Actually, setting resolution to 200 leads to a closer result (cf image
link below). There is still a frequency shift of a bit inferior to
0.005 ...
But it also means that I am spatially sampling the smallest wavelength
propagating in freespace by 200/(1.125) = 180 points !!!
I was expecting that 20 points/lambda would already give a very
accurate spectrum...
Am I misunderstanding meep's "resolution"?
Thanks in advance for your comments.
Best,
Guillaume
PS: The 0° incidence doesn't actually make the use of Bloch conditions
per se (setting a perfect magnetic conductor on vertical boundaries
should lead to the same result). So I tried kx=0.8 (in units of
2*pi/a: corresponds to an incident angle of 53.13° for the central
frequency), which leads to the same quite good reflexion and
transmission coefficients for res=200 and a big f-shift for res=40.
;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;
Image:
http://imagepaste.nullnetwork.net/viewimage.php?id=1060
or
http://dl.free.fr/gR4BReoB8
;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;
[email protected] a écrit :
Dear Meep Users and Developer,
I'm new to Meep and I'd like to thank the developer for this nice soft.
As a first exercice, I'm trying to retrieve the intensity transmission
and reflexion coefficients of a dielectric slab (Fabry-Perrot). I'm
dealing with this 1D problem in 2D.
The setup is the following:
- slab: thickness = 1 (meep units), permittivity=4
- substrate & superstrate: permittivity=1
- Bloch conditions (in what follows: normal incidence)
- E field perpendicular to your screen
- f=1, df=0.25
I represented on the attached (see url below) picture a more detailed
sketch of my meep setup corresponding to the .ctl file below. I also
represented R and T obtained using Meep as well as their analytical
counterparts. In this case, f=1 is resonant an should lead to T=1 &
R=0, but I am observing a shift in frequency in Meep results.
I'm sure I'm missing something. I unsuccessfully tried many things
found on the mailing
list archives, like:
- increasing the space between source & refl flux
- increasing sx size
- increasing the pml size
- increasing the resolution
- decreasing stop-when-fields-decayed in case some f get stuck in the slab
...
Thanks for your help.
Best,
Guillaume
;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;
Image:
http://imagepaste.nullnetwork.net/viewimage.php?id=1057
or
http://dl.free.fr/hfLzFxAxc
;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;
RUN in shell:
meep norm-run?=true slab.ctl | tee slab.out0
meep slab.ctl | tee slab.out
grep flux1: slab.out > flux.dat
grep flux1: slab.out0 > flux0.dat
;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;
FILE:
slab.ctl
;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;
(set-param! resolution 40)
(define-param nfreq 200)
(set! eps-averaging? false)
(define-param a 1.)
(define-param fcen 1.)
(define-param df 0.25)
(define-param eps 4.)
(define-param eps_im 0.0)
(define-param L (* 1. a) )
(define-param sigma (/ (* 2. pi fcen 0.0) eps) )
(define-param RCyl (* 0.16 a ))
(define-param sx (* 2. a) )
(define-param sy (* 6. a))
(define-param dpml (/ 2. (+ fcen (/ df 2))))
(define-param kx1 (/ -0. a) )
(define-param theta (asin (/ kx1 fcen) ) )
(define-param theta_deg (* 180. (/ 1 pi) (asin (/ kx1 fcen))) )
(define-param norm-run? false)
;(display "theta_deg=" ) (display theta_deg )(newline)
(define sypml (+ sy (* 2. dpml))) ; cell size, including PML
(set! geometry-lattice (make lattice (size sx sypml no-size)))
(set! pml-layers (list (make pml (thickness dpml) (direction Y))))
(define kx (* 1 kx1))
(set! k-point (vector3 kx 0 0))
(set! ensure-periodicity true)
(define (my-amp-func p) (exp (* 0+2i pi kx (vector3-x p))))
(if (not norm-run?)
(set! geometry (list
(make block (center 0 0) (size sx L infinity) (material (make
dielectric (epsilon eps))))))
)
(set! sources (list
(make source
(src (make gaussian-src (frequency fcen) (fwidth df)))
(component Ez)
(center 0. (* 0.45 sy)) (size sx 0)
(amp-func my-amp-func))))
(define trans ; transmitted flux
(add-flux fcen df nfreq
(make flux-region
(center 0 (* -0.4 sy)) (size sx 0) ) ) )
(define refl ; transmitted flux
(add-flux fcen df nfreq
(make flux-region
(center 0 (* 0.4 sy)) (size sx 0) ) ) )
(if (not norm-run?) (load-minus-flux "refl-flux" refl))
(run-sources+ (stop-when-fields-decayed
50 Ez
(vector3 0 (* 0. a) )
1e-10)
(at-beginning output-epsilon)
(at-end output-efield-z)
)
(if norm-run? (save-flux "refl-flux" refl))
(display-fluxes trans refl)
;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;
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