# Plane Wave Source in Ansys Lumerical FDTD — Lesson 2

### Physics and Applications

A planewave is generally used together with a periodic structure. In this video lesson, you will learn about three different types of plane wave sources: Bloch/periodic, BFAST, and diffracting.

### Setup & Tips

In this video lesson, we will demonstrate how to set up the planewave source using a simple grating example. You can download the simulation file and follow the steps shown below.

1. Click the arrow next to the “Sources” button in the main toolbar to open the drop-down menu
2. Click the “Plane wave” option which is the third in the list in the drop-down menu

Open the source edit window:

1. Make sure that the plane wave source is selected in the Objects Tree window. If not, click the source in the Objects Tree to select it.
2. Click the Edit button in the edit toolbar on the left (pencil icon), or use the 'E' keyboard shortcut to open the edit window.

Set properties in the source edit window:

General tab:

• Planewave type: Bloch/periodic
• Injection axis: y-axis
• Direction: Backward
• Angle theta: 15 degrees
• Angle phi: 0 degrees
• Polarization angle: 90 degrees

Geometry tab:

• x: 0 microns
• x span: 5 microns
• y: 2 microns

Frequency/Wavelength tab:

• Start wavelength: 0.8 microns
• Stop wavelength: 0.8 microns

Beam options tab:

• Shows a plot of the injected angle of the plane wave over the wavelength

Click the “OK” button at the bottom right of the source edit window to accept the settings

1. Check polarization and injection angle
• Electric field polarization direction is illustrated by the blue arrow
• Injection direction is indicated by the pink arrow
2. Make sure that monitors don’t overlap with the source injection region
• Click the “zoom” button in the view toolbar on the left (magnifying glass icon) and use the mouse to select a region in the XY viewport to zoom into
• Check that the grey shaded region at the source injection plane does not intersect with yellow lines which indicate monitors

Run simulation without structures:

1. Right-click the “blaze_grating” structure group in the Objects Tree to open the context menu and select the “Disable” option from the context menu
2. Click the “Run” menu from the simulation toolbar

Plot simulation E field and Poynting vector results:

1. After the simulation has completed, right-click on the “profile” monitor in the Objects Tree window and select Visualize->E from the context menu
• In the visualizer window, double-click in the “Vector operation” column in the Attributes table and select X, Y, or Z to plot Ex, Ey, or Ez respectively
2. Right-click the “profile” monitor in the Objects Tree window and select Visualize->P from the context menu
• In the visualizer under the “Plot types” on the right side of the window, select “Vector”

Run simulation with structure:

1. Click the “Layout” button in the simulation toolbar to switch back to layout mode
2. Right-click the “blaze_grating” structure group and select “Enable” from the context menu
3. Click the “Run” button from the simulation toolbar to run the simulation

Plot the reflection:

1. After the simulation has been completed, right-click the “R” monitor and select Visualize->T from the context menu.