, in a faulty node, the computational function of the node is lost while the communication function of the faulty node remains intact, and, in the second, the communication function is also lost. In this paper, 2 types of fault tolerable subsystem embedding schemes will be introduced. The first one embeds a complete binary tree into a n-cube with faulty nodes, and the second embeds two (n-1)-subcubes whose total number of faulty nodes is less than half the number of nodes. These schemes are divided into 4 types based on the above two models. First, we will discuss how different the successful percentages of embedding are for 2 of the different types of embedded binary trees that are based on the above two models. Then, we will analyze the possibility that the component nodes of an embedded binary tree can communicate via the faulty nodes that are located in the embedded binary tree. In the embedding process, each faulty node was replaced with a nonfaulty node that was located on another (n-1)-subcube and at a Hamming distance of 1 from the faulty node. The number of faults that led to the successful percentage of embedding will be presented as an upper bound. Next, we will discuss how different the successful embedding percentages are for the 2 types of irregular (n-1)-subcubes based on the two models; that is, if 2n-2+1 or more of the nonfaulty nodes in both of the (n-1)-subcubes can communicate or not via faulty nodes. Here also, the number of faults that led to a successful embedding percentage will be presented as a critical value.

A field theory for geometrical pattern identification is developed based on the postulate that various modified patterns are identified via invariant characteristics of pattern transformations. The invariant characteristics of geometrical patterns are written as the functional of the light intensity distribution of pattern, its spatial gradient, and also its spatial curvature. Some definite expressions of the invariant characteristic functional for two dimensional linear transformation are derived, and their invariant and feature extracting property are examined numerically. It is also shown that the invariant property is conserved even when patterns are deformed locally by introducing a "gauge field" as new degree of freedom in the functional in form of a covariant derivative. Based on this idea, we discuss a field theoretical model for pattern identification performed in biological systems.

Experiments were performed to investigate perceptual contributions of static and dynamic features of vocal tract characteristics to talker individuality. An ARX (Auto-regressive with exogenous input) speech production model was used to extract separately voice source and vocal tract parameters from a Japanese sentence, /aoiueoie/ ("Say blue top" in English) uttered by three males. The Discrete Cosine Transform (DCT) was applied to resolve formant trajectories of the speech signal into static and dynamic components. The perceptual contributions were quantitatively studied by systematically replacing the corresponding formant components of the sentences between the three talkers. Results of the experiments show that the static (average) feature of the vocal tract is a primary cue to talker individuality.

This paper deals with an orthogonal functional expansion of a non-linear stochastic functional of a stationary binary sequence taking 1 with unequal probability. Several mathematical formulas, such as multivariate orthogonal polynomials, recurrence formula and generating function, are given in explicit form. A formula of an orthogonal functional expansion for a stochastic functional is presented; the completeness of expansion is discussed in Appendix.

This paper analyzes pulse characteristics of actively mode-locked fiber lasers by including the group-velocity dispersion and the Kerr nonlinearity of the fiber, both of which have not been taken into account in the conventional theory of mode locking. We show that chirped sech pulses are generated from nonlinear and dispersive fiber lasers. By considering the stability of the laser, we also derive design rules for the generation of ultra-short pulses.

This paper proposes a novel low power dissipation technique for a low voltage OTA. A conventional low power OTA with a class AB input stage is not suitable for a low voltage operation (1. 5 V supply voltages), because it uses composite transistors (referred to CMOS pair) which has a large threshold voltage. On the other hand, the tail-current type OTA needs a large tail-current value to obtain a sufficient input range at the expense of power dissipation. Therefore, the conventional tail-current type OTA has a trade-off between the input range and the power dissipation to the tail-current value. The trade-off can be eliminated by the proposed technique. The technique exploits negative feedback control including a current amplifier and a minimum current selecting circuit. The proposed technique was used on Wang's OTA to create another OTA, named Low Power Wang's OTA. Also, SPICE simulations are used to verify the efficiency of Low Power Wang's OTA. Although the static power of Low Power Wang's OTA is 122 µW, it has a sufficient input range, whereas conventional Wang's OTA needs 703 µW to obtain a sufficient input range. However, we can say that as the input signal gets larger, the power of Low Power Wang's OTA becomes larger.

Multicasting is an important feature for any switching network being intended to support broadband integrated services digital networks (B-ISDN). This paper proposes an improved multicast packet switch based on Lee's nonblocking copy network. The improved design retains the desirable features of Lee's network including its nonblocking property while adopting techniques to overcome the various limitations mentioned in various literature. The proposed network architecture utilizes d-dilated banyan networks to increase the amount of cells that can be replicated within the copy network. Cell splitting is used to optimize the utilization of the network's available bandwidth. Furthermore, the proposed architecture allows for the modular expansion in capacity to accomodate changing traffic patterns. The modular design of the proposed switch likewise offers easy handling and replacement of faulty modules.

