Electro Absorption Photonic Modulator Design and Simulation (Part 1 - Theory)
Hi everybody, today I'm going to talk about the simulation of an electroabsorption modulator. My name is Majid from Ozen Engineering, Inc.
Introduction
First of all, I'll give you a brief introduction to electroabsorption modulators. Then, I will discuss how we can calculate the optical mode and absorption characteristics of the modulator. Finally, I will show you how to create a compact circuit model for the electroabsorption modulator.
Physics Behind Electroabsorption Modulators
The physics behind the electroabsorption modulator, particularly for the box and conductor, is based on the Franz-Keldysh effect. In this effect:
- We can observe the band diagram of the box and conductor, including the valence band and band gap energy.
- By applying a reverse bias voltage to the modulator, the band gap is tilted, allowing electrons to transition from the valence band to the conduction band at lower frequencies.
- This results in a redshift of the absorption coefficient versus photon energy curves, shifting them to longer wavelengths.
Quantum Structure
For quantum structures, such as those using indium gallium arsenide and gallium arsenide, we observe:
- A lower band gap, leading to photon confinement in the structure.
- When reverse bias voltage is applied, the band gap tilts, causing electrons to move towards positive poles and holes towards negative poles. This shifts the peak of the NCDL state.
- Absorption versus wavelength curves show excitonic peaks at zero voltage, which disappear when voltage is applied, resulting in a redshift.
Signal Analysis
For signal analysis of the modulator, we require:
- A DC bias voltage to tune the working region point.
- An AC signal for input electrical signal modulation.
The extinction ratio, confinement factor, absorption difference, and length are key parameters. We can control the confinement factor by changing the structure, for instance, using slow light, and increase the length to enhance the extinction ratio.
Modulator Design Schemes
Different schemes for modulator design include:
- Quantum dots: Voltage application decreases the absorption peak.
- Quantum wells or graphene: Voltage application results in a redshift and increased absorption.
- Bulk semiconductors: Voltage application results in smaller absorption at specific wavelengths.
Modulator Workflow Design
The workflow for designing a modulator involves:
- Using numerical analysis to calculate the modal effective index overlap with the gain region.
- Calculating modal properties such as effective index versus wavelength, group index, and confinement factor.
- Inserting these parameters into numerical multiphysics to calculate the absorption coefficient and transmission as a function of applied bias voltage.
- Calculating transmission versus wavelength and voltage, as well as group delay.
- Creating a circuit model in numerical interconnect to calculate the time domain modulator response.
Let's proceed to the numerical mode to calculate the modal properties.
Hi everybody, today I'm going to talk about the simulation of an electroabsorption modulator. My name is Majid from Ozen Engineering. First, I'll give you a brief introduction of an electroabsorption modulator.
Then I will talk about how we can calculate the optical mode and absorption characteristics of the modulator. Finally, I will show you how we can create a compact circuit model for the electroabsorption modulator. The physics behind the electroabsorption modulator is the Franz-Keldysh effect.
In this effect, when a reverse bias voltage is connected to the modulator, the band gap is tilted, and electrons can transient from the valence band to the conduction band by lower frequency. This results in a redshift of the absorption coefficient versus photon energy curves.
For instance, in this case, at a certain photon energy, there is no absorption coefficient when the voltage source is disconnected. However, when the voltage source is connected, an absorption coefficient is present.
For the quantum structure, such as a semiconductor structure with indium gallium arsenide and gallium arsenide, there is a lower band gap. This results in a confinement of photons in this region.
When a reverse bias voltage is connected to the quantum structure, the band gap is tilted, and the peak of the NCDL state shifts. This results in a redshift of the absorption versus wavelengths curve. For the signal analysis of the modulator, a DC bias voltage and AC signal are required.
The DC bias voltage can be used to tune the working region point. The swing voltage and input electrical signal can be used to generate an optical signal.
Regarding the confinement factor, it can be controlled by changing the structure, such as using a slow light or increasing the lengths to increase the extinction ratio.
In the design of the modulator, a numerical Ansys mode can be used to calculate the modal effective index overlap with the gain region.
The model property effective index versus wavelength group and the model property effective index versus wavelength group index confinement factor can then be calculated.
These parameters can be inserted into the numerical multiphysics in the charge part to calculate the absorption coefficient and transmission as a function of applied bus voltage.
The transmission versus wavelengths and voltage and group delay can then be calculated, and a circuit model can be created in the numerical interconnect to calculate the time domain modulator response. Let's go to the numerical mode to calculate the modal properties.
