On Apr 17, 2008, at 5:06 AM, fanguofang wrote > > I just use meep to calculate the loss of the > 300micrometer straight waveguide.The loss is very big.about just > 2e-5 of the source power.Is it normal?
You're not calculating the loss in the waveguide. (The loss in a uniform waveguide, with no absorption or disorder, is zero, even in the discretized system.) You're calculating the ratio of the energy density at the location of the source compared to the energy density farther along the waveguide. As you increase the resolution, you'll find that this ratio goes to infinity because the field of a point source in 2d diverges as the source location is approached. What you want is to put a flux-spectrum plane at some distance from the source, and another one even farther along the waveguide, if you want to do the equivalent of a "cut-back" loss-spectrum measurement. For a perfect waveguide, the ratio of the fluxes should go to 1 as you move the planes farther from the source. (For a finite distance from the source, the ratio will not be unity because some fraction of the source power couples into radiating fields rather than into the waveguide mode(s), and a flux plane a finite distance from the source will pick up some fraction of these radiating fields.) Regards, Steven G. Johnson _______________________________________________ meep-discuss mailing list [email protected] http://ab-initio.mit.edu/cgi-bin/mailman/listinfo/meep-discuss
