Hello Prof. Johnson and MEEP users, I tried to calculate the transmission/refection of a 2D photonic crystal slab by following the tutorial. However, the obtained spectra are not correct: T+R>1 (oscillation) as shown in the attached figure. My CTL file is enclosed below. In brief, the structure is consisting of 4-layer cylinders in air, with periodic boundary condition along the lateral direction and PML along the other direction. Could you please tell me what's wrong? I also wonder if there is reflection between the source plane and the structure. Thanks a lot.
Regards,
XY
======================================================
(define-param
sx 1) ; size of cell in X direction
(define-param sy 30) ; size of
cell in Y direction
(define pi (* 4 (atan 1))) ; 3.14159...
(set!
geometry-lattice (make lattice (size sx sy
no-size)))
(define-param freespace? false) ; if true, have no
structure
(set! geometry
(if freespace?
(list
(make block (center 0) (size infinity infinity
infinity) (material air)))
(list
(make
cylinder (center 0 -1.5) (radius r) (height infinity) (material Si))
(make cylinder (center 0 -0.5) (radius r) (height infinity) (material
Si))
(make cylinder (center 0 0.5) (radius r) (height
infinity) (material Si))
(make cylinder (center 0 1.5)
(radius r) (height infinity)
(material Si))
)))
(define-param kx 0.2)
(define-param
fcen 0.63373) ; pulse center
frequency
(define-param df 0.24) ; pulse width (in
frequency)
(define (my-amp-func p)
(exp (* 0+2i pi kx
(vector3-x p))))
(set! sources (list
(make
source
(src (make gaussian-src (frequency fcen)
(fwidth df)))
(component Ez) (amp-func my-amp-func)
(center 0 -10) (size sx 0))))
(set! pml-layers (list (make
pml (thickness 4) (direction Y))))
(set! k-point (vector3 kx 0
0))
(set-param! resolution
50)
(define-param nfreq 1500) ; number of frequencies at which
to compute flux
(define trans ; transmitted flux
(add-flux
fcen df nfreq
(make flux-region (center 0 5)
(size sx 0))))
(define refl ; reflected flux
(add-flux fcen
df nfreq
(make flux-region (center 0 -5) (size sx
0))))
(if (not freespace?) (load-minus-flux "refl-flux"
refl))
(run-sources+ 5000 (at-beginning output-epsilon))
(if
freespace? (save-flux "refl-flux" refl))
(display-fluxes trans
refl)
<<attachment: TR.png>>
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