A novel multiple-access optical network architecture is presented that not only employs the WDM technique but also divides networks. The subnetworks are connected to each other via a wavelength-dependent interconnection network, and pairs of subnetworks are optically linked with different combinations for each wavelength. Through an analysis of the throughput and delay for the slotted ALOHA protocol, the architecture is confirmed to be improved from the conventional one that employs only the WDM technique. For example, the improvement ratio of the throughput for a four-wavelength network is 2.4, and that for an eight-wavelength network is 4.4.

This paper presents a special-purpose LSI chip for inverse kinematics computation of robot manipulators. It is shown that inverse kinematic solutions of kinematically simple manipulators can be systematically described with the two-dimensional (2-D) vector rotation. The chip is fabricated with the 1.5-µm CMOS gate array. The arithmetic unit on the chip is designed using the COordinate Rotation DIgital Computer (CORDIC) algorithms, and it performs six types of operations based on the 2-D vector rotation at high speed. Pipelining is used to enhance the operating ratio of the unit to 100%. The computation time of a special purpose processor which is composed of the chip and a few memory chips is approximately 50 µs for a typical six degree-of-freedom manipulator. Moreover, the chip can be used for various types of manipulators, and the software development is very easy.

A configuration of multi/demultiplexer using a 4-port optical circulator and interference filters is presented. Owing to the circulator, interference filters for the signal separation can be set normal to the optical signal propagating direction. Demultiplexing operation for 3 wavelength-multiplexed signals, of which wavelength spacings are 1.8 and 4.9 nm, is experimentally confirmed.

Simple formula has been proposed to estimate baseband bandwidth of an optical transmission line made of different fibers spliced together. Using the formula, cumulative bandwidth is predicted merely from the bandwidth for each individual fiber. The usefulness of the formula has been confirmed by experiments.

Ring networks have been extensively studied and installed for communication services. In actual ring networks, nodes are usually allocated at random positions. Two nodes separated far from each other along the route of a ring network may be physically allocated near each other. Adding a supplementary link directly connecting such nodes can shorten the connection paths between the two nodes as well as between other neighboring node pairs. Aggregated length of connection paths of the network can be reduced. Although such a network can be regarded as being composed of two small ring networks sharing the supplementary link, we regarded the network as being modified from a single regular ring network by adding a supplementary link, and thus we quantitatively evaluated the effect of the network modification. We analyzed, for the first time, number of connection paths in the links of networks with or without a supplementary link. A full-mesh topology was assumed, and two types of connection were examined: a single-path and a 2-path connection. The results of this analysis were then used to evaluate system costs and reliability of the networks. The evaluation confirmed that adding a supplementary link is effective in terms of cost reduction and reliability improvement under certain conditions.

A very-high-speed ten-neuron analog neural network LSI chip is fabricated for the first time using super self-aligned Si bipolar process technology. The LSI consists of ten neurons and 100 electrically modifiable synaptic weights. The neural network nonlinear mapping function to solve the four-bit parity problem is successfully demonstrated at 150 mega-patterns/sec. The operation speed of this neural network is, to the best of the authors, knowledge, the fastest yet reported.

From theoretical or experimental point of view, graded-index multimode fibers are interesting and promissing transmission lines for future optical communication systems. Their transmission characteristics, however, have not been well recognized so far. Therefore, it is necessary to clarify the characteristics before considering graded-index multimode fibers for practical uses. Among the characteristics, optical loss and pulse dispersion are of paramount importance. This paper presents baseband frequency characteristics of recently produced graded-index multimode fibers in the frequency range from DC to 1.7 GHz. The characteristic dependence of graded-index multimode fibers on wavelength and excitation condition is also studied in comparison with that of a step-index multimode fiber. Wavelength, rather than excitation condition, is shown to be an important factor that determines the characteristics of the fiber. The wavelength dependence of the bandwidth has been found to be critically influenced by the profile of the fiber. In order to understand the detailed characteristics of graded-index multimode fibers, the measurement covering a wide frequency range, e. g., from DC to over 2 GHz, is necessary.

A multichannel crossover switching network using interconnection channels of collimated lights is proposed and demonstrated. Diffraction losses of the switching network are theoretically estimated.

This letter proposes a new-type of two-dimensional multichannel optical switch employing polarization control techniques. This switch has small-size and low-driving-power characteristics. It is demonstrated by an 88 optical switch.

High-speed learning of neural networks using the multifrequency oscillation method is demonstrated for first time. During the learning of an analog neural network integrated circuit implementing the exclusive-OR' logic, weight and threshold values converge to steady states within 2 ms for a learning speed of 2 mega-patterns per second.

This letter proposes a mechanical single-mode fiber-optic switch which interconnects a pair of probe fibers and pairs of line fibers to perform fault testing. The 16-channel switch array is fabricated and the switching performance is confirmed to be excellent.

Optical time- and wavelength-domain paths in future very-high-speed optical communications networks are discussed taking into account trends in current optical transmission and optical signal processing technologies. It is important to investigate optical STM cross-connect systems for time-domain paths in the earlier research phase to ensure the deployment of optical cross-connect technology. The configuration of an optical cross-connect system and the issues that need to be investigated are presented. We also report, for the first time, a preliminary experiment of an optical STM cross-connect system, using 20 Gbit/s optical signals.

This letter proposes a new-type electrostatically-driven fiber-optic micromechanical switch by fabrication of a 32-element switch array and examines its switching performances. Low-loss and high-extinction-ratio characteristics are confirmed.