Electrical Engineering - Theoretical Electrical Engineering (TET) (Universität Paderborn)

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: Topics, Publications, Team

Teaching: Course Portfolio, Current Courses, Current Projects

Announcements/News

15.05.2023: Verteidigung der Masterarbeit Carsten Spieker "Simulation des Materialverhaltens von Piezokeramiken mit dem Diskontinuierlichen Galerkin-Verfahren"

04/25/2023 | Titel: Simulation des Materialverhaltens von Piezokeramiken mit dem Diskontinuierlichen Galerkin-Verfahren Vortragender: Carsten Spieker Datum: 15.05.2023 Uhrzeit: 11:00 Uhr Sprache: Deutsch Raum: TET-Seminarraum P1.5.01.4

New publication: How to suppress radiative losses in high-contrast integrated Bragg gratings

03/31/2023 | Manfred Hammer, Henna Farheen, Jens Förstner How to suppress radiative losses in high-contrast integrated Bragg gratings In a context of photonic integrated circuits, waveguide Bragg gratings are frequently used for purposes of spectral…

New publication: "Numerical study of light backscattering from layers of absorbing irregular particles larger than the wavelength"

03/16/2023 | Samer Alhaddad, Jens Förstner, Yevgen Grynko https://ris.uni-paderborn.de/record/43018 https://doi.org/10.1016/j.jqsrt.2023.108557 Elsevier provides free access to the paper until May 4, 2023 via https://authors.elsevier.com/c/1glN2564SXn~o

01.03.2023: Master Thesis presentation Suraj Joshi: "Optimization of Silicon Horn Antennas for Efficient Broadside Emission"

02/27/2023 | Dear colleagues, dear students, on Wednesday, the 1st of March 2023, the following master presentation will take place in the TET group: Title: Optimization of Silicon Horn Antennas for Efficient Broadside Emission Presenter: Suraj Joshi Language…

New publication: "Asymmetric, non-uniform 3-dB directional coupler with 300-nm bandwidth and a small footprint"

01/04/2023 | Hamed Nikbakht, Mohammad Talebi Khoshmehr, Bob van Someren, Dieter Teichrib, Manfred Hammer, Jens Förstner, and B. Imran Akca https://ris.uni-paderborn.de/record/35128 https://doi.org/10.1364/ol.476537

02.12.2022: Master-Zwischenvortrag Carsten Spieker zu "Modellierung von piezoelektrischen Dämpfungsmodellen mit dem Diskontinuierlichen Galerkin-Verfahren"

12/07/2022 | Am 2. Dezember, um 9:30 Uhr, wird Carsten Spieker einen Master-Zwischenvortrag zum Thema: Modellierung von piezoelektrischen Dämpfungsmodellen mit dem Diskontinuierlichen Galerkin-Verfahren im TET-Seminarraum P1.5.01.4 halten. Wir freuen uns über…

Older announcements...

The five most recent publications

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A multi-mode super-fano mechanism for enhanced third harmonic generation in silicon metasurfaces

D. Hähnel, C. Golla, M. Albert, T. Zentgraf, V. Myroshnychenko, J. Förstner, C. Meier, Light: Science & Applications (2023), 12(1), pp. 97

Abstract

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DOI

We present strong enhancement of third harmonic generation in an amorphous silicon metasurface consisting of elliptical nano resonators. We show that this enhancement originates from a new type of multi-mode Fano mechanism. These ‘Super-Fano’ resonances are investigated numerically in great detail using full-wave simulations. The theoretically predicted behavior of the metasurface is experimentally verified by linear and nonlinear transmission spectroscopy. Moreover, quantitative nonlinear measurements are performed, in which an absolute conversion efficiency as high as ηmax ≈ 2.8 × 10−7 a peak power intensity of 1.2 GW cm−2 is found. Compared to an unpatterned silicon film of the same thickness amplification factors of up to ~900 are demonstrated. Our results pave the way to exploiting a strong Fano-type multi-mode coupling in metasurfaces for high THG in potential applications.

