The present state-of-the-art of high-power semiconductor lasers and their application is reviewed. Three phenomena which prevent semiconductor lasers from emitting high power, i.e. kink, roll-over and COD(catastrophic optical damage) in power-current characteristics are discussed and the means to solve are introduced. The two important problems, the removal of heat generated in lasers and collimation methods of diverging light emitted from lasers are described. The recent trends of application such as laser processing (cutting, welding, forming), pumping of solid state lasers, optical memory and display are reviewed.

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Starting with next generation high density optical disc, commercial use of GaN based violet laser diodes (LD) has been adopted in many new fields, such as bio-medical, reprographic, exposure and etc. Recently, the lasing wavelength has broadened to cover from ultraviolet (UV) to blue-green region, which enabled other new applications. In this paper, current status of GaN based LDs in UV to Blue-green region are reported and next target is discussed.

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This paper describes the development of super-high-power (SHP) AlGaInN-based blue-violet laser diode (LD) arrays. In 2001, the LD arrays were successfully fabricated using epitaxially laterally overgrown GaN substrates. The LD array consisted of 11 laser chips, each with 4 stripe emitters monolithically integrated. A maximum light output power of 4.2 W under continuous-wave (cw) operation at 25°C was achieved for the first time, demonstrating the highly uniform quality of the fabricated laser chips. In 2003, we reported a new SHP blue-violet LD composed of a single broad-area stripe emitter on a GaN substrate. A maximum light output power of 0.94 W under cw operation at 20 °C was achieved for the sample with the stripe width of 10 μm. An array of 11 of these LDs was also successfully fabricated, producing a combined light output power of over 6.1 W under cw operation at 20 °C.

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High power semiconductor lasers are expected as a light source with high brightness which is used in wide gamut projection display systems. A red high power laser array is developed for a Grating Light Valve (GLV) display at a wavelength of 643nm. To apply semiconductor laser arrays as a light source for display systems, there are three subjects: high power, long device lifetime and uniform beam profile.
This paper introduced our study of light source for projection display and recent research activities of broad area red high power lasers. Now, red laser arrays demonstrate good laser characteristics; the operating current is 6.80A at the optical output power of 3W under CW operation, the uniform beam profile which is suitable for the laser display, and the estimated life time is longer than 10000 hours. Obtaining high power and high energy conversion efficiency for both blue and green lasers are the next subjects.

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Diode laser systems of high power and power density have been growing for the various application fields of materials processing. In this paper, fundamental characteristics of high power diode laser systems and applicability to materials processing will be discussed.

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Recently, high power laser diodes (LDs) are appling the laser material processing. In this report, we have presented a brief overview of high power laser diode, and describe the basic technology of high power laser diodes and system for pumping solid state laser and direct applications.

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We have demonstrated ZnSe-based white LEDs with longer lifetime over 10,000hrs at 14.5A/cm² by introducing an i-ZnMgBeSe/p-ZnMgSe double cladding structure, which combined a very thin i-ZnMgBeSe layer for suppressing electron overflow and p-ZnMgSSe for efficient p-type carrier concentration. By adopting the double cladding layer instead of the conventional p-ZnMgSSe cladding layer, rapid degradation is suppressed and the lifetime tendency is similar to the LEDs consisting of a III-V semiconductor system. The device simulation and the temperature dependence of optical power showed that the i-ZnMgBeSe layer played the main role in increasing electron confinement. Our experimental data and reliability test results indicate that the suppression of the electron overflow is essential to obtain long lifetime acceptable for truly practical use.

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This paper deals with a development of “comprehensive" laser welding of thermoplastics with versatility in color and shape of products. Overlap welding of thermoplastics is one of the features of application of diode lasers. Most of thermoplastics are transparent to diode lasers; therefore it is need to weld plastic article with colorant. The influence of absorptance and transmittance of overlapping colored plastics were studied. Various colored plastics with infrared-transparent pigments were tested as the welding material. The appropriate absorptance and transmittance of overlapping colored plastic were examined. The feasibility of the technique of welding of transparent plastics using infrared-absorbing layer was also investigated. The temperature distribution within the plastics was calculated by numerical simulation in order to estimate the validity of the proposing experimental systems. It was confirmed by the experiments that the 35μm film, which shows only 10% in absorptance is enough to weld a pair of transparent articles as infrared-absorbing layer.

