new clean branch for modeExpansion code

doc/docs/ModeExpansionFiles/wvg-taper.cpp

@@ -0,0 +1 @@
+../../../libmeepgeom/wvg-taper.cpp

doc/docs/ModeExpansionFiles/wvg-taper.py

@@ -0,0 +1,363 @@
+import meep as mp
+import numpy as np
+import h5py as h5py
+import matplotlib.pyplot as plt
+import matplotlib.animation as animation
+
+##################################################
+# x-dependent width of waveguide
+##################################################
+def w_func(x, L, p, wA, wB):
+  if L==0:
+    return wA if x<0 else wB
+  x0=x/L
+  if (x0 < -0.5):
+    return wA;
+  elif (x0 > +0.5):
+    return wB;
+  elif p==2:
+    return 0.5*(wA+wB) + (wB-wA)*x0*(15.0 + x0*x0*(-40.0 + x0*x0*48.0))/8.0;
+  elif p==1:
+    return 0.5*(wA+wB) + (wB-wA)*x0*(1.5 - 2.0*x0*x0);
+  else: # default t p==0, simple linear taper
+    return 0.5*(wA+wB) + (wB-wA)*x0;
+
+##################################################
+# user-defined function for spatially-varying epsilon
+##################################################
+def my_eps_func(loc, L, p, wA, wB, eps_out, eps_in):
+
+    if ( abs(loc.y) > 0.5*w_func(loc.x, L, p, wA, wB) ):
+     return eps_out;    # outside waveguide
+    else:
+     return eps_in;     # inside waveguide
+
+##################################################
+# user-provided functions to estimate k-vectors for waveguide eigenmodes
+##################################################
+def equal_float(a,b,Tol=1.0e-6):
+    if ( abs(a-b) < Tol*max(abs(a),abs(b)) ):
+        return True;
+    else:
+        return False;
+
+def k_guess(freq, band_num, w):
+
+    # hard-coded dispersion relations for waveguides of given size
+    if ( equal_float(w,1.0) and equal_float(freq, 0.15) ):
+        if (band_num>=1): return mp.vec(0.419984,0)
+
+    if ( equal_float(w,3.0) and equal_float(freq, 0.15) ):
+        if (band_num==1):
+            return mp.vec(0.494499,0)
+        if (band_num==2):
+            return mp.vec(0.486657,0)
+        if (band_num==3):
+            return mp.vec(0.434539,0)
+        if (band_num==4):
+            return mp.vec(0.397068,0)
+        if (band_num==5):
+            return mp.vec(0.322812,0)
+        if (band_num>=6):
+            return mp.vec(0.211186,0)
+
+    return mp.vec(0.0,0.0)
+
+##################################################
+##################################################
+##################################################
+class wvg_taper:
+
+    ##################################################
+    # constructor
+    ##################################################
+    def __init__(self,
+                 wA=1.0, wB=3.0,        # smaller, larger waveguide thickness
+                 LWaveguide=3.0,        # length of each waveguide section
+                 LTaper=3.0, pTaper=0,  # taper length and smoothness index
+                 eps_waveguide=11.7,    # permittivity inside waveguide
+                 eps_ambient=1.0,       # permittivity of medium
+                 LY=6.0,                # width of computational cell
+                 DPML=0.5,              # PML thickness
+                 fcen=0.15, df=0.075,   # center frequency / width
+                 band_num=1,            # index of eigenmode source
+                 resolution=25.0,       # grid points per unit length
+               ): 
+
+        #--------------------------------------------------------------------
+        #- user-defined epsilon function
+        #--------------------------------------------------------------------
+        eps_func = lambda loc: my_eps_func(loc, LTaper, pTaper, wA, wB,
+                                           eps_ambient, eps_waveguide)
+
+        #--------------------------------------------------------------------
+        #- eigenmode source at midpoint of smaller waveguide
+        #--------------------------------------------------------------------
+        LX = 2.0*(DPML + LWaveguide) + LTaper;
+        xA = -0.5*LX + DPML + 0.5*LWaveguide;
