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- ItemSampling techniques applicable for the characterization of the quality of self pulsations in semiconductor lasers(Berlin : Weierstraß-Institut für Angewandte Analysis und Stochastik, 2002) Radziunas, MindaugasThe aim of the presented report is to demonstrate how the sampling techniques can be used to characterize the quality of self pulsations in a multi-section semiconductor laser and the synchronization of self pulsations with an optical or electrical periodically modulated signal. The developed tools are described and some examples are given.
- ItemMathematical modeling and numerical simulations of diode lasers with micro-integrated external resonators(Berlin : Weierstraß-Institut für Angewandte Analysis und Stochastik, 2016) Radziunas, MindaugasThis report summarizes our scientific activities within the project MANUMIEL (BMBF Program “Förderung der Wissenschaftlich-Technologischen Zusammenarbeit (WTZ) mit der Republik Moldau”, FKZ 01DK13020A). Namely, we discuss modeling of external cavity diode lasers, numerical simulations and analysis of these devices using the software package LDSL-tool, as well as the development of this software.
- ItemTraveling wave modeling of dynamics in semiconductor ring lasers(Berlin : Weierstraß-Institut für Angewandte Analysis und Stochastik, 2008) Radziunas, MindaugasWe use the traveling wave model for simulating and analyzing nonlinear dynamics of complex semiconductor ring laser devices. This modeling allows to consider temporal-spatial distributions of the counter-propagating slowly varying optical fields and the carriers, what can be important when studying non-homogeneous ring cavities, propagation of short pulses or fast switching. By performing numerical integration of the model equations we observe several dynamic regimes as well as transitions between them. The computation of ring cavity modes explains some peculiarities of these regimes.
- ItemStripe-array diode-laser in an off-axis external cavity : theory and experiment(Berlin : Weierstraß-Institut für Angewandte Analysis und Stochastik, 2009) Jechow, Andreas; Lichtner, Mark; Menzel, Ralf; Radziunas, Mindaugas; Skoczowsky, Danilo; Vladimirov, AndreiStripe-array diode lasers naturally operate in an anti-phase supermode. This produces a sharp double lobe far field at angles α depending on the period of the array. In this paper a 40 emitter gain guided stripe-array laterally coupled by off-axis filtered feedback is investigated experimentally and numerically. We predict theoretically and confirm experimentally that at doubled feedback angle 2α a stable higher order supermode exists with twice the number of emitters per array period. The theoretical model is based on time domain traveling wave equations for optical fields coupled to the carrier density equation taking into account diffusion of carriers. Feedback from the external reflector is modeled using Fresnel integration.
- ItemMode transitions in distributed-feedback tapered master-oscillator power-amplifier(Berlin : Weierstraß-Institut für Angewandte Analysis und Stochastik, 2008) Radziunas, Mindaugas; Tronciu, Vasile Z.; Bandelow, Uwe; Lichtner, Mark; Spreemann, Martin; Wenzel, HansTheoretical and experimental investigations have been carried out to study the spectral and spatial behavior of monolithically integrated distributed-feedback tapered master-oscillators power-amplifiers emitting around 973 nm. Introduction of self and cross heating effects and the analysis of longitudinal optical modes allows us to explain experimental results. The results show a good qualitative agreement between measured and calculated characteristics.
- ItemImproving the stability of distributed-feedback tapered master-oscillator power-amplifiers(Berlin : Weierstraß-Institut für Angewandte Analysis und Stochastik, 2009) Tronciu, Vasile Z.; Lichtner, Mark; Radziunas, Mindaugas; Bandelow, U.; Wenzel, H.We report theoretical results on the wavelength stabilization in distributed-feedback master-oscillator power-amplifiers which are compact semiconductor laser devices capable of emitting a high brilliance beam at an optical power of several Watts. Based on a traveling wave equation model we calculate emitted optical power and spectral maps in dependence on the pump of the power amplifier. We show that a proper choice of the Bragg grating type and coupling coefficient allows to optimize the laser operation, such that for a wide range of injection currents the laser emits a high intensity continuous wave beam.
- ItemBroadening of mode-locking pulses in quantum-dot semiconductor lasers : simulation, analysis and experiments(Berlin : Weierstraß-Institut für Angewandte Analysis und Stochastik, 2010) Radziunas, Mindaugas; Vladimirov, Andrei G.; Viktorov, Evgeny A.; Fiol, Gerrit; Schmeckebier, Holger; Bimberg, DieterWe consider a mode-locked quantum-dot edge-emitting semiconductor laser consisting of a reverse biased saturable absorber and a forward biased amplifying section. To describe the dynamics of this laser we use the traveling wave model taking into account carrier exchange processes between a reservoir and the quantum dots. A comprehensive parameter study is presented and an analysis of mode-locking pulse broadening with an increase of injection current is performed. The results of our theoretical analysis are supported by experimental data demonstrating a strong pulse asymmetry in a monolithic two section quantum dot mode-locked laser
- ItemTunable semiconductor ring laser with filtered optical feedback: Traveling wave description and experimental validation(Berlin : Weierstraß-Institut für Angewandte Analysis und Stochastik, 2017) Radziunas, Mindaugas; Khoder, Mulham; Tronciu, Vasile; Danckaert, Jan; Verschaffelt, GuyWe study experimentally and theoretically a semiconductor ring laser with four filtering channels providing filtered delayed optical feedback. To describe and analyze the wavelength selection and tuning in this device, we exploit the traveling-wave model determining the evolution of optical fields and carrier density along the ring cavity and filtering branches. The numerical results agree with the experimental observations: we can reproduce the wavelength tuning, the multiple wavelength emission, and the wavelength switching speed measured in these devices. The traveling-wave model allows us to study in detail the effect of the different laser parameters and can be useful for designing the future devices.
- ItemA multi-mode delay differential equation model for lasers with optical feedback(Berlin : Weierstraß-Institut für Angewandte Analysis und Stochastik, 2016) Radziunas, MindaugasIn this paper, we discuss the relations between the spatially-distributed traveling wave, Lang-Kobayashi, and a new multi-mode delay differential equation models for Fabry-Perot type semiconductor diode lasers with an external optical feedback. All these models govern the dynamics of the slowly varying complex amplitudes of the optical fields and carrier density. To compare the models, we calculate the cavity modes determined by the threshold carrier density and optical frequency of the steady states in all three models. These calculations show that the Lang-Kobayashi type model is in good agreement with the traveling wave model only for the small feedback regimes, whereas newly derived multi-mode delay differential equation model remains correct even at moderate and large optical feedback regimes.
- ItemTraveling wave modeling of nonlinear dynamics in multisection semiconductor lasers(Berlin : Weierstraß-Institut für Angewandte Analysis und Stochastik, 2016) Radziunas, MindaugasA hierarchy of 1 (time) + 1 (space) dimensional first-order partial differential equation (traveling wave) models is used for a description of dynamics in individual semiconductor lasers, various multisection semiconductor lasers, and coupled laser systems. Consequent modifications of the basic traveling wave model allow for taking into account different physical effects such as the gain dispersion, the thermal detuning, the spatial hole burning of carriers, the nonlinear gain saturation, or various carrier exchange processes in quantum dot lasers. For illustration, the model was applied for simulations of dynamics in complex ring laser with four branches of filtered feedback. Finally, several advanced techniques for model analysis such as calculation of instantaneous optical modes, finding of steady states, and numerical continuation and bifurcation analysis of the model equations were discussed and illustrated by example simulations.