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We report high-power technologies in 0.8μm Al-free InGaAsP/InGaP/AlGaAs laser diodes. To realize the high-power operation, the improvement of catastrophic optical mirror damage (COMD) power density level is required. In addition to the use of low surface recombination velocity of Al-free materials, optimization of waveguide thickness in broad waveguide strucuture with tensile-strained barriers and current blocking structure near facets has lead to high COMD power density level. Highly stable operation of Al-free laser diodes with these structures has been obtained over 2500 hours at 2W from a stripe width of 50μm. Applications of high power laser diodes are also described.

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The thermal conditions of high power 660-nm laser diodes (LDs) which kink phenomena in P-I curves occur are investigated. It was clearly revealed that the kink occurs when temperature in the stripe portion of LD rise to a certain value. The kink power of newly developed LD, based on this result, can be increased as high as 250 mW at 80°C under pulse operation. This is the highest power recorded among narrow stripe LDs with a wavelength of 660 nm. It is promising for the high-speed (16x) recordable DVD systems.

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We fabricated ultra high power ultraviolet (UV) light emitting diodes (LEDs), whose emission wavelength is 365 nm. We found that, in order to improve the external quantum efficiency (η_ex) of UV-LEDs, it is very important to reduce the optical self-absorption and the threading dislocation density (TDD) of epi-layers. Therefore, at first, UV-LEDs epi-layers were grown on high-quality GaN templates (TDD=1x10⁸/cm²) with sapphire substrates, and then the GaN templates and the sapphire substrates were removed by using laser-induced lift-off and polishing techniques. Moreover, in order to enhance the extraction efficiency, a higher reflectance Ag p-type electrode and patterned surface were used for this LED chip. As a result, we obtained the low self-absorption and low TDD UV-LEDs with practical high power and high quantum efficiency.

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We have newly introduced a two-step-growth structure and a ridge stripe with steep sidewalls formed with a dry-etching process in the fabrication of a buried ridge stripe structure of a high-power 660 nm laser diode instead of a conventional three-step-growth structure and a ridge stripe with gentle sidewalls formed with a conventional wet-etching process in order to reduce the operating current. We have found that the two-step-growth structure provides better heat dissipation and the dry-etched ridge stripe structure offers higher characteristic temperature. The operating current under pulsed 200 mW at 70°C of the fabricated laser diode is 270 mA. This is the lowest value ever reported so far, to our knowledge. These laser diodes exhibit a kink level and a maximum light output power of 220 mW and higher than 300 mW, respectively. These laser diodes have also operated stably for 1500 h at 70°C with a light output power of 200 mW under the pulsed condition.

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High-efficiency ultraviolet (UV) light sources are very attractive for application to white lighting, high-density memories, medical fields, etc. We have demonstrated that 300-370 nm UV emission is considerably enhanced by the introduction of several percent of In into AlGaN due to an In-segregation effect. We fabricated 310 nm band UV LEDs with quaternary InAlGaN emitting layers on sapphire substrate and obtained sub-milliwatt output power. We also fabricated 350 nm band InAlGaN-based quantum-well (QW) LEDs on GaN substrates in order to eliminate the effects of threading dislocations. The maximum UV output power obtained was as high as 7.4 mW under room temperature (RT) CW operation. The maximum external quantum efficiency (EQE) was 1.1% with an injection current of 50 mA, which is the highest EQE ever obtained for 350 nm band UV LEDs with top-emission geometry.

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The diode-pumped slab laser for inertial fusion energy driver has been demonstrated, which produces the 1053-nm output energy of 10 J at 10 Hz. The glass slab laser amplifier has been pumped by quasi-CW 290 kW AlGaAs laser-diode arrays at 803 nm. The optical system can compensate for thermal effects by use of zig-zag optical propagation, image-relayed telescope, and 45° Faraday rotator. The output energy of 10.6 J at 1 Hz with the optical to optical conversion efficiency of 19.9% has been successfully obtained. Also the 10 Hz operation has been performed with a 5.1 J output eneregy.

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For the purpose to use a laser diode (LD) for direct material processing, the wave-front of a single-mode LD have been measured and corrected. The wave-front of the output beam of 0.1 W LD at 940 nm wavelength through a newly designed collimator lens was measured, and the wave-front error of about 1λ was corrected by the Laser Ablative Shaping (LAS) method. After 2 times of wave-front correction, the residual wave-front error was reduced to better than λ/4. The output beam was focused on to the plastic plates to make micro-marking for production tracing.

