Joerg Hader

Highly strained InGaAs∕GaAs multiwatt vertical-external-cavity surface-emitting laser emitting around 1170nm

We develop and demonstrate a multiwatt highly strained InGaAs∕GaAs vertical-external-cavity surface-emitting laser with a free lasing wavelength of around 1170nm. This laser can be tuned from ∼1147to∼1197nm. This low-cost compact wavelength agile laser can potentially provide high-power coherent light in a wide yellow-orange band by the intracavity frequency doubling.

Microscopic modeling of GalnNAs semiconductor lasers

We calculate microscopically the gain and absorption, linewidth enhancement factor and carrier capture times for a GaInNAs/GaAs quantum-well laser operating in the 1.3 micrometers wavelength regime. The results are compared to those for an InGaAsP/InP and an InGaAlAs/InP structure with similar fundamental transition energies. The much higher confinement for carriers in the GaInNAs quantum well is shown to lead to larger gain bandwidths and, for low to moderate carrier densities, to lower linewidth enhancement factors than for the later two material systems. On the other hand, the high depth of the wells leads to longer carrier capture times in GaInNAs/GaAs.

Modeling high-power semiconductor lasers: from microscopic physics to device applications

A robust, modular and comprehensive simulation model, built on a first-principles microscopic physics basis, includes the fully time-dependent and spatially resolved internal optical, carrier and temperature fields within an arbitrary geometry edge-emitting high-power semiconductor laser device. The simulator is designed to run interactively on a multi- processor shared memory graphical supercomputer by utilizing a highly efficient algorithm running in parallel over multiple CPUs. The experimentally validated semiconductor optical response is computed using a microscopic approach that includes the relevant bandstructure of the Quantum Well and confining barrier regions together with a fully quantum mechanical many-body calculation that takes all occupied bands into account. The latter quantity is introduced into the simulator via a multidimensional look-up table that captures the local dependence of the gain and refractive index of the structure over a broad range of frequencies and carrier densities. The simulator is designed in a modular form so as to be able to include differing device geometries (broad area, flared, multiple contacts, arrays, ..), filters (DBR or DFB grating sections), index/gain-guiding, temperature and current profiles and so on. Results will be presented for both broad area and MOPA devices.

Extraction of semiconductor microchip differential gain by use of optically pumped semiconductor laser

The small-signal modulation response of a vertical external cavity surface emitting laser is analyzed to determine its resonance frequency in relation to photon density, allowing nondestructive extraction of characteristic parameters of chips, such as internal loss and differential gain.

Integration of microscopic gain modeling into a commercial laser simulation environment

We demonstrate the integration of microscopic gain calculation into the laser design tool LaserMOD, which is derived from the Minilase II simulator. A microscopic many body theory of the semiconductor allows for the accurate modeling of the spectral characteristics of the material gain. With such a model, the energetic position of the gain peak, the collision broadening, and therefore, the absolute magnitude of the gain can be predicted based solely on material parameters [2]. In contrast, many simpler approaches rely on careful calibration of model parameters requiring additional effort due to fabrication of samples and experimental studies. In our full scale laser simulation multi dimensional carrier transport, interaction with the optical field via stimulated and spontaneous emission, as well as the optical field itself is computed self consistently. We demonstrate our approach on an example of a Fabry-Perot laser structure with GaInAsP multiple quantum wells for 1.55 μm emission wavelength.

Modeling and Experimental Result Analysis for High Power VECSELs

We present a comparison of experimental and microscopically based model results for optically pumped vertical external cavity surface emitting semiconductor lasers. The quantum well gain model is based on a quantitative ab-initio approach that allows calculation of a complex material susceptibility dependence on the wavelength, carrier density and lattice temperature. The gain model is coupled to the macroscopic thermal transport, spatially resolved in both the radial and longitudinal directions, with temperature and carrier density dependent pump absorption. The radial distribution of the refractive index and gain due to temperature variation are computed. Thermal managment issues, highlighted by the experimental data, are discussed. Experimental results indicate a critical dependence of the input power, at which thermal roll-over occurs, on the thermal resistance of the device. This requires minimization of the substrate thickness and optimization of the design and placement of the heatsink. Dependence of the model results on the radiative and non-radiative carrier recombination lifetimes and cavity losses are evaluated.

Coherent electric-field effects in semiconductors

A microscopic many-body theory is presented which allows one to compute the linear and nonlinear optical properties of semiconductor superlattices in the presence of static and time-dependent electric fields applied in the growth direction. For static fields the Bloch-oscillation dynamics, the role of Coulomb effects, carrier relaxation, phonon scattering, and inter- and intraband polarization dephasing is analyzed. The observability of dynamic localization using optical spectroscopy is discussed for alternating applied fields.

VCESL Theory & Experiment

Ultrafast nonequilibrium kinetic hole-burning in electron/hole carrier distributions dictates the outcome of short pulse generation in inverted semiconductor quantum wells, makes the gain picture redundant and agrees well with recent experimental observations.

Quantum design of active semiconductor materials for targeted wavelengths : A predictive design tool for edge emitters and OPSLs

Performance metrics of every class of semiconductor amplifier or laser system depend critically on semiconductor QW optical properties such as photoluminescence (PL), gain and recombination losses (radiative and nonradiative). Current practice in amplifier or laser design assumes phenomenological parameterized models for these critical optical properties and has to rely on experimental measurement to extract model fit parameters. In this tutorial, I will present an overview of a powerful and sophisticated first-principles quantum design approach that allows one to extract these critical optical properties without relying on prior experimental measurement. It will be shown that an end device L-I characteristic can be predicted with the only input being intrinsic background losses, extracted from cut-back experiments. We will show that textbook and literature models of semiconductor amplifiers and lasers are seriously flawed.

Optical Gain Enhancement in VECSELs with Photonic-Band-Edge Active Region Design

Using a numerical model we evaluate the enhancement of the optical gain due to the small group-velocity of the light near the band-edge of a multiple quantum well periodic structure of an optically pumped VECSEL.