Lumerical Fdtd Tutorial Link

Right-click "Mesh" → Add "Mesh Override Region."

Lumerical uses an "Auto-Shutoff" feature to stop the simulation when the energy in the simulation volume drops below a threshold (typically $10^-5$). lumerical fdtd tutorial

FDTD requires a finite volume to solve Maxwell's equations. Right-click "Mesh" → Add "Mesh Override Region