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Everywhere in the world, the highest quality and quantity of lighting is required during the surgical operations. However, the surgical approach has had many types and various angles, common ceiling surgical halogen lighting system cannot provide an adequate amount of beams because the surgeons' heads hinder the illuminations from reaching the operation field. The evolution of solid-state-lighting is currently going to be developed due to the progress of white light emitting diodes (LEDs). We proposed and developed the new lighting equipment that is a surgical lighting goggle composed of InGaN-YAG (yttrium aluminum garnet):Ce3+-based white LEDs. Here, we newly design surgical lighting system composed of white LEDs equipped on both sides of goggles. In fact, we have succeeded in the first internal shunt operation in the left forearm using the surgical LED lighting system on 11th Sept 2000. Since the white LEDs used were composed of InGaN-blue-emitters and YAG-yellow-phosphors, the color rendering property was not sufficient in the reddish colors. After our first challenge for medical application of white LEDs, we have been trying to improve the luminance power of white LED, the color rendering in red colors and the spectral distribution of white LED to render inherent color of raw flesh such as skin, blood, fat tissue and internal organs. We have produced new concepts for LED lighting sources and new several generations of LED lighting goggles.

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Transversal single mode fiber laser at 1116nm constructed by both a high optical output diode laser and an air-hole type double-clad fiber has been developed for the 1310nm Raman amplification. The special edge filters without substrates make possible to manufacture the laser system using the air-hole type double-clad fiber easily. The laser system and its characteristics are introduced in this report.

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We developed new high power diode lasers and welding system applied to automobile industry.
This paper describes the developed machine concept and the possibility of replacement to high power diode laser welding for tailored blank processing which has been performed by CO₂ lasers or YAG lasers.

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Recently, IP telephony services in wired network are started, and paid attention for its charge-free nature due to IP technology. On the other hand, the Hot-Spot service, which provides one to access the Internet at the public space such as cafe, using the IEEE wireless LAN has been evolved, and it is expected that the IP telephony service on the Hot-Spot network will be developed. However, the IP telephony quality on the IEEE802.11a wireless LAN has not been fully studied yet. In this paper, we discuss about the quality of IP telephony service on the IEEE802.11a wireless LAN from the aspect of R-value, and show ability to improve the IP telephony quality on the Hot-Spot network employing PLC function defined in the ITU-T Recommendation G.711 Appendix I.

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In binary digital transmission, a bit error rate (BER) is the most important evaluation standard. But actual transmission line does not give any bit error rate, because a bit error occurs by existence of analog noise power. If these noisy communication channel which shows a certain random and burst bit error rate, called a transmission line simulator, can be constructed artificially, it is very useful for evaluation of data transmission quality. This paper proposes the theoretical design method of transmission line simulator using a combination of the maximum length sequence generator and binary counter circuits or two maximum length sequence generators. The feature of this proposed systems is that an average bit error rate is controlled by changing the length of shift register. The fundamental concept and its characteristics are described.

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Mobile robots are recently being used in various environments. Since errors in position and posture occur while operating the mobile robots in these environments, positioning and posturing are very important. Several researches are currently under progress for these corrections. For example, we often use sensors such as accelerometer, the Cooperative Positioning System (CPS), or the Global Positioning System (GPS). In our research, we propose a method using a 2.4[GHz] specific small power microwave. In our method, we consider that the most important aspect is phase synchronization between transmitters and between transmitter and receivers. However, the proposed system does not require this synchronization. Therefore, our system has a simple structure, high quality and easy upgradeability. We simulate this Local Positioning and Posturing System (LPPS) and examine the results.

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In Mpeg/Audio coding, an audio signal is effectively compressed as compared with an original audio signal. The technique of compression is the lossy compression by using human's perceptual characteristic. Since human's perceptual characteristic at high frequency bands is relatively weaker than other frequency bands, and this characteristic is efficiently used in compression. In other words, SNR (Signal to Noise Ratio) for decoded audio signal in high frequency bands is worse than in other frequency bands.
In this paper, we propose our method which improve SNR for high frequency component by what we propose, when compressed audio signal is in decoding. In order to realize the purpose, we will add compensating process to Mpeg/Audio decoding process. This process calculated high frequency component which is fell off for high effective compress rate in encoding process, in frequency domain. The result that is calculated compensation of high frequency is synthesized with the result of ordinary Mpeg/Audio decoding, so that synthesized audio signal improve SNR for high frequency component, without bad influence to other frequency components (i.e. making other frequency components to be worse).

