Publications
Articles in Refereed Journals

J. Yan, M. Majumdar, S. Ruffo, Y. Sato, Ch. Beck, R. Klages, Transition to anomalous dynamics in a simple random map, Chaos. An Interdisciplinary Journal of Nonlinear Science, 34 (2024), pp. 023128/1023128/18, DOI 10.1063/5.0176310 .

J. Yan, R. Moessner, H. Zhao, Prethermalization in aperiodically kicked manybody dynamics, Phys. Rev. B., 109 (2024), pp. 064305/1064305/14, DOI 10.1103/PhysRevB.109.064305 .

A.G. Vladimirov, D. Dolinina, Neutral delay differential equation model of an optically injected Kerr cavity, Physical Review E. Statistical, Nonlinear, and Soft Matter Physics, 109 (2024), pp. 024206/1024206/10, DOI 10.1103/PhysRevE.109.024206 .
Abstract
A neutral delay differential equation (NDDE) model of a Kerr cavity with external coherent injection is developed that can be considered as a generalization of the Ikeda map with second and higherorder dispersion being taken into account. It is shown that this model has solutions in the form of dissipative solitons both in the low dissipation limit, where the model can be reduced to the LugiatoLefever equation (LLE), and beyond this limit, where the soliton is eventually destroyed by the Cherenkov radiation. Unlike the standard LLE, the NDDE model is able to describe the overlap of multiple resonances associated with different cavity modes. 
E. Kuhn, A. Tränhardt, Influence of scattering effects on the interaction between longitudinal modes in laser diodes, Phys. Rev. B., 108 (2023), pp. 115304/1115304/15, DOI 10.1103/PhysRevB.108.115304 .
Abstract
A predictive model of scattering processes in semiconductor lasers is derived, enabling us to model relaxation processes starting from wellknown parameters such as the dielectric constant. The resulting effective mode interaction terms are explicitly calculated for an (InGa)N quantum well using Coulomb scattering. In contrast to the method used so far to model mode competi tion phenomena in FabryPérot type laser diodes, the model correctly includes e.g. accelerated scattering at higher densities or temperatures and eliminates the scattering rate as an unknown parameter. The effective mode interaction term derived in this work can be used for the simulation of the mode dynamics in various laser diode types, for example broad area laser diodes, where multiple transversal and longitudinal modes are active. Thus, our model offers an increased pre dictability and improved modelling of switchon behavior. 
A. Roche, S. Slepneva, A. Kovalev, A. Pimenov, A.G. Vladimirov, M. Giudici, M. Marconi, G. Huyet, Decoherence and turbulence sources in a long laser, Physical Review Letters, 131 (2023), pp. 053801/1053801/7, DOI 10.1103/PhysRevLett.131.053801 .
Abstract
We investigate the turnon process in a laser cavity where the roundtrip time is several orders of magnitude greater than the active medium timescales. In this long delay limit the electromagnetic field buildup can be mapped experimentally roundtrip after roundtrip. We show how coherence settles down starting from a stochastic initial condition. In the early stages of the turnon, we show that power dropouts emerge, persist for several roundtrips and seed dark solitons. These latter structures exhibit a chaotic dynamics and emit radiation that can lead to an overall turbulent dynamics depending on the cavity dispersion. 
O. Burylko, M. Wolfrum, S. Yanchuk, J. Kurths, Timereversible dynamics in a system of two coupled active rotators, Proceedings of the Royal Society of Edinburgh. Section A. Mathematics, 479 (2023), pp. 20230401/120230401/23, DOI 10.1098/rspa.2023.0401 .
Abstract
We study two coupled active rotators with Kuramototype coupling and focus our attention to specific transitional regimes where the coupling is neither attractive nor repulsive. We show that certain such situations at the edge of synchronization can be characterized by the existence of a timereversal symmetry of the system. We identify two different cases with such a timereversal symmetry. The first case is characterized by a nonreciprocal attractive/repulsive coupling. The second case is a reciprocal coupling exactly at the edge between attraction and repulsion. We give a detailed description of possible different types of dynamics and bifurcations for both cases. In particular, we show how the timereversible coupling can induce both oscillation death and oscillation birth to the active rotators. Moreover, we analyse the coexistence of conservative and dissipative regions in phase space, which is a typical feature of systems with a timereversal symmetry. We show also, how perturbations breaking the timereversal symmetry and destroying the conservative regions can lead to complicated types of dissipative dynamics such as the emergence of longperiod cycles showing a burstinglike behavior. 
A. Grin, K.R. Schneider, Location of the limit cycle for a class of Lienard systems by means of DulacCherkas functions, Georgian Academy of Sciences. A. Razmadze Mathematical Institute. Memoirs on Differential Equations and Mathematical Physics, 90 (2023), pp. 1525.

