高度計算電磁気学の発展で可能になる新型ナノフォトニック素子

電磁気学における高度計算技術の発展に伴い、かつて理論の範囲をはるかに越えた複雑な波干渉現象に基づいたナノフォトニック素子の設計・モデリング・実現が始めて可能になる。近年、学術研究で開発されたオープンソースCADソフトがますます大規模な並列計算に活用される傾向があり、有力かつ柔軟性に優れたこのツールではあらゆる材料・あらゆる形状で製作したデバイスの光学性質や光との相互作用を数理モデリングで把握できる様になりつつある。 計算能力のこの様な進歩につれて、以前手計算ではもちろん、有料CADソフトでも扱えなかった構造・物質・自然現象などが新時代の無料ソフトで調べられ、電子工学や基礎物理における未開拓地が実質的な研究対象になる。

現代電磁気学モデリング用オープンソースソフトの主流を大別すれば2種類(つまり、微分方程式方と積分方程式方)あるが、本セミナーではその両方を紹介する。まず、微分方程式方である有限差分時間領域方(FDTD)を実装したオープンソースパッケージ MEEPの実用例として、 (1)ナノ構造をした薄膜シリコン太陽電池で光トラッピング性質を発揮する目新しい構成に到る工夫過程、そして(2)ナノ組織有機発行ダイオードからの光収穫最適化という2解析例を紹介する。そして、表面積分方程式方を実装したオープンソースパッケージ SCUFF-EMの実用例として、(1) 周期的・非周期的なナノパターンで定義された非対称構造で入射偏光により周波数が変わるアンテナ、(2) 熱力学・量子力学変動に由来する熱伝導・カシミール力を最大にする非対称ナノ粒子の最適化という2設計例を紹介する。

最後に、我々のベンチャー企業SIMPETUSで公開クラウドにおける高性能計算(high-performance computing, HPC)を活かした大規模デバイス設計を促進する取り組みを概略する。

Leveraging Advances in Computational Electrodynamics
to Enable New Kinds of Nanophotonic Devices

Advances in computational electrodynamics have the potential to enable fundamentally new kinds of nanophotonic devices based principally on complex, non-analytical wave-interference effects. Powerful, flexible, open-source software tools have now been made available for use in large-scale, parallel computations to model the interaction of light with practically any kind of material in any arbitrary geometry. These recent developments in computational capability make possible the investigation of various emergent structures, materials, and physical phenomena that were previously beyond the reach of theoretical analysis---including not only pencil-and-paper calculation but even commercial software tools, which tend to be less versatile and even less readily available to academic researchers.

Modern open-source tools for computational electromagnetism may be broadly divided into two categories---differential-equation solvers and integral-equation solvers---and this seminar will cover both. We will first demonstrate how advances in finite-difference time-domain (FDTD) methods for computational electromagnetics, as implemented by the open-source package MEEP, can lead to entirely new designs for light trapping in nanostructured thin-film silicon solar cells and light extraction from nanostructured organic light-emitting diodes (OLEDs). Then we will discuss two applications of surface-integral-equation algorithms as implemented by the open-source package SCUFF-EM: (1) designing antennas defined by periodic and aperiodic nanopatterning with polarization-sensitive frequency response, and (2) optimizing the shapes and material content of asymmetric nanoparticles to maximize radiative heat transfer, Casimir forces, and other phenomena induced by thermal and quantum-mechanical fluctuations.

Finally, we will describe our efforts at Simpetus to leverage scalable, cluster computing in the public cloud for large-scale device design.

About the Speakers

Ardavan Oskooi is the Founder and CEO of Simpetus, a San Francisco-based startup accelerating photonics innovation and discovery with simulations. Ardavan received his Sc. D. from MIT, where he worked with Professors Steven G. Johnson and John D. Joannopoulos (thesis: Computation & Design for Nanophotonics) to develop MEEP. Ardavan has published 13 first-author articles in peer-reviewed journals and the book Advances in FDTD Computational Electrodynamics: Photonics and Nanotechnology. He has a masters in Computation for Design and Optimization from MIT and completed his undergraduate studies, with honors, in Engineering Science at the University of Toronto. Prior to launching Simpetus, Ardavan worked with Professors Susumu Noda at Kyoto University and Stephen R. Forrest at the University of Michigan on leveraging MEEP to push the frontier of optoelectronic device design.

Homer Reid is Lecturer in Applied Mathematics at MIT, where his research encompasses computational quantum field theory and chemistry in addition to computational electromagnetism. Homer completed his PhD in physics at MIT, where he worked with Professors Jacob White and Steven G. Johnson to create the fluctuating-surface-current approach to fluctuational electrodynamics, and is the developer of the open-source SCUFF-EM package for surface-integral modeling of deterministic and fluctuational electromagnetism problems. Before completing his PhD in theoretical physics, Homer worked as an experimental condensed-matter physicist and as an analog/RF integrated-circuit designer at a semiconductor company. Homer lived in Japan for 6 years and is fluent in Japanese.