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The problem of adaptive robust tracking and model following is considered for a class of linear dynamical systems with multiple delayed state perturbations, time-varying uncertain parameters, and external disturbance. A class of adaptive output feedback controllers is proposed for robust tracking of dynamical signals. Based on the strictly positive realness of the nominal system, it is shown from the Kalman-Yakubovitch lemma that the proposed adaptive robust output feedback tracking controller can guarantee the zero-error tracking. Finally, a numerical example is given to demonstrate the validity of the results.

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This paper proposes a practical method of collision-free motion planning for multi-degree of freedom manipulators. The proposed method has mainly two concepts. Under this method, the motion planning is considered in real space instead of configuration space in order to reduce the calculation amount. Meanwhile, it is well known that a path planning is executed without local minima under a potential field based on Laplace's equation because such environment has no minimal point. Therefore, we introduced an electrostatic field based on Laplace's equation for path planning of multi-degree of freedom manipulator. Specifically, the path planning of the end-effecter of manipulator is executed under the potential field produced by solving Laplace's differential equation. On the other hand, for the determination of the whole manipulator's shape after the end-effecter position has been derived, we implemented the form changing of the electrical-charged wire in the electrostatic field. Here, this electrical-charged wire is named as “Electrified Wire". By using this method, the collision-free shape of manipulator can be determined easily. For the explanation of this method, we produced the collision-free motion planning of 10DOF manipulator as a simple example.

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In this paper, based on the maximum neural network, we propose a new parallel algorithm that can escape from local minima and has powerful ability of searching the globally optimal or near-optimum solution for the maximum independent set problem (MISP). Given a graph, the aim of the MISP is to find the largest set of vertices such that no two vertices in the set are connected by an edge. The MISP is a classic optimization problem in computer science and in graph theory with many real-world applications, and is also known to be NP-complete. By adding a nonlinear self-feedback to the maximum neural network, we proposed a parallel algorithm that introduces richer and more flexible nonlinear dynamics and can prevent the network from getting stuck at local minima. After the nonlinear dynamics has vanished, the proposed algorithm then is fundamentally reined by the gradient descent dynamics and usually converges to a stable equilibrium point. A large number of instances have been simulated to verify the proposed algorithm.

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In this paper, we propose a new artificial pulse neural network model which utilizes short term synaptic depression (STSD) for attention control. Compared with classic integrator-type neurons, pulse neurons are known for their superior ability to handle temporal information, as well as the easiness to implement new found properties of biological neurons. STSD is one of such properties. While recent researches indicate that STSD shows some interesting behaviours like gain controls, its usefulness for artificial neural networks is still unclear. The proposed model is a brand new pulse neural network to utilize STSD for movie processing. This model is composed of four layers of pulse neurons. The input is the brightness information of the current image of the movie, and the output is the area which requires system's attention. Due to STSD between the input layer and the first hidden layer, it is capable of keeping its attention on things like fast moving objects, while ignoring static or slow objects even if they are flickering. Experimental results show that this model has the basic abilities for attention control.

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According to the knowledge of brain science, it is suggested that there exists cerebral functional localization, which means that a specific part of the cerebrum is activated depending on various kinds of information human receives. The aim of this paper is to build an artificial model to realize functional localization based on Genetic Network Programming (GNP), a new evolutionary computation method recently developed. GNP has a directed graph structure suitable for realizing functional localization. We studied the basic characteristics of the proposed system by making GNP work in a functionally localized way.

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This paper is concerned with adaptive robust stabilization problem for a class of cascaded nonlinear systems with uncertain time-delay and unknown parameters. The cascaded system consists of two subsystems which are ξ-subsystem driven by the control input and x-subsystem forced by the output y of the ξ-subsystem. First, an extension of LaSalle-Yoshizawa theorem is given for the nonlinear time-delay systems, which provides a sufficient condition for convergence to zero of partial states with boundedness of the system. And then, it is shown that an adaptive robust stabilizing controller can be designed by this theorem, if the nominalξ-subsystem can be rendered strictly passive and the unforced x-subsystem is asymptotically stable. It is also shown that the proposed design method can be extended to the case where the ξ-subsystem has a triangular structure. A numerical example is given to demonstrate the effectiveness of the proposed method.

