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;; phase map 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 0.35) ; grating period
(define-param gh 0.6) ; 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-param nfreq 21) ; number of frequency bins
(define-param odd-z? true)
(define pulse-src (list (make source
(src (make gaussian-src (frequency fcen) (fwidth df)))
(component (if odd-z? Ez Hz))
(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) (phase (if odd-z? +1 -1)))))
(set! symmetries symm)
(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+ 100)
(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+ 300)
(define res (get-eigenmode-coefficients mode-mon (list 1) #:eig-parity (if odd-z? (+ ODD-Z EVEN-Y) (+ EVEN-Z ODD-Y))))
(define coeffs (list-ref res 0))
(map (lambda (nf)
(let ((mode-wvl (/ (list-ref freqs nf)))
(mode-tran (/ (sqr (magnitude (array-ref coeffs 0 nf 0))) (list-ref input-flux nf)))
(mode-phase (angle (array-ref coeffs 0 nf 0))))
(print "grating" nf ":, " mode-wvl ", " mode-tran ", " mode-phase "\n")))
(arith-sequence 0 1 nfreq))
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