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[1668134855]

I am illuminating a grating with a plane wave source while using an FDTD simulation. The planesource is set below the grating, and has the same size as the grating. However, when the simulation starts, the planesource region automatically enlarged as about twice the original length. I'm wondering why it happens and how could I avoid.

Before simulation:

After simulation:

[Amrita Pati]

Hi,

Typically "Periodic/Bloch" type plane waves are used to study the interaction of ideal planewaves with the unit cell of an infinitely periodic geometry. In these cases, we simulate just one period of the grating with periodic/bloch BCs. To make sure that the plane wave is ideal, we want the plane waves to span across the entire simulation region so that there is no diffraction at the edges. To use a finite planwave, you may use a "diffracting" type planewave or a Gaussian source.

Regards,
Amrita