Yes, when x dimension is infinite and if it has no isolated nano objects you should use periodic BCs;
Finite sized y diraction should use PML.
For 2D simulation, you can set the source polarization angle 90 to excite Ez.
I would strongly suggest you to watch some videos:https://optics.ansys.com/hc/en-us/sections/360007813194-FDTD100-List-of-videos
to get more information.
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