On Thu, 27 Apr 2006, Florencio Garcia wrote:
I'm trying (as an exercise) to calculate the reflectance and
transmittance of a simple cubic lattice. I have a gaussian source, which
is a 1x1 plane perpendicular to the Z direction. The frequency center is
0.5 and the fwidth is 0.8. However, when I plot the flux for the empty
space (the reference to divide the flux from structure later), the
spectrum that I get shows null intensity up to 0.5 and then it suddenly
increases and shows half of a gaussian over 0.5. In other words, there
is nothing under 0.5! If I do something similar in 2D with line sources
(and flux collectors), I don't see this problem and I get a nice
gaussian... What am I doing wrong?
Add the line:
(set-param! k-point (vector3 0))
The problem you are having is due to the fact that Meep defaults to
metallic boundary conditions, whereas you want periodic boundary
conditions. To turn on periodic boundaries, you have to specify the
k-point (k=0 for ordinary periodic boundaries).
With metallic structures, you effectively have a square metallic waveguide
structure in the z direction, and such a waveguide has a lower cutoff
frequency below which there is no guided mode. Hence, you see low
transmission below this cutoff. In 2d, on the other hand, for the Ex
polarization (perpendicular to the boundaries), there is no cutoff which
is why things looked okay to you..
Steven
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