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;; true: plot the scattered fields in the air region adjacent to the grating
;; false: plot the diffraction spectra based on a 1d cross section of the scattered fields
(define-param field-profile? true)
(set-param! resolution 50) ; pixels/μm
(define-param dpml 1.0) ; PML thickness
(define-param dsub 2.0) ; substrate thickness
(define-param dpad 1.0) ; flat-surface padding
(define-param dair ; air region thickness adjacent to grating
(if field-profile? 10 dpad))
(define-param gp 1.0) ; grating periodicity
(define-param gh 0.5) ; grating height
(define-param gdc 0.5) ; grating duty cycle
(define-param num-cells 5) ; number of grating unit cells
(define-param wvl 0.5) ; center wavelength
(define fcen (/ wvl)) ; center frequency
(set! k-point (vector3 0))
(define glass (make medium (index 1.5)))
(set! pml-layers (list (make pml (thickness dpml))))
(set! symmetries (list (make mirror-sym (direction Y))))
(define sx (+ dpml dsub gh dair dpml))
(define sy (+ dpml dpad (* num-cells gp) dpad dpml))
(set! geometry-lattice (make lattice (size sx sy no-size)))
(define src-pt (vector3 (+ (* -0.5 sx) dpml (* 0.5 dsub))))
(define pw-source (list (make source
(src (make gaussian-src (frequency fcen) (fwidth (* 0.2 fcen)) (is-integrated? true)))
(component Ez)
(center src-pt)
(size 0 sy))))
(set! sources pw-source)
(set! geometry (list (make block
(material glass)
(size (+ dpml dsub) infinity infinity)
(center (+ (* -0.5 sx) (* 0.5 (+ dpml dsub)))))))
(define mon-pt (vector3 (- (* 0.5 sx) dpml (* 0.5 dair))))
(define flat-fields (add-dft-fields (list Ez) fcen fcen 1 (volume (center mon-pt) (size (if field-profile? dair 0) (- sy (* 2 dpml))))))
(run-sources+ 100)
(output-dft flat-fields "flat")
(reset-meep)
(set! pml-layers (list (make pml (thickness dpml))))
(set! symmetries (list (make mirror-sym (direction Y))))
(set! geometry-lattice (make lattice (size sx sy no-size)))
(set! k-point (vector3 0))
(set! sources pw-source)
(set! geometry (list (make block
(material glass)
(size (+ dpml dsub) infinity infinity)
(center (+ (* -0.5 sx) (* 0.5 (+ dpml dsub)))))))
(set! geometry (append geometry
(map (lambda (n)
(make block
(material glass)
(size gh (* gdc gp) infinity)
(center (+ (* -0.5 sx) dpml dsub (* 0.5 gh)) (+ (* -0.5 sy) dpml dpad (* (+ n 0.5) gp)) 0)))
(arith-sequence 0 1 num-cells))))
(define grating-fields (add-dft-fields (list Ez) fcen fcen 1 (volume (center mon-pt) (size (if field-profile? dair 0) (- sy (* 2 dpml))))))
(run-sources+ 100)
(output-dft grating-fields "grating")
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