Electroabsorption modulators are high speed devices that are rapidly being commercialised and finding applications in a number of areas, particularly in telecommunications. A CW laser diode modulated by an electroabsorption modulator constitutes an extremely stable, robust and simple source of high quality, high repetition rate ultrashort optical pulses. In this paper we describe the capabilities and limitations of such pulse sources, and present nonlinear pulse compression and manipulation techniques that allow one to overcome these limitations. We also present the design of a new class of comb-like dispersion-profiled fibre compressor. Such a compressor is easily fabricated from commercially available fibres and represents a simple yet powerful way of extending the range of pulse durations available. As the electroabsorption modulator is essentially a high speed switch it is also applicable to optical processing problems, and we report the application of such a device to demultiplexing.

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.

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 proposes a method of constructing single-electron logic subsystems on the basis of the binary decision diagram (BDD). Sample subsystems, an adder and a comparator, are designed by combining single-electron BDD devices. It is demonstrated by computer simulation that the designed subsystems successfully produce, through pipelined processing, an output data flow in response to the input data flow. The operation error caused by thermal agitation is estimated. An output interface for converting single-electron transport into binary-voltage signals is also designed.

A new broadband space diversity (B-SD) combining method, which is a key technique in the growth of digital microwave radio system, is proposed. In this B-SD combining method, two received signals, whose bandwidths are 280 MHz, are combined. To develop this combining method, an optimum control algorithm is developed that monitors power levels of all primary carriers and controls the endless phase shifter so that the higher level signal is decreased and the lower level signal is increased. This paper describes the proposed B-SD combining method which effectively operates over a wide bandwidth. Performance evaluations based on simulations and theoretical estimations are given. It is proven that this combining method offers the same performance obtained by the conventional narrowband SD combining method and can be applied to over 50% cases of the propagation paths observed in Japan. The suitability of the proposed combining method and the calculation methods adopted is demonstrated experimentally.

In order to investigate the nonlinearity and color responses of visual evoked potentials (VEPs), which have been useful in objectively detecting human color vision characteristics, a nonlinear system identification method was applied to VEPs elicited by isoluminant color stimuli, and the relationship between color stimuli and VEPs was examined. VEPs of normal subjects elicited by chromatically modulated stimuli were measured, and their binary kernels were estimated. Results showed that a system with chromatically modulated stimuli and VEP responses can be expressed by binary kernels up to the second order and that first- and second-order binary kernels depended on the color of the stimulus. The characteristics of second-order kernels reflected the difference between two chromatic channels. Opponent-color responses were included in first-order binary kernels, suggesting that they could be used as an index to test human color vision.

Detection of facial emotions are mainly addressed by computer vision researchers based on facial display. Also detection of vocal expressions of emotions is found in research work done by acoustic researchers. Most of these research paradigms are devoted purely to visual or purely to auditory human emotion detection. However we found that it is very interesting to consider both of these auditory and visual informations together, for processing, since we hope this kind of multimodal information processing will become a datum of information processing in future multimedia era. By several intensive subjective evaluation studies we found that human beings recognize Anger, happiness, Surprise and Dislike by their visual appearance, compared to voice only detection. When the audio track of each emotion clip is dubbed with a different type of auditory emotional expression, still Anger, Happiness and Surprise were video dominant. However Dislike emotion gave mixed responses to different speakers. In both studies we found that Sadness and Fear emotions were audio dominant. As a conclusion to the paper we propose a method of facial emotion detection by using a hybrid approach, which uses multimodal informations for facial emotion recognition.

A deterministic pushdown automaton (dpda) having just one stack symbol is called a deterministic restricted one-counter automaton (droca). A deterministic one-counter automaton (doca) is a dpda having only one stack symbol, with the exception of a bottom-of-stack marker. The class of languages accepted by droca's which accept by final state is a proper subclass of the class of languages accepted by doca's. Valiant has proved the decidability of the equivalence problem for doca's and the undecidability of the inclusion problem for doca's. Thus the decidability of the equivalence problem for droca's is obvious. In this paper, we evaluate the upper bound of the length of the shortest input string (shortest witness) that disproves the inclusion for a pair of real-time droca's which accept by accept mode, and present a direct branching algorithm for checking the inclusion for a pair of languages accepted by these droca's. Then we show that the worst-case time complexity of our algorithm is polynomial in the size of these droca's.