A. Grin, K.R. Schneider, Global algebraic PoincaréBendixson annulus for van der Pol systems, Electronic Journal of Qualitative Theory of Differential Equations, (2023), pp. 35/135/12, DOI 10.14232/ejqtde.2023.1.35 .
Abstract
By means of planar polynomial systems topologically equivalent to the van der Pol system we demonstrate an approach to construct algebraic transversal ovals forming a parameter depending PoincaréBendixson annulus which contains a unique limit cycle for the full parameter domain. The inner boundary consists of the zerolevel set of a special DulacCherkas function which implies the uniqueness of the limit cycle. For the construction of the outer boundary we present a corresponding procedure 
N.N. Nefedov, A.O. Orlov, L. Recke, K.R. Schneider, Nonsmooth regular perturbations of singularly perturbed problems, Journal of Dynamics and Differential Equations, 375 (2023), pp. 206236, DOI 10.1016/j.jde.2023.08.006 .

T. Witke, E. Kuhn, F. Teichert, Ch. Gossler, U.Th. Schwarz, A. Thränhardt, Angledependent light scattering in tissue phantoms for the case of thin bone layers with predominant forward scattering, Journal of Biophotonics, published online on 29.11.2023, DOI 10.1002/jbio.202300358 .

F. Severing, U. Bandelow, S. Amiranashvili, Spurious fourwave mixing processes in generalized nonlinear Schrödinger equations, Journal of Lightwave Technology, 41 (2023), pp. 53595365, DOI 10.1109/JLT.2023.3261804 .
Abstract
Numerical solutions of a nonlinear Schödinger equation, e.g., for pulses in optical fibers, may suffer from the spurious fourwave mixing processes. We study how these nonphysical resonances appear in solutions of a much more stiff generalized nonlinear Schödinger equation with an arbitrary dispersion operator and determine the necessary restrictions on temporal and spatial resolution of a numerical scheme. The restrictions are especially important to meet when an envelope equation is applied in a wide spectral window, e.g., to describe supercontinuum generation, in which case the appearance of the numerical instabilities can occur unnoticed. 
M. Stöhr, E.R. Koch, J. Javaloyes, S.V. Gurevich, M. Wolfrum, Square waves and Bykov Tpoints in a delay algebraic model for the KerrGiresTournois interferometer, Chaos. An Interdisciplinary Journal of Nonlinear Science, 33 (2023), pp. 113105/1113105/11, DOI 10.1063/5.0173320 .
Abstract
We study theoretically the mechanisms of square wave formation of a vertically emitting microcavity operated in the GiresTournois regime that contains a Kerr medium and that is subjected to strong timedelayed optical feedback and detuned optical injection. We show that in the limit of large delay, square wave solutions of the timedelayed system can be treated as relative homoclinic solutions of an equation with an advanced argument. Based on this, we use concepts of classical homoclinic bifurcation theory to study different types of square wave solutions. In particular, we unveil the mechanisms behind the collapsed snaking scenario of square waves and explain the formation of complexshaped multistable square wave solutions through a Bykov Tpoint. Finally we relate the position of the Tpoint to the position of the Maxwell point in the original timedelayed system 
M. Stöhr, M. Wolfrum, Temporal dissipative solitons in the MorrisLecar model with timedelayed feedback, Chaos. An Interdisciplinary Journal of Nonlinear Science, 33 (2023), pp. 023117/1023117/9, DOI 10.1063/5.0134815 .
Abstract
We study the dynamics and bifurcations of temporal dissipative solitons in an excitable system under timedelayed feedback. As a prototypical model displaying different types of excitability we use the MorrisLecar model. In the limit of large delay soliton like solutions of delaydifferential equations can be treated as homoclinic solutions of an equation with an advanced argument. Based on this, we use concepts of classical homoclinic bifurcation theory to study different types of pulse solutions and to explain their dependence on the system parameters. In particular, we show, how a homoclinic orbit flip of a single pulse soliton leads to the destabilization of equidistant multipulse solutions and to the emergence of stable pulse packages. It turns out that this transition is induced by a heteroclinic orbit flip in the system without feedback, which is related to the excitability properties of the MorrisLecar model 
