Hi every one,
I am an undergraduate student and doing my final year project
on FDTD method for Photonic crystals. I am new user of meep
and tried various simulation on Bragg Gratings. I have
following questions
1 -- Why do I get Transmission curve greator than 1 if it is normalized
to the incident field?
2 -- Why do I get a strange transmission curve for the 2-D photonic
crystal shown below the curve. It seems to be a linear curve
like the following:
| /
| /
| /
| /
------------
o o o o o o o o o o
o o o o o o o o o o
o o o o o o o o o o
o o o o o o o o o o
o o o
o o o o o o o o o o
o o o o o o o o o o o
o o o o o o o o o o
o o o o o o o o o o o
3 -- How to normalize a waveguides transmission curve if it has no
defect in it, because for normalization we do two runs i.e. one with
the defect or some structure inside it and than with no defect or
structure inside it like the following structure.
o o o o o o o o o o
o o o o o o o o o o
o o o o o o o o o o
o o o o o o o o o o
< -- waveguide with no defect in it?
o o o o o o o o o o
o o o o o o o o o o o
o o o o o o o o o o
o o o o o o o o o o o
or a simple slab waveguide or parallel plate waveguide.
Can any one help me in this problem.
I used the follwoing ctl file and is there any effeicient way or function
to generate the structure shown above.
;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;
; 2-D Photonic crystal Simulation.
;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;
(define-param sx 42) ; Size of the computational grid in x direction
(define-param sy 42) ; Size of the computational grid in y direction
(define-param dpml 2) ; PML layer thickness
(define-param no-PHC? false)
;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;
; No. of holes both in x and y directions
;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;
(define-param N 28)
;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;
; Geometry lattice of the compuational cell
;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;
(set! geometry-lattice (make lattice (size (+ sx 3) (+ sy 3) no-size)))
;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;
(set! geometry
; (list
; (make block
; (center 0 0)
; (size (+ sx 1) 2 infinity)
; (material (make dielectric (epsilon 1.45)))))
(append ; combine lists of objects:
(list (make block (center 0 0) (size (+ sx 1) (+ sy 1) infinity)
(material (make dielectric (epsilon 1.45)))))
(geometric-object-duplicates (vector3 1.5 0) 0 (- N 1)
(make cylinder (center -20.25 -20.25) (radius 0.5) (height infinity)
(material (make dielectric (epsilon 1.47)))))
(geometric-object-duplicates (vector3 1.5 0) 0 (- N 1)
(make cylinder (center -20.25 -18.75) (radius 0.5) (height infinity)
(material (make dielectric (epsilon 1.47)))))
(geometric-object-duplicates (vector3 1.5 0) 0 (- N 1)
(make cylinder (center -20.25 -17.25) (radius 0.5) (height infinity)
(material (make dielectric (epsilon 1.47)))))
(geometric-object-duplicates (vector3 1.5 0) 0 (- N 1)
(make cylinder (center -20.25 -15.75) (radius 0.5) (height infinity)
(material (make dielectric (epsilon 1.47)))))
(geometric-object-duplicates (vector3 1.5 0) 0 (- N 1)
(make cylinder (center -20.25 -14.25) (radius 0.5) (height infinity)
(material (make dielectric (epsilon 1.47)))))
(geometric-object-duplicates (vector3 1.5 0) 0 (- N 1)
(make cylinder (center -20.25 -12.75) (radius 0.5) (height infinity)
(material (make dielectric (epsilon 1.47)))))
(geometric-object-duplicates (vector3 1.5 0) 0 (- N 1)
(make cylinder (center -20.25 -11.25) (radius 0.5) (height infinity)
(material (make dielectric (epsilon 1.47)))))
(geometric-object-duplicates (vector3 1.5 0) 0 (- N 1)
(make cylinder (center -20.25 -9.75) (radius 0.5) (height infinity)
(material (make dielectric (epsilon 1.47)))))
(geometric-object-duplicates (vector3 1.5 0) 0 (- N 1)
(make cylinder (center -20.25 -8.25) (radius 0.5) (height infinity)
(material (make dielectric (epsilon 1.47)))))
(geometric-object-duplicates (vector3 1.5 0) 0 (- N 1)
(make cylinder (center -20.25 -6.75) (radius 0.5) (height infinity)
(material (make dielectric (epsilon 1.47)))))
