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Fachgebiet Theoretische Elektrotechnik (TET)
Prof. Dr. Jens Förstner

Willkommen im Fachgebiet Theoretische Elektrotechnik (TET)

Unser Forschungsgebiet ist die theoretische Beschreibung von photonischen und optoelektronischen Systemen wie optischen Nanoantennen, dielektrischen Wellenleitern, photonischen Kristallen, Metamaterialien, plasmonischen Systemen, oder biologischen/biomimetischen photonischen Strukturen. Unsere Stärke liegt in der Kombination von hochentwickelten Materialmodellen mit modernsten numerischen Methoden zur Simulation elektromagnetischer Felder.

Forschung: ThemenPublikationenTeam

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Die fünf neuesten Publiktionen


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Negative polarization of light at backscattering from a numerical analog of planetary regoliths

Y. Grynko, Y. Shkuratov, S. Alhaddad, J. Förstner, Icarus (2022), 384, pp. 115099

We model negative polarization, which is observed for planetary regoliths at backscattering, solving a full wave problem of light scattering with a numerically exact Discontinuous Galerkin Time Domain (DGTD) method. Pieces of layers with the bulk packing density of particles close to 0.5 are used. The model particles are highly absorbing and have irregular shapes and sizes larger than the wavelength of light. This represents a realistic analog of low-albedo planetary regoliths. Our simulations confirm coherent backscattering mechanism of the origin of negative polarization. We show that angular profiles of polarization are stabilized if the number of particles in a layer piece becomes larger than ten. This allows application of our approach to the negative polarization modeling for planetary regoliths.


Broadband optical Ta2O5 antennas for directional emission of light

H. Farheen, L. Yan, V. Quiring, C. Eigner, T. Zentgraf, S. Linden, J. Förstner, V. Myroshnychenko, Optics Express (2022), 30(11), pp. 19288

Highly directive antennas with the ability of shaping radiation patterns in desired directions are essential for efficient on-chip optical communication with reduced cross talk. In this paper, we design and optimize three distinct broadband traveling-wave tantalum pentoxide antennas exhibiting highly directional characteristics. Our antennas contain a director and reflector deposited on a glass substrate, which are excited by a dipole emitter placed in the feed gap between the two elements. Full-wave simulations in conjunction with global optimization provide structures with an enhanced linear directivity as high as 119 radiating in the substrate. The high directivity is a result of the interplay between two dominant TE modes and the leaky modes present in the antenna director. Furthermore, these low-loss dielectric antennas exhibit a near-unity radiation efficiency at the operational wavelength of 780 nm and maintain a broad bandwidth. Our numerical results are in good agreement with experimental measurements from the optimized antennas fabricated using a two-step electron-beam lithography, revealing the highly directive nature of our structures. We envision that our antenna designs can be conveniently adapted to other dielectric materials and prove instrumental for inter-chip optical communications and other on-chip applications.


Semi-guided waves in integrated optical waveguide structures

L. Ebers, 2022

In this work, the electromagnetic wave propagation in integrated optical waveguides is studied by using semi-analytical and numerical simulation methods. In the first part, 2-D high-index contrast Si/SiO2 dielectric slab waveguide configurations are investigated. The structures are excited with semi-guided waves at oblique angles of propagation. Due to this, power transfer to specific outgoing modes can be suppressed, resulting in completely lossless configurations. The excitation is further examined for incoming, laterally confined wave bundles of semi-guided waves to realize practically more relevant 3-D configurations. Additionally, a stepwise angular spectrum method in combination with full vectorial 2-D finite element solutions for subproblems of lower complexity to numerically simulate the wave propagation in full 3-D planar lens-like waveguides is presented. In the second part, the wave propagation in lithium niobate waveguide structures is examined, which are used for quantum optical effects. On the one hand, superconducting nanowires on titanium in-diffused lithium niobate waveguides with an additional tapered silicon layer are used for single photon detection. The wave propagation in these 3-D multiscale tapers is studied by introducing a unidirectional finite element modal matching method. On the other hand, lithium niobate rib waveguides on silicon dioxide platforms are analyzed, focusing on the nonlinear parametric down-conversion process used for the generation of entangled photons.


Small-scale online simulations in guided-wave photonics

M. Hammer, in: Integrated Optics: Devices, Materials, and Technologies XXVI, SPIE, 2022, pp. 1200414

Online solvers for a series of standard 1-D or 2-D problems in integrated optics will be discussed. Implemented on the basis of HTML/JavaScript/SVG with core routines compiled from well tested C++-sources, the quasi-analytical algorithms require a computational load that can be handled easily even by current mobile devices. So far the series covers the 1-D guided modes of dielectric multilayer slab waveguides and the oblique plane wave reflection from these, the modes of rectangular channel waveguides (in an approximation of effective indices), bend modes of curved multilayer slabs, whispering-gallery resonances (“Quasi-Normal-Modes”) supported by circular dielectric cavities, the hybrid modes of circular multi-step-index optical fibers, bound and leaky modes of 1-D complex multilayers, including plasmonic surface modes, and, with restrictions, quite general rectangular scattering problems in 2-D.


Resonant evanescent excitation of OAM modes in a high-contrast circular step-index fiber

M. Hammer, L. Ebers, J. Förstner, in: Complex Light and Optical Forces XVI, SPIE, 2022, pp. 120170F

Resonant evanescent coupling can be utilized to selectively excite orbital angular momentum (OAM) modes of high angular order supported by a thin circular dielectric rod. Our 2.5-D hybrid-analytical coupled mode model combines the vectorial fields associated with the fundamental TE- and TM-modes of a standard silicon photonics slab waveguide, propagating at oblique angles with respect to the rod axis, and the hybrid modes supported by the rod. One observes an efficient resonant interaction in cases where the common axial wavenumber of the waves in the slab matches the propagation constant of one or more modes of the rod. For certain modes of high angular order, the incident wave is able to transfer its directionality to the field in the fiber, exciting effectively only one of a pair of degenerate OAM modes


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Gruppenleitung

Prof. Dr. Jens Förstner

Theoretische Elektrotechnik (TET)

Jens Förstner
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+49 5251 60-3013
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