Laserdynamik

Publikationen

Monografien

• L. Kuen, E. Kuhn, H. Wenzel, P. Crump, M. Radziunas, Numerical study of spatio-temporal dynamics in all semiconductor PCSELs, P. Baldella, ed., IEEE Xplore, 2025, pp. 107--108, (Collection Published), DOI 10.1109/NUSOD64393.2025.11199659 .

• O. Burylko, M. Wolfrum, S. Yanchuk, Reversible saddle--node separatrix-loop bifurcation, A. Timokha, ed., Analytical and Approximate Methods for Complex Dynamical Systems. Understanding Complex Systems., Springer Cham., 2025, pp. 101--119, (Monograph Published), DOI 10.1007/978-3-031-77378-5_7 .
  Abstract
  We describe the unfolding of a special variant of the codimension-two Saddle--Node Separatrix-Loop (SNSL) bifurcation that occurs in systems with time-reversibility. While the classical SNSL bifurcation can be characterized as the collision of a saddle--node equilibrium with a limit cycle, the reversible variant (R-SNSL) is characterised by as the collision of a saddle-node equilibrium with a boundary separating a dissipative and a conservative region in phase space. Moreover, we present several reversible versions of the SNIC (Saddle--Node on Invariant Circle) bifurcation and discuss the role of an additional reversible saddle equilibrium in all these scenarios. As an example, we provide a detailed bifurcation scenario for a reversible system of two coupled phase rotators (a system on a 2D torus) involving a R-SNSL bifurcation.

• O. Omel'chenko, M. Wolfrum, Stationary and travelling synchronisation patterns in systems of coupled active rotators, A. Timokha, ed., Analytical and Approximate Methods for Complex Dynamical Systems. Understanding Complex Systems., Springer Cham., 2025, pp. 121--134, (Monograph Published), DOI 10.1007/978-3-031-77378-5_8 .
  Abstract
  We study a system of active rotators interacting by short range attractive and long range repulsive coupling. In such systems, one can observe a huge variety of emerging patterns. This includes Turing patterns and coherence-incoherence patterns such as bumps and chimera states. Here, we focus on the transition from stationary to travelling patterns in a drift instability. We elaborate in detail the mathematical framework for a treatment of such states in the continuum limit and present numerical results to discuss the dynamical effects in finite size systems.

• L. Zschiedrich, F. Betz, F. Binkowski, L. Kuen, M. Hammerschmidt, S. Burger, Efficient photonic component analysis via AAA rational approximation, P. Baldella, ed., IEEE Xplore, 2025, pp. 115--116, (Collection Published), DOI 10.1109/NUSOD64393.2025.11199710 .
  Abstract
  We review the application of the AAA algorithm for rational approximation of the optical response function in photonic devices. Originally developed to efficiently interpolate sampled response data, the AAA algorithm also enables the accurate and stable computation of resonances, e.g., quasinormal modes (QNMs), along with their corresponding field distributions. Our approach applies to general nonlinear eigenproblems and can handle branch cuts without introducing spurious or artificial modes. It can further be applied to analyze VCSEL systems and photonic waveguides.

• U. Bandelow, M. Radziunas, H. Wenzel, Self-consistent thermal--opto--electronic model for the dynamics in high-power semiconductor lasers, G. Rademacher, M. Mazur, eds., 2025 IEEE Photonics Society Summer Topicals Meeting Series (SUM), IEEE, 2025, (Chapter Published), DOI 10.1109/SUM65312.2025.11121789 .
  Abstract
  High-power broad-area diode lasers (BALs) generate significant heat, impacting performance. A 2+1 dimensional traveling wave (TW) model incorporates heating effects through an iterative coupling of electro-optical (EO) and heat-transport (HT) solvers. This method analyzes heat sources, temperature profiles, and thermally induced refractive index changes.