+        xB = +0.5*LX - DPML - 0.5*LWaveguide;
+        sources = [ mp.EigenModeSource(src=mp.GaussianSource(fcen, fwidth=df),
+                                       center=mp.Vector3(xA,0.0),
+                                       size=mp.Vector3(0.0,LY),
+                                       eig_band=band_num
+                                      )
+                  ]
+
+        self.sim=mp.Simulation( cell_size=mp.Vector3(LX, LY),
+                                resolution=resolution,
+                                boundary_layers=[mp.PML(DPML)],
+                                force_complex_fields=True,
+                                epsilon_func = eps_func,
+                                sources=sources
+                              )
+
+        self.sim.run(mp.at_beginning(mp.output_epsilon), until=1.0)
+        f=self.sim.fields;
+
+        #--------------------------------------------------
+        # add DFT flux regions at midpoints of smaller and larger waveguides
+        #--------------------------------------------------
+        YP            = 0.5*LY - DPML;
+        self.vA       = mp.volume( mp.vec(xA, -YP), mp.vec(xA,+YP) )
+        self.vB       = mp.volume( mp.vec(xB, -YP), mp.vec(xB,+YP) )
+        nf=1;
+        self.fluxA=f.add_dft_flux_plane(self.vA, fcen-0.5*df, fcen+0.5*df, nf);
+        self.fluxB=f.add_dft_flux_plane(self.vB, fcen-0.5*df, fcen+0.5*df, nf);
+
+        #--------------------------------------------------
+        # save some other fields in the wvg_taper class for later use
+        #--------------------------------------------------
+        self.xA       = xA;
+        self.xB       = xB;
+        self.wA       = wA;
+        self.wB       = wB;
+        self.LTaper   = LTaper;
+        self.pTaper   = pTaper;
+        self.fcen     = fcen;
+        self.df       = df;
+        self.band_num = band_num;
+
+    ##################################################
+    # plot permittivity over the computational grid
+    ##################################################
+    def plot_eps(self):
+
+     eps=self.sim.get_array(center    = mp.Vector3(0,0),
+                            size      = self.sim.cell_size,
+                            component = mp.Dielectric)
+
+     interp='gaussian'
+     cmap='coolwarm'
+     LX=self.sim.cell_size.x;
+     LY=self.sim.cell_size.y;
+     extent=[-0.5*LX,0.5*LX,-0.5*LY,0.5*LY];
+     plt.figure()
+
+     # plot epsilon grid
+     plt.rc('xtick', labelsize=15) 
+     plt.rc('ytick', labelsize=15) 
+     plt.imshow(eps.transpose(), interpolation=interp, cmap=cmap, extent=extent)
+     plt.xlabel(r"$x$",fontsize=40)
+     plt.ylabel(r"$y$",fontsize=40,rotation=0)
+     plt.colorbar()
+
+     # add lines and annotations to indicate locations of flux planes
+     plt.plot(self.xA*np.ones(100), np.linspace(-0.5*LY, 0.5*LY, 100), "--", lw=5, color='white')
+     plt.text(self.xA, -0.5*LY-0.5, r'$x_A$', fontsize=40, horizontalalignment='center')
+     plt.plot(self.xB*np.ones(100), np.linspace(-0.5*LY, 0.5*LY, 100), "--", lw=5, color='white');
+     plt.text(self.xB, -0.5*LY-0.5, r'$x_B$', fontsize=40, horizontalalignment='center')
+
+     plt.show(block=False)
+
+    ##################################################
+    # subroutine invoked by plot_modes and plot_flux
+    # to plot field components stored in an hdf5 file
+    ##################################################
+    def plot_fields(self, num_rows, plot_row, file_name, row_name, is_flux):
+
+      # read (tranverse) field components on cross-sectional plane from file
+      file = h5py.File(file_name + ".h5", 'r')
+      suffix = "_0" if is_flux else "";
+      ey = file["ey" + suffix + ".r"][()] + 1j*file["ey" + suffix + ".i"][()];
+      ez = file["ez" + suffix + ".r"][()] + 1j*file["ez" + suffix + ".i"][()];
+      hy = file["hy" + suffix + ".r"][()] + 1j*file["hy" + suffix + ".i"][()];
