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

# Python Module: varFDTD_y_branch.py

#

# Description:

# This module defines the y_brach_init_() function used in the

# optimization for inverse design of the SOI Y-branch in 2D

#

# Steps include:

# 1. Define the base simulation parameters

# 2. Add non-dispersive materials

# 2. Define the geometry of input and output waveguides

# 3. Set up source and monitors and simulation region

#

# Copyright 2019, Lumerical Solutions, Inc.

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

 

######## IMPORTS ########

# General purpose imports

import lumapi

import numpy as np

from scipy.constants import c

 

def y_branch_init_(mode):

 

## CLEAR SESSION

mode.switchtolayout()

mode.selectall()

mode.delete()

 

## SIM PARAMS

size_x=40e-6;

size_y=20e-6;

mesh_x=200e-9;

mesh_y=200e-9;

finer_mesh_size=19e-6;

mesh_accuracy=4;

lam_c = 1.550e-6;

thickness=2e-6;

separation=5e-6; #waveguide separation

coupler_length=24e-6;

width=2.4e-6; #waveguide

length=10e-6; #connecting waveguide

 

## MATERIAL

opt_material=mode.addmaterial('Dielectric');

mode.setmaterial(opt_material,'name','Si: non-dispersive');

n_opt = mode.getindex('Si (Silicon) - Palik',c/lam_c);

mode.setmaterial('Si: non-dispersive','Refractive Index',n_opt);

#print(n_opt);

 

sub_material=mode.addmaterial('Dielectric');

mode.setmaterial(sub_material,'name','SiO2: non-dispersive');

n_sub = mode.getindex('SiO2 (Glass) - Palik',c/lam_c);

mode.setmaterial('SiO2: non-dispersive','Refractive Index',n_sub);

mode.setmaterial('SiO2: non-dispersive',"color", np.array([0, 0, 0, 0]));

 

air_material=mode.addmaterial('Dielectric');

mode.setmaterial(opt_material,'name','air');

mode.setmaterial('air','Refractive Index',1);

 

wg_material=mode.addmaterial('Dielectric');

mode.setmaterial(opt_material,'name','SU-8');

mode.setmaterial('SU-8','Refractive Index',1.573);

 

## GEOMETRY

 

#INPUT WAVEGUIDE

 

mode.addrect();

mode.set('name','input wg');

mode.set('x span',10e-6);

mode.set('y span',width);

mode.set('z span',thickness);

mode.set('y',-separation/2);

mode.set('x',-coupler_length/2-length/2);

mode.set('z',0);

mode.set('material','SU-8');

 

mode.addrect();

mode.set('name','input wg 2');

mode.set('x span',10e-6);

mode.set('y span',width);

mode.set('z span',thickness);

mode.set('y',separation/2);

mode.set('x',-coupler_length/2-length/2);

mode.set('z',0);

mode.set('material','SU-8');

 

#OUTPUT WAVEGUIDES

 

mode.addrect();

mode.set('name','output wg top');

mode.set('x span',10e-6);

mode.set('y span',width);

mode.set('z span',thickness);

mode.set('y',separation/2);

mode.set('x',coupler_length/2+length/2);

mode.set('z',0);

mode.set('material','SU-8');

 

mode.addrect();

mode.set('name','output wg bottom');

mode.set('x span',10e-6);

mode.set('y span',width);

mode.set('z span',thickness);

mode.set('y',-separation/2);

mode.set('x',coupler_length/2+length/2);

mode.set('z',0);

mode.set('material','SU-8');

 

mode.addrect();

mode.set('name','sub');

mode.set('x span',100e-6);

mode.set('y span',100e-6);

mode.set('z span',10e-6);

mode.set('y',0);

mode.set('x',0);

mode.set('z',0);

mode.set('material','SiO2: non-dispersive');

mode.set('override mesh order from material database',1);

mode.set('mesh order',3);

mode.set('alpha',0.8);

 

## varFDTD

mode.addvarfdtd();

mode.set('mesh accuracy',mesh_accuracy);

mode.set('x min',-size_x/2);

mode.set('x max',size_x/2);

mode.set('y min',-size_y/2);

mode.set('y max',size_y/2);

mode.set('z',0);

mode.set('z span',4e-6);

 

mode.set('effective index method','variational');

mode.set('can optimize mesh algorithm for extruded structures',1);

mode.set('clamp values to physical material properties',1);

 

mode.set('x0',-1.3e-6);

mode.set('number of test points',4);

mode.set('test points',np.array([[0, 0],[1.3e-6, 0.4e-6], [1.3e-6, -0.4e-6], [1.3e-6, 0]]));

 

## SOURCE

mode.addmodesource();

mode.set('direction','Forward');

mode.set('injection axis','x-axis');

#mode.set('polarization angle',0);

mode.set('y',-separation/2);

mode.set("y span",width);

mode.set('x',-coupler_length/2-5e-6);

mode.set('center wavelength',1550e-9);

mode.set('wavelength span',0);

mode.set('mode selection','fundamental mode');

 

 

## MESH IN OPTIMIZABLE REGION

mode.addmesh();

mode.set('x',0);

mode.set('x span',finer_mesh_size);

mode.set('y',0);

mode.set('y span',finer_mesh_size);

mode.set('dx',mesh_x);

mode.set('dy',mesh_y);

mode.set('z span',4e-6);

 

## OPTIMIZATION FIELDS MONITOR IN OPTIMIZABLE REGION

 

mode.addpower();

mode.set('name','opt_fields');

mode.set('monitor type','2D Z-normal');

mode.set('x',0);

mode.set('x span',0.95*size_x);

mode.set('y',0);

mode.set('y span',0.95* size_y);

mode.set('z',0);

 

## FOM FIELDS

 

mode.addpower();

mode.set('name','fom');

mode.set('monitor type','Linear Y');

mode.set('x',coupler_length/2+1.5e-6);

mode.set('y',0);

mode.set('y span',size_y);

mode.set('z',0);

 

 

if __name__ == "__main__":

mode = lumapi.MODE(hide = False)

y_branch_init_(mode)

input('Press Enter to escape...')