I'm working on finding Q factors and resonant frequencies of point defects in hexagonal lattices in photonic crystal slabs. I first found the photonic band gap for my particular structure to be 0.25281 - 0.32389 (normalized frequencies) using MPB. With this in mind, I used a Gaussian point source placed in a non-symmetric location within the defect area. The center frequency of the source was set at the mid-gap frequency and the frequency width of the source set to make the highest source frequency = gap top frequency and lowest source frequency = gap bottom frequency.
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). I am working with defects that are enlarged air holes in a hexagonal lattice of air holes - acceptor type defects - that theoretically should pull states into the band gap from the lower frequency dielectric band. Thus, it makes physical sense that some of these types of defects could produce defects just above the gap bottom frequency. My question - is there anything wrong with my approach and the use of the Gaussian source with frequency width = band gap frequency range. Based on what I've written, do you think these lower frequency modes near the gap bottom are real resonant defect modes? If not, is there any way to eliminate them and determine the true fundamental cavity modes? Thank you, Rob _______________________________________________ meep-discuss mailing list [email protected] http://ab-initio.mit.edu/cgi-bin/mailman/listinfo/meep-discuss