On-demand indistinguishable and entangled photons at telecom frequencies using tailored cavity designs

D. Bauch, D. Siebert, K. Jöns, J. Förstner, S. Schumacher, 2023

Abstract

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The biexciton-exciton emission cascade commonly used in quantum-dot systems to generate polarization entanglement yields photons with intrinsically limited indistinguishability. In the present work we focus on the generation of pairs of photons with high degrees of polarization entanglement and simultaneously high indistinguishibility. We achieve this goal by selectively reducing the biexciton lifetime with an optical resonator. We demonstrate that a suitably tailored circular Bragg reflector fulfills the requirements of sufficient selective Purcell enhancement of biexciton emission paired with spectrally broad photon extraction and two-fold degenerate optical modes. Our in-depth theoretical study combines (i) the optimization of realistic photonic structures solving Maxwell's equations from which model parameters are extracted as input for (ii) microscopic simulations of quantum-dot cavity excitation dynamics with full access to photon properties. We report non-trivial dependencies on system parameters and use the predictive power of our combined theoretical approach to determine the optimal range of Purcell enhancement that maximizes indistinguishability and entanglement to near unity values in the telecom C-band at $1550\,\mathrm{nm}$.

https://arxiv.org/pdf/2303.13871.pdf

How to suppress radiative losses in high-contrast integrated Bragg gratings

M. Hammer, H. Farheen, J. Förstner, Journal of the Optical Society of America B (2023), 40(4), pp. 862

Abstract

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DOI

High-contrast slab waveguide Bragg gratings with 1D periodicity are investigated. For specific oblique excitation by semi-guided waves at sufficiently high angles of incidence, the idealized structures do not exhibit any radiative losses, such that reflectance and transmittance for the single port mode add strictly up to one. We consider a series of symmetric, fully and partly etched finite gratings, for parameters found in integrated silicon photonics. These can act as spectral filters with a reasonably flattop response. Apodization can lead to more box shaped reflectance and transmittance spectra. Together with a narrowband Fabry–Perot filter, these configurations are characterized by reflection bands, or transmittance peaks, with widths that span three orders of magnitude.

ogr-afterreview.pdf -

Optimized silicon antennas for optical phased arrays

H. Farheen, A. Strauch, J.C. Scheytt, V. Myroshnychenko, J. Förstner, in: Integrated Optics: Devices, Materials, and Technologies XXVII, SPIE, 2023, pp. 124241D

Abstract

DOI

We demonstrate a large-scale two dimensional silicon-based optical phased array (OPA) composed of nanoantennas with circular gratings that are balanced in power and aligned in phase, required for producing desired radiation patterns in the far-field. The OPAs are numerically optimized to have an upward efficiency of up to 90%, targeting radiation concentration mainly in the field of view. We envision that our OPAs have the ability of generating complex holographic images, rendering them an attractive candidate for a wide range of applications like LiDAR sensors, optical trapping, optogenetic stimulation and augmented-reality displays.

Tailoring the directive nature of optical waveguide antennas

H. Farheen, L. Yan, T. Leuteritz, S. Qiao, F. Spreyer, C. Schlickriede, V. Quiring, C. Eigner, C. Silberhorn, T. Zentgraf, S. Linden, V. Myroshnychenko, J. Förstner, in: Integrated Optics: Devices, Materials, and Technologies XXVII, SPIE, 2023, pp. 124241E

Abstract

DOI

We demonstrate the numerical and experimental realization of optimized optical traveling-wave antennas made of low-loss dielectric materials. These antennas exhibit highly directive radiation patterns and our studies reveal that this nature comes from two dominant guided TE modes excited in the waveguide-like director of the antenna, in addition to the leaky modes. The optimized antennas possess a broadband nature and have a nearunity radiation efficiency at an operational wavelength of 780 nm. Compared to the previously studied plasmonic antennas for photon emission, our all-dielectric approach demonstrates a new class of highly directional, low-loss, and broadband optical antennas.

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