Actively mode-locked strained-InGaAsP multiquantum-well lasersintegrated with electroabsorption modulators and distributed Braggreflectors

This paper describes picosecond pulse generation at 20 Gb/s by monolithic mode-locked lasers integrated with electroabsorption modulators and distributed Bragg reflectors. The electroabsorption modulator using strained-InGaAsP multiquantum wells acts as a pulse shortening gate when a sinusoidal voltage is driven at a large reverse bias voltage. To obtain transform-limited picosecond pulses, the required spectral bandwidth of the distributed Bragg reflector is estimated. Pulse generation around 4 ps with a time-bandwidth product of 0.5 has been performed at a repetition rate of 20 GHz. Driving conditions of the modulator, such as bias voltage and modulation frequency, are investigated. It is shown that an increase in the intensity noise is the main factor limiting performance     

A current-type PWM rectifier with active damping function

A new control method for current-type pulse-width modulation (PWM) rectifiers which can provide active damping function is presented. This damping function is effective only on the harmonic components of AC input current selectively. Thus steady-state waveform distortion and transient oscillation of the input current are reduced by the active damping effects. The active damping function can be realized by feedback control of an LC filter connected to the AC side of the rectifier, and it does not require any additional components in the main circuits, permitting a simple circuit configuration. The control system of the proposed PWM rectifier is analyzed by using a simple block diagram developed in the present paper. From the analytical results, the influence of the circuit parameters and control delay on the active damping effects and the stability of the operation are clarified to establish the design method. To confirm the effectiveness of the active damping function, some results of basic experiments are included. As an example of application of the active damping function, the proposed rectifier is applied to reduce the harmonic currents generated by conventional rectifiers operating in parallel with the proposed rectifier. Some experimental results in this application are also included     

Laboratory and field verification of a new approach to stress measurements using a dilatometer tool

A new method is proposed for in-situ stress measurements. The stresses are estimated from the borehole pressure required to open axial fractures emanating from the borehole, similar to hydrofracture stress measurements. However, the borehole is pressurized by inflation of a dilatometer, such as a packer and a sleeve, and the borehole pressure to reopen the fractures is detected from circumferential deformation of the borehole. The fractures are induced by hydraulic fracturing or sleeve fracturing in advance. To demonstrate this method, we developed a new dilatometer tool. The tool consists essentially of a packer around which deformation transducers sensitive to circumferential strain are affixed at 10°–30° intervals. The packer is inflated to touch the borehole wall, and then the packer pressure is increased step-wise and the resultant strains recorded. Initially, the circumferential strain developed around the borehole is radially symmetric. However, this becomes strongly asymmetric once the fractures begin to open. Thus, the records of strain at different locations around the borehole indicate both the reopening pressure and the orientation of fractures. In the case of a vertical borehole, the detected reopening pressure allows us to estimate the maximum horizontal stress on condition that the minimum horizontal stress is estimated using other approaches.     

Electrochemical processes for formation, processing and gate control of III-V semiconductor nanostructures

This paper reviews recent efforts by authors’ group to utilize electrochemical processes for formation, processing and gate control of III-V semiconductor nanostructures. Topics include precise photo-anodic and pulsed anodic etching of InP, formation of arrays of 〈0 0 1〉-oriented straight nanopores in n-type (0 0 1)InP by anodization and their possible applications and macroscopic and nanometer-scale metal contact formation on GaAs, InP and GaN by a pulsed in situ electrochemical process, which remarkably reduces Fermi level pinning. All the results indicate that electrochemical processes can achieve unique and important results, which the conventional semiconductor technology cannot realize, anticipating their increased importance in future semiconductor nanotechnology and nanoelectronics.     

Development of Superconducting AC Generator

The superconducting ac generator is expected to be the optimum choice among ac generation systems in the future because of its reduced size, weight, high efficiency, and its contribution to stability of power systems and higher generator terminal voltage. Conceptual design on a 2P-1000MVA class superconducting ac generator has been completed to clarify problems and to confirm advantages. Fundamental studies are performed on key technologies that have to be solved for realization of superconducting generators. As a summary of those fundamental studies, a scaled-down superconducting generator of 3000kVA capacity is constructed and tested. Also clarified are effects of major design parameters for commercial superconducting ac generators such as dimensions, reactances, and weight.     

Optical Fiber Facilities for Subscriber Loops

This paper gives an overview of the introduction and subsequent development of optical fiber cable and its application to subscriber networks enabling economical broad-band services, such as video and high-speed digital data transmissions. This paper also outlines NTT's developments on subscriber optical fiber cable technology-in particular, the five-fiber ribbon cable structure, mass-fusion splicing machine, and multifiber connector-in its ongoing endeavors to establish economical and flexible subscriber optical fiber networks which provide optical fibers to each subscriber.     

Development of a city‐type compact wind power generation system

It is necessary to use renewable energy, such as photovoltaic, wind power, and biomass energy, from the viewpoint of CO₂ regulation and environmental protection of the Earth. In recent years, the tendency is toward larger wind power generation systems to achieve cheaper electricity. Generators having capacities of 1500 kW to 2000 kW tend to dominate the market. However, a large wind power generation system has limitations in terms of location and can be installed only in the suburbs. At the same time, a city‐type compact wind power generation system, designed for city needs, has more flexibility and can be installed in the residential areas of a city. In this paper, we introduce an original control operation system called a “pump‐up” operation system, designed to effectively use the city wind, and report the results of its field test. © 2006 Wiley Periodicals, Inc. Electr Eng Jpn, 158(2): 56–63, 2007; Published online in Wiley InterScience ( www.interscience.wiley.com ). DOI 10.1002/eej.20440     

Rail gun experiment (HYPAC) at ISAS [meteorite impact simulation]

A railgun for the study of the interaction of meteorites with planetary surfaces and the interaction of space debris was developed. The authors have attained a velocity constantly higher than 5 km/s, with a maximum of 6 km/s. The importance of plasma confinement behind the projectile to prevent a leakage is shown to realize a high velocity. An effective acceleration using an aluminum rail is also shown