FIBER OPTIC SERVICES
LaserMOD™ Product Overview
LaserMOD™ is a photonic device design tool for simulating optical and electronic properties of semiconductor lasers. LaserMOD combines the most versatile, user-friendly, and easy to learn GUI in the market, with a powerful, robust simulation engine, which provides for the self-consistent solution of electro-thermal transport and optical field propagation. Device applications currently include edge emitting, such as Fabry-Perot type, and vertical surface emitting (VCSEL) lasers. Resulting from ongoing development effort, future releases of this tool will address DFB, SOA and PBG cavity-based lasers. Together with the other component design products from RSoft Design Group, LaserMOD is well positioned to meet the design need for optoelectronic integrated circuits.
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Convenient CAD Layout
LaserMOD shares the same advanced parametric CAD technology that is used by the other component design tools in RSoft Design Group's tool suite, such as BeamPROP™ and FullWAVE™. The GUI is structured to lead the engineer through the design of a semiconductor laser. Convenient layout utilities assist in defining the geometry. Predefined region types such as multiple quantum wells or distributed Bragg reflectors enable quick and intuitive input of the corresponding layers as well as the associated material parameters. Arbitrary profiles for doping or material composition can be defined and verified via designated utilities.
Intuitive Simulation Controls
After the layout is completed, the mesh generator creates a non-uniform mesh, which can be controlled via local and global parameters. Isolated computation modules allow the user to analyze aspects of the design before running involved full-scale self-consistent laser simulations. These simulation modules provide customized dialogs to adjust physical models as well as numerical settings. A mode calculation module provides a variety of mode solvers for analyzing the wave guiding properties of the design. Gain computations can be performed for varying temperature and carrier densities allowing for optimization of the active layers. Finally, the interplay of the different aspects of the laser design can be simulated by solving for the optical field propagation and carrier transport self-consistently. A bias table editor provides an intuitive tool to control the bias conditions applied during the full-scale laser simulation. After the simulation is completed or as data becomes available, a post-processing and visualization utility provides a list of standard and customizable plots, which allow for displaying and analyzing the device characteristics.
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The simulation capabilities of the package are based on the renowned Minilase-II program, developed at the University of Illinois, in Urbana-Champaign. LaserMOD solves the electro-thermal transport, optical properties, and carrier-photon interactions, using a fully coupled numerical scheme on a spatial discretization of the device geometry specified by the CAD layout. A methodology for carrier transport has been developed and established for silicon device simulation in multiple dimensions that LaserMOD adapts for material systems common to semiconductor lasers, to describe electronic transport through bulk regions, in which active layers may be embedded. The injection current into the active quantum well region determines the carrier densities within bound quantum well states and therefore, the degree of inversion. For carrier transport through bulk semiconductor regions the drift-diffusion system of equations is applied (carrier continuity equations, Poisson's equation). This set of equations has been extended to an electro-thermal transport model appropriate for describing self-heating effects. LaserMOD includes a complete set of models for carrier mobility, radiative and non-radiative recombincomplete set of models for carrier mobility, radiative and non-radiative recombination, thermionic emission, quantum corrections, etc.
Advanced Quantum Models
Advanced quantum mechanical models are applied to multiple quantum wells in active regions. Bound states are coupled to classical carrier transport in continuum states via incomplete carrier capture due to carrier-carrier and carrier-phonon scattering. A Schroedinger equation determines the charge distribution. The material gain is calculated based on an 8x8 KP bandstructure calculation. Import of gain, spontaneous emission and refractive index data computed based on an advanced many-body gain theory is facilitated through a gain library interface, which enables the use of external models or measured tabulated data.
Optical Field Propagation
The optical field is expanded in terms of eigenmodes. The intensity within these modes is described by photon rate equations, which are solved fully coupled with the electro-thermal transport. A selection of solvers is available for mode calculations, providing an optimal choice for any given structure (Beam Propagation Method, Finite Difference Time Domain, Transfer Matrix, Ritz Iteration). The integration with BeamPROP and FullWAVE enables LaserMOD to take advantage of their respective mode solving capabilities.
