Fabrication of aluminium foams from powder by hot extrusion and foaming

In order to produce aluminium foams for light-weight and energy absorbing structures of automobiles, a method for fabricating aluminium foam from powder mixed with a foaming agent by using a mould is proposed. The method consists of four sequential processes: powder compacting, extruding, foaming and moulding. In the experiment for fabricating aluminium foam from powder, the conditions of powder extrusion and foaming by the heated die are determined from the density of the aluminium foams made without a mould. The experimental results show that the relative density of the aluminium foam made under appropriate conditions is 0.22. In moulding of aluminium foam, a stainless steel pipe is used as a mould and the cylindrical aluminium foam is produced by filling into the pipe mould. The distribution of relative density within the aluminium foam bar is in a range of 0.2–0.3 by rapid cooling of the pipe. To examine the ratio of deformation energy to weight of the pipe including the aluminium foam, a compression test using a press is carried out. The deformation energy of the pipe can be increased with aluminium foam filled by the proposed method.     

Very-high-speed optical signal processing

Challenges of next-generation transmission technologies are summarized in the context of creating future terabit-per-second networks. The technologies will be realized through both the separate and combined evolution of inherent lightwave capabilities along with time-, wavelength-, and space-domain optical processing techniques. Optical signal processing techniques in the tens of gigabit per second range for future high-speed transmission systems and broadband networks are reviewed     

Novel high-efficiency concentrator for optical fiber communication

A novel high-efficiency concentrator based on nonimaging optics has been designed and fabricated with micromachining technique. The shape of the concentrator utilizes compound parabolic concentrator (CPC), which can concentrate the all rays that have the angles less than a critical angle &thetas;_c. The theoretical concentration efficiency was calculated by ray trace simulation considering the reflectance of the concentrator's reflective layer. The metal reflection layer of reflectance 95% was formed by gold-nickel mirror plating method in a glass hole. As a result, the concentration efficiency of the concentrator was measured as 89%     

Tunable wavelength filter using nano-sized droplets of liquidcrystal

An electrically tunable optical filter has been developed that uses a polymer containing fine droplets of nematic liquid crystal as the active cavity in a Fabry-Perot interferometer (FPI). This FPI filter, whose finesse was 62, had a free spectral range of 37 nm in the 1.55-μm range with a full-width at half maximum of 0.6 nm and a transmission loss of 2.4 dB. The polarization dependent loss was smaller than 0.17 dB. The transmitted peak wavelength decreased with an electric field. This resulted in a tuning range of 10 nm at 300 V. The switching time was about 370 μs     

A high-precision low-voltage bipolar current mirror circuit and its compensation for stability

A current mirror circuit is widely utilized as an important building block in analogue signal processing circuits. This paper describes a high-precision low voltage bipolar current mirror circuit. Well known current mirror circuits, such as a simple current mirror and a Wilson current mirror, have a trade-off between low-voltage operation and accuracy of the current gain. The accuracy of the proposed current mirror is high in spite of low current amplification factor (β) of transistors and large current output (or a large number of the multiple output). The current mirror circuit can operate at a 1V or less supply voltage. The high accuracy is realized by negative current feedback with high gain. Thus, the stability of the circuit and compensation methods are discussed. PSPICE simulation shows that the proposed current mirror circuit compensated using Miller components composed of a capacitor and a resistor is stable and can operate at a 1V supply voltage.     

A complex baseband platform for spatial-temporal mobile radio channel simulations

Joint spatial-temporal signal processing has been recognized as the key to reducing the effects of the intersymbol and cochannel interference seen in very high bit-rate mobile radio communications systems. Developing hardware simulators that can simulate mobile radio propagation scenarios in time and space domains is essential for evaluating the real-time performance of spatial-temporal signal processing schemes. This paper outlines a complex baseband platform developed for spatial-temporal mobile radio channel simulations. The platform consists of a complex baseband fading/array response simulator, a digital signal processor (DSP) board, and a general-purpose parameter estimator that uses systolic array implementation of the recursive least square (RLS) algorithm. Results of experiments conducted using the developed platform are presented to confirm the proper operation of the system.     

Distributed polarization-mode dispersion compensation using polarizers

We numerically evaluate the performance of two kinds of distributed polarization-mode dispersion compensation techniques using either linear or elliptic variable polarizers. Each in-line compensator is characterized by only one or two degrees of freedom and the average power is used as a monitor signal, which simplifies the control algorithm. The use of polarizers causes inevitable attenuation of the optical signal, which induces additional noise in amplified systems. Nevertheless, the noise enhancement due to the distributed polarizer-induced loss is shown to be limited in systems operated with erbium-doped fiber amplifiers in gain saturation and the tolerable differential group delay can be improved if the frequency of insertions is increased.     

Performance analysis and comparison of optical 3R regenerators utilizing self-phase modulation in fibers

Performance of fiber-based optical signal regenerators consisting of a synchronous amplitude modulator, a highly nonlinear fiber, and an optical bandpass filter is analyzed. The regenerators are operated in two different schemes: one utilizes solitonlike pulse compression in anomalous-dispersion fiber and subsequent filtering, and the other utilizes spectrum broadening in normal-dispersion fiber and subsequent spectrum slicing. Regeneration performance is compared for the two schemes in terms of the shape of energy transfer function and abilities of noise and timing-jitter reduction. Although both types of regenerators show good regenerator performance, the one based on spectrum broadening and slicing has better ability to stabilize signal amplitude while requiring larger signal power launched into the nonlinear fiber. The effectiveness of the regenerators in single-channel quasi-linear highly dispersed pulse transmission and dispersion-managed soliton transmission is also numerically examined.