Thursday, January 20, 2005, 11:00-17:30, ETF E1

Sponsored by **OptETH** and **
Fred Tischer Lecture
Series**

Organizer: Ch. Hafner, Computational Optics Group, IFH, ETH

No registration required for attending the workshop

Registration for the **lunch**: Please send an email to
christian.hafner@ifh.ee.ethz.ch

**Last update ****
21.1.2005**

11:00-11:20 M. Agio (mario.agio@phys.chem.ethz.ch), A.F. Koenderink, and V. Sandoghdar (ETH-NOG): The Finite-Difference Time-Domain codes at the Nano-Optics Group (PDF not available, please contact the first author for more information)

11:20-11:40 N. Moll (nim@zurich.ibm.com), A. Jebali, R. Harbers, S. Gulde, R. F. Mahrt (IBM,
ETH-IFH): Photonic engineering of nonlinear-optical properties of hybrid
materials for efficient ultra-fast optical switching (PDF not available, please
contact the first author for more information)

11:40-12:00 A.F. Koenderink (femius.koenderink@phys.chem.ethz.ch), B. C. Buchler, and V. Sandoghdar (ETH-NOG):
Controlled near-field coupling to optical resonances in photonic crystal
membranes (PDF not available, please contact the first author for more
information)

12:00-12:20 Wataru Nakagawa (wataru.nakagawa@unine.ch) (University of Neuchatel): Accurate
Electromagnetic Modeling of Metal-Coated Scanning Near-field Optical Microscopy
(SNOM) Probes (PDF not available, please contact the first author for more
information)

12:20-12:40 Damir Pasalic (dpasalic@ifh.ee.ethz.ch) (ETH-IFH): A Rigorous Analysis of Traveling Wave
Photodetectors

12:40-13:20 Lunch (offered by OptETH, Fred Tischer), Discussions

13:20-13:40 Bernd Witzigmann (bernd@iis.ee.ethz.ch), Matthias Streiff (ETH-IIS): Optical Modes in
Microcavities PDF of full presentation

13:40-14:00 Jasmin Smajic (jasmin.smajic@ch.abb.com) (ABB): 3D simulation of photonic crystal structures
using FEM PDF of full presentation

14:00-14:20 Christian Hafner (ETH-IFH) MMP Simulation of Optical Nanostructures
PDF of full presentation

14:20-14:40 Kakhaber Tavzarashvili (kakhaber@ifh.ee.ethz.ch) (ETH-IFH): Photonic Crystal Simulations using the Method of Auxiliary Sources PDF of full presentation

14:40-15:00 Rik Harbers (rharbers@ifh.ee.ethz.ch), Niko Moll, Rainer Mahrt, Daniel Erni, Werner Bächtold (ETH-IFH, IBM): Enhancement of the Mode Coupling in Photonic Crystal-Based Organic Lasers (PDF will be available after publication of the results)

15:00-15:20 Break, Discussions

15:20-15:40 Lyudmyla Raguin-Illyashenko (mila.raguin@inf.ethz.ch), P. Arbenz (ETH-ICS): Boundary Integral Equation Method for the Numerical Modeling of Particles with Arbitrary Shape (PDF not available, please contact the first author for more information)

15:40-16:00 Bogdan Cranganu-Cretu (bogdan.cranganu-cretu@ch.abb.com) (ABB): Direct Boundary Integral Equation Method for Electromagnetic Scattering at Partly Coated Dielectric Objects PDF of full presentation

16:00-16:20 Lavinia Rogobete (lavinia.rogobete@phys.chem.ethz.ch), Vahid Sandoghdar, Carsten Henkel (ETH-NOG, University Potsdam): Radiative properties in a sub-wavelength environment characterized with boundary integral equations (PDF not available, please contact the first author for more information)

16:20-16:40 Nicolas Guérin (nguerin@ifh.ee.ethz.ch) (ETH-IFH): Optimization of metallic bi-periodic photonic crystals - Application to compact directive antennas PDF of full presentation

16:40-17:00 R. Hiptmair (hiptmair@sam.math.ethz.ch), P. Ledger (ETH-SAM): The Curse of Dispersion PDF of full presentation

17:00-17:30 Final Discussions

Abstracts:

11:00-11:20 M. Agio, A.F. Koenderink, and V. Sandoghdar (ETH-NOG)

