51 results
Search Results
Now showing 1 - 10 of 51
- ItemSemiconductor laser linewidth theory revisited(Basel : MDPI, 2021) Wenzel, Hans; Kantner, Markus; Radziunas, Mindaugas; Bandelow, UweMore 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 self-contained 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 time-dependent coupled-wave 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 (K-factor) and the effective α-factor including the effects of nonlinear gain (gain compression) and refractive index (Kerr effect), gain dispersion, and longitudinal spatial hole burning in multi-section cavity structures. The effect of linewidth narrowing due to feedback from an external cavity often described by the so-called 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 two-section distributed Bragg reflector laser.
- ItemEfficient Current Injection Into Single Quantum Dots Through Oxide-Confined p-n-Diodes(New York, NY : IEEE, 2016) Kantner, Markus; Bandelow, Uwe; Koprucki, Thomas; Schulze, Jan-Hindrik; Strittmatter, Andre; Wunsche, Hans-JurgenCurrent injection into single quantum dots embedded in vertical p-n-diodes featuring oxide apertures is analyzed in the low-injection regime suitable for single-photon emitters. The experimental and theoretical evidence is found for a rapid lateral spreading of the carriers after passing the oxide aperture in the conventional p-i-n-design. By an alternative design employing p-doping up to the oxide aperture, the current spreading can be suppressed resulting in an enhanced current confinement and increased injection efficiencies, both, in the continuous wave and under pulsed excitation.
- ItemDynamical regimes in a monolithic passively mode-locked quantum dot laser(Berlin : Weierstraß-Institut für Angewandte Analysis und Stochastik, 2010) Vladimirov, Andrei; Bandelow, Uwe; Fiol, Gerrit; Arsenijevi´c, Dejan; Kleinert, Moritz; Bimberg, Dieter; Pimenov, Alexander; Rachinskii, DmitriiOperation regimes of a two section monolithic quantum dot (QD) mode-locked laser are studied experimentally and theoretically, using a model that takes into account carrier exchange between QD ground state and 2D reservoir of a QD-in-a-well structure, and experimentally. It is shown analytically and numerically that, when the absorber section is long enough, the laser exhibits bistability between laser off state and different mode-locking regimes. The Q-switching instability leading to slow modulation of the mode-locked pulse peak intensity is completely eliminated in this case. When, on the contrary, the absorber length is rather short, in addition to usual Q-switched mode-locking, pure Q-switching regimes are predicted theoretically and observed experimentally.
- 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.
- ItemDispersion of nonlinear group velocity determines shortest envelope solitons(Berlin : Weierstraß-Institut für Angewandte Analysis und Stochastik, 2011) Amiranashvili, Shalva; Bandelow, Uwe; Akhmediev, Nail N.We demonstrate that a generalized nonlinear Schrödinger equation (NSE), that includes dispersion of the intensity-dependent group velocity, allows for exact solitary solutions. In the limit of a long pulse duration, these solutions naturally converge to a fundamental soliton of the standard NSE. In particular, the peak pulse intensity times squared pulse duration is constant. For short durations this scaling gets violated and a cusp of the envelope may be formed. The limiting singular solution determines then the shortest possible pulse duration and the largest possible peak power. We obtain these parameters explicitly in terms of the parameters of the generalized NSE.
- ItemPersistence of rouge waves in extended nonlinear Schrödinger equations : integrable Sasa-Satsuma case(Berlin : Weierstraß-Institut für Angewandte Analysis und Stochastik, 2012) Bandelow, Uwe; Akhmediev, Nail N.We present the lowest order rogue wave solution of the Sasa-Satsuma equation (SSE) which is one of the integrable extensions of the nonlinear Schrödinger equation (NLSE). In contrast to the Peregrine solution of the NLSE, it is significantly more involved and contains polynomials of fourth order rather than second order in the corresponding expressions. The correct limiting case of Peregrine solution appears when the extension parameter of the SSE is reduced to zero.
- ItemSolitons on a background, rogue waves, and classical soliton solutions of Sasa-Satsuma equation(Berlin : Weierstraß-Institut für Angewandte Analysis und Stochastik, 2013) Bandelow, Uwe; Akhmediev, NailWe present the most general multi-parameter family of a soliton on a background solutions to the Sasa-Satsuma equation. The solution contains a set of several free parameters that control the background amplitude as well as the soliton itself. This family of solutions admits nontrivial limiting cases, such as rogue waves and classical solitons, that are considered in detail.
- ItemTime-dependent simulation of thermal lensing in high-power broad-area semiconductor lasers(Berlin : Weierstraß-Institut für Angewandte Analysis und Stochastik, 2019) Zeghuzi, Anissa; Wünsche, Hans-Jürgen; Wenzel, Hans; Radziunas, Mindaugas; Fuhrmann, Jürgen; Klehr, Andreas; Bandelow, Uwe; Knigge, AndreaWe propose a physically realistic and yet numerically applicable thermal model to account for short and long term self-heating within broad-area lasers. Although the temperature increase is small under pulsed operation, a waveguide that is formed within a few-ns-long pulse can result in a transition from a gain-guided to an index-guided structure, leading to near and far field narrowing. Under continuous wave operation the longitudinally varying temperature profile is obtained self-consistently. The resulting unfavorable narrowing of the near field can be successfully counteracted by etching trenches.
- ItemEfficient coupling of electro-optical and heat-transport models for broad-area semiconductor lasers(Berlin : Weierstraß-Institut für Angewandte Analysis und Stochastik, 2018) Radziunas, Mindaugas; Fuhrmann, Jürgen; Zeghuzi, Anissa; Wünsche, Hans-Jürgen; Koprucki, Thomas; Brée, Carsten; Wenzel, Hans; Bandelow, UweIn this work, we discuss the modeling of edge-emitting high-power broad-area semiconductor lasers. We demonstrate an efficient iterative coupling of a slow heat transport (HT) model defined on multiple vertical-lateral laser cross-sections with a fast dynamic electro-optical (EO) model determined on the longitudinal-lateral domain that is a projection of the device to the active region of the laser. Whereas the HT-solver calculates temperature and thermally-induced refractive index changes, the EO-solver exploits these distributions and provides time-averaged field intensities, quasi-Fermi potentials, and carrier densities. All these time-averaged distributions are used repetitively by the HT-solver for the generation of the heat sources entering the HT problem solved in the next iteration step.
- ItemTraveling wave analysis of non-thermal far-field blooming in high-power broad-area lasers(Berlin : Weierstraß-Institut für Angewandte Analysis und Stochastik, 2019) Zeghuzi, Anissa; Radziunas, Mindaugas; Wünsche, Hans-Jürgen; Koester, Jan-Philipp; Wenzel, Hans; Bandelow, Uwe; Knigge, AndreaWith rising current the lateral far-field angle of high-power broad-area lasers widens (far-field blooming) which can be partly attributed to non-thermal effects due to carrier induced refractive index and gain changes that become the dominant mechanism under pulsed operation. To analyze the non-thermal contribution to far-field blooming we use a traveling wave based model that properly describes the injection of the current into and the diffusion of the carriers within the active region. Although no pre-assumptions regarding the modal composition of the field is made and filamentation is automatically accounted for, the highly dynamic time-dependent optical field distribution can be very well represented by only few modes of the corresponding stationary waveguide equation obtained by a temporal average of the carrier density and field intensity. The reduction of current spreading and spatial holeburning by selecting proper design parameters can substantially improve the beam quality of the laser.