Learning Forum

[Chris Chase]

I see that if there are 2 dbrs back to back, the mesh size is set internally to a common value even though mesh sizes are overridden in 2 dbrs individually by mesh override region, for integer number of mesh cells per period. Is it a bug or there is some other way to get desired value. My python script is below :

 

 

 

import importlib.util 

spec_win = importlib.util.spec_from_file_location('lumapi', 'C:\\Program Files\\Lumerical\\v222\\api\\python\\lumapi.py')

import numpy as np

lumapi = importlib.util.module_from_spec(spec_win) 

spec_win.loader.exec_module(lumapi)

if not ( 'fdtd' in locals()  or 'fdtd' in globals()  ):

    fdtd = lumapi.FDTD("A")   

##############################################    

N_DBR1=4

N_DBR2=3

n1= 3.487

n2= 2.941

n3= 2.990

NUM_MESH_PER_DBR_PERIOD=6

################################################

fdtd.switchtolayout();

fdtd.deleteall();

##################   declare simulation, structure and mesh groups

props={"dimension":"2D","x": 0, "x span" :2e-6, "y min": 0, "y max": 4e-6,

       "z": 0, "mesh accuracy":1,"set simulation bandwidth":1,

       "simulation wavelength min":1e-6,"simulation wavelength max":1.1e-6} 

fdtd.addfdtd (properties=props);

props={"x": 0,"y": 0, "z": 0,"name":"epilayer_struct"} 

fdtd.addstructuregroup(properties=props);

props={"x": 0,"y": 0, "z": 0,"name":"mesh_group",} 

fdtd.addgroup (properties=props);

################# draw substrate

y_pos=0e-6; 

t=2e-6; 

props = {"x":0,"z":0,"x span":1e-6,"z":0,"z span":0, 

         "y min": y_pos,"y max": y_pos+t,"index" : n1 , "name":"substrate" } ;

fdtd.addrect(properties=props); fdtd.addtogroup("epilayer_struct");

y_pos+=t

################################################################################

#######   DBR 1

###############################################################################

print("DBR1 bot : " + str(y_pos) )

y_pos_DBR1_bot=y_pos

for k in np.arange(N_DBR1):

    t=89.3e-9; 

    props = {"x":0,"z":0, "x span":1e-6,"y min": y_pos,  "y max": y_pos+t, 

              "index" : n2,"name":"DBR1_n2",  "alpha":0.2} ;

    fdtd.addrect(properties=props); fdtd.addtogroup("epilayer_struct");

    y_pos+=t

    ####################

    t=75.3e-9; 

    props = {"x":0,"z":0, "x span":1e-6,"y min": y_pos, "y max": y_pos+t, 

              "index" : n1,"name":"DBR1_n1"} ;

    fdtd.addrect(properties=props);fdtd.addtogroup("epilayer_struct");

    y_pos+=t

    ####################

y_pos_DBR1_top=y_pos

print("DBR1 top : " + str(y_pos) )

####### add mesh DBR1

dy=(y_pos_DBR1_top-y_pos_DBR1_bot)/N_DBR1/NUM_MESH_PER_DBR_PERIOD

print("dy mesh DBR1 : " + str(dy))

props = {"x":0,"z":0,"x span":1.5e-6   ,"y min": y_pos_DBR1_bot, "y max": y_pos_DBR1_top,  

          "name":"mesh_DBR1","set maximum mesh step":1,

          "override y mesh":1,"override x mesh":0,"override z mesh":0,"dy":dy} ;

fdtd.addmesh(properties=props); fdtd.addtogroup("mesh_group");

###############################################################################

#######   DBR 2

###############################################################################

print("DBR2 bot : " + str(y_pos) )

y_pos_DBR2_bot=y_pos

for k in np.arange(N_DBR2):

    t=87.8e-9; 

    props = {"x":0,"z":0, "x span":1e-6,"y min": y_pos,"y max": y_pos+t, 

              "index" : n3, "name":"DBR2_n3","alpha":0.5} ;

    fdtd.addrect(properties=props); fdtd.addtogroup("epilayer_struct");

    y_pos+=t

    ####################

    t=75.3e-9; 

    props = {"x":0,"z":0, "x span":1e-6,"y min": y_pos,"y max": y_pos+t, 

              "index" : n1,"name":"DBR2_n1"} ;

    fdtd.addrect(properties=props); fdtd.addtogroup("epilayer_struct");

    y_pos+=t

    ####################

y_pos_DBR2_top=y_pos

print("DBR2 top : " + str(y_pos) )  

####### add mesh DBR2  

dy=(y_pos_DBR2_top-y_pos_DBR2_bot)/N_DBR2/NUM_MESH_PER_DBR_PERIOD

print("dy mesh DBR2 : " + str(dy))

props = {"x":0,"z":0,"x span":1.5e-6   ,"y min": y_pos_DBR2_bot,"y max": y_pos_DBR2_top,  

          "name":"mesh_DBR2","set maximum mesh step":1,

          "override y mesh":1,"override x mesh":0, "override z mesh":0,"dy":dy          } ;

fdtd.addmesh(properties=props); fdtd.addtogroup("mesh_struct");

##############################################################################

#### LINE MONITOR to get y mesh 

##############################################################################

props = {"monitor type":"Linear Y","x":0,"z":0,"y min":1.5e-6   ,"y max": 4e-6} ;

fdtd.addpower(properties=props);

##########################

fdtd.run();

######### y mesh

y=fdtd.getresult("monitor","y") ;print( np.diff(y[:,0]) )