M. Kantner, L. Mertenskötter, Accurate evaluation of selfheterodyne laser linewidth measurements using Wiener filters, Optics Express, 31 (2023), pp. 1599416009, DOI 10.1364/OE.485866 .
Abstract
Selfheterodyne beat note measurements are widely used for the experimental characterization of the frequency noise power spectral density (FNPSD) and the spectral linewidth of lasers. The measured data, however, must be corrected for the transfer function of the experimental setup in a postprocessing routine. The standard approach disregards the detector noise and thereby induces reconstruction artifacts, i.e., spurious spikes, in the reconstructed FNPSD. We introduce an improved postprocessing routine based on a parametric Wiener filter that is free from reconstruction artifacts, provided a good estimate of the signaltonoise ratio is supplied. Building on this potentially exact reconstruction, we develop a new method for intrinsic laser linewidth estimation that is aimed at deliberate suppression of unphysical reconstruction artifacts. Our method yields excellent results even in the presence of strong detector noise, where the intrinsic linewidth plateau is not even visible using the standard method. The approach is demonstrated for simulated time series from a stochastic laser model including 1 / ftype noise. 
A.G. Vladimirov, Temporal cavity soliton interaction in passively modelocked semiconductor lasers, Optics, 4 (2023), pp. 433446, DOI 10.3390/opt4030031 .
Abstract
Weak interaction due to gain saturation and recovery of temporal cavity solitons in a delay differential model of a long cavity semiconductor laser is studied numerically and analytically using an asymptotic approach. It is shown that apart from usual soliton repulsion leading to a harmonic modelocking regime a soliton attraction is also possible in a laser with nonzero linewidth enhancement factor. It is shown numerically that the attraction can lead either to a soliton merging or to a pulse bound state formation.
Contributions to Collected Editions

L. Mertenskötter, M. Kantner, Bayesian estimation of laser linewidth from delayed selfheterodyne measurements, Conference on Structural Nonlinear Dynamics and Diagnosis (CSNDD 2023), Marrakesh, Morocco, May 15  17, 2024, M. Belhaq, ed., 301 of Springer Proceedings in Physics, Springer, Singapur, 2024, pp. 269279, DOI 10.1007/9789819979585_21 .
Abstract
We present a statistical inference approach to estimate the frequency noise characteristics of ultranarrow linewidth lasers from delayed selfheterodyne beat note measurements using Bayesian inference. Particular emphasis is on estimation of the intrinsic (Lorentzian) laser linewidth. The approach is based on a statistical model of the measurement process, taking into account the effects of the interferometer as well as the detector noise. Our method therefore yields accurate results even when the intrinsic linewidth plateau is obscured by detector noise. The regression is performed on periodogram data in the frequency domain using a Markovchain Monte Carlo method. By using explicit knowledge about the statistical distribution of the observed data, the method yields good results already from a single time series and does not rely on averaging over many realizations, since the information in the available data is evaluated very thoroughly. The approach is demonstrated for simulated time series data from a stochastic laser rate equation model with 1 / ftype nonMarkovian noise. 
L. Ermoneit, B. Schmidt, J. Fuhrmann, Th. Koprucki, L.R. Schreiber, M. Kantner, Simulation of singleelectron shuttling for spinqubit transport in a SiGe quantum bus, in: Book of Abstracts of the International Workshop on Computational Nanotechnology 2023 (IWCN 2023), X. Orios Plaedvall, G. Abadal Berini, X. Cartoixà Soler, A. Cummings, C.F. Destefani, D. Jiménez Jiménez, J. Mart'in Mart'inez, R. Rodr'iguez Mart'inez, A. Benali, eds., pp. 8889.

