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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

Simulation leitungsgeführter Störspannungen von DC-DC-Wandlern

T. Baumgarten, P. Scholz, D. Sievers, J. Förstner, in: Elektromagnetische Verträglichkeit - Internationale Fachmesse und Kongress 2018, 2018, pp. 47

OpenCL-based FPGA Design to Accelerate the Nodal Discontinuous Galerkin Method for Unstructured Meshes

T. Kenter, G. Mahale, S. Alhaddad, Y. Grynko, C. Schmitt, A. Afzal, F. Hannig, J. Förstner, C. Plessl, in: Proc. Int. Symp. on Field-Programmable Custom Computing Machines (FCCM), IEEE, 2018

The exploration of FPGAs as accelerators for scientific simulations has so far mostly been focused on small kernels of methods working on regular data structures, for example in the form of stencil computations for finite difference methods. In computational sciences, often more advanced methods are employed that promise better stability, convergence, locality and scaling. Unstructured meshes are shown to be more effective and more accurate, compared to regular grids, in representing computation domains of various shapes. Using unstructured meshes, the discontinuous Galerkin method preserves the ability to perform explicit local update operations for simulations in the time domain. In this work, we investigate FPGAs as target platform for an implementation of the nodal discontinuous Galerkin method to find time-domain solutions of Maxwell's equations in an unstructured mesh. When maximizing data reuse and fitting constant coefficients into suitably partitioned on-chip memory, high computational intensity allows us to implement and feed wide data paths with hundreds of floating point operators. By decoupling off-chip memory accesses from the computations, high memory bandwidth can be sustained, even for the irregular access pattern required by parts of the application. Using the Intel/Altera OpenCL SDK for FPGAs, we present different implementation variants for different polynomial orders of the method. In different phases of the algorithm, either computational or bandwidth limits of the Arria 10 platform are almost reached, thus outperforming a highly multithreaded CPU implementation by around 2x.

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.

Oblique Semi-Guided Waves: 2-D Integrated Photonics with Negative Effective Permittivity

M. Hammer, L. Ebers, A. Hildebrandt, S. Alhaddad, J. Förstner, in: 2018 IEEE 17th International Conference on Mathematical Methods in Electromagnetic Theory (MMET), IEEE, 2018

Semi-guided waves confined in dielectric slab waveguides are being considered for oblique angles of propagation. If the waves encounter a linear discontinuity of (mostly) arbitrary shape and extension, a variant of Snell's law applies, separately for each pair of incoming and outgoing modes. Depending on the effective indices involved, and on the angle of incidence, power transfer to specific outgoing waves can be allowed or forbidden. In particular, critical angles of incidence can be identified, beyond which any power transfer to non-guided waves is forbidden, i.e. all radiative losses are suppressed. In that case the input power is carried away from the discontinuity exclusively by reflected semi-guided waves in the input slab, or by semi-guided waves that are transmitted into other outgoing slab waveguides. Vectorial equations on a 2-D cross sectional domain apply. These are formally identical to the equations that govern the eigenmodes of 3-D channel waveguides. Here, however, these need to be solved not as an eigenvalue problem, but as an inhomogeneous problem with a right-hand-side that is given by the incoming semi-guided wave, and subject to transparent boundary conditions. The equations resemble a standard 2-D Helmholtz problem, with an effective permittivity in place of the actual relative permittivity. Depending on the properties of the incoming wave, including the angle of incidence, this effective permittivity can become locally negative, causing the suppression of propagating outgoing waves. A series of high-contrast example configurations are discussed, where these effects lead to - in some respects - quite surprising transmission characteristics.

Application of the Discontinuous Galerkin Time Domain Method in Nonlinear Nanoplasmonics

Y. Grynko, J. Forstner, in: 2018 IEEE 17th International Conference on Mathematical Methods in Electromagnetic Theory (MMET), IEEE, 2018


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:

Tuesdays 11-12, and on request, but
not 20.11., instead 23.11 9-10,
not 11.12, instead 14.12 9-10,
not 18.12., instead 17.12. 15:30-16:30

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 (current): CoursesProjects

Frequently asked questions (FAQ)

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