The Finite-Difference Time-Domain codes at the Nano-Optics Group

The Finite-Difference Time-Domain (FD-TD) method is among the most widely used
numerical techniques that solve Maxwell's equations. Its major feature is the
ability to treat complex structures with a simple algorithm, but at the price of
large CPU and memory usage. Nevertheless, the continuous improvement of
computers makes this method more and more affordable and of practical use. After
reviewing the basics of the FD-TD approach, I will briefly present the two- and
three-dimensional implementations available at the Nano-Optics Group, showing
what kind of modeling we can do. Emphasis will be given on solutions for
integrated optics, specifically photonic crystals and microcavities, and
near-field optics.

11:20-11:40 N. Moll , A. Jebali, R. Harbers, S. Gulde, R. F. Mahrt (IBM, ETH-IFH)

Photonic engineering of nonlinear-optical properties of hybrid materials for
efficient ultra-fast optical switching

All-optical switching is becoming a key point with the steady increase of
bandwidth demand. Switching elements in hybrid organic/inorganic photonic
nanostructures could lead to higher channel rates and the base for more space-,
power- and cost-efficient routing devices. Combing organic films with high
Kerr-nonlinearities and highly optimized resonant structures is a promising way
to allow fast switching with low switching energies. Therefore, the design of
resonator structures is optimized and solid knowledge about the deposition of
organic films on structured inorganic substrates is necessary. Hybrid structures
consisting of an inorganic micro-cavity with an organic material are
investigated experimentally and theoretically.

11:40-12:00 A.F. Koenderink, B. C. Buchler, and V. Sandoghdar (ETH-NOG)

Controlled near-field coupling to optical resonances in photonic crystal
membranes

Solid state optical resonators that confine light in ultrasmall volumes
currently enjoy wide interest, partly rooted in cavity quantum electrodynamics
and partly motivated by applications, including spontaneous emission control,
low threshold lasers, optical switching and sensors. A particular advantage of
photonic crystal microcavities is that one can achieve subwavelength cavity
dimensions while keeping high quality factors of up to 10^5. In our group we use
scanning probe techniques to realize controlled coupling between such optical
resonances and nano-objects in the near-field. By performing Finite Difference
Time Domain (FDTD) as well as perturbative analytic calculations, we demonstrate
that near-field probes can be used to tune the resonance of a microcavity over a
large range while maintaining a high quality factor. Furthermore, we have used
FDTD simulations to assess the prospects for control of spontaneous emission
rates by positioning emitters in the near field of photonic crystal membranes.
Sizeable enhancement and inhibition of emission is possible, in qualitative
agreement with two-dimensional plane-wave models.

12:00-12:20 Wataru Nakagawa (University of Neuchatel)

Accurate Electromagnetic Modeling of Metal-Coated Scanning Near-field Optical
Microscopy (SNOM) Probes

We apply commercially available FITD electromagnetic modeling software to
analyze optical propagation in microfabricated metal-coated SNOM probes.
Specifically, we investigate the influence of the input optical polarization,
the probe shape, and nanoscale defects in the metal layer on the emitted near
field of the probe. Finally, we also consider the limitations imposed by
computational workload on this type of analysis.

12:20-12:40 Damir Pasalic (ETH-IFH)

A Rigorous Analysis of Traveling Wave Photodetectors PDF of full
presentation

Traveling wave photodetectors (TWPDs) are opto-electrical transducers, specially
suitable for modern ultra-wide-band optical communication systems. The TWPDs’
ability to maintain high efficiency and broad bandwidth even under high-power
optical illumination is important in microwave fiber optic links, especially
since optical pre-amplification is utilized more widely. The analyses of
traveling wave photodetectors, performed in the literature so far are mostly
based on the equivalent circuit or transmission line models. However, these
models are linked to the specific geometries of the photodetectors and often, do
not compare well with the measurements. In this project, we have developed an
efficient, hybrid method for rigorous analysis of TWPDs. The analysis is
performed in two stages: a semiconductor and an electromagnetic (EM) stage. The
semiconductor analysis is based on 2D drift diffusion (DD) method. It takes into
account effects like bias voltage, carrier lifetime and drift velocity, and
intensity of the applied optical power. As a result of the semiconductor
simulation, we obtain current density at the cross-section of the photodetector.
The obtained current density is than applied to the input of the full-wave EM
simulator to obtain microwave characteristics of interest: bandwidth, RF
velocity, fields, etc. The EM simulations are performed using the time-domain
TLM method. The obtained results are compared with the available experimental
data and a good agreement was observed.

