Publications
Articles in Refereed Journals

A. Hajizadeh, A. Matysiak, M. Wolfrum, P.J.C. May, R. König, Auditory cortex modelled as a dynamical network of oscillators: Understanding eventrelated fields and their adaptation, Biological Cybernetics, 116 (2022), pp. 475499, DOI 10.1007/s00422022009367 .
Abstract
Adaptation, the reduction of neuronal responses by repetitive stimulation, is a ubiquitous feature of auditory cortex (AC). It is not clear what causes adaptation, but shortterm synaptic depression (STSD) is a potential candidate for the underlying mechanism. We examined this hypothesis via a computational model based on AC anatomy, which includes serially connected core, belt, and parabelt areas. The model replicates the eventrelated field (ERF) of the magnetoencephalogram as well as ERF adaptation. The model dynamics are described by excitatory and inhibitory state variables of cell populations, with the excitatory connections modulated by STSD. We analysed the system dynamics by linearizing the firing rates and solving the STSD equation using timescale separation. This allows for characterization of AC dynamics as a superposition of damped harmonic oscillators, socalled normal modes. We show that repetition suppression of the N1m is due to a mixture of causes, with stimulus repetition modifying both the amplitudes and the frequencies of the normal modes. In this view, adaptation results from a complete reorganization of AC dynamics rather than a reduction of activity in discrete sources. Further, both the network structure and the balance between excitation and inhibition contribute significantly to the rate with which AC recovers from adaptation. This lifetime of adaptation is longer in the belt and parabelt than in the core area, despite the time constants of STSD being spatially constant. Finally, we critically evaluate the use of a single exponential function to describe recovery from adaptation. 
S. Yanchuk, M. Wolfrum, T. Pereira, D. Turaev, Absolute stability and absolute hyperbolicity in systems with discrete timedelays, Journal of Differential Equations, 318 (2022), pp. 323343, DOI 10.1016/j.jde.2022.02.026 .
Abstract
An equilibrium of a delay differential equation (DDE) is absolutely stable, if it is locally asymptotically stable for all delays. We present criteria for absolute stability of DDEs with discrete timedelays. In the case of a single delay, the absolute stability is shown to be equivalent to asymptotic stability for sufficiently large delays. Similarly, for multiple delays, the absolute stability is equivalent to asymptotic stability for hierarchically large delays. Additionally, we give necessary and sufficient conditions for a linear DDE to be hyperbolic for all delays. The latter conditions are crucial for determining whether a system can have stabilizing or destabilizing bifurcations by varying time delays. 
S. Amiranashvili, U. Bandelow, Unusual scenarios in fourwavemixing instability, Physical Review A, 105 (2022), pp. 063519/1063519/6, DOI 10.1103/PhysRevA.105.063519 .
Abstract
A pump carrier wave in a dispersive system may decay by giving birth to blue and redshifted satellite waves due to modulation or fourwave mixing instability. We analyse situations where the satellites are so different from the carrier wave, that the redshifted satellite either changes its propagation direction (k < 0, ω > 0) or even gets a negative frequency (k, ω < 0). Both situations are beyond the envelope approach and require application of Maxwell equations. 
A.G. Vladimirov, Short and longrange temporal cavity soliton interaction in delay models of modelocked lasers, Physical Review E. Statistical, Nonlinear, and Soft Matter Physics, 105 (2022), pp. 04420710442076, DOI 10.1103/PhysRevE.105.044207 .
Abstract
Interaction equations governing slow time evolution of the coordinates and phases of two interacting temporal cavity solitons in a delay differential equation model of a nonlinear mirror modelocked laser are derived and analyzed. It is shown that nonlocal pulse interaction due to gain depletion and recovery can lead either to a development of harmonic modelocking regime, or to a formation of closely packed incoherent soliton bound state with weakly oscillating intersoliton time separation. Local interaction via electric field tails can result in an antiphase or inphase stationary or breathing harmonic modelocking regime. 
M. Wolfrum, S. Yanchuk, O. D'huys, Multiple selflocking in the KuramotoSakaguchi system with delay, SIAM Journal on Applied Dynamical Systems, 21 (2022), pp. 17091725, DOI 10.1137/21M1458971 .
Abstract
We study the KuramotoSakaguchi system of phase oscillators with a delayed meanfield coupling. By applying the theory of large delay to the corresponding OttAntonsen equation, we explain fully analytically the mechanisms for the appearance of multiple coexisting partially locked states. Closely above the onset of synchronization, these states emerge in the Eckhaus scenario: with increasing coupling, more and more partially locked states appear unstable from the incoherent state, and gain stability for larger coupling at a modulational stability boundary. The partially locked states with strongly detuned frequencies are shown to emerge subcritical and gain stability only after a fold and a series of Hopf bifurcations. We also discuss the role of the Sakaguchi phase lag parameter. For small delays, it determines, together with the delay time, the attraction or repulsion to the central frequency, which leads to supercritical or subcritical behavior, respectively. For large delay, the Sakaguchi parameter does not influence the global dynamical scenario. 
