A VCSEL (Vertical cavity surface emitting laser) is a type of diode laser that emits a near-Gaussian beam perpendicular to the top surface. VCSELs offer many advantages in fabrication and performance over conventional edge-emitting lasers where light is emitted on one or two edges of the chip. In this example, we present how to build the VCSEL structure, simulate and analyse reflectivity, modes and frequencies. This example runs on Ansys Lumerical Multiphysics software (from 2025 R1.1 version and later) and require an Ansys Lumerical Enterprise license.
Overview
Understand the simulation workflow and key results
[Optional] Step 1: Automatic structure construction and simulation objects setup from a layer table (.csv)
The data from the .csv file can be used to automatically set up all the VCSEL layers, including DBR mirrors and MQW layers. However, the contact and aperture oxide layers need to be added separately using script or graphical user interface.
Step 2: Cold cavity simulation
With the “calculate cold cavity spectrum” option enabled, the optical properties of the VCSEL can be simulated. As a first step, the cavity reflectivity can be simulated to quickly estimate the cavity resonance frequency. Furthermore, with the cavity eigenmode simulation, the supported mode shapes and frequencies are calculated. Cavity dipole simulation can also be performed to determine supported frequencies and beam profiles for different active layer source polarizations.
Run and Results
Instructions for running the model and discussion of key results
Step 1: Automatic structure construction and simulation objects setup from a layer table (.csv)
- Open a new VCSEL project and set the working directory to the folder that contains all the example files.
- Open and run [[main.lsf]] script file. The simulation file will be created. Both VCSEL and CHARGE solvers and simulation regions are added.
- Open and run [[set_additional_structures.lsf]]. The script will add the top contact and the aperture oxide.
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Note: The file with the VCSEL structure data must be saved in csv format. |
The script will automatically set the geometry and add the optical properties of the materials depending on their composition. The III-V Semiconductor Optical Material Data Tool – Ansys Optics is used for adding the optical properties.
Furthermore, two simulation regions are added, one for the optical simulation and one for the charge transport simulation. The boundaries of the optical simulation region are automatically set to PML (apart from the boundary that corresponds to the axis of the cylindrical symmetry).
Users can add extra objects such as substrate, contacts, CHARGE electrical boundary conditions and monitors for both VCSEL and CHARGE simulations. Also, the electrical and optical material properties can be checked and adjusted. Finally, the VCSEL and CHARGE/MQW solver options can be adjusted.
Step 2: Cold cavity simulation
Eigenmode simulation and Reflectivity analysis
- Open the [[vcsel_T_shape_optical_reference.ldev]] simulation file and run it with the “with source” option, that can be found under the Optical/Modal Analysis tab of the VCSEL solver, disabled.
- Run the [[plot_eigenmode_results.lsf]] to visualize the reflectivity analysis, the eigenmode field profiles and frequencies.
The reflection and transmission spectrum are plotted. The cavity resonance can be determined, and it corresponds to 982nm.
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Note: The reflectivity analysis results can be visualized before running the simulation, by clicking on the partition button on the VCSEL solver tab. |
The above reflectivity results correspond to the whole VCSEL cavity since “All” is selected in the “reflectivity structure group” option in the VCSEL solver “General” tab. The analysis can be also performed for sub-groups of the structure by selecting the proper group in the “reflectivity structure group” option. Furthermore, in the VCSEL solver “Reflectivity” tab, the wavelength range, number of wavelengths and incident angles can be set.
The frequency of each mode versus mode number and Fourier index is also plotted. As shown below, for Fourier index 1 only four modes have been found around the specified frequency.
The electric and magnetic components of mode number 1 and Fourier index 1 are shown below. This mode is predominantly TE mode, but not fully since it has a significant Ez component.
Dipole simulation
- Switch to layout and under the Optical/Modal Analysis tab of the VCSEL solver enable the “with source” option, change the "sweep type" to "linspace" and run the simulation with the settings shown below.
- Run [[plot_dipole_results.lsf]] to visualize the frequencies and beam profiles.
For Fourier index 1, the power versus mode number is the following:
The power vs wavelength for each Fourier index is also plotted.
The electric and magnetic field components of mode number 24 and Fourier index 1, which corresponds to one of the two power peaks (the other peak corresponds to mode 6), is shown below.
Visualize the z component of the Poynting vector for mode number 24 and Fourier index 1 from the optical field monitor. The peak of the Poynting vector is approximately at radius of 0um, which agrees with the position of maximum intensity in the field distribution inside the cavity for mode number 24 and Fourier index 1 shown in the previous image.
- Switch to layout and under the Optical/Modal Analysis tab use the settings shown below and re-run the simulation.
- Run [[plot_dipole_results.lsf]] to visualize the frequencies and beam profiles.
For Fourier index 0, the power versus mode number is the following:
The power vs wavelength for each Fourier index is also plotted.
The electric and magnetic field components of mode number 17 and Fourier index 0, which corresponds the power peak, is shown below.
Visualize the z component of the Poynting vector for mode number 17 and Fourier index 0 from the optical field monitor. The peak of the Poynting vector is approximately at radius of 1um, which agrees with the position of maximum intensity in the field distribution inside the cavity for mode number 17 and Fourier index 0 shown in the previous image.
Important model settings
Description of important objects and settings used in this model
Cold cavity simulation: For running a cold cavity simulation the option "calculate cold cavity spectrum" in VCSEL solver "General" tab must be enabled.
Reflectivity analysis: In order to calculate the reflectivity spectrum of the whole VCSEL structure, the option "All" must be selected in the "reflectivity structure group" option in VCSEL solver "General" tab. If the reflectivity of a sub-group is of interest, this group must be selected in the "reflectivity structure group" option. The wavelength range as well as the incident angles for the reflectivity analysis can be set in the VCSEL solver "Reflectivity" tab. The reflectivity analysis results can be visualized after partitioning or after running the simulation.
Cylindrical axis: Since VCSEL solver supports VCSLEs with cylindrical symmetry, it is important to correctly set the axis of the cylindrical symmetry in the "General" tab under "Optical" tab of the VCSEL solver. The simulation region must be also set correctly so that the axis of symmetry corresponds to the VCSEL axis.
Wavelength/Frequency: When performing eigenmode analysis, the "Model Analysis" tab under "Optical" tab requires a single wavelength/frequency value and the number of eigenmodes to be considered in the calculation around the selected value. The wavelength/frequency for the eigenmode calculation should be set close to the expected wavelength of operation of the VCSEL. When running a simulation with dipole source, the input in the "Model Analysis" tab corresponds to the wavelength/frequency range of the dipole source.
Number of Fourier components: Although the use of 2-3 Fourier components is usually enough, users can set a larger number of Fourier components to check the cavity modes and the cavity response for different dipole postions and orientations.
Additional Resources
Additional documentation, examples and training material
See Also
- Automatic Layer Import for VCSEL Design Tool
- VCSEL solver – Simulation object
- VCSEL Solver Introduction
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