+      hz = file["hz" + suffix + ".r"][()] + 1j*file["ez" + suffix + ".i"][()];
+      if np.size(ey.shape)>1:
+        ey = np.real(ey[1,:]);
+        ez = np.real(ez[1,:]);
+        hy = np.real(hy[1,:]);
+        hz = np.real(hz[1,:]);
+
+      # plot ey,ez,hy,hz
+      eMax=max(np.absolute(ey).max(), np.absolute(ez).max());
+      hMax=max(np.absolute(hy).max(), np.absolute(hz).max());
+      NY=ey.shape[0];
+      yMax=self.vA.get_min_corner().y();
+      yRange=np.linspace(-yMax,yMax,NY);
+      r0=4*(plot_row-1);
+
+      # plot labels
+      plt.subplot(num_rows,4,r0+1); plt.plot(yRange,ey); plt.ylim(-eMax,eMax);
+      plt.subplot(num_rows,4,r0+2); plt.plot(yRange,ez); plt.ylim(-eMax,eMax);
+      plt.subplot(num_rows,4,r0+3); plt.plot(yRange,hy); plt.ylim(-hMax,hMax);
+      plt.subplot(num_rows,4,r0+4); plt.plot(yRange,hz); plt.ylim(-hMax,hMax);
+      plt.subplot(num_rows,4,1);    plt.title(r're($E_y$)',fontsize=40)
+      plt.subplot(num_rows,4,2);    plt.title(r're($E_z$)',fontsize=40)
+      plt.subplot(num_rows,4,3);    plt.title(r're($H_y$)',fontsize=40)
+      plt.subplot(num_rows,4,4);    plt.title(r're($H_z$)',fontsize=40)
+      plt.subplot(num_rows,4,r0+1); plt.ylabel(row_name,fontsize=32, rotation=0,
+                                               horizontalalignment='right')
+      plt.show(block=False);
+
+    ##################################################
+    # generate plots of eigenmode profiles
+    ##################################################
+    def plot_modes(self, nbMax=7):
+
+       ##################################################
+       # calculate the eigenmodes and write field components
+       # on cross-sectional planes to HDF5 files
+       ##################################################
+       f     = self.sim.fields;
+       vA    = self.vA;
+       vB    = self.vB;
+       fcen  = self.fcen;
+
+       plt.clf();
+
+       # eigenmode #1 in narrower waveguide
+       nb=self.band_num;
+       k0=k_guess(fcen,nb,self.wA);
+       modeA = f.get_eigenmode(fcen, mp.X, vA, vA, nb, k0, True, 0, 0.0, 1.0e-4)
+       f.output_mode_fields(modeA, self.fluxA, vA, "modeA");
+       self.plot_fields(nbMax, 1, "modeA", "Mode A1", False);
+
+       # eigenmodes #1-6 in wider waveguide
+       for nb in range(1,nbMax):
+         k0=k_guess(fcen,nb,self.wB);
+         modeB = f.get_eigenmode(fcen, mp.X, vB, vB, nb, k0, True, 0, 0.0, 1.0e-4)
+         file_name="modeB" + str(nb);
+         row_name="Mode B" + str(nb);
+         f.output_mode_fields(modeB, self.fluxB, vB, file_name);
+         self.plot_fields(nbMax, nb+1, file_name, row_name, False);
+
+       for np in range(25,29):
+           plt.subplot(nbMax,4,np); plt.xlabel(r'$y$',fontsize=32)
+
+    ##################################################
+    # add an eigenmode-source excitation for the #band_numth mode
+    # of the smaller waveguide, then timestep to accumulate DFT
+    # flux in the larger waveguide.
+    # if frame_interval>0, a movie is created showing
+    # the fields on the xy plane with one frame
+    # every frame_interval time units (in meep time)
+    ##################################################
+    def get_flux(self, frame_interval=0):
+
+       #--------------------------------------------------
+       #--------------------------------------------------
+       #--------------------------------------------------
+       nextFrameTime = 1e100;
+       f=self.sim.fields;
+       vA=self.vA;
+       vB=self.vB;
+       LTaper=self.LTaper;
+       pTaper=self.pTaper;
+       origin=mp.Vector3(0,0,0)
+       LX=self.sim.cell_size.x;
+       LY=self.sim.cell_size.y;
+       extent=[-0.5*LX,0.5*LX,-0.5*LY,0.5*LY];
+       full_grid=mp.Vector3(LX, LY, 0)
+       frames=[]
+       fig=0
+       plt.ion()
+       num_frames=0
+       if frame_interval>0:
+         fig=plt.figure();
+         nextFrameTime=f.round_time();
+
+       #--------------------------------------------------
+       # timestep until Poynting flux through larger waveguide has 