M. Heida, M. Kantner, A. Stephan, Consistency and convergence for a family of finite volume discretizations of the FokkerPlanck operator, ESAIM: Mathematical Modelling and Numerical Analysis, 55 (2021), pp. 30173042, DOI 10.1051/m2an/2021078 .
Abstract
We introduce a family of various finite volume discretization schemes for the FokkerPlanck operator, which are characterized by different weight functions on the edges. This family particularly includes the wellestablished ScharfetterGummel discretization as well as the recently developed squareroot approximation (SQRA) scheme. We motivate this family of discretizations both from the numerical and the modeling point of view and provide a uniform consistency and error analysis. Our main results state that the convergence order primarily depends on the quality of the mesh and in second place on the quality of the weights. We show by numerical experiments that for small gradients the choice of the optimal representative of the discretization family is highly nontrivial while for large gradients the ScharfetterGummel scheme stands out compared to the others. 
L. Mertenskötter, K. Busch, R. DE J. LeónMontiel, Entangled twophoton absorption spectroscopy with varying pump wavelength, Journal of the Optical Society of America. B, 38 (2021), pp. C63C68, DOI 10.1364/JOSAB.428531 .
Abstract
In virtualstate spectroscopy, information about the energylevel structure of an arbitrary sample is retrieved by Fourier transforming sets of measured twophoton absorption probabilities of entangled photon pairs where the degree of entanglement and the delay time between the photons have been varied. This works well for simple systems but quickly becomes rather difficult when many intermediate states are involved. We propose and discuss an extension of entangled twophoton absorption spectroscopy that solves this problem by means of repeated measurements at different pump wavelengths. Specifically, we demonstrate that our extension works well for a variety of realistic experimental setups. 
S. Slepneva, A. Pimenov, Nonlinear dynamical properties of frequency swept fiberbased semiconductor lasers, Journal of Physics: Photonics, 3 (2021), pp. 044002/1044002/11, DOI 10.1088/25157647/ac1324 .
Abstract
We investigate dynamics of semiconductor lasers with fiberbased unidirectional ring cavity that can be used as frequency swept sources. We identify key factors behind the reach dynamical behaviour of such lasers using stateoftheart experimental and analytical methods. Experimentally, we study the laser in static, quasistatic and synchronisation regimes.We apply experimental methods such as optical heterodyne or electric field reconstruction in order to characterise these regimes or study the mechanisms of transition between them. Using a delay differential equation model, we demonstrate that the presence of chromatic dispersion can lead to destabilisation of the laser modes through modulational instability, which results in undesirable chaotic emission. We characterise the instability threshold both theoretically and experimentally, and demonstrate deterioration of the FDML regime near the threshold. 
I. Franović, O.E. Omel'chenko, M. Wolfrum, Bumps, chimera states, and Turing patterns in systems of coupled active rotators, Physical Review E. Statistical, Nonlinear, and Soft Matter Physics, 104 (2021), pp. L052201/1L052201/5, DOI 10.1103/PhysRevE.104.L052201 .
Abstract
Selforganized coherenceincoherence patterns, called chimera states, have first been reported in systems of Kuramoto oscillators. For coupled excitable units, similar patterns where coherent units are at rest, are called bump states. Here, we study bumps in an array of active rotators coupled by nonlocal attraction and global repulsion. We demonstrate how they can emerge in a supercritical scenario from completely coherent Turing patterns: a single incoherent unit appears in a homoclinic bifurcation, undergoing subsequent transitions to quasiperiodic and chaotic behavior, which eventually transforms into extensive chaos with many incoherent units. We present different types of transitions and explain the formation of coherenceincoherence patterns according to the classical paradigm of shortrange activation and longrange inhibition. 
V.V. Klinshov, S.Y. Kirillov, V.I. Nekorkin, M. Wolfrum, Noiseinduced dynamical regimes in a system of globally coupled excitable units, Chaos. An Interdisciplinary Journal of Nonlinear Science, 31 (2021), pp. 083103/1083103/11, DOI 10.1063/5.0056504 .
Abstract
We study the interplay of global attractive coupling and individual noise in a system of identical active rotators in the excitable regime. Performing a numerical bifurcation analysis of the nonlocal nonlinear FokkerPlanck equation for the thermodynamic limit, we identify a complex bifurcation scenario with regions of different dynamical regimes, including collective oscillations and coexistence of states with different levels of activity. In systems of finite size this leads to additional dynamical features, such as collective excitability of different types, noiseinduced switching and bursting. Moreover, we show how characteristic quantities such as macroscopic and microscopic variability of inter spike intervals can depend in a nonmonotonous way on the noise level. 
M. Nizette, A.G. Vladimirov, Generalized Haus master equation model for modelocked classB lasers, Physical Review E. Statistical, Nonlinear, and Soft Matter Physics, 104 (2021), pp. 014215/1014215/13, DOI 10.1103/PhysRevE.104.014215 .
Abstract