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Internet service provided by TCP connections are often susceptible to Denial of Service attack, especially SYN Flood from external hosts even internal on the network. In our research, we materialise a stateless session establishment mechanism at SYN packet in TCP 3Way Hand Shake then avoid consuming in that CPU, memory and others. We suggest SPP (SYN Packet Pacifier) in this paper. We arranged SPP within FreeBSD Kernel as the system based on above principles. SPP is a secure defense system and an effective DoS counter measure rather than the former methods such as SYN Cache and SYN Cookie.

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It is known that the synchronization phenomenon emerges from the coupling system of some nonlinear oscillations, and that behavior of synchronization depends on coupling parameters. At first, we propose the method to estimate coupling parameters which realize synchronization starting at the desired time by solving the parameter optimization problem. On the other hand, the periodic cycle of nonlinear oscillation depends on its parameters (bifurcation parameters). The relation between a periodic cycle and bifurcation parameters can be known by describing the bifurcation diagram. Secondly, we formulate the parameter optimization problem to estimate the bifurcation parameters which realize the desired periodic cycle without a bifurcation diagram. Finally, we formulate the integrated type of parametr optimization problem to find the bifurcation parameters of nonlinear oscillations with the desired periodic cycle, as well as the coupling parameters to realize the desired synchronization simultaneously. In order to solve this problem, we use the gradient method based on variational method. As a result of this method, we can realize the synchronization with desired periodic cycle starting at the desired time.

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In this paper, a new wavelet based de-noising method for noisy chaotic signal using the trajectory parallel measure method is proposed. As the chaotic signal is similar to noise, the traditional de-noising criterion based on the noise variance is not successful when applying to noisy chaotic signal filtering and prediction. In order to reduce the observation noise, the threshold can be determined based on whether the signal is chaotic or close to noise using the trajectory parallel measure. Further, the method is applied to the prediction problem of chaotic signal.
In order to verify the effectiveness of the proposed method, it is demonstrated that the observation noise component is effectively reduced compared with the traditional method in the numerical experiments. The usefulness for chaotic signal prediction is also examined in the simulations.

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We propose a new 2-opt base method in a Memetic algorithm, that is, Genetic Algorithms(GAs) with a local search. The basic idea is from the fast 2-opt⁽¹⁾ method and the improved 2-opt method⁽²⁰⁾. Our new search method uses the “Priority" employed in the improved 2-opt method. The “Priority" represents the contribution level in exchange of genes. Matayoshi's method exchanges genes based on previous contribution to the fitness value improvement. We propose a new search method by using the concept of the Priority. We call our method the search area expanding strategy method in the improved 2-opt method. Our method escalates the search area by using “Priority". In computer experiment, it is shown that the computation time to find exact solution depends on the value of the Priority. If our method does not set an appropriate priority beforehand, then we propose the method to adapt to suitable value. If improvement does not achieved for certain generations, our dynamic priority method tries to modify the priority by the mutation operation.
Experimental results show that the search area expanding strategy method embedded with the dynamic priority setting method can find the exact solution at earlier generation than other methods for comparison.

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A synchronous digital circuit for encoding differential Manchester and inverse differential Manchester codes is presented. The design is based on a new representation of these codes as Moore state machines, which is extracted from a new code definition through encoding equations. The encoder utilizes two flip-flops, one OR gate and one X-OR gate, which can be easily implemented in hardware using standard ICs or part of an LSI / VLSI circuit.

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Radio Frequency Identification (RFID) has been used as a method fr obtaining information from objects to which it is attached. This paper proposes an architecture of a telemetry system with operability, capability to variety of housing and continuity to the future for the utility services such as Electricity, Gas and Water system. And this paper also examines the feasibility of the wireless link using RFID. The result proves that the proposed Telemetry System for utility services could be implemented with sufficient throughput, when the RFID with collision avoidance and symmetrical communication protocol is employed to the wireless link.

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Wrong:Satohi Iwakata
Right:Satoshi Iwakata

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