In the near future, the packet switching system will need a large switching capacity. But, large processor can not be obtained in cheap way. So, it seems better to use smaller processors in a distributed fashion to obtain a large switching capacity. If several small switching devices are interconnected, it will be possible to increase the traffic handling capacity. Depending on the topology of the network, overall processing characteristics are different. Switching networks like torus etc. have the problem, because their nodes have the transit traffic. According to the increase of the switching network size, the transit traffic becomes large and the overall traffic efficiency of the network decreases significantly. The mesh network, in which all nodes are interconnected, does not have that problem, because there is no transit traffic in any node. This paper describes the composition of mesh type distributed packet switching systems. Flexible architectures are proposed, which are based on the building block structure. A node of these architectures is composed of several switching elements, and one or two intranode switches. Using these architectures, the addition of a new node to the system can be done without any modification of the fundamental units. The experimental system has been designed and built.

Phenomenon of silica-fiber loss increase, which is induced by an electric current applied in water, is reported. It is found from experimental results that the loss increase is caused by hydrogen molecules, which are electrolytically produced and are diffused into the fiber interstitially. Furthermore, both infrared loss and Ramanscattering spectra are measured for a fiber dissolved by H₂, HD, and D₂ molecules to make clear assignment for loss peak. As a result, it is found that the absorption loss peaks are associated with a connection between molecular vibration and SiO₄ tetrahedral vibrations in the silica glass.

Low temperature excess loss of fusion-spliced fibers packaged by a new packaging method is investigated. The package consists of a heat-shrinkable tube, an adhesive tube and a resistance heating rod. Based on the theoretical analysis using the theory of elasticity, the packaging structure using a rigid resistance rod, which has a high compression modulus, low linear expansion coefficient and large cross-sectional area, is recommended for reducing the loss increase at low temperatures. By using carbon fiber-reinforced carbon (CFRC) for such a resistance rod, the loss increase at -40 is found to be less than 0.03 dB per package.

An improved theory to obtain circularly polarized (CP) waves from a singly fed microstrip antenna is presented. This theory indicates that a singly fed circularly polarized (SFCP) microstrip antenna, in general, is able to produce CP waves at two different frequencies, which are just slightly separated. The two CP operating frequencies can be found through an iterative process. Furthermore, the optimum feed location loci can be determined numerically. Finally, the theoretical results for two kinds of SFCP antennas are compared with the experimental results. The agreement is quite good and the theory validity is confirmed.

A recognition method of handprinted Thai characters by using local features is described. In the method, Freeman chain code and directional differences of contour tracing are utilized for extracting concavities and convexities of characters. Several local features are used to calculate similarities between arc portions and similarity between characters. Similar arcs are detected from characters of different categories to make a dictionary of arcs. Then, a dictionary of characters containing lists of names of character arcs is made to obtain a compact dictionary of models. By applying the method to 69 categories (828 data) of Thai characters, a recognition rate of 99.3% for learning data, and a recognition rate of 88.9% for test data have been obtained.

This paper presents a surface emitting injection laser with improved short cavity structure operating at 1.30 µm (77 K) of wavelength. The selective etching technique has been applied to take out the InP substrate in order to reduce the absorption loss and resultant cavity length was 7 µm. The threshold was as low as 50 mA at 77 K. The device operated up to 140 K with one single longitudinal mode and small wavelength change (0.64 /degree). The near-field diameter was 9 µm and the far-field angle (FWHM) was 9 degrees. The polarization was linear.

A new GaAs monolithic negative feedback amplifier using a dual-gate MESFET for A.G.C. function has been developed. Such a low NF value as 1.8 to 2.5 dB with a gain of 10 to 12 dB over a frequency range of 50 to 2,000 MHz has been obtained. The gain reduction of about 30 dB was achieved over the same frequency range by means of the second-gate bias. A comparison of the performance between negative feedback amplifiers using a dual-gate FET and a single-gate FET is also discussed.

Lasing gain and threshold current density in GaAs/AlGaAs multi-quantum-well lasers are theoretically analyzed. Split energy levels in multi-quantum-well structure are calculated. The lasing gain and electron lifetime by the spontaneous emission effect are calculated taken into account both the split energy levels and broadening effect by the intraband relaxation of electron wave. It is found that the gain can not be much higher than that in conventional double heterostructure, because the gain is broadened by the intraband relaxation effect even in the quantum-well structure. Conditions of laser structure to get much lower threshold current density are discussed. The most important condition to reduce the threshold current density is to increase confinement factor of the optical field into the well layers.

Various methods have been proposed for the generation of constant envelope signals. It is the purpose of this paper to show systematic methods to generate a class of constant envelope signals with linear or nonlinear phase. Unlike other methods, our technique does not require nonlinear elements and the distortion is controlled by the parameters of the signal.

A new type of passive TE/TM mode splitter device using the ion-exchanged LiNbO₃ waveguide is proposed and demonstrated. The characteristics of this device is estimated by the Beam Propagation Method based on a simple model. The extinction ratio is predicted to amount to 40 dB in the optimal case. This device is experimentally demonstrated in the X-junction configuration by using the Ag⁺-exchanged waveguide an Ti-indiffused one, and the extinction ratio is measured to be 10.5 dB, while the calculated value is 15 dB.

A new coding scheme of binary images is proposed. This coding scheme not only obtains high compression efficiencies, but also produces coded data which are suitable for computer processing.

We measured response times of visual pattern recognition for various figures and characters on a TV screen when visual field of subjects were restricted to various visual angles, using a television eye camera and a newly developed equipment for restricting human visual field effectively, and estimated size of central vision according to the result of measurement.