1.55µm GaInAsP/InP BH lasers with multiple p-n current blocking layer were fabricated entirely by low-pressure OMVPE. The undercut portions were filled in a manner similar to mass transport process. The laser shows a threshold current of 48 mA at 300 K under CW operation.

This paper describes a design method for a 446 Mb/s optical repeater with four kinds of monolithic integrated circuits. It is mainly concerned with the circuit division, optical receiver and timing amplifier design methods. Repeater circuit is divided based on maximum allowable gain and power consumption. Allowable gain determined by IC package crosstalk characteristics at 400 MHz transmission band is presented here. Allowable maximum power consumption of 1 W/chip is also determined. Effective amplification bandwidth adjustment methods for the optical receiver and the d.c. drift control (DCFB) system design method, specific in the d.c. coupled monolithic integrated optical receiver, are described. Finally, a useful design method for small-phase-shift timing amplifier is proposed. This is a circuit parameter optimizing method which monitors operating point dependence of small signal amplification bandwidth. The 446 Mbit/s submerged optical repeater has successfully been developed using these design methods.

To utilize the common-key encryption foe the message protection in a communication network, it is desired to settle the problem of how to distribute the common keys. This paper discusses a sort of schemes (the direct schemes, we call) that smartly provide different keys in different communications. Such a property has not attained via the basic scheme for the public key distribution systems proposed by Diffie and Hellman. This paper shows that the recently introduced five direct schemes are classified into three sets (called sequences) of infinite schemes, and points out that there are some tight relations among the sequences. And it is clarified which is the best in the three sequences by a systematic evaluation of the complexities for the normal update and for the deliberate forgery of the shared common keys.

The letter deals with theoretical analysis on Lamb waves propagating in a composite membrane of ZnO and SiO2. Calculation was done for the lowest pseudo symmetric (S0) and antisymmetric (A0) modes. It was shown that, for example, when the thickness of each film is of the order of 0.1 wavelengths or less, S0 mode has a large electromechanical coupling coefficient of about 6% and a velocity of more than 5,000 m/s. A0 mode, as may be expected, has a quite small velocity of less than 1,500 m/s with an electromechanical coupling coefficient of about 3%. The result suggests that it may be possible to realise various monolithic acoustic wave devices based on Lamb waves propagating in the ZnO/SiO2 composite membrane.

We show that if a signal (random or deterministic) is sampled nonuniformly (with Poisson or uniform distribution) and then low pass filtered, the output signal is equal to the input signal plus an additive white noise uncorrelated to the input signal. Hence, the power spectrum of random nonuniform samples and SNR is derived. Similar results can be derived for uniform sampling with some missing samples or with time jitter. We finally, show that the original signal can be recovered exactly (in the mean squared error sense) from random nonuniform samples by an iterative method provided that the average sampling rate is greater than the Nyquist rate.

Consider the diffusion approximation for queues in randomly varying environment. The environmental variation may be the changes of arrival rates and/or changes of service rates caused by changes in message transmission under occasional crisis. The problem is to seek the queue size distribution conditional on the process being under different environment. The problem arises, for example, when we consider the delay distribution for each type of bursty customers in MG/G/1 queues, where MG represents nonhomogeneous renewal process GIi with i being two-state Markov process. To solve the problem, we define and analyze a diffusion process on R++R+ with the elementary returning boundaries. The forward equation and its stationary solutions are derived. Then it is applied to GI+IPP/G/1 queues and queues with service interruption, where IPP represents the interrupted Poisson process. Numerical examples are given in order to evaluate the accuracy of our approach. Finally a corrected diffusion parameter diminishing errors for general service time distributions is proposed.

Two types of surface acoustic waveguides were studied for use in collinear acousto-optic devices. These waveguides are indispensable for integration and improvement of controll efficiency. Ta2O5 strip waveguides and Al v/v waveguides placed on optical slab waveguides on Y-X LiNbO3 were found to improve the SAW propagation properties. In particular, the SAW excited with a focused IDT was coupled into the Ta2O5 strip waveguide with the coupling loss less than 2 dB and the propagation loss less than 1 dB. The propagation properties and the beam profiles were measured by optical probing. Furthermore, phase velocities of guided waves were measured in fairly good agreement with the calculated ones.

This letter defines a new distance µ(X,Y) based on the Hamming distance H(X,Y) and discusses its properties. Here, µ(X,Y) = a minimum distance of H(X,Y) or H(X,Y), where Y is a complementary value of Y. At last its application for encipherment field is discussed.

This paper describes the outline of a database controlled telecommunications network system and analyzes its traffic handling characteristics using basic models. In this system, control is carried out by regional control centers each having a copy of the network information stored in its database. Calls are screened at the originating office to prevent those with little or no possibility of completion from entering the network, and optimum routes for those with high possibility of completion are determined using global network information stored in the database. Major shortcomings arise from the discrepancies between the actual network states and their images in the database, and from the distribution of control. Basic models paying attention to one of the transit trunk groups are used to analyze the primary performance of this system. For each model, an analysis of the trunk state probability is first made, and the result used to calculate the loss probability and ineffective connection rate. The results show that a proper reservation of trunks combined with rapid database update can yield good performance, and that delays within practical ranges are acceptable in maintaining performance in this system.

