Hi Mohammad, I have encountered this same problem as well. One trick to minimize the dispersion is to make the pulse center frequency at the high end of the frequencies you are interested in, thus using the flatter end of the dispersion curve. I do this by scaling the geometry larger, not by changing fcen and df (I use 1 and 2 as you have in your code). Another thing to try is to define a dispersive model for your material that is relatively flat in the region of interest. This is all I know to try; if there are any other solutions, I would be interested in hearing them as well.
Matt Miskiewicz On Mon, Aug 23, 2010 at 6:17 AM, mohammad mousavi < [email protected]> wrote: > *Dear Professor Steven and all MEEP users* > > I have tried to analyze a simple nonlinear (CHI3) 1D-straght structure with > fix index=3.48 but unfortunately it looks like a dispersive material. i.e. > the index changes by wavelength so I checked the index by another structure > like below: > > I have used MEEP example for epsilon: > > http://ab-initio.mit.edu/wiki/index.php/Meep_Tutorial/Material_dispersion > > *But I have changed it like this (a simple linear material with > epsilon=12.1104):* > > (reset-meep) > > > > (set! geometry-lattice (make lattice (size no-size no-size no-size))) > > (set-param! resolution 50) > > > > (set! default-material (make dielectric (epsilon 12.1104))) > > > > (define-param fcen 1) > > (define-param df 2) > > (set! sources (list (make source > > (src (make gaussian-src (frequency > fcen) (fwidth df))) > > (component Ez) (center 0 0 0)))) > > > > (define-param kmin 0.3) > > (define-param kmax 3) > > (define-param k-interp 99) > > (define kpts (interpolate k-interp (list (vector3 kmin) (vector3 kmax)))) > > > > (define all-freqs (run-k-points 200 kpts)) ; a list of lists of frequencies > > > > (map (lambda (kx fs) > > (map (lambda (f) > > (print "eps:, " (real-part f) ", " (imag-part f) > > ", " (sqr (/ kx f)) "\n")) > > fs)) > > (map vector3-x kpts) all-freqs) > > > > > > *Output is:* > > Epsilon varies from 12.11 to 12.98 for frequencies (0.3 to 2). I > have attached the plot. > > Is there any error that MEEP can’t keep index fix for different frequency? > > What should I do to fix index? > > Thanks. > > > _______________________________________________ > meep-discuss mailing list > [email protected] > http://ab-initio.mit.edu/cgi-bin/mailman/listinfo/meep-discuss >
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