On Fri, 27 Apr 2007, Rob wrote: > My problem is that I seem to getting resonant frequencies near the gap > bottom frequency that (based on trying to repeat simulations from > literature) I do not believe are the actual fundamental modes of the > cavity. For my example, the modes appear at frequencies such as 0.2553, > 0.2571, 0.25509, and 0.2607 and have both negative and postive Q values > in the +/- 200 to 600 range. In addition to these lower frequency modes > near the gap bottom, I get higher frequency modes, which I believe are > the actual fundamental cavity modes (again based on literature).
This is not a problem per se---it is a real physical effect. At the edge of the gap, by definition you have an extremum of the bands and therefore the slope of the bands goes to zero. The slope, of course, is the group velocity, so these are slow-light modes which persist for a long time before escaping. For this reason, one almost always observes moderate-Q resonant modes at the band edge(s), in addition to the localized defect modes one observes in the gap. If you look at the fields (by exciting with a narrow-bandwidth source), then you will see that these band-edge states are precisely standing wave modes corresponding to the band edge (thus, they are not localized spatially at all). Cordially, Steven G. Johnson _______________________________________________ meep-discuss mailing list [email protected] http://ab-initio.mit.edu/cgi-bin/mailman/listinfo/meep-discuss
