This paper is concerned with an experimental approach to determining the feasibility of an optical PCM system at high bit rates. One necessary development is a high speed modulation technique using a semiconductor injection laser. The other is a high sensitivity receiving technique. First, this paper shows that high speed modulation with less pattern effect and less extinction ratio degradation can be effectively performed by adding the undershoot and overshoot to the driving current pulse in an injection laser. Second, this paper shows that a current feedback amplifier, consisting of an emitter-grounded bipolar transistor, is advantageous in high sensitivity of a high speed optical PCM receiving circuit, and to increase in repeater spacing. Finally, it is shown experimentally that the repeater spacing can be lengthened up to 5 km with a conventional graded index multimode fiber or up to 5.9 km with a single-mode fiber. It is confirmed by experiments that an optical transmission could be applied to a long distance and large capacity transmission system.

Given a set of n data records with Li, data length and Pi, access frequency of data record Ri (1in), each data record is allocated in one of buckets, whose size is L, minimizing the access delay D, DPiPjdij dij: distance from allocated data record Ri to Rj, while satisfying the constraint that the size of data records in each bucket does not exceed L. The property of optimal allocation is investigated and an allocation heuristic is given whose slight modification gives the optimal allocation for the data records of up to 2 unit data length.

This paper demonstrates that the practical implementation of single b-Adjacent bit-group Error Correcting (SbEC) Code gives a modularized high reliability memory unit. By the application of rotational coding techniques to this code, not only a high speed parallel encoding/decoding network (memory translator), but also a memory unit can be organized in modular distributed forms, well suited for applying the LSI logic technologies to this memory translator and for achieving the high reliability and high maintainability memory unit. The parity check matrix of this code, which is easily decodable, can be expressed by the rotational operating matrix and the basic generating-submatrix. The basic hardware implementation of each modular organized translator consists of three circuitry portions which can be well designed for LSI logic. As an illustrative example, the most practical and optimum rotational (72, 64) S2EC code is implemented. The translator of this code is organized in four modular distributed forms. LSI logic patterns of each translator module require 30 to 50 input-output leads and 100 to 270 gates. The operational speed of this translator is almost equal to that of the conventional high speed SEC-DED (Single Error Correcting - Double Error Detecting) codes. As a result, this memory unit consists of four identical modules, each of which includes not only one of these translator modules, but also a storage portion and a input-output selector portion.

Atmospheric refractivity gradient in the vicinity of the equator were analyzed, based on the radiosonde data in Indonesia and Singapore. Further study was made for estimation on the variation of refractivity gradient in the South-East Asian area, by means of combining with the results in and around Japan.

We have developed LITHAN (LIsten-THink-ANswer) speech understanding system which automatically recognizes continuously uttered speech utilizing higher linguistic information such as syntactic, semantic and pragmatic information. This system predicts possible words utilizing linguistic information at the unrecognized portion of the input utterance, and identifies each predicted word by the use of the optimum matching algorithm between a recognized phoneme string and the representative one in the word dictionary. We propose an effective tree search method of parsing when the results of phoneme recognition and word identification are not error free. LITHAN uses many types of a priori information; the statistic of each phoneme; the similarity matrix between phonemes; the word dictionary; the spoken grammar with the additional information as regards the spoken grammar; the semantic and pragmatic information. We have applied this efficient, flexible system to restricted utterances with vocabulary of about 100 words which concerned with operational commands and queries of the status of a computer network. According to the results tested on a sample 200 sentences spoken by 10 male speakers at a normal speed, 64% of the sentences and 93% of the output words were correctly recognized.

A new method of the information reduction of the three-dimensional image is proposed and experimentally verified. This method, the optically sectionned holography, is based on the principle of the coincidence of the time of arrival of the object and the reference beam in the holography. The resolution in depth is analyzed by taking into account the phantom imaging of the optical sectioned holography. The result gives the information content of the obtained hologram. The resulted information content is in the same order to that of the monocular three-dimensional image. So, this system can reduce the fairly amount of the information, comparing to the Burckhard's sampled holography. The system for the optically sectioned hologram by using the mode-locked, and the second harmonic generating c. w. Nd: Y AG laser is experimentally realized, and the optically sectioned holograms are obtained. From these holograms, the three-dimensional image of the original object is restored. A c. w. dye-laser is also used to obtain the optically sectioned hologram. The resulted resolution in depth is about 5 mm, which corresponds to the pulse width of the Nd: Y AG laser.

In this paper, the authors propose a new mode analyzer. This mode analyzer is composed of an obliquely polished optical fiber and a high index prism placed in contact with the oblique section. Modes which have the different equivalent refractive indices are separated due to the different angles of refraction. A mode analyzer using a focusing fiber was made, and modes were successfully separated. The refractive index n(0) at the center axis, the coefficient g of the parabolic term in the refractive index distribution, and the refractive index in the cladding were evaluated from the measurement of angles of refraction. The obtained value of refractive index n(0) at the center axis almost agreed with the value obtained by the interference method. As the application of this mode analyzer, the measurement of group-delay differences of modes and amplitude distribution of modes in a long fiber, and the measurement of the constants of fiber are considered.

Anomalous re-entrant hysteresis loops and maximum of the coercive force have been found near 130 K in polycrystalline GdIG ferrite. A qualitative explanation of the observed phenomena is given. It is suggested based on the Snoek's model of magnetic after effect that Fe2 ion may be responsible for pinning the domain wall.