(geometric-object-duplicates (vector3 1.5 0) 0 (- N 1)
(make cylinder (center -20.25 -5.25) (radius 0.5) (height infinity)
(material (make dielectric (epsilon 1.47)))))
(geometric-object-duplicates (vector3 1.5 0) 0 (- N 1)
(make cylinder (center -20.25 -3.75) (radius 0.5) (height infinity)
(material (make dielectric (epsilon 1.47)))))
(geometric-object-duplicates (vector3 1.5 0) 0 (- N 1)
(make cylinder (center -20.25 -2.25) (radius 0.5) (height infinity)
(material (make dielectric (epsilon 1.47)))))
;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;
; Defect Area
(geometric-object-duplicates (vector3 1.5 0) 0 (- 1 1)
(make cylinder (center 0 0) (radius 0.5) (height infinity)
(material (make dielectric (epsilon 1.47)))))
(geometric-object-duplicates (vector3 1.5 0) 0 (- 1 1)
(make cylinder (center 1.5 0) (radius 0.5) (height infinity)
(material (make dielectric (epsilon 1.47)))))
(geometric-object-duplicates (vector3 1.5 0) 0 (- 1 1)
(make cylinder (center -1.5 0) (radius 0.5) (height infinity)
(material (make dielectric (epsilon 1.47)))))
;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;
(geometric-object-duplicates (vector3 1.5 0) 0 (- N 1)
(make cylinder (center -20.25 2.25) (radius 0.5) (height infinity)
(material (make dielectric (epsilon 1.47)))))
(geometric-object-duplicates (vector3 1.5 0) 0 (- N 1)
(make cylinder (center -20.25 3.75) (radius 0.5) (height infinity)
(material (make dielectric (epsilon 1.47)))))
(geometric-object-duplicates (vector3 1.5 0) 0 (- N 1)
(make cylinder (center -20.25 5.25) (radius 0.5) (height infinity)
(material (make dielectric (epsilon 1.47)))))
(geometric-object-duplicates (vector3 1.5 0) 0 (- N 1)
(make cylinder (center -20.25 6.75) (radius 0.5) (height infinity)
(material (make dielectric (epsilon 1.47)))))
(geometric-object-duplicates (vector3 1.5 0) 0 (- N 1)
(make cylinder (center -20.25 8.25) (radius 0.5) (height infinity)
(material (make dielectric (epsilon 1.47)))))
(geometric-object-duplicates (vector3 1.5 0) 0 (- N 1)
(make cylinder (center -20.25 9.75) (radius 0.5) (height infinity)
(material (make dielectric (epsilon 1.47)))))
(geometric-object-duplicates (vector3 1.5 0) 0 (- N 1)
(make cylinder (center -20.25 11.25) (radius 0.5) (height infinity)
(material (make dielectric (epsilon 1.47)))))
(geometric-object-duplicates (vector3 1.5 0) 0 (- N 1)
(make cylinder (center -20.25 12.75) (radius 0.5) (height infinity)
(material (make dielectric (epsilon 1.47)))))
(geometric-object-duplicates (vector3 1.5 0) 0 (- N 1)
(make cylinder (center -20.25 14.25) (radius 0.5) (height infinity)
(material (make dielectric (epsilon 1.47)))))
(geometric-object-duplicates (vector3 1.5 0) 0 (- N 1)
(make cylinder (center -20.25 15.75) (radius 0.5) (height infinity)
(material (make dielectric (epsilon 1.47)))))
(geometric-object-duplicates (vector3 1.5 0) 0 (- N 1)
(make cylinder (center -20.25 17.25) (radius 0.5) (height infinity)
(material (make dielectric (epsilon 1.47)))))
(geometric-object-duplicates (vector3 1.5 0) 0 (- N 1)
(make cylinder (center -20.25 18.75) (radius 0.5) (height infinity)
(material (make dielectric (epsilon 1.47)))))
(geometric-object-duplicates (vector3 1.5 0) 0 (- N 1)
(make cylinder (center -20.25 20.25) (radius 0.5) (height infinity)
(material (make dielectric (epsilon 1.47)))))))
(set! pml-layers (list (make pml (thickness dpml))))
(set-param! resolution 20)
(define-param fcen 0.6452) ; pulse center frequency
(define-param df 0.25) ; pulse width (in frequency)
(define-param nfreq 1000) ; No. of frequencies on which flux is to be
calculated
(set! sources (list
(make source
(src (make gaussian-src (frequency fcen) (fwidth df)))
(component Ex)
(center -21 0)
(size 0 5))))
(define trans ; transmitted flux
(add-flux fcen df nfreq
(make flux-region
(center 20 0) (size 0 5))))
(run-sources+ (stop-when-fields-decayed 50 Ex (vector3 0 0) 1e-3)
(at-beginning output-epsilon)
;(to-appended "ex" (at-every 0.6 output-efield-x))
)
(display-fluxes trans) ; print out the flux spectrum
--
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