Using the multiscale technique we develop a generalized version of the classB Haus modelocking model that accounts for both the slow gain response to the averaged value of the field intensity and the fast gain dynamics on the scale comparable to the pulse duration. We show that unlike the standard classB Haus modelocked model, our model is able to describe not only Qswitched instability of the fundamental modelocked regime, but also the appearance of harmonic modelocked regimes with the increase of the pump power. 
A. Zeghuzi, J.P. Koester, M. Radziunas, H. Christopher, H. Wenzel, A. Knigge, Spatially modulated broadarea lasers for narrow lateral farfield divergence, Optics Express, 29 (2021), pp. 2513325141, DOI 10.1364/OE.430804 .
Abstract
A novel laser design is presented that combines a longitudinallateral gainloss modulation with an additional phase tailoring achieved by etching rectangular trenches. At 100 A pulsed operation, simulations predict a farfield profile with 0.3degree full width at half maximum where a 0.4degreewide main lobe contains 40% of the emitted optical output power. While farfield measurements of these structured lasers emitting 10 ns long pulses with 35 W peak power confirm a substantial enhancement of radiation within the central onedegree angular range, the measured farfield intensity outside of the obtained central peak remains high. 
H. Wenzel, M. Kantner, M. Radziunas, U. Bandelow, Semiconductor laser linewidth theory revisited, APPS. Applied Sciences, 11 (2021), pp. 6004/16004/29, DOI 10.3390/app11136004 .
Abstract
More and more applications require semiconductor lasers distinguished not only by large modulation bandwidths or high output powers, but also by small spectral linewidths. The theoretical understanding of the root causes limiting the linewidth is therefore of great practical relevance. In this paper, we derive a general expression for the calculation of the spectral linewidth step by step in a selfcontained manner. We build on the linewidth theory developed in the 1980s and 1990s but look from a modern perspective, in the sense that we choose as our starting points the timedependent coupledwave equations for the forward and backward propagating fields and an expansion of the fields in terms of the stationary longitudinal modes of the open cavity. As a result, we obtain rather general expressions for the longitudinal excess factor of spontaneous emission (Kfactor) and the effective Alphafactor including the effects of nonlinear gain (gain compression) and refractive index (Kerr effect), gain dispersion and longitudinal spatial hole burning in multisection cavity structures. The effect of linewidth narrowing due to feedback from an external cavity often described by the socalled chirp reduction factor is also automatically included. We propose a new analytical formula for the dependence of the spontaneous emission on the carrier density avoiding the use of the population inversion factor. The presented theoretical framework is applied to a numerical study of a twosection distributed Bragg reflector laser. 
S. Amiranashvili, M. Radziunas, U. Bandelow, K. Busch, R. Čiegis, Additive splitting methods for parallel solutions of evolution problems, Journal of Computational Physics, 436 (2021), pp. 110320/1110320/14, DOI 10.1016/j.jcp.2021.110320 .
Abstract
We demonstrate how a multiplicative splitting method of order Pcan be utilized to construct an additive splitting method of order P+3. The weight coefficients of the additive method depend only on P, which must be an odd number. Specifically we discuss a fourthorder additive method, which is yielded by the LieTrotter splitting. We provide error estimates, stability analysis of a test problem, and numerical examples with special discussion of the parallelization properties and applications to nonlinear optics. 
A.G. Vladimirov, M. Tlidi, M. Taki, Dissipative soliton interaction in Kerr resonators with highorder dispersion, Physical Review A, 103 (2021), pp. 063505/1063505/7, DOI 10.1103/PhysRevA.103.063505 .
Abstract
We consider an optical resonator containing a photonic crystal fiber and driven coherently by an injected beam. This device is described by a generalized LugiatoLefever equation with fourth order dispersion We use an asymptotic approach to derive interaction equations governing the slow time evolution of the coordinates of two interacting dissipative solitons. We show that Cherenkov radiation induced by positive fourthorder dispersion leads to a strong increase of the interaction force between the solitons. As a consequence, large number of equidistant soliton bound states in the phase space of the interaction equations can be stabilized. We show that the presence of even small spectral filtering not only dampens the Cherenkov radiation at the soliton tails and reduces the interaction strength, but can also affect the bound state stability. 
A.G. Vladimirov, S. Suchkov, G. Huyet, S.K. Turitsyn, Delaydifferentialequation model for modelocked lasers based on nonlinear optical and amplifying loop mirrors, Physical Review A, 104 (2021), pp. 033525/1033525/8, DOI 10.1103/PhysRevA.104.033525 .
Abstract
Delay differential equation model of a NOLMNALM modelocked laser is developed that takes into account finite relaxation rate of the gain medium and asymmetric beam splitting at the entrance of the nonlinear mirror loop. Asymptotic linear stability analysis of the continuous wave solutions performed in the limit of large delay indicates that in a classB laser flip instability leading to a period doubling cascade and development of squarewave patterns can be suppressed by a short wavelength modulational instability. Numerically it is shown that the model can demonstrate large windows of regular fundamental and harmonic modelocked regimes with single and multiple pulses per cavity round trip time separated by domains of irregular pulsing.
Contributions to Collected Editions