We will propose one approach to the estimation of bit error rates arising from urban impulsive noise for mobile digital radio communications. In the analysis of the incidence of impulsive noise-induced error mechanism, it is experimentally shown here that if the strength of impulsive noise is measured as a peak value and this value is converted into a receiver IF bandwidth, the way in which an error is generated differs depending on whether this peak value is larger or smaller than the signal level. In addition, from this simulation experiment conducted by using the impulsive noise simulator, it was confirmed that if the number of errors generated by each noise impulse is determined microscopically from the ratio of the impulsive noise peak value to the signal level, the cumulative value of this error generation rate over the entire noise level distribution becomes the radio channel error. In addition, the results of outdoor experiments conducted at 8 kbps in the 150 MHz and 400 MHz bands in the Tokyo Metropolitan area are compared with the results of indoor experiments. Although complete evaluation will not be possible because the adopted evaluation method for impulsive noise was conventional CISPR quasi-peak value, it is concluded that the error generation mechanism discussed here can be applied to the outdoor experiment results, since good agreement is found between outdoor and indoor experiments.

The direct two-dimensional Fourier transform method enables a fast image reconstruction. The key problem of this method is in the interpolation from polar to Cartesian samples. In this paper we present a more efficient interpolation method than the previous one without decreasing the accuracy of the reconstructed image.

A method for the synthesis of stray-insensitive bandpass switched-capacitor filters (SCF's) using fully balanced switched-capacitor immittance converters (SCIC's) is presented. In the proposed method only one operational amplifier is needed per node (excluding the grounded node) in the passive ladder prototype.

We present a new access protocol with priority functions in a ring-shaped local area network utilizing the token passing method. This protocol provides an asynchronous TDMA scheme to the terminals with the low class traffic, and the terminals with the high class traffic can transmit their messages between the consecutive transmissions of low class traffic. The protocol is shown to be effective for the environment where multifarious traffic is accommodated in the network. It gives the higher priority in transmission to the traffic which requires the real time transmission, while the lower priority is given to the one which may not require so strict real time transmission. We provide an approximate analytical method for obtaining the average message delay in our protocol. The performance of our protocol is compared with that of existing access protocol for two example network models, one is the network with balanced load and the other is not. As a result, it is observed in both the example networks that the characteristics of transmission delay for the messages with higher priority is much improved compared with other existing method without introducing much service degradation for lower priority traffic.

Some properties of an optimum set of paths which pass all arcs of a graph are presented. It is shown that the unique existence of the optimum set depends on the configuration of a graph. The set is of use as the minimum set of test cases to the path test.

The dynamic performance of amorphous-silicon transistor circuits has been numerically analyzed. A novel dynamic circuit composed of amorphous-silicon Schottky-barrier diodes and field-effect transistors has been shown to have a superior performance, and the optimum circuit parameters have been discussed. The circuit having 1µm-long, self-aligned transistors has been predicted to be operable at multi-MHz rates.

An optimal control theoretic approach has played a key role in the development of a new assumed-mode approximation scheme for time-dependent partial differential equations. Under the new method, the approximation system of ordinary differential equations is generated as the solution to an optimal quadratic servo problem for the Gelerkin approximation system. The new scheme is shown to be convergent even when the Galerkin scheme is divergent. Furthermore, it does not require the basis functions to satisfy the boundary conditions. This feature would greatly alleviate the basis choice problem for complex dynamic systems defined on a multidimensional spatial domain. The new scheme of this paper could be an invaluable last resort in many cases where all the known approximation schemes have hailed.

A new method of high Q measurement in oscillating systems is proposed by using laser light wave. In order to prove the method simply, X-cut quartz was used as an oscillating element.

A new method for evaluating optical fiber strain in a bent cable is proposed. The method is applied to fiber strain measurement in an actual optical cable and is found to be effective.

Several types of machines have been proposed to improve the performance of data base management systems, especially the relational one. Among them, a cellular logic type data base machine such as RAP is characterized by its simple structure. Whereas this type of machine outperforms the conventional DBMS software by orders of magnitude for the relatively light load operations such as selection and update, it exhibits poor performance for the heavy load operations such as join and projection. This is because it adopts the nested loop algorithm which is very inefficient. Join has been so far the major performance bottle neck. In this paper we propose a performance enhancement mechanism for the cellular logic data base machine. A novel relational algebra processing algorithm based on the dynamic clustering feature of hash is presented. By introducing the hashing hardware, join operation is much accelerated in comparison with the conventional cellular logic data base machine. Its execution time is evaluated by simulation experiments. It has also been a major problem to handle large relations which cannot fit into the cell memories, where frequent paging degrades the performance severaly. A bucket based staging scheme has been proposed, through which the enhanced architecture can perform the join of large relations efficiently.

The worst month statistics of rain attenuation at 34.5 and 81.8 GHz along a terrestrial path of 1.3 km and rain rate were analyzed. The relation between the worst month percentage and the yearly percentage is independent of frequency. The results we obtained on the worst month statistics show a good agreement with Brussaard and Watson's semi-empirical model.