On Mon, 7 Aug 2006, Ashifi wrote:
I would like to know if there is a way of forming a grating that extends
to infinity inside the computational domain (using the C++ interface).
The computational domain absorbing boundary condition in Meep simulates
free space, right?
No, the PML absorbing material absorbs light for whatever medium overlaps
the PML. So, if you overlap the PML with your grating then it will absorb
waves in the grating.
HOWEVER, PML has some intrinsic problems when it is applied to
discontinuous periodic structures. The basic difficulty is that PML is
essentially an analytic continuation of Maxwell's equations into
complex-coordinate space, but a discontinuous periodic function is not
analytic.
This means that, as a practical matter, when you use PML overlapping a
periodic structure, you are relying more on the adiabatic turn-on of the
PML absorptivity than on the "perfectness" of the PML. So, especially if
you operate near a low-group velocity band edge, you may need to make the
PML very thick (overlap many periods) to be effective.
Cordially,
Steven G. Johnson
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