A. Roche, U. Gowda, A. Kovalev, E. Viktorov, A. Pimenov, A.G. Vladimirov, M. Marconi, M. Giudici, G. Huyet, S. Slepneva, Defect mediated turbulence in a long laser, in: Realtime Measurements, Rogue Phenomena, and SingleShot Applications VI, D.R. Solli, G. Herink, S. Bielawski, eds., 11671 of Proceedings of SPIE, SPIE. Digital Library, 2021, pp. 116710D/1116710D/6, DOI 10.1117/12.2578727 .
Abstract
In this paper, we experimentally and theoretically analyse the formation and interaction of dark solitons in a long laser. The laser includes a semiconductor optical amplifier (SOA), centred around 1300nm, an intracavity filter and a fibre cavity whose length can vary from 20m to 20km. Near the lasing threshold the laser exhibits slowly evolving power dropouts the circulate the cavity. These dropouts are associated with the formation of NozakiBekki Holes (NBH), also referred to as dark solitons. We observe both experimentally and numerically that the core of these holes exhibit chaotic dynamics and emit short light pulses. These pulses are found to be blue shifted with respect to the frequency of the dark solitons and therefore travel with a faster group velocity. These pulses are strongly damped, as they are detuned with respect to the filter transmission, but they may lead to the creation of new dark solitons. These pulses also play a major role in the development of optical turbulence when the filter is set at a frequency above 1310nm. In this case, the laser displays numerous dark solitons per round trip and the fast travelling pulses act as an interaction between the solitons, which can lead to the development of defect mediated turbulence. 
A. Roche, U. Gowda, A. Kovalev, E. Viktorov, A. Pimenov, A.G. Vladimirov, M. Marconi, M. Giudici, G. Huyet, S. Slepneva, The formation of localised structures from the turn on transient of a long laser, in: Physics and Simulation of Optoelectronic Devices XXIX, B. Witzigmann, M. Osiński, Y. Arakawa, eds., 11680 of Proceedings of SPIE, SPIE Digital Library, 2021, pp. 116800N/1116800N/6, DOI 10.1117/12.2578648 .

