Electro Absorption Photonic Modulator Design and Simulation (Part 2 - Lumerical Mode)
In this session, we will continue in numerical mode to calculate the optical performance of electro-absorption modulators. Our focus is on a specific type of modulator, and we will explore the quantum confined Stark effect, which was described in a previous talk.
Device Model
Our device model is a PIN semiconductor structure. It includes:
- N-type material: Gallium Arsenide (GaAs)
- Superlattice: A combination of Gallium Arsenide and Aluminum Gallium Arsenide (AlGaAs)
Material Definition
To define the materials, you can download the Three-Fives Semiconductor Optical Material Data Tools from the specified website. After running the script, you can define the composition of AlGaAs by setting the parameter X to 0.3.
Steps to Define Material
- Open the script and run the simulation.
- Select AlGaAs and set X to 0.3.
- Define the wavelength range and add the material to the database.
Superlattice Material
The superlattice consists of two materials:
- Material 1: Gallium Arsenide (GaAs)
- Material 2: Aluminum Gallium Arsenide (AlGaAs)
Refractive Index Calculation
To calculate the refractive index of the superlattice:
- Generate the lambda using the line space command.
- Calculate the refractive index for each material.
- Use the formula to calculate the average index of the superlattice.
Geometry Creation
We will create the geometry in the Lumerical mode:
- Gallium Arsenide (GaAs) top layer
- Superlattice layers
- Multi-quantum well structure
Quantum Well Structure
The quantum well structure includes:
- Barrier Thickness: 20 nanometers
- Well Thickness: 9.4 nanometers
- Number of Quantum Wells: 2
Simulation and Analysis
We use the FDTD solver for simulation:
- Solver Type: 2D Normal
- Boundary Condition: Metal
Mode Calculation
We calculate the modes to determine the effective index, wavelength loss, and other parameters. The first mode has an effective index of 3.5.
Confinement Factor
The confinement factor is calculated as the power fraction of the optical mode within the active layer.
Frequency Analysis
We perform a frequency sweep to extract the group index and refractive index over a range of wavelengths.
Results
The results of the analysis include:
- Confinement Factor: 0.6
- Effective Index: 3.5
- Group Index: 4.2
These parameters will be used in a numerical multi-physics simulation.
So now we want to continue in numerical mode to calculate the optical performance of electro-absorption modulators. We will focus on this type of modulator, which utilizes the quantum-confined Stark effect. You can find an example of this file [here](http://www.example.com).
Our device model is a pin semiconductor, consisting of an n-type region with a super lattice. The super lattice material consists of two layers: gallium arsenide and aluminum gallium arsenide.
We can define the composition of these materials using the three-fives semiconductor optical material data tools, which can be downloaded from [this website](http://www.three-fives.com/tools).
To create a super lattice, we can use the following formula to generate the refractive index of the super lattice: index\_super\_lattice = (index1 \* dimension1 + index2 \* dimension2) / (dimension1 + dimension2) where index1 and index2 are the refractive indices of the two materials, and dimension1 and dimension2 are the thicknesses of the two layers.
Now, let's create the geometry of our device in the Lumerical mode. We have a gallium arsenide top layer, a super lattice top layer, a multi-quantum well structure, and a gallium arsenide bottom layer.
The dimensions of these layers are as follows: * Gallium arsenide top: 0.3 micrometers * Super lattice top: 0.1 micrometer * Multi-quantum well: 20 nanometer barrier, 9.4 nanometer well * Gallium arsenide bottom: 1.3 micrometers Next, we need to add a solver to our device.
We can use a 2D FDTD solver with a normal boundary condition and a mesh size of 1 nanometer. Now, we can run the simulation and analyze the results. In the mode calculation, we can see the effective index, wavelength loss, and other parameters of the modes in our structure.
We are interested in the confinement factor, which is the power fraction of the optical mode within the active layer. We can calculate this by integrating the power in the active region and dividing by the total power.
Next, we can perform a frequency sweep from 4.85 to 8.5 micrometers to calculate the group index and refractive index of the mode. We can visualize the results and see the group index, confinement factor, and other parameters of the mode.
Finally, we can use these variables and parameters in a numerical multi-physics simulation.