13:20-13:40 Bernd Witzigmann, Matthias Streiff (ETH-IIS)

Optical Modes in Microcavities PDF of full
presentation

Optical microcavities, which are wavelength-sized resonators, are used in
semiconductor lasers, optical sensors and novel generation light-emitting
diodes. Using a finite-element method, the modes in microcavities are determined
by solving Maxwell's vectorial wave equation with open boundaries. The method
takes into account diffraction and radiation of electromagnetic waves. In
consequence, realistic microcavities without any restrictions regarding
structure and size may be investigated.

13:40-14:00 Jasmin Smajic (ABB)

3D simulation of photonic crystal structures using FEM PDF of full
presentation

A 3D approach for the electromagnetic simulation of photonic crystal structures
using the vector finite element method (FEM) in frequency domain is presented. A
short introduction to the numerical difficulties concerning the 3D simulation of
photonic crystal structures using FEM is given, such as the problem of 3D PhC
waveguide excitation and the selection of the type of the absorbing boundary
condition. The limitations and basic problems of available commercial simulation
tools using FEM (FEMLAB 3.0) are also mentioned. Matrix conditioning - mesh
quality, memory requirements, direct and iterative linear solvers,
preconditioning, and other important topics will be discussed and illustrated
with various calculation examples including the very recent results of the
analysis of 3D PhC waveguides, sharp bends and power dividers.

14:00-14:20 Christian Hafner (ETH-IFH)

MMP Simulation of Optical Nanostructures PDF of full
presentation

The Multiple Multipole Program (MMP) is a semi-analytic boundary method that
provides highly accurate and reliable results based on relatively small matrix
equations. Additional techniques for solving eigenvalue problems, periodic
symmetry problems, embedding solutions of simplified problems, and for speeding
up sequences of computations are available. These techniques make MMP attractive
for the detailed analysis of many optical nano structures such as photonic
crystals, gratings, waveguides, resonators, SNOM, etc. including strongly
frequency-dependent, lossy materials that can be described by a complex
permittivity and a complex permeability. Because of the high accuracy, MMP is
also well suited to model optimizations performed with either deterministic or
stochastic optimizers. After a short introduction to MMP, typical examples are
presented.

14:20-14:40 Kakhaber Tavzarashvili (ETH-IFH)

Photonic Crystal Simulations using the Method of Auxiliary Sources
PDF of full
presentation

The Method of Auxiliary Sources (MAS) is used for the comprehensive study of
doped Finite Photonic Crystals (FPC) made of biisotropic, chiral and other
complex materials. The primitive cells of the FPC are supposed to have a given
crystallographic structure with certain defects, such as extrinsic inclusions,
vacancies, dislocations and so on. In this work, an efficient solution of wave
propagation and scattering problems in such crystals is presented, including the
treatment of eigenvalue and eigenfield problems and the FPC band structure
calculation. A new program package to analyze and visualize the processes in the
FPC is described and its possibilities for the design of FPC devices with
desired properties are demonstrated.

14:40-15:00 Rik Harbers, Niko Moll, Rainer Mahrt, Daniel Erni, Werner Bächtold (ETH-IFH, IBM)

Enhancement of the Mode Coupling in Photonic Crystal-Based Organic Lasers

The mode coupling of organic photonic crystal lasers is enhanced by using a
photonic crystal that consists of a thin layer of a high-index material. The
high-index material increases the index contrast, the confinement in the
waveguide and thus the mode coupling. Using such a photonic crystal gives rise
to new design criteria. We investigate these criteria, and employ them in the
design of an organic photonic crystal laser. Calculations of the coupling
constant of the organic laser show that using high-index materials results in
much higher coupling constants and thus smaller devices.