A. Zeghuzi, J.P. Koester, M. Radziunas, H. Christopher, H. Wenzel, A. Knigge, Narrow lateral far field divergence obtained with spatially modulated broadarea lasers, in: 2021 27th International Semiconductor Laser Conference (ISLC), IEEE Xplore, IEEE, 2021, pp. 12, DOI 10.1109/ISLC51662.2021.9615888 .
Preprints, Reports, Technical Reports

A. Pimenov, A. Vladimirov, Temporal solitons in an optically injected Kerr cavity with two spectral filters, Preprint no. 2948, WIAS, Berlin, 2022, DOI 10.20347/WIAS.PREPRINT.2948 .
Abstract, PDF (990 kByte)
We investigate theoretically the dynamical behavior of an optically injected Kerr cavity where the chromatic dispersion is induced by propagation of light through two Lorentzian spectral filters with different widths and central frequencies. We show that this setup can be modeled by a second order delay differential equation that can be considered as a generalization of the Ikeda map with included spectral filtering, dispersion, and coherent injection terms. We demonstrate that this equation can exhibit modulational instability and bright localized structures formation in the anomalous dispersion regime. 
S. Amiranashvili, Modeling of ultrashort optical pulses in nonlinear fibers, Preprint no. 2918, WIAS, Berlin, 2022, DOI 10.20347/WIAS.PREPRINT.2918 .
Abstract, PDF (17 MByte)
This work deals with theoretical aspects of pulse propagation. The core focus is on extreme, fewcycle pulses in optical fibers, pulses that are strongly affected by both dispersion and nonlinearity. Using Hamil tonian methods, we discuss how the meaning of pulse envelope changes, as pulses become shorter and shorter, and why an envelope equation can still be used. We also discuss how the standard set of dispersion coefficients yields useful rational approximations for the chromatic dispersion in optical fibers. Three more specific problems are addressed thereafter. First, we present an alternative framework for ultra short pulses in which nonenvelope propagation models are used. The approach yields the limiting, shortest solitons and reveals their universal features. Second, we describe how one can manipulate an ultrashort pulse, i.e., to change its amplitude and duration in a predictable manner. Quantitative theory of the manipu lation is presented based on perturbation theory for solitons and analogy between classical fiber optics and quantum mechanics. Last but not least, we consider a recently found alternative to the standard splitstep approach for numerical solutions of the pulse propagation equations. 
A. Grin, K.R. Schneider, Global algebraic PoincaréBendixson annulus for van der Pol systems, Preprint no. 2864, WIAS, Berlin, 2021, DOI 10.20347/WIAS.PREPRINT.2864 .
Abstract, PDF (278 kByte)
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 
A.G. Vladimirov, M. Tlidi, M. Taki, Dissipative soliton interaction in Kerr resonators with highorder dispersion, Preprint no. 2843, WIAS, Berlin, 2021, DOI 10.20347/WIAS.PREPRINT.2843 .
Abstract, PDF (1126 kByte)
We consider an optical resonator containing a photonic crystal fiber and driven coherently by an injected beam. This device is described by a generalized LugiatoLefever equation with fourth order dispersion We use an asymptotic approach to derive interaction equations governing the slow time evolution of the coordinates of two interacting dissipative solitons. We show that Cherenkov radiation induced by positive fourthorder dispersion leads to a strong increase of the interaction force between the solitons. As a consequence, large number of equidistant soliton bound states in the phase space of the interaction equations can be stabilized. We show that the presence of even small spectral filtering not only dampens the Cherenkov radiation at the soliton tails and reduces the interaction strength, but can also affect the bound state stability. 
L. Mertenskötter, K. Busch, R. DE J. LeónMontiel, Entangled twophoton absorption spectroscopy with varying pump wavelength, Preprint no. 2837, WIAS, Berlin, 2021, DOI 10.20347/WIAS.PREPRINT.2837 .
Abstract, PDF (647 kByte)
In virtualstate spectroscopy, information about the energylevel structure of an arbitrary sample is retrieved by Fourier transforming sets of measured twophoton absorption probabilities of entangled photon pairs where the degree of entanglement and the delay time between the photons have been varied. This works well for simple systems but quickly becomes rather difficult when many intermediate states are involved. We propose and discuss an extension of entangled twophoton absorption spectroscopy that solves this problem by means of repeated measurements at different pump wavelengths. Specifically, we demonstrate that our extension works well for a variety of realistic experimental setups.
Talks, Poster

A. Pimenov, Localized structures in a passive ring cavity with two filters under optical injection, Nonlinear Waves and Turbulence in Photonics 2022, WIAS Berlin, July 15, 2022.