M. Kantner, L. Mertenskötter, Estimation of frequency noise characteristics and datadriven modeling of narrowlinewidth semiconductor lasers, in: 23nd International Conference on Numerical Simulation of Optoelectronic Devices (NUSOD 2023), P. Bardella, A. Tibaldi, eds., IEEE, 2023, pp. 5556, DOI 10.1109/NUSOD59562.2023.10273522 .
Abstract
The design of narrowlinewidth lasers requires stochastic laser models providing a realistic description of the noise in the device. We present a statistical inference approach to extract the frequency noise characteristics and model parameters of narrowlinewidth lasers from delayed selfheterodyne beat note experiments. By exploiting prior knowledge about the statistical distribution of the measurement data, accurate estimates of the parameters of the free running laser can be achieved even in the presence of considerable detector noise. The approach is demonstrated for simulated time series data using a stochastic laser rate equation model including 1/ftype noise. 
M. Kantner, L. Mertenskötter, Wienerfilter enhanced estimation of the intrinsic laser linewidth from delayed selfheterodyne beat note measurements, in: 2023 Conference on Lasers and ElectroOptics Europe & European Quantum Electronics Conference (CLEO/EuropeEQEC), IEEE, 2023, pp. 8889, DOI 10.1109/CLEO/EuropeEQEC57999.2023.10232191 .
Abstract
Narrowlinewidth lasers exhibiting low phase noise are core elements of coherent optical communication systems, gravitational wave interferometers and emerging quantum technologies (e.g., optical atomic clocks, matterwave interferometers, iontrap quantumcomputers etc.). For many of these applications, the performance depends critically on the laser's intrinsic (Lorentzian) linewidth [1], which is typically obscured by additional 1/flike technical noise. Because of this socalled flicker noise, the laser linewidth alone is not a welldefined quantity and needs to be specified for a given measurement time. For a detailed characterization of the frequency noise exhibited by the laser, the measurement of the frequency noise power spectral density (FNPSD) is required. 
M. Radziunas, E. Kuhn, H. Wenzel, B. King, P. Crump, Calculation of optical modes in large emission area photonic crystal surfaceemitting lasers, in: 23nd International Conference on Numerical Simulation of Optoelectronic Devices (NUSOD 2023), P. Bardella, A. Tibaldi, eds., IEEE, 2023, pp. 8990, DOI 10.1109/NUSOD59562.2023.10273475 .
Abstract
We discuss numerical challenges in constructing and resolving spectral problems for photonic crystal surfaceemitting lasers with large (up to several mm 2 ) emission area. We show that finite difference schemes with moderate and large domain discretization steps provide sufficient accuracy of several major (lowestthreshold) modes of particular device designs.
Preprints, Reports, Technical Reports