• A. Thayil, L. Ermoneit, M. Kantner, Epitaxial profile optimization for valley splitting enhancement in Si/Sige spin-qubits, IEEE Xplore, 2025, pp. 11185961/1--11185961/4, (Collection Published), DOI 10.1109/SISPAD66650.2025.11185961 .
  Abstract
  The presence of two nearly degenerate conduction band valley states is a critical challenge for electron spin-qubits in silicon since it can lead to leakage of quantum information. Several heuristic strategies have been proposed to enhance the energy gap between these two states, also referred to as the valley splitting. In this work, we focus on the systematic optimization of the valley splitting in Si/SiGe heterostructures through the precise engineering of the Ge atom distribution within the quantum well, i.e., epitaxial profile optimization. Our approach is based on envelope-function theory accounting for the effects of strain, compositional alloy disorder and non-trivial resonances. Our main result is a novel design, called the modulated wiggle well, that provides a reliably large deterministic enhancement of the valley splitting (assisted by shear strain). Previously proposed designs are recovered systematically as special cases of our constrained variational optimization problem.

Artikel in Referierten Journalen

• M. Zhuocheng, J. Yan, Z. Hongzheng, L.-Y. Peng, Stable time rondeau crystals in dissipative many-body systems, Phys. Rev. B., 112 (2025), pp. L140301/1--L140301/8, DOI 10.1103/2yzx-jfky .

• D. Kane, M. Radziunas, Chaotic semiconductor laser systems - bandwidth enhancement predicted by numerical simulations, Laser Physics Letters, 22 (2025), pp. 096201/1--096201/6, DOI 10.1088/1612-202X/ae027c .
  Abstract
  Numerical simulations using a traveling wave model are used to predict the radio frequency (rf) bandwidth and relative total rf power of chaotic output from a semiconductor laser (SL) with a delayed optical feedback system. By tailoring the linewidth enhancement factor (LEF) and nonlinear gain compression of the SL, improvements of a factor of two in the 80%-of-the-rf-power bandwidth, five in the rf bandwidth above 40 dB, and ten in the integrated rf power of the chaos, compared to values for a commercial-like SL, are predicted to be possible. The SL parameter values to be targeted will require device designers and fabricators to explore ways to decrease relaxation oscillation damping while, preferably, still achieving a high relaxation oscillation frequency. Higher values of LEF are a feature of poorer quality SLs of the past and can be expected to be achieved by reversion to past device recipes.

• R. Čiegis, S. Amiranashvili, On the stability and efficiency of high-order parallel algorithms for 3D wave problems, Mathematical Modelling and Analysis, 30 (2025), pp. 553-570, DOI 10.3846/mma.2025.23819 .
  Abstract
  In this work, we investigate the stability conditions for four new high-order ADI type schemes proposed to solve 3D wave equations with a non-constant sound speed coefficient. This analysis is mainly based on the spectral method, therefore a basic benchmark problem is formulated with a constant sound speed coefficient. For a case of general non-constant coefficient the stability analysis is done by using the energy method. Our main conclusion states that the selected ADI type schemes use different factorization operators (mainly due to the need to approximate the artificial boundary conditions on the split time levels), but the general structure of the stability factors are similar for all schemes and thus the obtained CFL conditions are also very similar. The second goal is to compare the accuracy and efficiency of the selected ADI solvers. This analysis also includes parallel versions of these schemes. Two schemes are selected as the most effective and accurate.

• N. Thomè, M. Wolfrum, K. Krischer, Hierarchical clustering in mean-field coupled Stuart--Landau oscillators, Chaos. An Interdisciplinary Journal of Nonlinear Science, 35 (2025), 083124, DOI 10.1063/5.0271508 .
  Abstract
  Clustered solutions in oscillator networks provide an important insight into how a system might diversify from a synchronous solution into spatiotemporal complex solutions. They can therefore form a link between fully synchronized and incoherent states. Despite their fundamental role in coupled oscillator dynamics, our understanding of how these clusters form and differentiate is still quite limited. Here, we study an ensemble of globally coupled Stuart--Landau oscillators and focus on the question of how 3-cluster solutions emerge from 2-cluster solutions and how the different 3-cluster solutions are organized in parameter space. We show that the arrangement of the clusters is dictated by a co-dimension 2 point, which we coin Type-II cluster singularity. Furthermore, our study points to a hierarchical structure of higher cluster solutions.