15:20-15:40 Lyudmyla Raguin-Illyashenko, P. Arbenz (ETH-ICS)

Boundary Integral Equation Method for the Numerical Modeling of Particles with
Arbitrary Shape

To investigate certain properties of opto-electronic device components we
propose a variant of the boundary integral equation method. Our approach arises
from the fact that every component of the electromagnetic field can be expressed
in terms of a Green's function. One of the key points is the recently developed
global parameterization formulas for representing the particle contour in terms
of fast convergent functional series. This approach provides a means to study
individual particles as well as particle clusters in free space and with
dielectric background for both TE and TM polarizations. We developed a numerical
simulation tool based on these semi-analytical techniques that provides three
primary advantages. First, it requires very little time and computer resources
to obtain desired characteristics. Second, the obtained solutions are highly
accurate due to taking into account geometrical singularities of the particle
boundary and utilization of analytical regularization schemes for the numerical
treatment of the integral equation singularities. Third, the numerical
simulation tool allows essential flexibility to study the particles of almost
arbitrary shape. The efficiency of the method is demonstrated by solving
electro-magnetic field scattering and propagation problems for planar dielectric
nanoparticles. In particular, we demonstrate that the near-field distribution
and the far-field directivity strongly depend on the shape, orientation and
morphology of the nanoparticle.

15:40-16:00 Bogdan Cranganu-Cretu (ABB)

Direct Boundary Integral Equation Method for Electromagnetic Scattering at
Partly Coated Dielectric Objects PDF of full
presentation

We present a new variational direct boundary integral equation approach for
solving the scattering and transmission problem for dielectric objects partially
coated with a PEC (Perfect Electric Conductor) layer. The main idea is to use to
use the electromagnetic Calderon projector along with transmission conditions or
the electromagnetic fields. This leads to a symmetric variational formulation,
which lends itself to Galerkin discretization by means of divergence-conforming
discrete surface currents (edge vectorial elements). Some numerical experiments
are presented to confirm the efficacy of the new method.

16:00-16:20 Lavinia Rogobete, Vahid Sandoghdar, Carsten Henkel (ETH-NOG, University Potsdam)

Radiative properties in a sub-wavelength environment characterized with boundary
integral equations

Our goal is to study the fluorescence dynamics, radiation pattern and field
distributions of single emitters in the vicinity of nanoscopic systems. The
problem is placed in the regime of Rayleigh scattering and quasistatic fields.
In our numerical approach we transform the partial differential Maxwell
equations with polarization source into boundary integral equations that we
solve using a moment method. We treat a two-dimensional model (infinite in the z
direction) and consider p-polarized dipoles located in the xy-plane. We validate
the numerics by checking them against known analytical solutions. We show that
the method is an accurate and elegant tool for solving emitters in the presence
of dielectric or metallic objects as well as infinite interfaces.

16:20-16:40 Nicolas Guérin (ETH-IFH)

Optimization of metallic bi-periodic photonic crystals - Application to compact
directive antennas PDF of full
presentation

Three-dimensional electromagnetic problems require huge computing resources. One
way to go through is to consider periodic structures in order to reduce the
investigation domain to one cell of the structure. We describe here a numerical
study for the diffraction by bi-periodic (in two directions) metallic photonic
crystals. We use an integral method based on the Harrington formalism. The
development of a fast bi-periodic Green's function allows us to reduce the
unknowns to the first cell. We investigate then structures made of a source
surrounded by a bi-periodic metallic photonic crystal above a ground plane. The
field diffracted by the source is expanding in a plane wave packet using FFT,
then we solve a grating problem for each plane wave. Theses structures are
employed for the design of directive antennas in the domain of microwave
telecommunications, these antennas are more compact than classical solutions and
use a single feeding device. Many properties can be derived from the
transmission properties of the grids in transmission illuminated by a plane
wave. The calculation of the reflectivity for one grid enables an efficiently
optimization of the parameters in order to obtain the suitable properties. The
efficiency of antennas are analyzed and compared in terms of polarization,
directivity and bandwidth. The results are confirmed by experiments in an
anechoic chamber.

16:40-17:00 R. Hiptmair, P. Ledger (ETH-SAM)

The Curse of Dispersion PDF of full presentation

Whenever we discretize high
frequency wave propagation problems in the frequency domain on the level of
partial differential equations (i.e. the Helmholtz equation or vector wave
equation), the numerical dispersion will be the main source of error. This
cripples standard low order finite element approaches, because for decreasing
wavelengths more and more points per wavelength are required for sufficient
accuracy. We are going to review a few strategies for tackling the dispersion
problem

1) The use of high order finite element schemes, 2) Plane wave modulation in the
context of finite element schemes, and 3) Discontinuous Galerkin approaches with
plane waves