1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
|
;; diffraction spectra of a binary phase grating from the Meep tutorial
(set-param! resolution 60) ; pixels/μm
(define-param dpml 1.0) ; PML thickness
(define-param dsub 3.0) ; substrate thickness
(define-param dpad 3.0) ; padding between grating and PML
(define-param gp 10.0) ; grating period
(define-param gh 0.5) ; grating height
(define-param gdc 0.5) ; grating duty cycle
(define sx (+ dpml dsub gh dpad dpml))
(define sy gp)
(define cell (make lattice (size sx sy no-size)))
(set! geometry-lattice cell)
(define boundary-layers (list (make pml (thickness dpml) (direction X))))
(set! pml-layers boundary-layers)
(define-param wvl-min 0.4) ; min wavelength
(define-param wvl-max 0.6) ; max wavelength
(define fmin (/ wvl-max)) ; min frequency
(define fmax (/ wvl-min)) ; max frequency
(define fcen (* 0.5 (+ fmin fmax))) ; pulse frequency center
(define df (- fmax fmin)) ; pulse frequency width
(define pulse-src (list (make source
(src (make gaussian-src (frequency fcen) (fwidth df)))
(component Ez)
(center (+ (* -0.5 sx) dpml (* 0.5 dsub)) 0 0)
(size 0 sy 0))))
(set! sources pulse-src)
(set! k-point (vector3 0 0 0))
(define glass (make medium (index 1.5)))
(set! default-material glass)
(define symm (list (make mirror-sym (direction Y))))
(set! symmetries symm)
(define-param nfreq 21)
(define mon-pt (vector3 (- (* 0.5 sx) dpml (* 0.5 dpad)) 0 0))
(define flux-mon (add-flux fcen df nfreq (make flux-region (center mon-pt) (size 0 sy 0))))
(run-sources+ (stop-when-fields-decayed 50 Ez mon-pt 1e-9))
(define input-flux (get-fluxes flux-mon))
(define freqs (get-flux-freqs flux-mon))
(reset-meep)
(set! geometry-lattice cell)
(set! pml-layers boundary-layers)
(set! sources pulse-src)
(set! k-point (vector3 0 0 0))
(set! default-material air)
(set! geometry (list (make block
(material glass)
(size (+ dpml dsub) infinity infinity)
(center (+ (* -0.5 sx) (* 0.5 (+ dpml dsub))) 0 0))
(make block
(material glass)
(size gh (* gdc gp) infinity)
(center (+ (* -0.5 sx) dpml dsub (* 0.5 gh)) 0 0))))
(set! symmetries symm)
(define mode-mon (add-flux fcen df nfreq (make flux-region (center mon-pt) (size 0 sy 0))))
(run-sources+ (stop-when-fields-decayed 50 Ez mon-pt 1e-9))
(define-param nmode 10)
(define res (get-eigenmode-coefficients mode-mon (arith-sequence 1 1 nmode) #:eig-parity (+ ODD-Z EVEN-Y)))
(define coeffs (list-ref res 0))
(define kdom (list-ref res 3))
(map (lambda (nm)
(map (lambda (nf)
(let ((mode-wvl (/ (list-ref freqs nf)))
(mode-angle (rad->deg (acos (/ (vector3-x (list-ref kdom (+ (* nm nfreq) nf))) (list-ref freqs nf)))))
(mode-tran (/ (sqr (magnitude (array-ref coeffs nm nf 0))) (list-ref input-flux nf))))
(if (> nm 0) (set! mode-tran (* 0.5 mode-tran)))
(print "grating" nm ":, " mode-wvl ", " mode-angle ", " mode-tran "\n")))
(arith-sequence 0 1 nfreq)))
(arith-sequence 0 1 nmode))
|