• H. Wenzel, E. Kuhn, B. King, M. Radziunas, Theory of the linewidth-power product of photonic-crystal surface-emitting lasers, IEEE J. Quantum Electron., 61 (2025), pp. 2400114/1--2400114/14, DOI 10.1109/JQE.2024.3524133 .

• J. Yan, Coherence and transients in nonlocally coupled dissipative kicked rotors, Physical Review E. Statistical, Nonlinear, and Soft Matter Physics, 112 (2025), pp. 054222/1--054222/11, DOI 10.1103/652d-6vhw .
  Abstract
  The dynamics of nonlocally coupled dissipative kicked rotors is rich and complex. In this study, we consider a network of rotors where each interacts equally with a certain range of its neighbors. We focus on the influence of the coupling strength and the coupling range, and show both analytically and numerically the critical transitions in the phase diagram, which include bifurcations of simple spatiotemporal patterns and changes in basin sizes of coherent states with different wavenumbers. We highlight that this diagram is fundamentally different from those found in other coupled systems such as in coupled logistic maps or Lorenz systems. Finally, we show an interesting domain-wall phenomenon in the coupled chaotic rotors, where a super-long transient interface state (partially regular and partially chaotic) is observed and can persist exponentially long as the coupling range increases up to a critical threshold.

• S. Amiranashvili, U. Bandelow, R. Čiegis, Stability of the additive splitting methods for the generalized nonlinear Schrödinger equation, Mathematics - Open Access Journal, 13 (2025), pp. 1301/1--1301/19, DOI 10.3390/math13081301 .
  Abstract
  Splitting methods provide an efficient approach to solving evolutionary wave equations, especially in situations where dispersive and nonlinear effects on wave propagation can be separated, as in the generalized nonlinear Schrödinger equation (GNLSE). However, such methods are explicit and can lead to numerical instabilities. We study these instabilities in the context of the GNLSE. Results previously obtained for multiplicative splitting methods are extended to additive splittings. An estimate of the largest possible integration step is derived and tested. The results are important when many solutions of GNLSE are needed, e.g., in optimization problems or statistical calculations.

• M. Radziunas, H. Wenzel, B. King, P. Crump, E. Kuhn, Dynamical simulations of single-mode lasing in large-area all-semiconductor PCSELs, , 50 (2025), pp. 1953--1956, DOI 10.1364/OL.553405 .
  Abstract
  We perform modeling and dynamic simulations of all-semiconductor photonic crystal surface- emitting lasers (PCSELs). A two-dimensional photonic crystal consists of a GaAs layer with InGaP features, repeating periodically in both lateral directions. In our dynamic simulations, we demon- strate for the first time that photonic crystals with large isosceles triangular features, having a base angle close to 71.5°, enable suppression of higher-order modes and achieve single-mode, high-quality lasing in large-area all-semiconductor PCSELs under moderate and even high pump levels.

Beiträge zu Sammelwerken

• R. Čiegis, S. Amiranashvili, On the stability and efficiency of high-order parallel algorithms for 3D wave problems, in: 28 th International Conference Mathematical Modelling and Analysis- Abstracts, R. Čiegis, ed., Vilnius Gediminas Technical University Scientific Book, 2025, pp. 31, DOI 10.3846/mma.2025-043-K .
  Abstract
  In this work, we investigate the stability conditions for four new high-order ADI type schemes proposed to solve 3D wave equations with a non-constant sound speed coefficient. This analysis is mainly based on the spectral method, therefore a basic benchmark problem is formulated with a constant sound speed coefficient. For a case of general non-constant coefficient the stability analysis is done by using the energy method. Our main conclusion states that the selected ADI type schemes use different factorization operators (mainly due to the need to approximate the artificial boundary conditions on the split time levels), but the general structure of the stability factors are similar for all schemes and thus the obtained CFL conditions are also very similar. The second goal is to compare the accuracy and efficiency of the selected ADI solvers. This analysis also includes parallel versions of these schemes. Two schemes are selected as the most effective and accurate.

