Uday Khankhoje <[EMAIL PROTECTED]> writes: > > Hi all, > > I am simulating a TE-like mode in a photonic crystal slab with a defect. > I had a few conceptual questions; > > 1. Does it make a difference which source I use to excite the cavity > mode: Hz, Ex or Ey? [z is the direction perpendicular to the slab, which > is itself in the xy plane.] > > 2. I run harminv after the source has turned off. > a. When I filter the modes using Ex, Ey or Hz I get different Qs. What > then, would be the actual Q of the cavity? > b. Is there a relation between a field with respect to which you filter > the modes, and the choice of the initial (exciting) source? > > Occasionally, I get negative Qs as well, even though the simulation has > been run for long enough, and harminv is run after the fields have > turned off. What is this indicative of? > > Thanks a lot. > Warm regards, > Uday > Here's a quote of Steven's previous answer to the negative Qs question:
"Remember that there is some error bar in the harminv results. If the Q is so large (decay rate is so small) that the error bar is bigger than the decay rate, this can cause it to report negative Q values. The solution is just to run for a longer time, or alternatively using a narrower-bandwidth source usually helps. If you do all this and you still see a negative Q, this means you may have exponential growth (-Q = growth lifetime). This may come from a numerical instability, or of course it will happen if you include gain in your system. You can also get -Q values if you run harminv before your source has turned off -- in that case, you are just looking at growth in the mode because energy is being pumped into it. Steven" To fix this problem, I personnally do the following: 1. Increase the resolution in the cell 2. Decrease the source bandwith 3. Turn on the eps-averaging This usually fixes the problems related to negative Qs. Nic _______________________________________________ meep-discuss mailing list [email protected] http://ab-initio.mit.edu/cgi-bin/mailman/listinfo/meep-discuss
