Showing papers by "Hiroshi Ishikawa published in 2003"
TL;DR: A method to solve exactly a first order Markov random field optimization problem in more generality than was previously possible is introduced, which maps the problem into a minimum-cut problem for a directed graph, for which a globally optimal solution can be found in polynomial time.
Abstract: We introduce a method to solve exactly a first order Markov random field optimization problem in more generality than was previously possible. The MRF has a prior term that is convex in terms of a linearly ordered label set. The method maps the problem into a minimum-cut problem for a directed graph, for which a globally optimal solution can be found in polynomial time. The convexity of the prior function in the energy is shown to be necessary and sufficient for the applicability of the method.
602 citations
TL;DR: In this article, the authors investigated ultrafast refractive index dynamics in a multiquantum-well InGaAsP-InGaAs semiconductor optical amplifier that is operated in the gain regime by using a pump-and-probe approach.
Abstract: We investigate ultrafast refractive index dynamics in a multiquantum-well InGaAsP-InGaAs semiconductor optical amplifier that is operated in the gain regime by using a pump-and-probe approach. The pump-and-probe pulses are cross-linearly polarized. We observe a phase shift of 200/spl deg/ if the amplifier is pumped with 120 mA of current, but find that the phase shift vanishes if the injection current is increased to 160 mA. Our results indicate a contribution of two-photon absorption to the nonlinear phase shift that opposes the phase shift introduced by the gain. Finally, we observe that the phase shift comes up and disappears within a picosecond.
38 citations
TL;DR: In this article, the influence of disordered defects on the transmission properties of optical delay lines based on coupled cavity waveguides (CCW's) was investigated, and the modification of transmission for a line-defect waveguide in a 2D photonic crystal (PC) upon bending was examined by numerical simulation.
Abstract: We investigate, experimentally and theoretically, the influence of disordered defects on the transmission properties of optical delay lines based on coupled cavity waveguides (CCW's). Also, the modification of transmission for a line-defect waveguide in a two-dimensional (2D) photonic crystal (PC) upon bending is examined by numerical simulation. We reveal that the effect of waveguide bending on the transmission properties of PC circuits is very similar to that of disordered defects on the transmission properties of CCW's. It is shown that the broad impurity band of a one-dimensional CCW will evolve into sharp defect modes upon increasing the disorder. Using a symmetric Mach-Zehnder structure formed in a 2D PC as an example, we show that a PC circuit containing multiple bends and branches of different properties generally gives rise to sharp resonant modes whose linewidth is inversely proportional to the size of the PC circuit. This might be an intrinsic problem in realizing PC circuits.
24 citations
Proceedings Article•
23 Mar 2003
TL;DR: In this article, a novel absorptive inter-subband transition all-optical switch with low switching energy using InGaAs/AlAlAS/AlSb coupled quantum wells was reported.
Abstract: We report a novel absorptive intersubband transition all-optical switch with low switching energy using InGaAs/AlAs/AlAsSb coupled quantum wells. Very low saturation energy density of 34 fJ/?m2 and switching energy of 10 pJ for 10 dB extinction ratio were observed.
21 citations
TL;DR: In this paper, room temperature dephasing time (T2) estimates of 1.55 μm intersubband transitions (ISBT) are presented in InGaAs/Alas/AlAsSb coupled double quantum wells.
Abstract: Room-temperature dephasing time (T2) estimates of 1.55 μm intersubband transitions (ISBT) are presented in InGaAs/AlAs/AlAsSb coupled double quantum wells. In this material, optimized for ISBT at communication wavelengths for all-optic switching application, we also studied the doping-density dependence of the four-wave-mixing decay time as a function of incident excitation intensity. A T2 value of about 292±40 fs is estimated at an intensity corresponding to the saturation intensity in samples that are doped to 2×1019 cm−3. This value is in good agreement with the value estimated from earlier calculations.
5 citations
01 Jan 2003
TL;DR: This paper proposes a new method of versioning for XML data stored using relational database, whose main features are that plural versions are created from the previous version of the XML data, and the cost for retrieval of any version is almost equal.
Abstract: Recently, XML documents are not only used for data-exchange, but also used as formats for databases. When XML data with update is considered, management of the versions is very important. In this case, however, traditional line-based document versioning systems, e.g. RCS, are inefficient, because they don't preserve the logical structure of the XML data. Furthermore, much research has been carried out on storage using relational databases; nevertheless version management in such an environment hasn't been researched extensively. In this paper, we propose a new method of versioning for XML data stored using relational database. The main features are that plural versions are created from the previous version of the XML data, and the cost for retrieval of any version is almost equal. Keyword X M L,Relational Database,Ve r s i o n i n g,Ve r s i o n s,Branch,SAX Parser
1 citations
01 Jan 2003
TL;DR: In this article, a Sagnac-interferometric arrangement was used for switching of 200 fs optical pulses, and the switching principles were based on gain and index saturation dynamics on a sub-picosecond timescale.
Abstract: We explain how a semiconductor optical amplifier in a Sagnac-interferometric arrangement can be used for switching of 200 fs optical pulses. The switching principles are based on gain and index saturation dynamics on a sub-picosecond timescale. We have carried out pump and probe experiments to measure the ultrafast refractive index dynamics of a multi-quantum well InGaAsP- InGaAs semiconductor optical amplifier that is operated in the gain regime. The pump and probe pulses are cross-linearly polarized. We observe a phase shift of 200 degrees if the amplifier is pumped with 120 mA of current, but find that the phase shift vanishes if the injection current is increased to 160 mA. Our results indicate a contribution of two-photon absorption to the nonlinear phase shift that opposes the phase shift introduced by the gain. Finally, we observe that the phase shift comes up and disappears within a picosecond. © 2003 JSAP
01 Jan 2003
01 Jan 2003
TL;DR: An efficient XML storage method without using DTDs is proposed, which generates a schema for few number of tables with little redundancy by some statistics of XML documents.
Abstract: Many XML storage methods based on relational databases have already been proposed. These conventional stor- age methods, however, increase the number of tables because of a wide variety of structures of XML documents and make the search cost high. Although there are also storage methods using DTD which is a document model, the descriptive power of DTDs is insufficient in some cases. In this paper, an efficient XML storage method without using DTDs is proposed, which generates a schema for few number of tables with little redundancy by some statistics of XML documents. In order to reduce the number of tables, appropriate data types for the characteristic structures are defined. We try to store elements of a few occurrences in the same table. Which elements are stored in the same table is decided by using a function evaluating the