An improvement of the fiber-optic transceiver having both transmitter and receiver functions of optical time-domain reflectometers is examined. The improvement is achieved by introducing an external optical amplifier without changing the previously reported configuration. The characteristics of the transmitted Q-switched pulse and the receiver gain is studied theoretically and experimentally to estimate the performance improvement. It is found that the introduction of the external optical amplifier is a simple and effective way to the performance improvement.

Given N real weights w1, w2, . . . , wN stored in one-dimensional array, we consider the problem for finding an optimal interval I [1, N] under certain criteria. We shall review efficient algorithms developed for solving such problems under several optimality criteria. This problem can be naturally extended to two-dimensional case. Namely, given a NN two-dimensional array of N2 reals, the problem seeks to find a subregion of the array (e. g. , rectangular subarray R) that optimizes a certain objective function. We shall also review several algorithms for such problems. We shall also mention applications of these problems to region segmentation in image processing and to data mining.

This paper describes the mechanisms of power-distribution-plane resonance in multilayer printed circuit boards and the techniques to control the resonance. The power-distribution-plane resonance is responsible for high-level emissions and circuit malfunctions. Controlling the resonance is an effective technique, so adequate characterization of the resonance is necessary to achieve control. The resonance characteristics of four-layer printed circuit boards are investigated experimentally and theoretically by treating the power-distribution planes as a parallel-plate transmission line with decoupling circuits. Analysis of the forward traveling wave shows that the resonance frequency is determined by the phase delay due to wave propagation and by the phase progress of interconnect inductance in the decoupling circuit. Techniques to control the resonance characteristics are investigated. The resonance can be shifted to a higher frequency by adding several decoupling circuits adjacent to the existing decoupling capacitor or by increasing the number of via holes connecting the capacitor mounting pads to the power-distribution planes.

A new manufacturing process for advanced Fiber Bragg Gratings which uses phase plates is described. Its high versatility allows to achieve many type of filters in optical fibers (phase-shifted, apodised, Fabry-Perot).

The legal firing sequence problem (LFS) asks if it is possible to fire each transition some prescribed number of times in a given Petri net. It is a fundamental problem in Petri net theory as it appears as a subproblem, or as a simplified version of marking reachability, minimum initial resource allocation, liveness, and some scheduling problems. It is also known to be NP-hard, however, even under various restrictions on nets (and on firing counts), and no efficient algorithm has been previously reported for any class of nets having general edge weights. We show in this paper that LFS can be solved in polynomial time (in O(n log n) time) for a subclass of state machines, called cacti, with arbitrary edge weights allowed (if each transition is asked to be fired exactly once).

We study the problem of stabilizing a general nonlinear control system globally based on direct gradient descent control which is a dynamic feedback control law. The direct gradient descent control and the general nonlinear control system (original system) form a new system (extended system). Under an appropriate assumption we can make the extended system become globally asymptotically stable if its unforced system is stable in the sense of Lyapunov.

This paper surveys how geometric information can be effectively used for efficient algorithms with focus on clustering problems. Given a complete weighted graph G of n vertices, is there a partition of the vertex set into k disjoint subsets so that the maximum weight of an innercluster edge (whose two endpoints both belong to the same subset) is minimized? This problem is known to be NP-complete even for k = 3. The case of k=2, that is, bipartition problem is solvable in polynomial time. On the other hand, in geometric setting where vertices are points in the plane and weights of edges equal the distances between corresponding points, the same problem is solvable in polynomial time even for k 3 as far as k is a fixed constant. For the case k=2, effective use of geometric property of an optimal solution leads to considerable improvement on the computational complexity. Other related topics are also discussed.

The two dimensional mesh is widely considered to be a promising parallel architecture in its scalability. In this architecture, processors are naturally placed at intersections of horizontal and vertical grids, while there can be three different types of communication links: (i) The first type is the most popular model, called a mesh-connected computer: Each processor is connected to its four neighbours by local connections. (ii) Each processor of the second type is connected to a couple of (row and column) buses. The system is then called a mesh of buses. (iii) The third model is equipped with both buses and local connections, which is called a mesh-connected computer with buses. Mesh routing has received considerable attention for the last two decades, and a variety of algorithms have been proposed. This paper provides an overview of lower and upper bounds for algorithms, with pointers to the literature, and suggests further research directions for mesh routing.

For NP-hard combinatorial optimization problems, approximation algorithms with high performances have been proposed. In many of these algorithms, mathematical programming techniques have been used and proved to be very useful. In this survey, we present recent mathematical programming techniques as well as classic fundamental techniques, by showing how these techniques are used in designing high-quality approximation algorithms for NP-hard combinatorial optimization problems.

For measuring high frequency ultrasonic fields which are often spatially distributed and transient, an array probe with small element sensors is highly required. In this paper, we propose a fiber-optic micro-probe array which is based on wavelength-division-multiplexing technique. The element sensor consists of a micro optical cavity of 100 µm long made at the end of optical fiber. Optical path length of the cavity is changed by the applied acoustic field, and the modulation of output light intensity is monitored at another end of the fiber for the information of the acoustic field. Array of sensor elements and a light source as well as a photo detector are connected together by an optical star coupler. The Fabry-Perot resonance wavelength of each sensor element is designed different one another, and the outputs from the sensors are discriminated by sweeping the wavelength of light source with the use of a tunable semiconductor laser. In this paper, the performance of the micro-probe array is discussed experimentally.