A. Gerdes, Synchronization patterns in globally coupled StuartLandau oscillators, FrenchGerman WEHeraeusSeminar : Outstanding Challenges in Nonlinear Dynamics, Les Houches, France, March 20  25, 2022.

A. Gerdes, Synchronization patterns in globally coupled StuartLandau oscillators, Leibniz MMS Days 2022, Potsdam, April 25  27, 2022.

A. Gerdes, Synchronization patterns in globally coupled StuartLandau oscillators, Dynamics Days Europe 2022, UK, August 22  26, 2022.

A. Gerdes, Synchronization patterns in globally coupled StuartLandau oscillators, Dynamics Days Europe 2022, August 22  26, 2022, University of Aberdeen, UK, August 22, 2022.

A. Gerdes, Synchronization patterns in globally coupled StuartLandau oscillators, Workshop on Control of SelfOrganizing Nonlinear Systems, September 26  28, 2022, LEUCOREA Tagungszentrum, Lutherstadt Wittenberg, September 27, 2022.

A. Gerdes, Synchronization patterns in globally coupled StuartLandau oscillators, Leibniz MMS Days 2022, April 25  27, 2022, WIAS, Potsdam, April 25, 2022.

A. Pimenov, Chromatic dispersion in delayed differential equations for optical cavities and localized structures, MURPHYS 2022 International Conference on Multiple Scale Systems and Hysteresis, May 30  June 3, 2022, Mathematical Institute, Silesian University, Opava, Czech Republic, May 30, 2022.

S. Amiranashvili, Unusual ways of fourwave mixing instability, Nonlinear Waves and Turbulence in Photonics 2022, WIAS Berlin, July 14, 2022.

F. Severing, How numerics add to the instabilities of the generalised nonlinear Schrödinger equation, Nonlinear Waves and Turbulence in Photonics 2022, Berlin, July 14  15, 2022.

F. Severing , Nonlinear Schrödinger Equation  Flawless description of modulation instability?, Student Chapter Poster Session (SCPS) 2022 (Online Event), Sussex, UK, February 20, 2022.

S. Amiranashvili, Seminar zum Thema: Nicht Hermiteschen Operationen, August 10  11, 2022, TU Wien, Austria.

M. Radziunas, Modeling and simulation of semiconductor lasers for high emission power applications, 25th International Conference Mathematical Modelling and Analysis, May 30  June 2, 2022, Vilnius Gediminas Technical University, Druskininkai, Lithuania, June 1, 2022.

M. Wolfrum, Bumps, chimera states, and Turing patterns in systems of coupled active rotators, FrenchGerman WEHeraeusSeminar: Outstanding Challenges in Nonlinear Dynamics, March 20  25, 2022, Wilhelm und Else HeraeusStiftung, Les Houches, France, March 23, 2022.

M. Wolfrum, Stability properties of temporal dissipative solitons in DDEs, Delay Days Utrecht 2022, Hasselt University, Utrecht, Netherlands, May 12, 2022.

M. Wolfrum, Synchronization transitions in systems of coupled phase oscillators, Leibniz MMS Days 2022, April 25  27, 2022, WIAS, Potsdam, April 26, 2022.

M. Stöhr, Bifurcations and instabilities of temporal dissipative solitons in DDE systems with large delay, Control of SelfOrganizing Nonlinear Systems, Potsdam, August 29  September 2, 2021.

A. Gerdes, Synchronization patterns in globally coupled StuartLandau oscillators, Control of SelfOrganizing Nonlinear Systems, Potsdam, August 29  September 2, 2021.

