; Calculating 2d ring-resonator modes using cylindrical coordinates,; from the Meep tutorial.(define-param n 3.4) ; index of waveguide(define-param w 1) ; width of waveguide(define-param r 1) ; inner radius of ring(define-param pad 4) ; padding between waveguide and edge of PML(define-param dpml 2) ; thickness of PML(define sr (+ r w pad dpml)) ; radial size (cell is from 0 to sr)(set! dimensions CYLINDRICAL)(set! geometry-lattice (make lattice (size sr no-size no-size))); in cylindrical coordinates, the phi (angular) dependence of the fields; is given by exp(i m phi), where m is given by:(set-param! m 3)(set! geometry (list		(make block (center (+ r (/ w 2))) (size w infinity infinity)		      (material (make dielectric (index n))))))(set! pml-layers (list (make pml (thickness dpml))))(set-param! resolution 10); If we don't want to excite a specific mode symmetry, we can just; put a single point source at some arbitrary place, pointing in some; arbitrary direction.  We will only look for TM modes (E out of the plane).(define-param fcen 0.15) ; pulse center frequency                            (define-param df 0.1)  ; pulse width (in frequency) (set! sources (list               (make source                 (src (make gaussian-src (frequency fcen) (fwidth df)))                 (component Ez) (center (+ r 0.1) 0))))	       ; note that the r -> -r mirror symmetry is exploited automatically(run-sources+ 200 (after-sources (harminv Ez (vector3 (+ r 0.1)) fcen df))); Output fields for one period at the end.  (If we output; at a single time, we might accidentally catch the Ez field when it is; almost zero and get a distorted view.)  We'll append the fields; to a file to get an r-by-t picture.  We'll also output from -sr to -sr; instead of from 0 to sr.(run-until (/ 1 fcen) 	   (in-volume (volume (center 0) (size (* 2 sr)))		      (at-beginning output-epsilon)		      (to-appended "ez" 				   (at-every (/ 1 fcen 20) output-efield-z))))