D. Dolinina, G. Huyet, D. Turaev, A.G. Vladimirov, Desynchronization of temporal solitons in Kerr cavities with pulsed injection, Preprint no. 3099, WIAS, Berlin, 2024.
Abstract, PDF (1036 kByte)
A numerical and analytical study was conducted to investigate the bifurcation mechanisms that cause desynchronization between the soliton repetition frequency and the frequency of external pulsed injection in a Kerr cavity described by the LugiatoLefever equation. The results suggest that desynchronization typically occurs through an AndronovHopf bifurcation. Additionally, a sim ple and intuitive criterion for this bifurcation to occur is proposed. 
L. Ermoneit, B. Schmidt, Th. Koprucki, J. Fuhrmann, T. Breiten, A. Sala, N. Ciroth, R. Xue, L.R. Schreiber, M. Kantner, Optimal control of conveyormode spinqubit shuttling in a Si/SiGe quantum bus in the presence of charged defects, Preprint no. 3082, WIAS, Berlin, 2023, DOI 10.20347/WIAS.PREPRINT.3082 .
PDF (9473 kByte) 
M. Radziunas, E. Kuhn, H. Wenzel, B. King, P. Crump, Optical mode calculation in largearea photonic crystal surfaceemitting lasers, Preprint no. 3075, WIAS, Berlin, 2023, DOI 10.20347/WIAS.PREPRINT.3075 .
Abstract, PDF (2060 kByte)
We discuss algorithms and numerical challenges in constructing and resolving spectral prob lems for photonic crystal surfaceemitting lasers (PCSELs) with photonic crystal layers and large (up to several tens of mm2) emission areas. We show that finite difference schemes created using coarse numerical meshes provide sufficient accuracy for several major (lowestthreshold) modes of particular device designs. Our technique is applied to the example of largearea all semiconductor PCSELs, showing how it can be used to optimize device performance. 
S. Amiranashvili, R. Čiegis, Stability of the higherorder splitting methods for the generalized nonlinear Schrödinger equation, Preprint no. 3070, WIAS, Berlin, 2023, DOI 10.20347/WIAS.PREPRINT.3070 .
Abstract, PDF (372 kByte)
The numerical solution of the generalized nonlinear Schrödinger equation by explicit splitting methods can be disturbed by socalled spurious instabilities. They are manifested by the appearance of extraneous spectral peaks which change their position in the frequency domain and disappear with decreasing integration step. The spurious instabilities can coexist with the true physical ones, like modulation instability, in which case they are particularly difficult to detect. We consider an arbitrary multiplicative splitting method and discuss conditions necessary for the absence of spurious instabilities. 
L. Mertenskötter, M. Kantner, Frequency noise characterization of narrowlinewidth lasers: A Bayesian approach, Preprint no. 3065, WIAS, Berlin, 2023.
Abstract, PDF (1008 kByte)
We describe a Bayesian estimation approach to infer on the frequency noise characteristics of narrowlinewidth semiconductor lasers from delayed selfheterodyne beat note measurements. Our technique is grounded in a statistical model of the measurement process that accounts for both the impact of the interferometer and the detector noise. The approach yields accurate results, even in scenarios where the intrinsic linewidth plateau is obscured by detector noise. The analysis is carried out using a Markovchain Monte Carlo method in the frequency domain and exploits prior knowledge about the statistical distribution of the data. The method is validated using simulated time series data from a stochastic laser rate equation model incorporating 1/f type nonMarkovian noise. 
E. Kuhn, Simulation of the mode dynamics in broadridge laser diodes, Preprint no. 3061, WIAS, Berlin, 2023.
Abstract, PDF (554 kByte)
In this publication a method to simulate the mode dynamics in broadridge laser diode is presented. These devices exhibit rich lateral mode dynamics in addition to longitudinal mode dynamics observed in narrowridge laser diodes. The mode dynamics are strongly influenced by higher order effects, which are described by effective interaction terms and can derived from the band structure and the carrier scattering in the quantum well. The spatial dependency of pump current densities plays a crucial role in lateral mode dynamics, and thus, a DriftDiffusion model is employed to calculate the current densities with an additional capturing term. 
M. Radziunas, E. Kuhn, H. Wenzel, Solving a spectral problem for largearea photonic crystal surfaceemitting lasers, Preprint no. 3059, WIAS, Berlin, 2023, DOI 10.20347/WIAS.PREPRINT.3059 .
Abstract, PDF (2840 kByte)
We present algorithms for constructing and resolving spectral problems for novel photonic crystal surfaceemitting lasers with large emission areas, given by firstorder PDEs with two spatial dimensions. These algorithms include methods to overcome computerarithmeticrelated challenges when dealing with huge and small numbers. We show that the finite difference schemes, constructed using relatively coarse numerical meshes enable accurate estimation of several major, optical modes, which are essential in practical applications. 
A.G. Vladimirov, D. Dolinina, Neutral delay differential equation Kerr cavity model, Preprint no. 3025, WIAS, Berlin, 2023, DOI 10.20347/WIAS.PREPRINT.3025 .
Abstract, PDF (1308 kByte)
A neutral delay differential equation (NDDE) model of a Kerr cavity with external coherent injection is developed that can be considered as a generalization of the Ikeda map with second and higher order dispersions being taken into account. It is shown that this model has solutions in the form of dissipative solitons both in the limit, where the model can be reduced to the LugiatoLefever equation (LLE), and beyond this limit, where the soliton is eventually destroyed by the Cherenkov radiation. Unlike the standard LLE the NDDE model is able to describe the overlap of multiple resonances associated with different cavity modes.
Talks, Poster

L. Ermoneit, Optimal control of a SiGeQuantum bus for coherent electron shuttling in the presence of material defects, APS March Meeting, March 3  8, 2024, Minneapolis, USA, March 7, 2024.