Preprints, Reports, Technical Reports

• A. Thayil, L. Ermoneit, L.R. Schreiber, Th. Koprucki, M. Kantner, Optimization of Si/SiGe heterostructures for large and robust valley splitting in silicon qubits, Preprint no. 3249, WIAS, Berlin, 2025, DOI 10.20347/WIAS.PREPRINT.3249 .
  Abstract, PDF (7243 kByte)
  The notoriously low and fluctuating valley splitting is one of the key challenges for electron spin qubits in silicon (Si), limiting the scalability of Si-based quantum processors. In silicon-germanium (SiGe) heterostructures, the problem can be addressed by the design of the epitaxial layer stack. Several heuristic strategies have been proposed to enhance the energy gap between the two nearly degenerate valley states in strained Si/SiGe quantum wells (QWs), emphe.g., sharp Si/SiGe interfaces, Ge spikes or oscillating Ge concentrations within the QW. In this work, we develop a systematic variational optimization approach to compute optimal Ge concentration profiles that boost selected properties of the intervalley coupling matrix element. Our free-shape optimization approach is augmented by a number of technological constraints to ensure feasibility of the resulting epitaxial profiles. The method is based on an effective mass type envelope function theory accounting for the effects of strain and compositional alloy disorder. Various previously proposed heterostructure designs are recovered as special cases of the constrained optimization problem. Our main result is a novel heterostructure design we refer to as the emphmodulated wiggle well, which provides a large deterministic enhancement of the valley splitting along with a reliable suppression of the disorder-induced volatility. In addition, our new design offers a wide-range tunability of the valley splitting controlled by the vertical electric field, which offers new perspectives to engineer switchable qubits with on-demand adjustable valley splitting.

• N. Ciroth, A. Sala, R. Xue, L. Ermoneit, Th. Koprucki, M. Kantner, L.R. Schreiber, Numerical simulation of coherent spin-shuttling in a QuBus with charged defects, Preprint no. 3241, WIAS, Berlin, 2025, DOI 10.20347/WIAS.PREPRINT.3241 .
  Abstract, PDF (874 kByte)
  Recent advances in coherent conveyor-mode spin qubit shuttling are paving the way for large scale quantum computing platforms with qubit connectivity achieved by spin qubit shuttles. We developed a simulation tool to investigate numerically the impact of device imperfections on the spin-coherence of conveyor-mode shuttling in Si/SiGe. We simulate the quantum evolution of a mobile electron spin-qubit under the influence of sparse and singly charged point defects placed in the Si/SiGe heterostructure in close proximity to the shuttle lane. We consider different locations of a single charge defect with respect to the center of the shuttle lane, multiple orbital states of the electron in the shuttle with g-factor differences between the orbital levels, and orbital relaxation induced by electron-phonon interaction. With this simulation framework, we identify the critical defect density of charged point defects in the heterostructure for conveyor-mode spin qubit shuttle devices and quantify the impact of a single defect on the coherence of a qubit.

• M. Radziunas, D.M. Kane, Low-frequency fluctuations in semiconductor lasers with delayed optical feedback, Preprint no. 3226, WIAS, Berlin, 2025, DOI 10.20347/WIAS.PREPRINT.3226 .
  Abstract, PDF (5499 kByte)
  Low-frequency fluctuations in a semiconductor laser with optical feedback system are analyzed with a traveling wave model, and the concepts of instantaneous and compound cavity modes. Compound-cavity mode curves, including their height and width characteristics in the frequency/carrier-density-offset plane, provide good estimates of parameter ranges where low- frequency fluctuations occur. These ranges cover a larger part of the parameter space than is commonly realized.

