Kenzo Takahashi

Bio: Kenzo Takahashi is an academic researcher from Multimedia University. The author has contributed to research in topics: Laser diode & Transmission delay. The author has an hindex of 3, co-authored 8 publications receiving 38 citations. Previous affiliations of Kenzo Takahashi include University of Electro-Communications & University of Fukui.

Performance of wavelength-convertible multihop optical ShuffleNets employingconvolutional coding under hot-potato routing

Abstract: Performance analysis is carried out for a multihop optical ShuffleNet with full wavelength conversion to evaluate the effect of wavelength converters on the bit-error-rate (BER) and packet-error-rate (PER) performance. Computed results show that there is a significant decrease in BER with an increase in the number of wavelength converters nw for the same transmitter power. Further, an increase of nw is needed at increased network load g; for example, to achieve the maximum throughput, nw ≈ 10 and nw ≈ 20 are needed corresponding to g = 0.5 and g = 1.0. It is found that when convolutional coding is applied, the required number of wavelength converters is greatly reduced at the full load g = 1.0.

Performance evaluations of multi-layers ring network architecture

Abstract: Performance evaluations of the multi-layers ring network architecture with unicast/multicast function have been done recently by using non-parametric approach. It was claimed that the proposed architecture outperforms the conventional point-to-point multi-layers architecture in terms of the link cost and interface cost. This paper further investigates the impact of the traffic to the nodes in such architecture with unicast capability through optical packet switching simulations. It is found that there are serious packet losses at layer 3 if switches capacity are same at all levels; the required number of wavelengths/optical buffers increases exponentially in order to maintain a given packet loss rate when more layers exist in the architecture. Therefore, it shows that too many layers architecture may affect the networks performances.

Multihop optical network with convolutional coding

Abstract: We evaluate the bit-error-rate (BER) performance of a multihop optical ShuffleNet with and without convolutional coding. Computed results show that there is considerable improvement in network performance resulting from coding in terms of an increased number of traversable hops from a given transmitter power at a given BER. For a rate-1/2 convolutional code with constraint length K = 9 at BER = 10-9, the hop gains are found to be 20 hops for hot-potato routing and 7 hops for single-buffer routing at the transmitter power of 0 dBm. We can further increase the hop gain by increasing transmitter power.

Laser machining of structural ceramics—A review

Abstract: Outstanding mechanical and physical properties like high thermal resistance, high hardness and chemical stability have encouraged use of structural ceramics in several applications. The brittle and hard nature of these ceramics makes them difficult to machine using conventional techniques and damage caused to the surface while machining affects efficiency of components. Laser machining has recently emerged as a potential technique for attaining high material removal rates. This review paper aims at presenting the state of the art in the field of laser machining of structural ceramics and emphasizes on experimental and computational approaches in understanding physical nature of the complex phenomena.

Computational predictions in single-dimensional laser machining of alumina

Abstract: Machining of alumina was investigated in this study by using a JK 701 pulsed Nd:YAG laser. A hydrodynamic machining model was developed which incorporated the effect of multiple reflections on the amount of laser energy absorbed, the thermal effects for melting the material, vapor pressure effect for expelling out the molten material, material losses due to evaporation and the inverse effect of surface tension on the expelled depth .The model also incorporated the transient effect of laser beam de-focusing due to change in machined depth as a function of expelled material during machining for precise estimation of the melted depth during each pulse. It was observed that the material removal was a combination of melt expulsion and evaporation processes. The developed model would be an excellent tool for advance prediction of the total thermal energy and time required for removal and/or machining of desired depth of material.

ABCD matrix for reflection and refraction of Gaussian beams at the surface of a parabola of revolution.

Abstract: We report the formulation of an ABCD matrix for reflection and refraction of Gaussian light beams at the surface of a parabola of revolution that separate media of different refractive indices based on optical phase matching. The equations for the spot sizes and wave-front radii of the beams are also obtained by using the ABCD matrix. With these matrices, we can more conveniently design and evaluate some special optical systems, including these kinds of elements. (c) 2005 Optical Society of America