Periodic boundary condition

A periodic boundary condition simulated periodicity along a direction. Currently, periodicity is only allowed for normal-incident light. In this case, the electromagnetic fields wrap around the $x$ and $y$ directions. See the illustration to the lower right.

Illustration of periodic boundary conditions along the $x$ and $y$ directions of the computational domain.

Setting periodic boundary conditions

Periodic boundary conditions can be applied along the $x$ and/or $y$ directions in FDTD++, as illustrated by the image to the right[1]. This is accomplished using the BC keyword in the parameters file.

As an example, in order to set periodicity along both $x$ and $y$, one can add the following to the parameters file:  

 BC periodic 

or explicitly set periodicity along these directions:  

 BC periodic x BC periodic y 

The latter case also demonstrates how one may apply periodicity along only one direction.

Notes and references

1. An absorbing boundary condition is currently always set along $z$.