• V. Iachkula, D.A. Dolinina, A.G. Vladimirov, G. Huyet, Coherence properties of Kerr frequency combs under noisy injection and optical feedback, Preprint no. 3225, WIAS, Berlin, 2025, DOI 10.20347/WIAS.PREPRINT.3225 .
  Abstract, PDF (2718 kByte)
  Kerr frequency combs in high-Q optical microresonators hold great promise for precision metrology, high-speed communications, and low-noise photonics. Understanding their coherence properties is essential for realizing compact, energy-efficient, and low-noise light sources. The in- terplay between pulsed injection, intrinsic and external noise, and optical feedback plays a central role in achieving highly coherent microcombs. Here, we study the coherence dynamics of Kerr frequency combs under continuous-wave (CW) and pulsed pumping within the framework of the Lugiato?Lefever equation. Using asymptotic analysis, we quantify the phase noise and timing jit- ter induced by pump source fluctuations and thermal noise. Numerical simulations further reveal comb degradation due to CW pump noise, while the inclusion of optical feedback restores the comb and narrows the linewidth through a mechanism analogous to that of external-cavity lasers

• J. Yan, Bifurcations and intermittency in coupled dissipative kicked rotors, Preprint no. 3214, WIAS, Berlin, 2025, DOI 10.20347/WIAS.PREPRINT.3214 .
  Abstract, PDF (5275 kByte)
  We investigate the emergence of complex dynamics in a system of coupled dissipative kicked rotors and show that critical transitions can be understood via bifurcations of simple states. We study multistability and bifurcations in the single rotor model, demonstrating how these give rise to a variety of coexisting spatial patterns in a coupled system. A combined order parameter is introduced to characterize different spatial patterns and to reveal the coexistence of chaotic and regular attractors. Finally, we illustrate an intermittent phenomenon near the onset of chaos.

• L. Mertenskötter, J. Riebesehl, W. Stannat, W. Pohlandt, W. Kilian, Extended Kalman smoothing of free spin precession signals for precise magnetic field determination, Preprint no. 3196, WIAS, Berlin, 2025, DOI 10.20347/WIAS.PREPRINT.3196 .
  Abstract, PDF (1414 kByte)
  We present a novel application of the Extended Kalman Smoother (EKS) for high-precision frequency estimation from free spin precession signals of polarized 3^He. Traditional approaches often rely on nonlinear least-squares fitting, which can suffer from limited robustness to signal decay and time-dependent frequency shifts. By contrast, our EKS-based method captures both amplitude and frequency variations with minimal tuning, adapting automatically to fluctuations via an expectation-maximization algorithm. We benchmark the technique in extensive simulations that emulate realistic spin precession signals with exponentially decaying amplitudes and noisy frequency drifts. Compared to least- squares fits with fixed block lengths, EKS systematically reduces estimation errors, particularly when frequencies evolve or signal-to-noise ratios are moderate to high. We further validate these findings with experimental data from a free-precession decay 3^He magnetometer. Our results indicate that EKS-based analysis can substantially improve precision in nuclear magnetic resonance-based magnetometry, where accurate frequency estimation underpins abso- lute field determinations. This versatile approach promises to enhance the stability and accuracy of future high-precision measurements

• U. Bandelow, M. Radziunas, H. Wenzel, Self-consistent thermal-opto-electronic model for the dynamics in high-power semiconductor lasers, Preprint no. 3179, WIAS, Berlin, 2025, DOI 10.20347/WIAS.PREPRINT.3179 .
  Abstract, PDF (330 kByte)
  High-power broad-area diode lasers (BALs) generate significant heat, impacting performance. A 2+1 dimensional traveling wave (TW) model incorporates heating effects through an iterative coupling of electro-optical (EO) and heat-transport (HT) solvers. This method analyzes heat sources, temperature profiles, and thermally induced refractive index changes.

Vorträge, Poster

• M. Wolfrum, Triplet synchronization in higher-order networks, Mathematical Sciences Seminar Series, University College Cork, Ireland, February 26, 2026.

• L. Kuen, Numerical study of time dependent dynamical simulations of PCSELs, Nonlinear Dynamics in Semiconductor Lasers 2025, Berlin, June 16 - 18, 2025.

• L. Ermoneit, Coherent transport of semiconductor spin-qubits: Modeling, simulation and optimal control (online talk), MATH+ Spotlight talks, January 29, 2025.

• L. Ermoneit, Optimal control for coherent electron shuttling of a SiGe-quantum bus in the presence of charged defects, DPG-Frühjahrstagung der Sektion Kondensierte Materie (SKM), March 16 - 21, 2025, Universität Regensburg.

