Development of the frequency-dependent three-dimensional LOD-FDTD method and its application to the analysis of plasmonic devices

研究成果の概要 (和文) : 3次元の微小プラズモンデバイスを極めて高速に解析できる、局所的一次元(LOD)法に基づく陰的なFDTD法を開発した。畳み込みの計算が一度で済み高い精度の得られる台形則に基づく手法、さらに、Fundamental法と呼ばれる技法の導入により、計算式の右辺に微分項を含まない極めて簡便な定式化を行った。プラズモニックギャップ導波路をPCで解析したところ、陽的なFDTD法で85分かかった計算がほぼ同等の計算精度を維持しつつ37分に低減された。開発した手法を用いて、種々の3次元プラズモンデバイスを解析した。デバイス特性を2次元構造デバイスと比較しながら議論し、3次元解析の重要性を示した。研究成果の概要 (英文) : An implicit FDTD method based on the locally one-dimensional (LOD) scheme has been developed for the efficient analysis of three-dimensional (3-D) plasmonic devices. The trapezoidal recursive convolution technique has been adopted, in which a single convolution integral is required. In addition, a fundamental scheme has been introduced for efficient formulation of the algorithm, in which no spatial derivative exists in the right-hand side of the equations. The developed LOD-FDTD offers a reduced computation time from 85 min with the conventional explicit FDTD to 37 min for the analysis of a plasmonic gap waveguide. The characteristics of several 3-D plasmonic devices have been investigated using the LOD-FDTD. The 3-D results have been compared with those of 2-D models, showing the necessity of the 3-D analysis for an accurate evaluation of the plasmonic devices

Development of polarization conversion and control devices based on periodic and waveguide structures

研究成果の概要 (和文) : 導波路型および周期構造型の偏波変換・制御デバイスを解析し得る、効率のよい数値解法として、陽解法と陰解法に基づく有限差分時間領域法を金属膜のような分散性媒質を含む際にも取り扱えるように拡張した。構築した解法に基づき、周期構造型偏波変換器の動作メカニズムを明らかにした。また、導波路型偏波変換器を広帯域に動作させる手法を考案した。結果として、波長1.3μmから1.65μmの広帯域に渡って、15dB以上の消光比、0.5dB以下の挿入損を実現した。研究成果の概要 (英文) : To analyze polarization conversion and control devices based on periodic and waveguide structures, we develop explicit and implicit finite-difference time-domain methods for dispersion materials. The mechanism for splitting two polarizations has been explained using the surface plasmon effect. For the waveguide-type converter, the polarization conversion is obtained with an extinction ratio of more than 15dB and an insertion loss of less than 0.5dB over a wide wavelength range of1.3 to 1.65 μm

Efficient wave-optical simulations for the modeling of micro-optical elements

Modern optical fabrication technologies enable the realization of optical components in between very nanoscopic- and macroscopic scales without symmetries and with extraordinary accuracies. This opens up novel possibilities in the design of modern optical system. Nevertheless, the ability to take direct advantage out of these developments is intrinsically linked to profound numerical simulation tools to analyze, model and design these systems. Consequently, these demands trigger the steady development and improvement of algorithms, which advances the optical design process and therewith the functionality of related devices. It is one aim of this thesis to introduce and to discuss improved numerical techniques to model micro-optical systems. Moreover, it is a second aim of this thesis to also investigate the potential of these improved simulation methodologies to design micro-optical systems. In particular, an illumination concept is introduced, which allows to realize tailored illumination distributions in a highly integrated approach. Finally, it is a third aim of this thesis to use the improved simulation methodologies to solve inverse problems for the characterization of micro-optical components. In particular, the ability to resolve the origin of glass matrix distortions during fiber Bragg grating inscriptions will be discussed. Moreover, a computational sensing concept to characterize optical fibers will be introduced

Approximate degree in classical and quantum computing

In this book, the authors survey what is known about a particularly natural notion of approximation by polynomials, capturing pointwise approximation over the real numbers.FG-2022-18482 - Alfred P. Sloan Foundation; CNS-2046425 - National Science Foundation; CCF-1947889 - National Science FoundationAccepted manuscrip

Thermo-hydro-mechanical coupling within a geomechanical multiphase model framework with special reference to fractured rock masses in the vicinity of a geological disposal facility for radioactive waste

A novel numerical approach for the modelling of Thermo-Hydro-Mechanical (THM) processes in the vicinity of a Geological Disposal Facility (GDF) for the long-term storage of radioactive waste is presented. This work is based on a dual numerical code framework with a multiphase flow solver for thermo-hydraulic processes and a geo-mechanical solver for mechanical processes in fractured and fracturing rock masses. The method has a unique continuum-discontinuum configuration that allows each of the THM processes to be represented with the most suited formulation, thus improving the accuracy and complexity of the simulations. Thermal processes are implemented within the geo-mechanical solver using both an explicit and an implicit approach, the latter allowing the modelling of temperature over large time scales, an important feature in the context of geological disposal. Moreover, a novel thermal contact approach is presented to investigate the heat transfer between contacting solids and its application to heat transfer across fractures is discussed. Furthermore, a thermo-mechanical coupling formulation is derived in the geo-mechanical solver, enabling thermal expansion and thermally induced fracturing. Then, the THM coupling is finalised using a conservative projection method that enables information exchange between superimposed numerical meshes e.g. heat transfer between the thermo-hydraulic and the thermo-mechanical solvers. Both applications in porous media and with laminar flow are explored. Finally, the THM dual framework is applied to the modelling of thermal spalling occurring in the excavation walls of a deposition hole in a GDF. The potential of the method to offer new predictive capabilities and insights on unexplained experimental observations is demonstrated by considering the concurrence over time of THM factors influencing spalling, especially multi-phase flow in the continuum and explicitly represented fractures in the discontinuum.Open Acces

Combining SOA and BPM Technologies for Cross-System Process Automation

This paper summarizes the results of an industry case study that introduced a cross-system business process automation solution based on a combination of SOA and BPM standard technologies (i.e., BPMN, BPEL, WSDL). Besides discussing major weaknesses of the existing, custom-built, solution and comparing them against experiences with the developed prototype, the paper presents a course of action for transforming the current solution into the proposed solution. This includes a general approach, consisting of four distinct steps, as well as specific action items that are to be performed for every step. The discussion also covers language and tool support and challenges arising from the transformation

Pseudo-contractions as Gentle Repairs

Updating a knowledge base to remove an unwanted consequence is a challenging task. Some of the original sentences must be either deleted or weakened in such a way that the sentence to be removed is no longer entailed by the resulting set. On the other hand, it is desirable that the existing knowledge be preserved as much as possible, minimising the loss of information. Several approaches to this problem can be found in the literature. In particular, when the knowledge is represented by an ontology, two different families of frameworks have been developed in the literature in the past decades with numerous ideas in common but with little interaction between the communities: applications of AGM-like Belief Change and justification-based Ontology Repair. In this paper, we investigate the relationship between pseudo-contraction operations and gentle repairs. Both aim to avoid the complete deletion of sentences when replacing them with weaker versions is enough to prevent the entailment of the unwanted formula. We show the correspondence between concepts on both sides and investigate under which conditions they are equivalent. Furthermore, we propose a unified notation for the two approaches, which might contribute to the integration of the two areas