As a new method to improve pulse code modulation properties of semiconductor lasers, optical feedback is proposed where a part of the light output from a modulated laser is fed back into itself, with a time delay considerably less than one relaxation oscillation (RO) period. Rate equation approach is applied to investigate the modulation characteristics. Modulation bit rates for small pattern effects depend on the RO period and the current pulse width, and they appear discontinuously. By optical feedback, the RO period increases, and it becomes possible to decrease pattern effects at any given modulation period, if it is larger than the RO period without optical feedback. For current pulses with a short duration, output waveforms are improved by optical feedback through increase in the first RO spike width and elimination of its second spike. In preliminary experiments, using GaAs-AlXGa1XAs double heterostructure lasers with a combination of a microlens and a flat mirror, qualitative agreements were obtained between theoretical and experimental results. Improvements in the modulated output waveforms were observed for PCM-RZ pulses at up to 500 Mb/s.

Several basic properties of minimum-comparison selection algorithms are shown, and some exact values are obtained for Vt(n) for small n, where Vt(n) denotes the number of comparisons necessary to select the t-th largest of n elements. The upper bound for V5(10) is reduced to 16. Those results improve the table of the best upper bounds known for Vt(n) in the Knuth's book (Sorting and Searching).

This paper considers a 2-dissimilar unit warm standby system. The failure rates are constant but the repair rates need not be constant. We shall say that a major breakdown occurs in the system when both unit fail. The system fails if one unit under repair is not repaired within a fixed time measured from the instant at which major breakdown occurs, or if the number of major breakdowns during the mission period exceeds a fixed number. As a special case, this number is allowed to be infinite". The Laplace transform of the reliability and the mean time to system failure (MTSF) are derived. The special case of constant failure and repair rates is treated. We present the asymptotic results which describe the performance of system with short mean repair time. Also the case when allowed down time is negligible, compared to the mission time, is discussed.

A method of exact analysis for the cylindrical fiber with an arbitrary but azimuthally symmetric refractive-index distribution is given. The index distribution is simulated by a multilayer structure and the analysis is formulated exactly by using iterative multiplication of four by four matrices. Then the four by four matrices are approximately separated into two systems of two by two matrices with a good accuracy for the fiber with small index difference. In this way, the computing time is reduced almost 1/6 times compared with the former method. As an example of the application, the propagation modes of a focusing fiber are identified which previously were not exactly known. It is revealed that the group-velocity differences between the modes which are degenerate in the scalar analysis can be larger than those of the non-degenerate modes.

In the present paper, we introduce a new type of automata, called generalized group-matrix type automata, for representing general automata in connection with their automorphism groups. A family of subgroups of a given finite group, satisfying a certain condition, called the separation condition, will play a fundamental role.

Silicon avalanche photodiode with the Nπ1Pπ2P structure is fabricated, using the technology of epitaxitial growth after boron ion-implantation to bury a P layer. The diode with the excess noise factor of F5 is obtained at the multiplication factor of M100 for λµm.

Single material fibers made from low loss material may have excellent optical propagation properties related to absorption loss. Thin film fibers with a convex surface have self focussing properties similar to those of inhomogeneous fibers with quadratic index profile. Such optical waveguides seem to be useful for optical communications and integrated optics. By using the method of conformal mapping, fundamental characteristics of guides modes along optical films with a convex surface are found, and field distributions and dispersions of eigen modes that have not been clarified are shown in detail. These guided modes have Hermite Gaussian field distribution in transverse direction. The spot sizes of guided modes are inversely proportional to the square root of the product of their transverse wave number and the metrical coefficients (1a)lx, where β1 and β2 are phase constants of the material and the guided mode respectively. The factors (1a)lx derived from mapping function and are quadratic coefficients of the convex surface at the fiber boundaries. The dispersion characteristics of the guided modes are discussed and several numerical examples are presented.

To know the correlation between the surface contamination of semiconductors and electrical properties of semiconductor devices fabricated on the surface, the contamination of chemically etched Si surface was measured by Auger electron spectroscopy (AES) and Schottky contact was formed by evaporation of Au on that surface in situ. The various chemical etchants were used, including HF, HNO3, CH3COOH, their mixture, and alkaline etchant. The saturation current, the barrier height, and the n-value of the forward current-voltage characteristics of Au-Si Schottky contact were used for evaluating device characteristics, and in-depth profile of composition of the metal film on Si was also measuring by AES combined with ion-sputter etching. Following results are obtained; The barrier height of the Au-Si Schottky contact whose Si surface is contaminated by carbon is low and 0.810.02 eV, and not far from that of clean surface. On the other hand that of Si surface not so much contaminated by carbon but by oxygen is large and 0.830.01 eV, and the n-value is close to unity. This phenomena can be explained by assuming the vanishing of surface states of Si surface with small oxygen adsorption. This model cannot be applicable to heavily contaminated surface. The results of composition analysis show that a small amount of oxygen passivates Si surface and gives high barrier height.

A synthesis technique is presented for the multiple feedback (MF) active RC realization of transfer functions having complex frequency transmission zeros, and a biquadratic block in the MF structure is proposed, which is suitable for realizing the internal transfer function having complex zeros and poles.

This paper describes an investigation of the SAW beam diffraction on LiNbO3 crystal by the frequency-translated-holographic technique, which allows direct observation of SAW amplitude distributions. The observed diffraction patterns are found to change as a function of excitation frequencies, and to agree well with the theoretical amplitude distributions of the SAW's emitted from the multiple finger pairs of an interdigital transducer. The method of the angular spectrum of plane waves was used for the theoretical computations.

A digital technique for evaluating the half-power band-width of a resonance system is presented. It is based on the lateral shifting operation of the z-transform of the samples sequence on the z-plane. The shifting operation is carried out by using the binomial coefficients.

The purpose of the present note is to provide a necessary and sufficient condition in order that strongly connected group-matrix type automata, whose orders are prime, may be regular. Further, as an applications, a problem concerning factor automata of a strongly connected automaton will be discussed.