• L. Kuen, Numerical study of spatio-temporal dynamics in all-semiconductor PCSELs, NUSOD 2025, September 15 - 19, 2025, Lodz University of Technology, Poland.

• J. Yan, Spatial and temporal patterns in coupled dissipative kicked rotor systems, 29th Conference of Statistical Physics STATPHYS29, Florence, Italy, July 13 - 18, 2025.

• J. Yan, Spatiotemporal dynamics and bifurcations-- in a network of coupled dissipative kicked rotors, XLV Dynamics Days Europe 2025, June 23 - 27, 2025, Aristotele University of Thessaloniki, Greece.

• U. Bandelow, Instabilities in pulse propagation described by generalized nonlinear Schrödinger equations, NUSOD 2025, September 15 - 19, 2025, Lodz University of Technology, Poland.

• U. Bandelow, Numerical instabilities in nonlinear pulse propagation, Australian and New Zealand Conference on Optics and Photonics 2025 (ANZCOP), University of Auckland, New Zealand, December 10, 2025.

• U. Bandelow, Self-consistent thermal-opto-electronic model for the dynamics in high-power semiconductor lasers, IEEE Summer Topicals Meeting, July 21 - 23, 2025, IEEE Photonics Society, Berlin.

• U. Bandelow, Unusual wave-mixing processes in the context of modulation instability, 7th International Conference on Photonics Research, April 8 - 14, 2025, Convention Centre of the Liberty Hotels Lykia /Oludeniz, Mugla, Turkey.

• U. Bandelow, Unusual wave-mixing processes in the context of the modulation instability, Colloquium, University of Auckland, Departement of Physics, New Zealand, December 17, 2025.

• TH. Koprucki, Semiconductor modeling and simulation: Bridging mathematics, physics, and engineering, Award Ceremony for IHP's Junior Research Group, Leibniz-Institut für innovative Mikroelektronik, Frankfurt (Oder), June 3, 2025.

• M. Radziunas, Dynamic simulations of single-mode lasing in large emission area all-semiconductor PCSELs, International Workshop on PCSELs 2025, November 10 - 12, 2025, Glasgow, UK.

• M. Radziunas, Modeling and analysis of dynamics in semiconductor lasers, international Nano-Optoelectronics Workshop (iNOW'25), July 23 - 28, 2025, Wroclaw, Poland.

• M. Radziunas, Modeling and analysis of nonlinear dynamics in semiconductor lasers, The 28th International Conference Mathematical Modelling and Analysis MMA2025, May 26 - 29, 2025, Druskininkai, Lithuania.

• A. Thayil, Epitaxial profile optimization for deterministic valley splitting enhancement in Si/SiGe SpinQubits, International Conference on Simulation of Semiconductor Processes and Devices (SISPAD), Grenoble, France, September 24 - 26, 2025.

• A. Thayil, Optimization of valley splitting in Si/SiGe spin--qubits, APS Global Physics Summit 2025, March 16 - 21, 2025, Anaheim, USA.

• M. Wolfrum, Delay-differential equations in the limit of large delay, ICMC Summer Meeting on Differential Equations, February 3 - 5, 2025, Universidade de São Paulo, Instituto de ciências matemáticas e de computação, Sao Carlos, Brazil.

• M. Wolfrum, Hypernetworks induce hyperlocking, XLV Dynamics Days Europe 2025, June 23 - 27, 2025, Aristotele University of Thessaloniki, Greece, June 24, 2025.

• M. Wolfrum, Localized states and solitons in delay-differential equations with large delay (online talk), Nonlinear Evolutionary Dynamics (Online Seminar), National Center for Theoretical Sciences (NCTS), National Tsing Hua University, Hsinchu, Taiwan, Province Of China, February 26, 2025.

• J. Yan, Spatiotemporal dynamics and critical transitions in coupled dissipative systems, ``Complex Systems''. The official seminar of the Centre for Complex Systems., Queen Mary University of London, UK, November 6, 2025.