L. Mertenskötter, M. Kantner, H. Wenzel , U. Bandelow, Modeling and optimization of semiconductor lasers for quantum metrology applications, MATH+ Day 2021 (Online Event), Technische Universität Berlin, November 5, 2021.

U. Bandelow, Modeling and simulation of the dynamics in semiconductor lasers (online talk), 91st Annual Meeting of the International Association of Applied Mathematics and Mechanics, MS1: ``Computational Photonics''' (Online Event), March 15  19, 2021, Universität Kassel, March 16, 2021.

U. Bandelow , Ultrashort solitons in the regime of event horizons in nonlinear dispersive optical media, Solvay Workshop on Dissipative Solitons and Optical Frequency Comb Generation, September 15  16, 2021, International Solvay Institutes, Brussels, Belgium, September 16, 2021.

A. Gerdes, Synchronization patterns in globally coupled StuartLandau oscillators (online talk), Workshop on Control of SelfOrganizing Nonlinear Systems, October 14  15, 2021, Technische Universität, Berlin, October 14, 2021.

A. Gerdes, Synchronization patterns in globally coupled StuartLandau oscillators (online talk), SFB Symposium ``Dynamical patterns in complex networks'' (Online Event), Technische Universität, Berlin, October 29, 2021.

M. Kantner, Mathematical modeling and optimal control of the COVID19 pandemic (online talk), Mathematisches Kolloquium, Bergische Universität Wuppertal, April 27, 2021.

M. Kantner, Noise in semiconductor lasers (online talk), MATH+ Spotlight Seminar (Online Event), MATH+, July 14, 2021.

M. Radziunas, Cascaded polarizationcoupling of highpower broadarea semiconductor lasers (online talk), European Semiconductor Laser Workshop (ESLW) 2021 (Online Event), September 17  18, 2021, Télécom Paris and Institut Polytechnique de Paris, France, September 17, 2021.

M. Radziunas, Modeling, simulation, and analysis of dynamics in semiconductor lasers (online talk), Research seminar of the Institute of Computer Science (Online Event), Vilnius University, Lithuania, September 29, 2021.

A.G. Vladimirov, Short pulse solutions of timedelay laser models (online talk), Dynamics Days Europe 2021 (Online Event), Minisymposium MS34 ``Time Delayed Systems: Theory and Experiments'', August 23  27, 2021, Université Côte d'Azur, Nice, France, August 27, 2021.

M. Wolfrum, Bumps, chimera states, and Turing patterns in systems of coupled active rotators, Control of SelfOrganizing Nonlinear Systems, August 29  September 2, 2021, Potsdam, September 2, 2021.

M. Wolfrum, Modelocking and coherence echoes in systems of globally coupled phase oscillators (online talk), Nonlinear Dynamics of Oscillatory Systems (Online Event), September 19  22, 2021, Nizhny Novgorod, Russian Federation, September 21, 2021.

M. Wolfrum, Stability properties of temporal dissipative solitons in DDE systems (online talk), Dynamics Days Europe 2021 (Online Event), Minisymposium MS34: ``Time Delayed Systems: Theory and Experiment'', August 23  27, 2021, Université Côte d'Azur, Nice, France, August 27, 2021.

M. Wolfrum , Temporal dissipative solitons in systems of delaydifferential equations (online talk), SIAM Conference on Applications of Dynamical Systems (Online Event), Minisymposium 184 ``Traveling Pulses in Delay and Lattice Differential Equations'', May 23  27, 2021, Portland, Oregon, USA, May 27, 2021.
External Preprints

L. Schülen, A. Gerdes, M. Wolfrum, A. Zakharova, The solitary route to chimera states, Preprint no. 2204.00385, Cornell University Library, arXiv.org, 2022, DOI /10.48550/arXiv.2204.00385 .
Abstract
We show how solitary states in a system of globally coupled FitzHughNagumo oscillators can lead to the emergence of chimera states. By a numerical bifurcation analysis of a suitable reduced system in the thermodynamic limit we demonstrate how solitary states, after emerging from the synchronous state, become chaotic in a perioddoubling cascade. Subsequently, states with a single chaotic oscillator give rise to states with an increasing number of incoherent chaotic oscillators. In large systems, these chimera states show extensive chaos. We demonstrate the coexistence of many of such chaotic attractors with different Lyapunov dimensions, due to different numbers of incoherent oscillators.
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