April 12, 2024 at 6:37 pm
Guilin Sun
Ansys Employee

PML performance depends not only on its artifical material properies, but also on the incident angle and wavelength.  It is difficult to expain the reason. You can use 3 plane monitors and record data inside PML as suggested before. Then you can check which and where the intensity is strong in PML to identify the issue. You may also use 3 movie monitors to check where the exponential growth begins.

Have you tried to simulate half of the device? whar happens then? 

PML has several parameters with different functions: https://optics.ansys.com/hc/en-us/articles/360034382674-PML-boundary-conditions-in-FDTD-and-MODE 

There are two dedicated books regarding to PML. 

You may also try the legacy uniaxial PML as some times it works better.

You may also extend ymin further away from device if you identified it causes issues.

Occasionally, a new project file will work by only copying the geometry and monitors, but adding new FDTD region and changes its settings. Do not copy the old FDTD to the new project.