Hay Saurabh
PBC is suitable for periodic structures such as grating or nano hole array.
usually, we use it in a direction normal to the direction of propagation. say light propagates in z- direction
then, to show periodicity we can use PBC in x, y directions
APML means anisotropic perfect matched layer and it is suitable for to show that light is almost absorbed and there no reflections.
usually, we use it in direction of propagation.
in some cases one may use either magnetic or electric conductor as a boundary. then PMC or PEC. frankly, i did not use them before.