This paper proposes to apply random mapping methods of a pseudo random function to find collisions of a hash function. We test a hash function including a block cipher (see ISO/IEC 10118-2) with computers, where users can select its initial vector. In particular, the paper shows that a hash function with multiple stages generates a lot of collision hash values, so our probabilistic consideration of a small model for the hash function well explains the computational results. We show that it's feasible to find collisions between the selected messages in advance for 64-bit-size hash functions with WSs linked via an ordinary LAN (Local Area Network). Thus, it is dangerous to use the hash function -- single block mode -- defined in [6] and [7].

Recently reported multidimensional geometrically uniform signal constellations (L MPSK and Decomposed-Lattice constellations) are joined in the term of Generalized Permutation Alphabets (GPA). Possibility of a binary isometric labeling of GPA's is completely characterized. An algorithm for constructing generating groups of PSK-type GPA is proposed. We show that this concept, when is extended to the lattice, gives rise to a class of new coset codes which perform out best codes listed in [11].

This paper proposes a direct-sequence spread spectrum (DS/SS) communication system with a new diversity technique designed for indoor multi-path fading channels where path diversity isn't available. In this system, the transmitter sends a same signal from multiple antennas at the same time with intentional time delays, which allows the receiver to distinguish and combine the signals from different antennas. We also consider the combination of this scheme with the conventional receiving antenna diversity for additional diversity gain. Furthermore, it is found that the use of the multiple transmitting antennas decreases the effect of the multiple access interference.

The authors report on a 40-Gbit/s superdynamic decision IC fabricated with 0.12-µm GaAs MESFETs. The key to attaining high-speed decision IC is not only high-speed flip-flop circuits but also wideband input and output buffer circuits. 40 Gbit/s is the fastest operating speed of decision ICs fabricated with GaAs MESFETs.

It is well known that M-ary/spread spectrum (M-ary/SS) system is superior to direct-sequence spread spectrum system under AWGN, and can achieve high spectral efficiency. On the other hand, however, the main drawback of this system is that the synchronization acquisition is difficult. In this paper, we propose a new synchronization acquisition method of M-ary/SS system. This method acquires the code synchronization by introducing a symmetrical property in spreading sequences, and detecting this property with the differential decoding technique. As spreading sequences, a set of orthogonal sequences and a set of non-orthogonal sequences are considered. The strong features of proposed systems are that the systems can acquire the code synchronization in carrier band and can reduce the complexity of calculation greatly. Among the comparison results of the systems with newly proposed orthogonal and some specific non-orthogonal spreading sequences, it is especially noted that the latter can reduce the mean acquisition time and calculation complexity much greater than the former.

ITU (International Telecommunication Union) has issued request for submission of candidate technologies for IMT (International Mobile Telecommunication)-2000/FPLMTS radio interface in April 1997. In order to propose a candidate technology and to contribute to the production of a world wide standard of IMT-2000, ARIB (Association of Radio Industries and Businesses) has studied radio transmission technologies for IMT-2000. This paper shows the recent study results on IMT-2000 radio transmission technologies in ARIB. Now in ARIB detailed study to produce necessary specifications and prepare of a proposal on candidate radio transmission technology to ITU are being conduced based on wide band DS-CDMA technologies.

Considering that the application of the direct-sequence slotted spread ALOHA communications system to access/control channel is effective in communications systems with traffic channels operating at CDMA mode, the spread ALOHA communications system is discussed in terms of the system configuration and transmission efficiency. The transmission efficiency of the spread ALOHA communications system using a unified spread code is derived by means of two methods. One is based on the simulation of demodulation algorithm, and the other is based on the approximation by modeling. It becomes obvious from quantitative evaluation in terms of the probability of packet success and the throughput performance that the approximated results coincide with the simulated results, and that the modeling is very effective to estimate the transmission efficiency of the spread ALOHA communications system.

