# Microring Resonator with Gaussian Launcher (microringResonatorGaussian.sdf)

Keywords:

Microring Resonator, Unidirectional Mode Launcher, MAL, Guided Mode, Photonic Device, Semiconductor

## Problem Description

The Microring Resonator consist of two straight Silicon waveguides and a Silicon waveguide ring that sits between the straight Waveguides. All three waveguides rest on top of a Silicon Dioxide slab. The rest of the simulation domain is set to vacuum. Matched Absorbing Layers (MALs) are used to dampen the E, B and D fields near the boundary of the simulation, this is a way to dampen reflected fields from the simulation boundaries.

An approximation of the fundamental guided mode profile is launched as a wide band pulse in the input waveguide ( the waveguide in -y ). This input signal is launching in the +x direction.

This simulation can be performed with a VSimEM license.

## Opening the Simulation

The Microring Resonator example is accessed from within VSimComposer by the following actions:

• In the resulting Examples window expand the VSim for Electromagnetics option.
• Expand the Photonics option.
• Select Microring Resonator with Gaussian Launcher and press the Choose button.
• In the resulting dialog, create a New Folder if desired, and press the Save button to create a copy of this example.

All of the properties and values that create the simulation are now available in the Setup Window as shown in Fig. 240. You can expand the tree elements and navigate through the various properties. The right pane shows a 3D view of the geometry, as well as the grid, if actively shown. To show or hide the grid, expand the Grid element and select or deselect the box next to Grid.

Fig. 240 The Setup Window for The Microring Resonator Example

## Simulation Properties

This example contains a number of Constants defined to make the simulation easily modifiable.

General Simulation Parameters (Constants):
• WAVEL_MAX = largest wavelength in the wide band signal
• WAVEL_MIN = smallest wavelength in the wide band signal
• RESOLUTION = inverse of the number of cells per wavelength
• LENGTH_UNIT = This scales the simulation by the value. DO NOT CHANGE THIS PARAMETER
• WAVEGUIDE_PERMITTIVITY = permittivity of the waveguides ensure this is equal to the permittivity set in the CSG.
• WAVEL_SINGLE = The wavelength used in the single frequency signal
• WAVEL_RESOLVE = The wavelength used in calculation for the number of
cells in simulation.
General Simulation Parameters (Parameters):
• RING_RADIUS = radius of the ring in meters scaled by LENGTH_UNIT.
• WIDTH_WAVEGUIDE = Width of waveguides in meters scaled by LENGTH_UNIT.
• HEIGHT_WAVEGUIDE = Height of waveguides in meters scaled by LENGTH_UNIT.
• GAP_WIDTH = Width of the gap between ring and waveguides in meters scaled by LENGTH_UNIT.

This simulation uses a gaussian distribution in the transverse directions as an approximation to the fundamental spatial mode profile. One can also specify the time signal used to propagate the profile using either a single frequency or FreqWindow Space Time Functions. The SpacetTimeFunctions are assigned to the transverse components of CurrentDistributions, which can be found under the Field Dynamics drop-down of the simulation setup tree.

The Materials section contains just Silicon and Silica. This section is where one can add or edit materials that get attached to CSG objects. These Materials contain the relative permittivity.

In Field Dynamics there are FieldBoundaryConditions which set the boundary conditions of the simulation. In photonics simulations, Matched Absorbing Layers (MALs), are the most stable boundary conditions for preventing reflections.

## Running the Simulation

When the user has saved the setup, continue as follows:

• Proceed to the Run Window by pressing the Run button in the left column of buttons.
• When you are finished setting run parameters, click on the Run button in the upper left corner of the right pane. You will see the output of the run in the right pane. The run has completed when you see the output, “Engine completed” seen in Fig. 241

Fig. 241 GUI Run Window at completion.

## Analyzing the Results

Using Post analysis scripts one can extract transmission coefficients. This is possible due to the field slab histories that are located at each port in the simulation. Each port has an E and B slab history in order to integrate over the poynting flux. This integration is done in a post analysis script called computeSParamsFromHists.py.

Now go to the Analyze pane, select the computeSParamsFromHists.py analyzer, and press the Open button. Set the maxWavelength to 1.7, outSlabE to be eSlab3, outSlabB to be b. Upon hitting the Analyze button of the Analyze pane, we see that there will be a list of transmission maximum and the wavelength they occur at. This is seen in Fig. 242.

Fig. 242 VSim analyzer tab.

## Visualizing the results

After performing the above actions proceed to the Visualize Window by pressing the Visualize button in the left column of buttons.

One can visualize the transmission coefficients by performing the following:

• Near the top left corner of the window, make sure Data View is set to 1-D Fields.
• In the control Panel select S_eSlab3bSlab3 for graph1 and set graph 2-4 to None.

Once you have performed the above actions one’s screen should look like Fig. 243.

Fig. 243 Visualization of Transmission Coefficient

## Further Experiments

One can experiment by changing the GAP_WIDTH parameters. Then, one can run the computeSParamsViaOverlapIntegral.py script to extract S-Parameters. One can see now changing the GAP_WIDTH changes the S-Parameters.