The Complete Package
for VSCEL and Edge Emitters
LaserMOD is complete with material and model parameter libraries for most common compound semiconductors. The tool is capable of simulating 1D cross-sections, appropriate for analyzing broad area lasers or obtaining a quick estimate on the perfomance of more complicated structures, as well as full 2D laser cross-sections, necessary to account for the effects of carrier spreading and optical confinement by a waveguide. LaserMOD can perform full 3D VCSEL simulations quickly by taking advantage of the cylindrical symmetry of the device. Simulations can provide steady-state solutions, for analyzing CW performance, and transient solutions, for analyzing the pulsed or modulated performance of the device. External parasitics such as packaging can be accounted for in calculating the frequency response.
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LaserMOD provides a
complete set of post-processing and visualization capabilities. The
visualization utility offers a list of standard plots, which allow for
quickly displaying device characteristics of common interest, such as
IV, LI, spatial distribution of carriers, modal gain spectrum, energy
bands and many others. Access to virtually all simulation data is
provided for via customizable plotting features. A variety of plotting
utilities is available which allow the user to view the spatially
resolved plots from any perspective or cross-section.
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The Gain Library is a database system that allows the semiconductor laser simulator LaserMOD access to gain, refractive index, and photo-luminescence spectra for semiconductor quantum wells, which are calculated by Nonlinear Control Strategies (http://www.nlcstr.com/) using a sophisticated quantum many-body theory. Based on the information contained in the database, LaserMOD can perform electro/thermal/optical simulations of semiconductor quantum-well lasers. The gain database can be selected as an alternative to the built-in gain model of LaserMOD, providing several advantages in terms of reduced calibration effort and increased predictive capability of the overall simulation.
The data within the database is grouped in a set of libraries providing spectra for different quantum well/barrier material systems and target emission wavelength of the laser. Within a library the gain, refractive index, and photoluminescence spectra are tabulated for varying wavelength, temperature, carrier density, alloy composition of quantum wells/barriers, and quantum well width to allow the user to investigate variations in the active region design.
Comparison of measured photo-luminescence data with calculated spectra enables the user to characterize the sample in terms of deviations from the nominal quantum well/barrier geometry and composition. Furthermore, the inhomogeneous broadening indicating the amount of disorder present in the sample can be extracted for corresponding adjustment of the calculated spectra for further simulations.
Many-Body Gain Theory
The microscopic calculation of gain/absorption, refractive index, and photo-luminescence spectra is described in detail in references 1-4 below and references therein. It is based on solving the semiconductor Bloch equations, i.e. the equations of motions for the reduced density matrix, to obtain the optical susceptibility of the quantum well system. The real part of the susceptibility gives the carrier induced change of the refractive index and the imaginary part gives the gain/absorption. The photo-luminescence is derived from the gain/absorption using the Kubo-Martin-Schwinger relation. Coulomb-induced effects like bandgap renormalization, Coulomb enhancement of the absorption and excitonic resonances are taken into account self-consistently. The electron-electron and electron-phonon scattering processes are calculated in a second Born approximation enabling the prediction of spectral broadening and spectral shifts. The resulting scattering equations take the form of generalized quantum Boltzmann equations.
InGaAs 980nm Gain Library
The InGaAs 980nm Gain Library contains gain/refractive index/spontaneous emission spectra for InGaAs quantum wells embedded in GaAs barriers. The data is tabulated for Indium concentrations ranging from 8% to 24% and quantum well widths ranging from 4nm to 20nm targeting a laser emission wavelength of 980nm. The spectra cover temperature variations from 275K to 500K and variations of the carrier concentration up to 2x1013 cm-2 sheet density.
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LaserMOD™ is trade mark of RSoft Design Group, Inc.