The efficiency and reliability of an ultrasonic motor, operating in longitudinal-torsional degenerate-mode, are investigated. It is essential to miniaturize both longitudinal and torsional mode piezoelectric ceramic elements, in order to produce low-cost ultrasonic motors, and to realize a motor with low battery power consumption. The ultrasonic motor is designed with an accurate mechanical equivalent circuit, which can produce high design precision notwithstanding low computation cost. It is important in this design that the resonant frequencies of longitudinal mode and torsional mode coincide with each other under the pertinent rotor pressing force and longitudinal and torsional mode piezoelectric ceramic elements are located in the vibration nodes for the longitudinal mode and the torsional mode, respectively. As a result, the fabricated motor, whose rotor diameter was 12 mm, produced 480 r.p.m. no-load revolution speed, 0.55 kgfcm maximum torque, 50% maximum efficiency, 2.5 W consumed power and a lifetime over 1000 hours with continuous rotation.

We present a method for learning classification functions from pre-classified training examples and hypotheses written roughly by experts. The goal is to produce a classification function that has higher accuracy than either the expert's hypotheses or the classification function inductively learned from the training examples alone. The key idea in our proposed approach is to let the expert's hypotheses influence the process of learning inductively from the training examples. Experimental results are presented demonstrating the power of our approach in a variety of domains.

In this paper, we discuss the use of convolutional codes with a multi-antenna transmission scheme for DS/CDMA systems. The binary input data to a rate 1/M encoder produces M coded bits, which, in turn, are assigned to M different antennas and transmitted from each antenna simultaneously. An intentional delay of several chips duration is introduced at each antenna before transmission, which enables a receiver to distinguish the signals from different antennas. Because the proposed scheme utilizes spatial and time domains for coding, it can achieve not only implicit time-diversity through the use of coding with interleaving, but also space-diversity through the transmission from multiple antennas. Multi-antenna schemes with convolutional codes can perform better than conventional single antenna schemes with the same codes and transmission diversity technique with the same number of transmitting antennas, especially when a fading is relatively slow and interleaving size is limited.

In this paper, three issues concerning the linear adaptive receiver using the LMS algorithm for single-user demodulation in direct-sequence/code-division multiple-access (DS/CDMA) systems are considered. First, the convergence rate of the LMS algorithm in DS/CDMA environment is considered theoretically. Both upper and lower bounds of the eigenvalue spread of the autocorrelation matrix of receiver input signals are derived. It is cleared from the results that the convergence rate of the LMS algorithm becomes slow when the signal power of interferer is large. Second, fast converging technique using a prefilter is considered. The LMS based adaptive receiver using an adaptive prefilter adjusted by a Hebbian learning algorithm to decorrelate the input signals is proposed. Computer simulation results show that the proposed receiver provides faster convergence than the LMS based receiver. Third, the complexity reduction of the proposed receiver by prefiltering is considered. As for the reduced complexity receiver, it is shown that the performance degradation is little as compared with the full complexity receiver.

In general cases of pattern recognition, a pattern to be recognized is first represented by a set of features and the measured values of the features are then classified. Finding features relevant to recognition is thus an important issue in recognizer design. As a fundamental design framework taht systematically enables one to realize such useful features, the Subspace Method (SM) has been extensively used in various recognition tasks. However, this promising methodological framework is still inadequate. The discriminative power of early versions was not very high. The training behavior of a recent discriminative version called the Learning Subspace Method has not been fully clarified due to its empirical definition, though its discriminative power has been improved. To alleviate this insufficiency, we propose in this paper a new discriminative SM algorithm based on the Minimum Classification Error/Generalized Probabilistic Descent method and show that the proposed algorithm achieves an optimal accurate recognition result, i.e., the (at least locally) minimum recognition error situation, in the probabilistic descent sense.