Hi, I have encountered two problems considering FFT and harmonic inversion in my script, where I am simulating the Hz field dispersion in a Silicon ring resonator using the C++ version of meep.
I have verified that the script works for defining the structure, putting out sources, source specifications (frequency, width, etc..), and finally taking the time steps. After simulating for a specific amount of time, I have verified that the FFT of the absolute value of the complex field is correct, however showing only a peak at the negative frequency. I have used both FFTW and the built in function Fourier in Mathematica with the exact same result, and I have also double checked that the frequency axis is added in the right manner. Does anybody have an idea why this result is obtained? Also, after finishing the simulation I use harminv to obtain the Q-factor. The result however, changes drastically when I change the frequency range to be looked at. The following shows the obtained results for the same data using only different frequency ranges: ~$ harminv -t 0.0833910238 *0.187-0.201* < TEharminv20R2.5w0.5win.csv frequency, decay constant, Q, amplitude, phase, error 0.19078, 4.357929e-04, 1375.32, 1.60808, 0.97982, 1.036159e-07 0.191178, 5.360495e-04, 1120.43, 3.32427, -2.10099, 8.139749e-08 0.191571, 6.221637e-04, 967.332, 1.71167, 1.08882, 3.829374e-08 *0.195086, -8.104584e-05, -7562.16, 3.33775, 1.86002, 8.828809e-08 0.195287, -1.663230e-03, -368.867, 0.0761811, 2.19598, 2.319371e-07* 0.195306, 4.195639e-03, 146.24, 3.72938, -1.98314, 5.250726e-07 0.196096, 1.465365e-04, 4204.1, 2.4614, 0.0377144, 4.772317e-09 ~$ harminv -t 0.0833910238 *0.188-0.202* < TEharminv20R2.5w0.5win.csv frequency, decay constant, Q, amplitude, phase, error 0.190773, 3.375317e-04, 1775.63, 1.39718, 0.974673, 3.576035e-08 0.19118, 5.006266e-04, 1199.72, 3.2448, -2.11978, 4.602099e-08 0.191575, 6.893856e-04, 873.025, 1.81809, 1.13573, 3.352677e-08 *0.194925, 1.809500e-04, 3384.23, 1.66174, 0.421304, 1.416149e-07 0.195264, 7.552753e-05, 8122.07, 3.04011, 3.09178, 9.494499e-08* 0.196061, 4.195050e-05, 14682.6, 2.26327, -0.261581, 4.286864e-08 0.196721, -2.523319e-02, -24.4922, 0.300972, -1.08694, 3.612169e-05 ~$ harminv -t 0.0833910238 0.*188-0.200* < TEharminv20R2.5w0.5win.csv frequency, decay constant, Q, amplitude, phase, error 0.19078, 4.319929e-04, 1387.41, 1.59757, 0.976361, 9.810212e-08 0.191178, 5.345909e-04, 1123.48, 3.32147, -2.10338, 7.966483e-08 0.191571, 6.231303e-04, 965.832, 1.71348, 1.08949, 3.880842e-08 *0.195084, -4.968604e-05, -12334.9, 3.4041, 1.82307, 8.405681e-08* 0.195302, -1.673728e-03, -366.583, 0.0712175, 2.45427, 2.272548e-07 0.195309, 3.989449e-03, 153.801, 3.83195, -1.99455, 4.981835e-07 0.196097, 1.461204e-04, 4216.09, 2.45378, 0.043353, 5.413807e-09 Has anybody else bumped in to this problem?? Help would be very much appreciated. Regards, Jakob
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