We present the static and dynamic simulation of a long-wavelength
vertical-cavity surface-emitting laser (VCSEL) operating at around
1310 nm. The device consists of AlGaAs/GaAs distributed Bragg reflectors (DBRs) which are wafer-fused to both sides of the InP-based cavity with InAlGaAs quantum wells. A tunnel junction is used for current injection into the active region. The structure is simulated with a modified version of the commercial device simulator Synopsys Sentaurus Device. The fully-coupled two-dimensional electro-opto-thermal simulations use a microscopic physics-based model. Carrier transport is described by the continuity and Poisson equations and self-heating effects are accounted for by a thermodynamic equation. To obtain the opticalmodes, the wave equation is solved using a finite element approach. The optical gain model includes many-body effects. The equations are solved self-consistently. Calibrations of static (L-I, V-I curves) and dynamic characteristics (RIN) show good agreement with measurements at different temperatures. On this basis, the simulations reveal the critical factors that determine the modulation-current efficiency factor (MCEF) of the device.
Optical microcavities that contain single quantum dots have promising applications in quantum cryptography as sources of single photons. The realisation of efficient devices relies on the ability to fabricate electrically-pumped, high Q factor (Q>2000), wavelength-sized microcavities. In this work two approaches-oxide confined and micropillar structures-are compared by optical simulation.
The modification of the spontaneous emission-Purcell factor and emission coupling efficiency-in such devices is treated semiclassically here, assuming the weak coupling regime. Hence, the spontaneous emission rate and direction may be computed using the effective mode volume, resonant wavelength, and quality factor of the optical modes in the microcavity. In the context of this work, the optical modes of rotationally symmetric microcavities are determined by solving Maxwell's vectorial wave equation in the frequency domain employing vectorial finite elements, subject to an open boundary, taking into account diffraction and radiation of electromagnetic waves. Consequently, the spontaneous emission properties of realistic microcavities without any restrictions regarding structure and size may be investigated.
The optical mode solver is first calibrated with measured electroluminescence spectra of an oxide confined microcavity structure with oxide diameters ranging from 2.4 um to 0.7 um. Excellent agreement is achieved between measurements and simulations, which assures the predictive capability of the optical mode solver. For oxide confinements with diameters smaller than 1 um strong degradation of the Q factor and, hence, the Purcell factor is observed. Excessive diffraction losses are identified as the main cause of this effect in the present design. Furthermore, the advantages of micropillar structures with respect to this issue are demonstrated.
A novel spatially distributed noise model is used in a device simulator in order to describe relative intensity noise and frequency noise for semiconductor lasers. For charge carrier transport, continuity and Poisson equations are used and self-heating is considered by a thermodynamic equation. Spontaneous and stimulated recombination are calculated in the framework of the semiconductor Bloch equations using the second Born approximation to include many-body effects. The optical field is expanded into modes. The temporal behavior is described by a photon rate and a photon phase equation for each mode. Noise is taken into account by spatially distributed Langevin forces. The correlation functions are described directly in the frequency domain assuming small signal noise sources. All relevant equations are solved in a fully self-consistent fashion. Comparison of static characteristics and dynamic characteristics, such as relative intensity noise, with measurements show excellent agreement for a vertical-cavity surface-emitting laser (VCSEL).
We report on the simulation of 1.32μm vertical-cavity surface-emitting lasers (VCSELs). The device comprises a tunnel junction for current and optical confinement and features intra-cavity ring contacts. Distributed Bragg reflectors (DBRs) in the GaAs/AlGaAs material system form the optical cavity and are wafer-bonded to InP-based spacers. The active region consists of five InAlGaAs quantum wells (QW). For the simulations, a thermodynamic transport model is used for electrical and thermal calculations while the optical modes are computed by solving the vectorial Helmholtz equation with an finite element (FE) solver. Calibrations show good agreement with measurements and on this basis, electrical benefits of the TJ are studied. Moreover, the physics of thermal rollover are analyzed.
This work deals with the TCAD (technology computer aided design) based design of VCSEL (vertical-cavity surface emitting laser) devices. A comprehensive 2D electro-thermo-optical device model is presented. Furthermore, as examples, a micromechanical, electrostatically actuated vertical optical resonator is
investigated, a procedure for optimising the higher order mode suppression in a VCSEL is presented, and a coupled electro-thermo-optical simulation of a VCSEL is performed.
The laser device model employs the photon rate equation approach. It is based on the assumption that the shapes of the optical modes depend on the instantaneous value of the time-dependent dielectric function.
The optical fields in the VCSEL cavity are expanded into modes obtained from the complex frequency representation of the homogeneous vectorial Helmholtz equation for an arbitrary complex dielectric function. The 3D problem is transformed into a set of 2D finite element (FE) problems by using a Fourier series expansion of the optical field in azimuthal direction. For the bulk electro-thermal transport a 2D thermodynamic model is employed in a rotationally symmetric body. Heterojunctions are modeled using a thermionic emission model. Quantum wells are treated as scattering centres for
carriers. The optical gain and absorption model in the quantum well active region is based on Fermi's Golden Rule. The sub-bands in the quantum well are determined by solving the stationary effective mass Schroedinger equation with parabolic band approximation for the electrons, light and heavy holes.
We demonstrate a comprehensive multi-dimensional DBR laser simulation. The DBR laser under investigation consists of three longitudinally integrated waveguide sections: an active section providing the optical gain for the laser operation, a passive phase shift section which contains neither gratings nor active material and a DBR mirror section. This structure is representative for longitudinally integrated devices such as widely tunable sampled-grating laser diodes. In our physics-based approach, we solve the fully coupled semiconductor drift-diffusion equations for electrons and holes and the temperature diffusion equation, taking into account longitudinal current and heat flux. Gain calculation and the photon rate equation are included self-consistently. A general and comprehensive solution of the transverse optical field is combined with the longitudinal field distribution including general DBR sections. The simulator is applied for the design and optimization of state-of-the-art tunable lasers. It proofs to be an effective tool for bandgap engineering, for the optimization of the transverse confinement of the optical mode as well as the current, and for thermal management.
In this work the optical cavity of a vertical-cavity surface-emitting laser (VCSEL) is analyzed with the goal of performing a coupled electro-optical simulation of the device. For this simulation, the eigenmodes and the eigenvalues of the optical cavity have to be obtained. A common approach is to treat Maxwell's equations in the frequency domain and to solve the resulting algebraic eigenvalue equation. As an alternative, the electromagnetic problem is solved in time-domain. The response of the optical cavity is calculated by the finite-difference time-domain (FDTD) method. The optical wave propagation is modeled rigorously, including evanescent and propagating waves. From the FDTD simulation, a steady state optical intensity pattern is extracted. The eigenvalues of the dominant modes are determined using a Pade type approximation.