L. Mertenskötter, M. Kantner, Narrowlinewidth lasers, CLEO Conference, North Carolina, USA, May 5  10, 2024.

U. Bandelow, Applied mathematical research in nonlinear photonics at WIAS Berlin, Workshops on ``Nonlinear Photonics and Metasurfaces'', February 8, 2024, Australian National University, Canberra, Australia, February 8, 2024.

U. Bandelow, Applied mathematical research in photonics at WIAS Berlin, Workshops on ``Optics'', February 5, 2024, Monash University, Melbourne, Australia, February 5, 2024.

U. Bandelow, Hierarchies of integrable NLStype equations and selected solutions, Workshop 2411b ``Nonlinear Optics: Physics, Analysis, and Numerics'', March 10  15, 2024, Mathematisches Forschungsinstitut Oberwolfach, March 11, 2024.

U. Bandelow, Modeling and simulation of semiconductor devices at WIAS: From lasers to quantum technologies, Workshops on ``Quantum Technology'', February 6, 2024, University of Melbourne, Melbourne, Australia, February 6, 2024.

U. Bandelow, Modeling of pulse propagation in nonlinear dispersive media at WIAS Berlin, Workshops on ``Integrability for HigherOrder Optical Pulse Propagation'' associated with the meeting of the Australian and New Zeeland Association of Mathematical Physics (ANZAMP), February 6  9, 2024, Katoomba, Australia, February 9, 2024.

L. Ermoneit, B. Schmidt, J. Fuhrmann, Th. Koprucki, M. Kantner, Coherent spinqubit shuttling in a SiGe quantum bus: Devicescale modeling, simulation and optimal control, Leibniz MMS Days 2023, Potsdam, April 17  19, 2023.

L. Ermoneit, M. Kantner, Th. Koprucki, B. Schmidt, Coherent spinqubit shuttling for scalable quantum processors: Modeling, simulation and optimal control, MATH+ Day, HumboldtUniversität zu Berlin, October 20, 2023.

L. Ermoneit, Simulation of singleelectron shuttling for spinqubit transport in a SiGe quantum bus, International Workshop on Computational Nanotechnology, June 12  16, 2023, Barcelona, Spain, June 12, 2023.

E. Kuhn, Simulation of the mode dynamics in broad ridge laser diodes, 23nd International Conference on Numerical Simulation of Optoelectronic Devices (NUSOD 2023), September 18  22, 2023, Politecnico di Torino, Italy, September 19, 2023.

L. Mertenskötter, Kalman filtering of stochastic laser dynamics: Parameter and state space estimation from timedelayed measurements, International Conference on Structural Nonlinear Dynamics and Diagnosis, May 15  17, 2023, Marrakech, Morocco, May 17, 2023.

M. Stöhr, Bifurcations and instabilities of temporal dissipative solitons in DDEsystems with large delay (online talk), Workshop Complex Dynamical Systems  2023 (Hybrid Event), October 2  4, 2023, Institute of Mathematics of the National Academy of Sciences of Ukraine, Kyiv, Ukraine, October 4, 2023.

M. Stöhr, Square waves and Bykov Tpoints in DDEs with large delay, 12th Colloquium on the Qualitative Theory of Differential Equations, June 19  23, 2023, Bolyai Institute, University of Szeged, Hungary, June 22, 2023.

S. Amiranashvili, Numerical aspects of modulation instability, 26th International Conference on Mathematical Modelling and Analysis, May 30  June 2, 2023, University of Latvia, Jurmala, Latvia, June 1, 2023.

