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Welcome to the Theoretical Electrical Engineering group (TET)

Our main research interest is the theoretical description of photonic and optoelectronic systems like optical nanoantennas, dielectric waveguides, photonic crystals, metamaterials, plasmonic systems, or biological photonic structures. Our speciality is the combinations of advanced material models with state-of-the-art numerical methods for the simulation of electromagnetic fields. For students we offer a wide range of courses ranging from the theoretical foundation of electromagnetism and numerics to advanced courses on field simulation and photonics. 

Research: Overview, Publications, Team

Teaching: Course Portfolio, Current Courses, Current Projects


The five most recent publications

Open list in Research Information System

Optical transition between two optical waveguides layer and method for transmitting light

M. Hammer, J. Förstner, L. Ebers. Optical transition between two optical waveguides layer and method for transmitting light. 2019.

Tailored UV Emission by Nonlinear IR Excitation from ZnO Photonic Crystal Nanocavities

S.P. Hoffmann, M. Albert, N. Weber, D. Sievers, J. Förstner, T. Zentgraf, C. Meier, ACS Photonics (2018), pp. 1933-1942

Oblique incidence of semi-guided planar waves on slab waveguide steps: effects of rounded edges

L. Ebers, M. Hammer, J. Förstner, Optics Express (2018), pp. 18621-18632

Oblique propagation of semi-guided waves across slab waveguide structures with bent corners is investigated. A critical angle can be defined beyond which all radiation losses are suppressed. Additionally an increase of the curvature radius of the bends also leads to low-loss configurations for incidence angles below that critical angle. A combination of two bent corner systems represents a step-like structure, behaving like a Fabry-Perot interferometer, with two partial reflectors separated by the vertical height between the horizontal slabs. We numerically analyse typical high-index-contrast Si/SiO2 structures for their reflectance and transmittance properties. When increasing the curvature radius the resonant effect becomes less relevant such that full transmittance is reached with less critical conditions on the vertical distance or the incidence angle. For practical interest 3-D problems are considered, where the structures are excited by the fundamental mode of a wide, shallow rib waveguide. High transmittance levels can be observed also for these 3-D configurations depending on the width of the rib.

Unveiling and Imaging Degenerate States in Plasmonic Nanoparticles with Nanometer Resolution

V. Myroshnychenko, N. Nishio, F.J. García de Abajo, J. Förstner, N. Yamamoto, ACS Nano (2018), pp. 8436-8446

Metal nanoparticles host localized plasmon excitations that allow the manipulation of optical fields at the nanoscale. Despite the availability of several techniques for imaging plasmons, direct access into the symmetries of these excitations remains elusive, thus hindering progress in the development of applications. Here, we present a combination of angle-, polarization-, and space-resolved cathodoluminescence spectroscopy methods to selectively access the symmetry and degeneracy of plasmonic states in lithographically fabricated gold nanoprisms. We experimentally reveal and spatially map degenerate states of multipole plasmon modes with nanometer spatial resolution and further provide recipes for resolving optically dark and out-of-plane modes. Full-wave simulations in conjunction with a simple tight-binding model explain the complex plasmon structure in these particles and reveal intriguing mode-symmetry phenomena. Our approach introduces systematics for a comprehensive symmetry characterization of plasmonic states in high-symmetry nanostructures.

Polarization Conversion Effect in Biological and Synthetic Photonic Diamond Structures

X. Wu, F.L. Rodríguez-Gallegos, M. Heep, B. Schwind, G. Li, H. Fabritius, G. von Freymann, J. Förstner, Advanced Optical Materials (2018)

Polarization of light is essential for some living organisms and many optical applications. Here, an orientation dependent polarization conversion effect is reported for light reflected from diamond‐structure‐based photonic crystals (D‐structure) inside the scales of a beetle, the weevil Entimus imperialis. When linearly polarized light propagates along its 〈100〉 directions, the D‐structure behaves analogous to a half‐wave plate in reflection but based on a different mechanism. The D‐structure rotates the polarization direction of linearly polarized light, and reflects circularly polarized light of both handednesses without changing it. This polarization effect is different from circular dichroism occurring in chiral biological photonic structures discovered before. The structural origin of this effect is symmetry breaking inside D‐structure's unit cell. This finding demonstrates that natural photonic structures can exploit multiple functionalities inherent to the design principles of their structural organization. Aiming at transferring the inherent polarization effect of the biological D‐structure to technically realizable materials, three simplified biomimetic structural models are derived and it is theoretically demonstrated that they retain the effect. Out of these structures, functioning woodpile structure prototypes are fabricated.

Max number of publications reached - all publications can be found in our Research Infomation System.

Open list in Research Information System

Head of the group

Prof. Dr. Jens Förstner

Theoretical Electrical Engineering

Jens Förstner
+49 5251 60-3013
+49 5251 60-3524

Office hours:

During lecture-free time on request. On vacation from 8.3.-30.3.2019.

TET courses & projects

Course Portfolio

SoSe 2016: Courses, Projects

WS 2016/2017: Courses, Projects

SoSe 2017: CoursesProjects

WS 2017/2018: CoursesProjects

SoSe 2018: CoursesProjects

WS 2018/2019: CoursesProjects

SoSe 2019 (current): Courses, Projects

Frequently asked questions (FAQ)

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