The development of a far-infrared imaging system based on ultrafast THz time-domain spectroscopy has opened a new field of applications of femtosecond technology. We describe the principle of this new imaging technique and report recent progress to augment the possibilities of "T-ray" imaging. These include sub-wavelength-resolution near-field imaging and three-dimensional tomographic reconstruction of a samples refractive index profile.

This paper describes an MOS current-mode sample-and-hold (S/H) circuit that potentially operates with a sub-1. 5 V supply voltage, 20 MHz clock frequency, and less than 0. 1% linearity. A newly developed voltage-to-current converter suppresses the voltage change at an input terminal and achieves low-voltage operation with superior linearity. Sample switches are differentially placed at the inputs of a differential amplifier so that the feedthrough errors from switches cancel out. The MOS current-mode S/H circuit is designed and simulated using CMOS 0. 6 µm device parameters. Simulation results indicate that an operation with 20 MHz clock frequency, linearity error of less than 0. 1%, and 1 MHz input from a 1. 5 V power supply is achievable.

Recent advances in solid-state laser technology and ultrafast optics led to the generation of optical pulses as short as 5 femtoseconds with peak powers up to the subterawatt level from a compact kHz-repetition-rate all-solid-state laser. This source significantly pushes the frontiers of nonlinear optics. Exciting new possibilities include the investigation and exploitation of reversible nonlinear optical processes in solids at unprecedented intensity levels, the development of a compact laser-driven coherent soft-X ray source at photon energies near 1 keV, and the generation of attosecond xuv pulses. First, a brief review of recent milestones in the evolution of ultrafast laser technology is given, followed by a description of the high-power 5-fs source. The rest of the paper is devoted to applications in previously inaccessible regimes of nonlinear optics. We demonstrate that wide-gap dielectrics resist intensities in excess of 1014 W/cm2 in the sub-10 fs regime and the extension of high-harmonic generation in helium to wavelengths shorter than 2. 4 nm (Eph > 0. 5 keV).

In this paper, we describe the properties of an external cavity modelocked semiconductor laser with a tunability of wavelength, pulse width and repetition rate. This modelocked laser generates optical pulses with pulse widths down to 180 fs and with repetition rates up to 14 GHz in a 120 nm wavelength range near 1. 55 µm or 1. 3 µm. The generated pulses are close to the transform limit and are therefore suitable for very high speed communication systems. In addition to the tunability, this pulse source is a compact and mechanically stable device. We report on two applications of this pulse source in optical time division multiplexing experiments. In the first example the modelocked laser is used as an all-optical clock recovery. In the second example the modelocked laser was used to characterize an interferometric switch by pump-probe experiments.

This paper describes a method for analyzing active impedance, i. e. equivalent resistance and equivalent reactance, of a narrow-band transistor Colpitts crystal oscillator. This oscillator, employing an AT-cut resonator filter, has a very narrow-band width and an achievement of extremely low phase-noise characteristics is expected. The analysis proposed is based on an algebraic formula, which employs a nonlinear approximation for transistor gm, and a simplified circuit model. Calculated results are compared with the experimental results in the frequency characteristics of the oscillator active impedance with changing the driving signal current. Good agreement between the calculation and experimental results shows that the proposed technique is suitable for designing Colpitts crystal oscillators with resonator filters. In addition we apply this technique to the analysis of dual-mode crystal oscillators.

In this paper we review the stretched-pulse principle and discuss its inherent advantages for ultrashort pulse generation and transmission. An analytic theory of the stretched-pulse fiber laser is presented and shown to be in good agreement with experimental results. An extension of the stretched-pulse theory is applied to both fiber lasers and dispersion-allocated soliton transmission and then compared to numerical results. We also discuss the design and operation of an environmentally stable stretched-pulse fiber laser.

Input and output queueing two stage ATM switch model which is effective under variable hot-spot traffic is proposed. In order to prevent the degradation of performance due to hot-spot traffic, the hot-spot route is added in which cells destined to the hot-spot port bypass. The switch applies the backpressure mode basically. When the switch judges that the hot-spot port exists, it routes cells destined there to the hot-spot route and applies the queue loss mode on them. We evaluate both the cell loss probability and the mean system delay under the nonuniform traffic with variable hot-spot port by computer simulation. As the results, it is shown that our proposed switch can achieve better switching performance than those of conventional switches under variable traffic condition.