This paper reviews the use of fiber optic sensors for downhole monitoring in the oil and gas industry. Due to their multiplexing capabilities and versatility, the use of Bragg grating sensors appears to be particularly suited for this application. Several types of transducer have been developed, each of which can be addressed along a single (common) optical fiber in the well and read-out using a common surface instrumentation system.

This letter proposes a combined input- and crosspoint-queued (CIC) switch in which virtual output queuing (VOQ) is used at each input port. This CIC switch has a large buffer at each input port and a small buffer at each crosspoint. It does not require high-speed memory access or high-speed internal cell transmission lines. Since the performance of the CIC switch depends on the scheduling algorithms, we propose new scheduling algorithms for the CIC switch. Numerical results show that the mean cell delay time performance of the CIC switch using the proposed scheduling algorithms is better than that of an input-queued ATM switch. In addition, the required buffer size for the CIC switch using the proposed scheduling algorithms is smaller than that for a crosspoint-queued ATM switch.

A reliable and automatic parameter extraction technique for DFB lasers is developed. The parameter extraction program which is named "LAPAREX" is able to determine many device parameters from a measured sub-threshold spectrum only, including gain- and index-coupling coefficients, and spatial phases of the grating at front and rear facets. Injection current dependence of coupling coefficients in a gain-coupled DFBlaser is observed, for the first time, by making use of it.

Maximum Satisfiability Problem (MAX SAT) is one of the most natural optimization problems. Since it is known to be NP-hard, approximation algorithms have been considered. The aim of this survey is to show recent developments of approximation algorithms for MAX SAT.

In this paper, we review recent developments in interferometric fiber-optic gyroscopes for industrial applications. These gyroscopes use only elliptical-jacket or elliptical-core polarization-maintaining-fibers to make their optical systems immune to environmental effects, and they use open-loop or closed-loop signal processing circuitry. We have begun mass production of a gyroscope for automotive navigation and location systems. The more accurate gyroscopes have been applied to a number of consumer applications such as attitude control systems of unmanned agricultural helicopter, pipe-mapping and north-finding systems. For further enhancement in terms of size, cost, and accuracy, we have developed an application specific integrated circuit and an integrated optical circuit.

Coding scheme for a noisy multiple-access adder channel is proposed. When a T-user δ-decodable affine code C is given a priori, a qT-user λ δ-decodable affine code C* is produced by using a q q matrix B satisfying BA=λ Iq q, e. g. , a Hadamard matrix or a conference matrix. In particular, the case of δ=1 is considered for the practical purposes. A (2n-1)-user uniquely decodable (δ=1) affine code Cn with arbitrary code length n is recursively constructed. When Cn plays a role of C, a q(2n-1)-user λ-decodable affine code C* is obtained. The code length and the number of users of C* are more flexible than those of the Wilson's code. The total rate of the λ-decodable code in this paper tends to be higher than that of the λ-decodable code by Wilson as the number of users increases.

This paper reports the performance of an AC-voltage sensor with a LiNbO3 integrated retroreflective structure based on the Y-junction Mach-Zehnder interferometer. This structure is capable of realizing a low-cost sensor chip because of the small chip size and single optical-fiber connection. In the sensitivity and frequency response evaluation, detection sensitivities of 6.3 µ V / Hz have been measured with a frequency response from 6 Hz to 2 GHz. These measurement limitations were also analyzed theoretically and compared with the experimental results. This unique sensor enables precise voltage measurement in an EMI environment, even inside a computer.

Magnetic tape incorporating a soft magnetic alloy film has been developed to reduce the electromagnetic interference (EMI) noise current in an electrical cable. The advantage of the magnetic film compared to a ferrite core is shown using an eddy current loss model. The magnetic film exhibited the expected high-loss characteristics above 30 MHz. Laminated resin gives the tape sufficient strength to be wound inside a cable sheath. The fabricated 60- and 90-µm-thick tape wound along the whole cable length exhibited noise reduction ratios of 4 to 5 dB for both radiated emission in the range from 30 to 300 MHz, and surge immunity with a magnetic substance whose volume was one-sixth that of a conventional ferrite core. The tape also exhibited no significant degradation in the mechanical and environmental tests and showed the practical durability.

For a wireless communication system to work effectively without interference, the electromagnetic environment needs to be controlled. We experimentally and analytically investigated the requirements for controlling the electrical field strength and delay spread so as to achieve the best communication without electromagnetic interference in selected regions for a 2.4-GHz-band wireless LAN system. To control the coverage, partitions were placed around desks in a test environment and covered on the inside with electromagnetic absorbing board from the top of the desks to the top of the partitions; four indoor environments that combined one of two wall-material types and one of two partition heights were used. The transmission loss and delay spread were measured, then calculated using ray tracing to verify the effectiveness of using ray-tracing calculation. The throughput and BER characteristics were measured for the same environments to clarify the requirements for controlling the coverage. We found that covered and uncovered regions could be created by using partitions with absorbing boards and that the delay spread must be less than 15 ns and the received-signal must be stronger than -75 dBm for a region to be covered. We verified that the delay spread can be calculated to within 5 ns and the received-signal level can be calculated to within 5 dB of the measured data by using ray tracing. Therefore, ray tracing can be used to design antenna positions and indoor environments where electromagnetic environments are controlled for 2.4-GHz-band wireless LAN systems.

Nonlinear dynamics of xn+1=λ {4xn (1-xn)}q is studied in this paper. Different from the logistic map (q=1), in the case of q