What happens if the Source is Inside the PML region in FDTD simulations?

In most of the FDTD simulations, perfectly matched layers play an indispensable role by their ability to absorb the incoming waves to mimic free space propagation. Triggering effect for this animation is the simple curiosity of what would happen if a point source was embedded in the PML rather than the inner domain.

To illustrate this, we utilized the uniaxial PML (UPML) formulation in a 2D FDTD scenario in homogeneous medium. We present three parallel simulations in which the point sources are located (left) deep inside the PML, (middle) slightly inside the PML and (right) outside but close to the PML. As can be observed, the PML performs great in eliminating portions of the wave impinging normal (or close to the normal) to the PML surface. But for high oblique incidences, the decaying of the wave is not completely satisfied.

For the leftmost case where the source is deeply embedded in the PML, the wave cannot propagate in the -x and +x directions and quickly decay in both directions. However, along the -/+ y directions, the PML acts as a waveguide. Thanks to the upper and lower PML regions, the wave inside the PML continues to decay along the -/+ y directions.