Thanks much for your answer Ardavan, I will implement my code accordingly and let you know if I have an other issue. Best
2015-12-17 11:01 GMT-08:00 Ardavan Oskooi <ardavan.osk...@gmail.com>: > There are two things that need to be corrected in your simulation file to > properly observe the waveguide mode: > > 1) It's always better to compute the band diagram of your waveguide > structure first to determine the exact mode you want to excite. This would > be a 1D simulation in MPB where the Y-symmetry of the waveguide can be used > to separate the Z-EVEN modes into Y-EVEN and Y-ODD. For example, at a > frequency of 1.0, there is a Y-ODD mode at a wavevector of 1.4695. You > should also add Y-mirror symmetry to your Meep simulation to halve the size > of the computational volume. It's best to exploit as much of the symmetry > as possible. > > 2) The run function you are using, (run-until 600), is for a fixed time > interval. Since you do not know a priori how long it will take for the > modes to propagate through the waveguide, it's better to use something like > (run-sources+ (stop-when-fields-decayed 10 Ey (vector3 (+ dpml (* -0.5 sx) > pad) 0) 1e-6). This will run the simulation, periodically monitoring the > fields at the source location, until they have sufficiently decayed away. > In your case, you were running for too long as the Gaussian pulse had > already propagated through the waveguide and been absorbed by the PMLs at > the boundaries. What you were seeing in the field output at the end of the > simulation were just small numerical artifacts left in the computational > volume. > > > On 12/16/2015 05:01 PM, Nicolas Bachelard wrote: > >> Dear Meep community, >> >> I am using Meep to simulate the propagation on a singlemode waveguide in >> a 2D space. >> As I found on the Meep tutorial, I compute the transverse eigenmode of my >> waveguide >> to define my eigen-source. >> >> Then I look at the the evolution of my field (which is TE by the way) the >> shape of the >> singlemode is preserved along the waveguide (as expected). >> Nevertheless, I observe that there is a damping of the mode intensity >> along the waveguide. >> Since the mode is supposed to be supported by total internal reflection >> there should be no damping. >> Hence, I believe that I made a mistake. >> >> Does someone have any idea what I made wrong? >> I join the code below. >> >> Best regards >> >> (define-param eps 2.280100) ; dielectric constant of waveguide >> (define-param n_out 1.400000) ; dielectric constant of outside >> (define-param w 0.900000) ; width of waveguide >> (define-param sy 15.000000) ; size of cell in y direction (perpendicular >> to wvg.) >> (define-param pad 1.000000) ; padding between last hole and PML edge >> (define-param dpml 1.000000) ; PML thickness >> (define-param sx 100.000000) ; size of cell in x direction >> >> ; geometry >> (set! default-material (make dielectric (index n_out))) >> (set! geometry-lattice (make lattice (size sx sy no-size))) >> (set! geometry >> (append ; combine lists of objects: >> (list (make block (center 0 0) (size infinity w infinity) >> (material (make dielectric (epsilon eps)))) >> ))) >> >> ; PML >> (set! pml-layers (list (make pml (thickness dpml)))) >> (set-param! resolution 10.000000) >> >> ; Source TE >> (define-param fcen 1.060000) ; pulse center frequency >> (define-param df 0.500000) ; pulse width (in frequency) >> >> (set! k-point (vector3 6.660176 0 0)); Direction of eigen-source >> (set! sources (list >> (make eigenmode-source >> (src (make gaussian-src (frequency fcen) (fwidth 0.001000))) >> (component Ey) >> (size 0 (- sy (* 0 dpml))) >> (center (+ dpml (* -0.5 sx) pad) 0) >> (eig-kpoint k-point) >> (eig-match-freq? true) >> (eig-parity EVEN-Z) >> ) >> )) >> >> ; RUN >> (run-until 600.000000 >> (at-beginning output-epsilon) >> (to-appended "ey" (at-every 600.000000 output-efield-y)) >> ) >> >> -- >> >> ---------------------------------------------------------- >> Nicolas Bachelard, PhD >> NSF Nanoscale Science and Engineering Center (NSEC), >> University of California, Berkeley 3112 Etcheverry Hall, >> UC Berkeley, California 94720, USA >> >> >> _______________________________________________ >> meep-discuss mailing list >> meep-discuss@ab-initio.mit.edu >> http://ab-initio.mit.edu/cgi-bin/mailman/listinfo/meep-discuss >> > > > _______________________________________________ > meep-discuss mailing list > meep-discuss@ab-initio.mit.edu > http://ab-initio.mit.edu/cgi-bin/mailman/listinfo/meep-discuss -- ---------------------------------------------------------- Nicolas Bachelard, PhD NSF Nanoscale Science and Engineering Center (NSEC), University of California, Berkeley 3112 Etcheverry Hall, UC Berkeley, California 94720, USA
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