Learning Forum

[sagar]

Whenever we do a simulation with periodic boundary condition (PBC), it is considered an infinite unit cell array. How do we do that if we want to see the response with the finite size of the metasurface? In that case, we have to use PML on all six sides of the finite-sized metasurface, and we can not use a plane wave source. Another problem is associated with the large simulation volume, like 20 - 30 um in some cases, where each unit cell size is around 200 -300 nm. How do we deal with such a problem? 

[Kyle]

Hello, performing aperiodic simulations with plane wave sources can be challenging since the plane wave itself has infinite extent. In FDTD you can use a finite sized plane wave source by changing the "plane wave type" property of the plane wave source to "Diffracting" but it will diffract at the edges of the source.

You can avoid this using a TFSF source, but this is an advanced source and you should make sure you understand how it works. These pages have more information on the TFSF source:

• Total-Field Scattered-Field (TFSF) source - Simulation object – Ansys Optics
• Tips and best practices when using the FDTD TFSF source – Ansys Optics

Another option is adding an aperture to block the diffracting edges of the plane wave similar to the full lens simulation in the Small-Scale Metalens – Field Propagation example.