+       # decayed to 0.1% its max value
+       #--------------------------------------------------
+       pvInterval=1.0; # check PV decay every 1.0 meep time units
+       nextPVTime=f.round_time() + pvInterval;
+       MaxPV=0.0;
+       Stop=False;
+       SMax=0.0; # max poynting flux at any point
+       while Stop==False:
+
+         f.step();
+
+         # check for poynting-flux decay at regular intervals
+         FieldsDecayed=False;
+         if f.round_time() > nextPVTime:
+             nextPVTime += pvInterval;
+             ThisPV=f.flux_in_box(mp.X,vB)
+             if (ThisPV > MaxPV):
+                MaxPV = ThisPV;
+             elif (ThisPV < 0.001*MaxPV):
+                FieldsDecayed=True;
+
+         # write movie-frame files at regular intervals if requested
+         if f.round_time() > nextFrameTime:
+             nextFrameTime += frame_interval;
+             eps=self.sim.get_array(center=origin,size=full_grid,component=mp.Dielectric)
+             Sx=self.sim.get_array(center=origin,size=full_grid,component=mp.Sx)
+             SMax = max( abs(Sx.max()), SMax )
+             plt.clf();
+             eps=-eps*SMax/11.7;
+             plt.imshow(eps.transpose(), extent=extent,
+                        interpolation='gaussian', cmap='coolwarm')
+             plt.imshow(Sx.transpose(), alpha=0.5, extent=extent,
+                        interpolation='gaussian', cmap='coolwarm')
+             plt.savefig('L{}_p{}_f{}.png'.format(LTaper,pTaper,num_frames));
+             num_frames+=1;
+
+         SourcesFinished = f.round_time() > f.last_source_time();
+         Stop = (SourcesFinished and FieldsDecayed);
+
+       print("finished timestepping at {}".format(f.round_time()))
+       file_name="fluxB_p" + str(self.pTaper) + "_L" + str(self.LTaper);
+       f.output_flux_fields(wt.fluxB, wt.vB, file_name);
+       if self.LTaper==0:
+           row_name="Flux B\n(L=0)"
+       else:
+           row_name="Flux B\n(L=" + str(self.LTaper) + ", p=" + str(self.pTaper) + ")"
+       nbMax=7;
+       self.plot_fields(nbMax,1,file_name,row_name,True)
+       plt.subplot(nbMax,4,1);
+       for np in range(1,5):
+           plt.subplot(nbMax,4,np); plt.xlabel(r'$y$',fontsize=32)
+
+       # postprocessing to generate movie:
+       # ffmpeg -i frame%d.png output.mpg
+
+    ##################################################
+    # postprocessing: compute coefficients in normal-mode
+    # expansion of DFT fields in larger waveguide
+    ##################################################
+    def get_eigenmode_coefficients(self, flux, d, vol,
+                                   bands, k_guess, k_guess_data):
+      f=self.sim.fields
+      return f.get_eigenmode_coefficients(flux, d, vol, bands,
+                                          k_guess, k_guess_data)
+
+##################################################
+##################################################
+##################################################
+wt=wvg_taper(LTaper=0.0,pTaper=0,resolution=25)
+#wt.plot_modes()
+wt.get_flux(frame_interval=1);
+wt=wvg_taper(LTaper=1.0,pTaper=0,resolution=50)
+wt.get_flux(frame_interval=1);
+wt=wvg_taper(LTaper=2.0,pTaper=0,resolution=50)
+wt.get_flux(frame_interval=1);
+wt=wvg_taper(LTaper=3.0,pTaper=0,resolution=50)
+wt.get_flux(frame_interval=1);
+wt=wvg_taper(LTaper=3.0,pTaper=0,resolution=50)
+wt.get_flux(frame_interval=1);
+wt=wvg_taper(LTaper=3.0,pTaper=1,resolution=50)
+wt.get_flux(frame_interval=1);
+wt=wvg_taper(LTaper=3.0,pTaper=2,resolution=50)
+wt.get_flux(frame_interval=1);

libmeepgeom/Makefile.am

@@ -34,7 +34,10 @@ TESTS           = cyl-ellipsoid-ll array-slice-ll
 
 #LOG_COMPILER = $(RUNCODE)
 
-noinst_PROGRAMS = bend-flux-ll
+noinst_PROGRAMS = bend-flux-ll wvg-taper
+
+wvg_taper_SOURCES = wvg-taper.cpp
+wvg_taper_LDADD   = libmeepgeom.la $(MEEPLIBS)
 
 bend_flux_ll_SOURCES = bend-flux-ll.cpp
 bend_flux_ll_LDADD   = libmeepgeom.la $(MEEPLIBS)