S. Amiranashvili, Numerical aspects of modulation instability, Extreme Waves 2023, August 28  September 1, 2023, MaxPlanckInstitut für Physik komplexer Systeme, Dresden, August 28, 2023.

U. Bandelow, Laserdynamik  mathematische Modellierung, MBITechnikerschulung 2023, October 16, 2023, MaxBornInstitut, Wandlitz.

U. Bandelow, Modeling and simulation of semiconductor devices: From highpower lasers to quantum technologies, Winter School on IIISb Applications: NonVolatile Memories  A Modelling Perspective, February 27  March 3, 2023, Technische Universität Berlin, February 27, 2023.

U. Bandelow, Ultrashort solitons in the regime of event horizons in nonlinear optical media, Extreme Waves 2023, August 28  September 1, 2023, MaxPlanckInstitut für Physik komplexer Systeme, Dresden, August 29, 2023.

U. Bandelow, Unusual scenarios in the context of the modulation instability, Dissipative Solitons, Turbulence and Extreme Events in Nonlinear Photonics, September 6  8, 2023, International Solvay Institutes, Brussels, Belgium, September 7, 2023.

U. Bandelow, Unusual wavemixing processes in the context of the modulation instability, XIX International Workshop on Instabilities and Nonequilibrium Structures  INES 2023, December 4  8, 2023, Pontificia Universidad Catolica de Valparaiso, Chile, December 7, 2023.

M. Kantner, L. Ermoneit, B. Schmidt, J. Fuhrmann, A. Sala, L.R. Schreiber, Th. Koprucki, Optimal control of a SiGequantum bus for coherent electron shuttling in scalable quantum computing architectures, Silicon Quantum Electronics Workshop 2023, Kyoto, Japan, October 31  November 2, 2023.

M. Kantner, Modeling of semiconductor devices for quantum technologies: From singlephoton sources to spinqubit shuttles, CASA Colloquium (Centre for Analysis, Scientific Computing and Applications), Eindhoven University of Technology, Netherlands, April 5, 2023.

M. Kantner, Wiener filter enhanced estimation of the intrinsic laser linewidth from delayed selfheterodyne beat note measurements, 2023 Conference on Lasers and ElectroOptics/EuropeEuropean Quantum Electronics Virtual Conferences, Munich, June 26  30, 2023.

M. Radziunas, Calculation of optical modes in large emission area photonic crystal surfaceemitting lasers, 23nd International Conference on Numerical Simulation of Optoelectronic Devices (NUSOD 2023), September 18  22, 2023, Politecnico di Torino, Italy, September 19, 2023.

M. Radziunas, Modeling of photonic crystal surfaceemitting lasers, 26th International Conference on Mathematical Modelling and Analysis, May 30  June 2, 2023, University of Latvia, Jurmala, Latvia, May 30, 2023.

M. Radziunas, Modeling, simulation, and analysis of dynamics in semiconductor lasers: A brief overview of the WIASFBH collaboration, Leibniz MMS Days 2023, April 17  19, 2023, LeibnizInstitut für Agrartechnik und Bioökonomie (ATB), Potsdam, April 18, 2023.

A.G. Vladimirov, Neutral delay differential equation Kerr cavity model, Dissipative Solitons, Turbulence and Extreme Events in Nonlinear Photonics, September 6  8, 2023, International Solvay Institutes, Brussels, Belgium, September 8, 2023.

M. Wolfrum, Bumps, chimera states, and Turing patterns in systems of coupled active rotators, MiniWorkshop: Developing a Mathematical Theory for Coevolutionary Dynamical Networks, Centre for Mathematical Science at Lund University, Lund, Sweden, May 30, 2023.

M. Wolfrum, Bumps, chimera states, and Turing patterns in systems of coupled active rotators (online talk), Workshop Complex Dynamical Systems  2023 (Hybrid Event), October 2  4, 2023, Institute of Mathematics of the National Academy of Sciences of Ukraine, Kyiv, Ukraine, October 4, 2023.

M. Wolfrum, Dynamics of localized structures in DDEs with large delay, 12th Colloquium on the Qualitative Theory of Differential Equations, June 19  23, 2023, Bolyai Institute, University of Szeged, Hungary, June 21, 2023.

