Edeltraud Gehrig

Spatio-Temporal Dynamics and Quantum Fluctuations in Semiconductor Lasers

Introduction.- Advanced Semiconductor Lasers.- Semiconductor Laser Theory.- Spatio-Temporal Dynamics of In-Plane Lasers.- Polarization Dynamics of Vertical-Cavity Surface-Emitting Lasers.- Master-Oscillator Power-Amplifier Systems.- Conclusion.- References.- Subject Index.

Pulse Amplification and Spatio-Spectral Hole-Burning in Inhomogeneously Broadened Quantum-Dot Semiconductor Optical Amplifiers

We present a theoretical model for the description of carrier and light dynamics in a quantum dot semiconductor optical amplifier that includes the inhomogeneous broadening of the quantum dots (QDs) via a spatially resolved statistical approach. The model is based on Maxwell-Bloch equations and takes into account the scattering of charge carriers between 2-D wetting layer states and bound quantum dot states, the amplification, and the wave-guiding of the light fields in the optical cavity. Simulations allow the analysis of the occupation probability of the quantum dot levels at steady state and during optical excitation by a femtosecond pulse. The influence of homogeneously and inhomogeneously broadened quantum dot media on spatial and spectral hole burning is revealed and discussed. It is shown that spatially varying dot properties lead to the reshaping of the optical pulse in the active medium.

Dynamic Spatiotemporal Speed Control of Ultrashort Pulses in Quantum-Dot SOAs

We present theoretical and experimental results on the propagation of ultrashort pulses in quantum-dot (QD) laser amplifiers. The propagation time of the light pulses is controlled by the pulse itself (self-induced speed control) or by injection of a second pump pulse (external speed control). Our simulations on the basis of spatially and temporally resolved QD Maxwell-Bloch equations reveal that the excitation and relaxation dynamics induced by the propagating pulse or a pump pulse within the active charge carrier system leads to a complex gain and index dynamics that may either speed up or slow down the propagating light pulse. The physical effects allowing for the dynamic speed control could be ascribed to complex (coherent and incoherent) level dynamics leading to dynamic gain saturation and index dispersion. The dependence of the propagation time on injection current density and pulse energy is discussed. The numerical results of pulse reshaping and propagation times in the gain and absorptions regime are compared to experimental results

Mode-locking in broad-area semiconductor lasers enhanced by picosecond-pulse injection

We present combined experimental and theoretical investigations of the picosecond emission dynamics of broad-area semiconductor lasers (BALs). We enhance the weak longitudinal self-mode-locking that is inherent to BALs by injecting a single optical 50-ps pulse, which triggers the output of a distinct regular train of 13-ps pulses. Modeling based on multimode Maxwell-Bloch equations illustrates how the dynamic interaction of the injected pulse with the internal laser field efficiently couples the longitudinal modes and synchronizes the output across the laser stripe. Thus, our results reveal insight into the complex interplay between lateral and longitudinal dynamics in BALs, at the same time indicating their potential for short optical pulse generation.

Spatio-temporal dynamics of light amplification and amplified spontaneous emission in high-power tapered semiconductor laser amplifiers

We investigate the spatio-temporal light field dynamics in high-power semiconductor lasers with continuous-wave optical injection. The amplification processes that characterize this system occur during the propagation of the injected signal within the active area and can be attributed to spatially dependent gain and refractive index variations. Those are shown to be determined by dynamic interactions between the light fields and the active charge-carrier plasma. This microscopic light-matter-coupling is described by a spatially resolved microscopic theory based on Maxwell-Bloch-Langevin equations taking into account many-body interactions, energy transfer between the carrier and phonon system and, in particular, the spatio-temporal interplay of stimulated and amplified spontaneous emission and noise. Results of our numerical modeling visualize the dynamic spatio-spectral beam shaping experienced by the propagating light in amplifiers of tapered geometry. This reveals the microscopic physical processes that are responsible for the particular amplitude and spatial shape of the light beam at the output facet.

Femtosecond dynamics of active semiconductor waveguides-microscopic analysis and experimental investigations

We present theoretical and experimental results of nonlinear amplification and propagation of short optical pulses in Fabry–Perot semiconductor lasers. The theoretical description is based on spatially resolved Maxwell–Bloch–Langevin equations that take into account the spatially varying light-field dynamics including counterpropagation, diffraction, self-focusing, and the microscopic carrier dynamics including carrier heating and carrier relaxation. Femtosecond pump–probe measurements using upconversion and femtosecond-resolved pump–probe measurements and frequency-resolved optical gating on a Fabry–Perot laser allow a combined analysis of the transmitted pulses in real time and the spectral domain. The experimental results are compared with the microscopically calculated gain and index distributions, pulse shapes, and optical spectra. In order to assess the full potential of semiconductor lasers and amplifiers, a quantitative measurement and understanding of amplitude and phase dynamics is required. The computer simulations of the ultrashort dynamics of semiconductor waveguides with optical injection of light pulses provide insight into the dynamic spectral gain and index changes responsible for frequency drifts and self-phase modulation, visualization of propagation effects, and a time- and frequency-resolved analysis of the amplified light pulses.

Photonics of Quantum-Dot Nanomaterials and Devices: Theory and Modelling

Theory: Hierarchy of Microscopic and Phenomenological Models Light Meets Matter I: Microscopic Carrier Effects and Fundamental Light-Matter Interaction Light Meets Matter II: Dynamic Space-Time Coupling Performance and Characterisation of Quantum Dot Lasers and Amplifiers Nonlinear Light-Dynamics and Pulse Amplification in Active Dot Materials High-Speed Dynamics Noise and Disorder on the Nanoscale Luminescence Properties of Quantum Dot Microcavity Lasers.

Dynamic spatiotemporal pulse shaping in two-photon active biomolecular media

The propagation of ultrashort light pulses in two-photon media is investigated on the basis of a density-matrix formalism for the molecular levels and a wave equation for the dynamics of the light fields. The simulation shows that the dynamic light-matter coupling and level dynamics lead to saturation effects and space-dependent pulse shaping that determine the dynamic response of the molecular medium.

Dynamics of High-Power Diode Lasers

This review gives an overview of the theory and discusses aspects of space-time modeling of high-power diode lasers. The dynamic interaction between the optical fields, the charge carriers, and the interband polarization are described on the basis of microscopic spatially resolved Maxwell—Bloch equations for spatially inhomogeneous semiconductor lasers. Thereby the influence of dynamic internal laser effects such as diffraction, self-focusing, scattering, carrier transport, and heating on the performance of broad-area or tapered amplifiers as well as the individual device properties (i.e. its epitaxial structure and geometry) are self-consistently considered.

Experimental and theoretical study of the frequency response of laterally coupled diode lasers

We report on the combined theoretical and experimental observation of an increase of the small signal modulation response of a Laterally Coupled Diode Laser (LCDL) system beyond its relaxation oscillation frequency. The increase is achieved by means of lateral coupling. Theoretical approaches are presented to explain the experimental observations obtained with these LCDL devices. Our results shed light on the principle of diode laser coupling an open up new perspectives for LCDL for high-speed optical communications.