Dear Steven and MEEP users, I found a problem(may a bug?) when I use meep package to do simulations of plasmonic waveguide(metal-insulator-metal). The structure is very simple, similar to the waveguide structure in meep tutorial, but using silver instead of dielectric medium. The unit is set as 100nm and the resolution is 20, so the grid size is 5nm. The width of waveguide is set as 100nm (or 20 pixels). After some steps, a strange field pattern occur at the boundary of the waveguide (attached to this message). I have done many tests. When I change the width of 100nm to 99.999999nm, the problem is solved. I read the antisotropic_averaging.cpp and polarization.cpp, there may be a bug in grid plitting procedure of 2D structure. I don't know how to fix it, but I did many tests and found a way to avoid it. I found that, width/2 (in pixel) must set as N-0.5<width/2<N, N is a integer, otherwise there would be a dislocation at the boundary.
I used apt-get tools to install meep 0.10 directly in Debian lenny.
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My ctl script:
(define a 100e-9) ; define the unit, 100 nm
(define sx 20) ; size of x, 4 um
(define sy 5) ; size of y
(define dpml 1)
(use-output-directory)
(set! geometry-lattice
(make lattice (size sx sy no-size)))
; ------------------------------------
; define material silver
(define cc (/ (* 2 (* pi 3e+8)) a)) ; unit of frequency in meep
(define wp_ag (/ 1.3798e16 cc))
(define gamma_ag (/ 2.72293e13 cc))
(define Ag
(make dielectric (epsilon 3.7)
(polarizations (make polarizability
(omega 1e-20)
(gamma gamma_ag)
(delta-epsilon (* wp_ag wp_ag 1e40))))))
(define wid 1)
;(define wid 0.9999)
(set! default-material Ag)
(set! geometry
(list
(make block
(center 0 0)
(size sx wid infinity)
(material air))))
; set source
(set! sources (list
(make source
(src (make continuous-src (wavelength 6.5) (width 20)))
(component Hz)
(center -9 0)
(size 0 0))))
; ---------------------------------------------
(set! pml-layers (list
(make pml (thickness dpml) (direction X))))
(set! resolution 20)
(run-until 50 (at-beginning output-epsilon)
(at-every 2 (output-png Hz "-Zc dkbluered")))
Best wishes,
JL Liu
2008-12-28
hz-000044.00.png
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