M. Wolfrum, Phase sensitive excitability of a limit cycle, Conference on Nonlinear Data Analysis and Modeling: Advances, Appilcations, Perspective, Potsdam, March 15  17, 2023.
External Preprints

H. Wenzel, E. Kuhn, P. Crump, M. Radziunas, Theory of the linewidthpower product of photoniccrystal surfaceemitting lasers, Preprint no. 11246, Cornell University, 2024, DOI 10.48550/arXiv.2402.11246 .
Abstract
A general theory for the intrinsic (Lorentzian) linewidth of photoniccrystal surfaceemitting lasers (PCSELs) is presented. The effect of spontaneous emission is modeled by a classical Langevin force entering the equation for the slowly varying waves. The solution of the coupledwave equations, describing the propagation of four basic waves within the plane of the photonic crystal, is expanded in terms of the solutions of the associated spectral problem, i.e. the laser modes. Expressions are given for photon number, rate of spontaneous emission into the laser mode, Petermann factor and effective Henry factor entering the general formula for the linewidth. The theoretical framework is applied to the calculation of the linewidthpower product of airhole and allsemiconductor PCSELs. For output powers in the Watt range, intrinsic linewidths of a few tens of Hertz are predicted if stable single mode operation is ensured. 
D.M. Kane, M. Radziunas, Chaos spectrum  Semiconductor laser with delayed optical feedback, Preprint no. arXiv.2312.14353, Cornell University, 2023, DOI 10.48550/arXiv.2312.14353 .
Abstract
Maximizing the rf bandwidth associated with the chaotic output from tailored operation of nonlinear semiconductor laser systems is an ongoing research effort. The early pioneering research was done in semiconductor laser with delayed optical feedback systems, which continue to be researched. We report numerical simulations of this system, using a travelling wave model. The results provide new insights into the impact of key device parameters affecting the chaos bandwidth and spectrum. Linewidth enhancement factor and the nonlinear gain saturation parameter are found to be the most important parameters when seeking to optimize the chaotic output. We reassess a standard definition being used to report chaos bandwidth. We propose that more spectral information should be reported if numerical and experimental research results are to be of most value into the future. A database from previous experimental study is also analyzed to connect with the predictions of the numerical simulations. This elucidates the links between the chaos bandwidth achieved in real systems and the semiconductor laser parameters. The results inform recommendations for semiconductor laser parameters that will better support broadband chaos generation in whatever semiconductorgainmediumbased nonlinear system approach is being used. They elucidate the physics of both the envelope and the fine structure of the rf spectrum of coherence collapse. 
M. Kantner, L. Mertenskötter, Accurate evaluation of selfheterodyne laser linewidth measurements using Wiener filters, Preprint no. arXiv:2301.10645, Cornell University, 2023, DOI 10.48550/arXiv.2301.10645 .
Abstract
Selfheterodyne beat note measurements are widely used for the experimental characterization of the frequency noise power spectral density (FNPSD) and the spectral linewidth of lasers. The measured data, however, must be corrected for the transfer function of the experimental setup in a postprocessing routine. The standard approach disregards the detector noise and thereby induces reconstruction artifacts, i.e., spurious spikes, in the reconstructed FNPSD. We introduce an improved postprocessing routine based on a parametric Wiener filter that is free from reconstruction artifacts, provided a good estimate of the signaltonoise ratio is supplied. Building on this potentially exact reconstruction, we develop a new method for intrinsic laser linewidth estimation that is aimed at deliberate suppression of unphysical reconstruction artifacts. Our method yields excellent results even in the presence of strong detector noise, where the intrinsic linewidth plateau is not even visible using the standard method. The approach is demonstrated for simulated time series from a stochastic laser model including 1 / ftype noise.
Research Groups
 Partial Differential Equations
 Laser Dynamics
 Numerical Mathematics and Scientific Computing
 Nonlinear Optimization and Inverse Problems
 Interacting Random Systems
 Stochastic Algorithms and Nonparametric Statistics
 Thermodynamic Modeling and Analysis of Phase Transitions
 Nonsmooth Variational Problems and Operator Equations