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Due to the complexity of vertical-cavity surface-emitting laser (VCSEL) device design, it is often beneficial to divide the simulations of the device into several simpler, independent simulations, before performing a fully coupled simulation that integrates all relevant physical effects. The VCSEL Design Tool offers capabilities to solve for each independent sub-simulation as well as the fully coupled simulation within a single design environment.
This article provides a brief overview of workflows related to VCSEL devices, including geometry import, individual simulations, and the coupled simulations. Each sub-topic is linked to useful knowledge-based articles and examples for in-depth description and practice. A summary of procedures is shown in the diagram below to help you assess the objectives of each type of workflow. Prior to conducting the fully coupled simulation, it is strongly recommended to conduct the sub-steps outlined in red.
Layer Import
Typically, a VCSEL device will contain many heterogeneous layers. While it is possible to construct these layers manually using geometry objects in the design environment, it is typically easier to create layers as a spreadsheet and importing the spreadsheet to create the device geometry automatically.
VCSEL supports this functionality through a series of scripts. For specific usage of these scripts and details of spreadsheet construction, see the KB article on using the layer importing script for VCSEL.
Estimation Using stackrt
Prior to conducting finite element simulations, you can use a built-in analytical solver utilizing STACK to estimate the reflectivity of the laser cavity. To estimate the reflectivity, select the structure group where reflectivity is to be estimated in the “General” tab under the VCSEL solver object.
Analysis options with the stackrt interface can be configured using the “Reflectivity” tab under the VCSEL solver object. For more information regarding reflectivity calculations and its associated options, see the Knowledge Base Article on Stack Optical Solver.
After configuring the reflectivity calculation options, the calculation is performed once the simulation is partitioned, and result is available in the “stack_reflection_transmission_coefficient” object attached to the VCSEL solver object. The outputted results are formatted in the same way as the stackrt script command.
Cold Cavity Simulation (Standalone Optical Simulation)
Standalone optical simulations can be used to aid the design of the laser cavity without having to employ the expensive process of fully coupled electrical-thermal-optical simulations. These simulations can be exploited to obtain detailed cavity response such as supported mode shapes (i.e., the distribution of electric and magnetic fields for each mode), frequency, and obtain beam profiles for different active layer source polarizations.
Cold cavity simulations are enabled by checking the “calculate cold cavity spectrum” option in the “General” tab of the VCSEL solver object, and can be conducted without a source, or with a dipole source of a specific frequency, location, and orientation.
To add a source, the “with source” option can be enabled in the “Modal Analysis” tab within the “Optical Tab” of the VCSEL solver object, and its orientation and position in cartesian coordinates can be specified.
Standalone MQW Simulation
Standalone MQW simulations can be conducted on the active layer to determine the alignment of gain peak to cavity reflectivity peaks, and to obtain polarization dependence of gain in the active layer. This simulation can accurately capture physical phenomena inside the active layer using a quantum-mechanical approach. Further refinement to include access effects can be achieved by coupling MQW and CHARGE together, which will be discussed below.
To conduct standalone MQW simulations, see the MQW Product Reference Manual and the MQW Standalone Application Gallery example.
Standalone CHARGE Simulation
Standalone CHARGE simulations can be conducted on the distributed Bragg reflector (DBR) structures near the active layer to obtain key electrical characteristics such as access resistance to the active layer. This simulation accurately captures classical carrier transport into the active layer using the drift-diffusion approach. Further refinement to include quantum mechanical effects in the active layer can be achieved by coupling MQW and CHARGE together, as described below.
To conduct standalone CHARGE simulations, see the CHARGE Product Reference Manual and the CHARGE video course.
Standalone HEAT Simulation
Standalone HEAT simulation can be conducted on the VCSEL device to estimate joule heating of the device using a simplified transport model. This allows for independent estimation of self-heating effects which can then be further refined using CHARGE+HEAT simulations and verified by the fully coupled simulation.
To conduct HEAT simulations, see the HEAT Product Reference Manual and the HEAT video course.
CHARGE and HEAT Coupled Simulations
CHARGE and HEAT can be self-consistently coupled (without coupling to the optical and MQW solvers) to obtain more accurate results on joule heating with the full drift-diffusion model implemented in CHARGE.
CHARGE and MQW Coupled Simulations
CHARGE and MQW can be self-consistently coupled (without coupling to the heat and optical solvers) to obtain accurate results on gain and spontaneous emission information in the active layer. These simulations will only be valid up until the lasing threshold, beyond which the optical cavity solution from VCSEL is required.
To conduct MQW and CHARGE coupled simulations, see the application gallery example on MicroLED.
Fully Coupled Simulation
Fully coupled electrical-optical-thermal simulation of the laser structure can be performed to obtain full characteristics of the VCSEL device, incorporating all relevant physics. To enable fully coupled simulation, ensure “calculate cold cavity spectrum” option is not enabled, and select the solvers in the “General” tab of the VCSEL solver object for the coupled physics.
It is important to note that due to multiple physics involved, while accurate, fully coupled simulations are significantly more computationally expensive compared to standalone simulations. It is recommended that during the design process, you select the simulation of the correct complexity according to needs of the problem.
See Also
VCSEL Design Tool - User Manual, VCSEL Solver Introduction, Automatic Layer Import, Troubleshooting Convergence Errors in VCSEL