EME: GDS
To simulate more complex structures, a GDS import function is used to support any geometry that can be created on a mask GDS file. This example shows how an s-bend structure can be created in a GDS file, imported to EMode, and simulated as part of a directional coupler.
This code example is licensed under the BSD 3-Clause License.
First, the GDS is created.
from phidl import Path, CrossSection, Device
import phidl.geometry as pg
import phidl.path as pp
from phidl import quickplot as qp
## Parameters
width_wg = 0.6 # [um]
gap_input = 2.0 # [um]
gap_output = 0.3 # [um]
L_bend = 6.0 # [um]
## Create the first CrossSection
X1 = CrossSection()
X1.add(width = width_wg,
offset = -gap_input/2 - width_wg/2, layer = 1,
name = 'wg1', ports = ('in1', 'out1'))
X1.add(width = width_wg,
offset = gap_input/2 + width_wg/2, layer = 1,
name = 'wg2')
## Create the second CrossSection
X2 = CrossSection()
X2.add(width = width_wg,
offset = -gap_output/2 - width_wg/2, layer = 1,
name = 'wg1', ports = ('in2', 'out2'))
X2.add(width = width_wg,
offset = gap_output/2 + width_wg/2, layer = 1,
name = 'wg2')
## Transition from first to second CrossSection
Xtrans = pp.transition(cross_section1 = X1, cross_section2 = X2, width_type = 'sine')
P3 = pp.straight(length = L_bend)
WG_trans = P3.extrude(Xtrans)
## Place all CrossSection extrusions
D = Device()
wgt = D << WG_trans
## Quickplot to view
qp(D)
## Save gds file
D.write_gds('sbend.gds')
Next, the directional coupler device is created and simulated for a short coupler length. The sweep function is used to optimize the coupler length for 100 % coupling, and the propagation is re-plotted.
import emodeconnection as emc
from matplotlib import pyplot as plt
import numpy as np
import sys
## Set simulation parameters
wavelength = 1550 # [nm] wavelength
dx, dy = 20, 10 # [nm] resolution
h_core = 220 # [nm] waveguide core height
h_clad = 1200 # [nm] waveguide top and bottom clad
width_wg = 600 # [nm]
gap = 300 # [nm]
input_gap = 2000 # [nm]
window_height = h_core + h_clad*2
num_modes = 2 # [-] number of modes
BC = 'TE-v'
## Connect and initialize EMode
em = emc.EMode()
## Settings
em.settings(wavelength = wavelength,
x_resolution = dx, y_resolution = dy,
window_height = window_height,
num_modes = num_modes, boundary_condition = BC,
background_refractive_index = 'SiO2')
## Draw shapes
em.shape(name = 'BOX', refractive_index = 'SiO2',
height = h_clad)
em.shape(name = 'core', refractive_index = 'Si',
height = h_core, etch_depth = h_core)
## Create profiles
em.settings(window_width = 5200)
em.label(label = 'slab')
em.settings(window_width = 3200)
em.shape(name = 'core', mask = [width_wg, width_wg],
mask_offset = [-gap/2-width_wg/2, gap/2+width_wg/2])
em.label(label = 'coupler')
## Draw EME sections
em.section(name = 'sbend', section_type = 'gds',
gds = 'sbend.gds', profile = 'slab',
shape_to_mask = 'core', num_modes = num_modes,
length = 10e3, # modify length of gds
minimum_z_step = 50, overlap_variation = 0.05)
em.section(name = 'coupler', section_type = 'straight',
profile = 'coupler', length = 30e3,
num_modes = num_modes)
em.section(section_type = 'copy',
section_name = 'sbend', mirror = True)
## Run EME and plot results
em.EME()
em.plot()
## Sweep the coupler length and plot results
data = em.sweep(key='section, coupler, length',
values = np.arange(0, 200.1e3, 5000),
result = ['S_matrix'])
S = data['S_matrix']
plt.plot(data['values']*1e-3, np.abs(S[:,1,0,0])**2*100)
plt.xlabel("Coupler length (\u03BCm)")
plt.ylabel("Transmission (%)")
plt.autoscale(enable=True, axis='x', tight=True)
plt.ylim([0,100])
plt.show()
## Plot final design for 100 % coupler
em.section(name = 'coupler', length = 180e3)
em.EME()
em.plot()
## Close EMode
em.close()
%% Set simulation parameters
wavelength = 1550; % [nm] wavelength
dx = 20; dy = 10; % [nm] resolution
h_core = 220; % [nm] waveguide core height
h_clad = 1200; % [nm] waveguide top and bottom clad
width_wg = 600; % [nm]
gap = 300; % [nm]
input_gap = 2000; % [nm]
window_height = h_core + h_clad*2;
num_modes = 2; % [-] number of modes
BC = 'TE-v';
%% Connect and initialize EMode
em = emodeconnection();
%% Settings
em.settings('wavelength', wavelength, ...
'x_resolution', dx, 'y_resolution', dy, ...
'window_height', window_height, ...
'num_modes', num_modes, 'boundary_condition', BC, ...
'background_refractive_index', 'SiO2');
%% Draw shapes
em.shape('name', 'BOX', 'refractive_index', 'SiO2', ...
'height', h_clad);
em.shape('name', 'core', 'refractive_index', 'Si', ...
'height', h_core, 'etch_depth', h_core);
%% Create profiles
em.settings('window_width', 5200);
em.label('label', 'slab');
em.settings('window_width', 3200);
em.shape('name', 'core', 'mask', [width_wg, width_wg], ...
'mask_offset', [-gap/2-width_wg/2, gap/2+width_wg/2]);
em.label('label', 'coupler');
%% Draw EME sections
em.section('name', 'sbend', 'section_type', 'gds', ...
'gds', 'sbend.gds', 'profile', 'slab', ...
'shape_to_mask', 'core', 'num_modes', num_modes, ...
'length', 10e3, ... % modify length of gds
'minimum_z_step', 50, 'overlap_variation', 0.05);
em.section('name', 'coupler', 'section_type', 'straight', ...
'profile', 'coupler', 'length', 30e3, ...
'num_modes', num_modes);
em.section('section_type', 'copy', ...
'section_name', 'sbend', 'mirror', true);
%% Run EME and plot results
em.EME();
em.plot();
%% Sweep the coupler length and plot results
data = em.sweep('key', 'section, coupler, length', ...
'values', 0:5000:200e3, ...
'result', ['S_matrix']);
S = data.S_matrix;
figure;
plot(squeeze(data.values)*1e-3, abs(squeeze(S(1,1,1,2,:))).^2*100);
hold on;
plot(squeeze(data.values)*1e-3, abs(squeeze(S(1,2,1,2,:))).^2*100);
xlabel(append('Coupler length (', char(181), 'm)'));
ylabel('Transmission (%)');
xlim([min(data.values*1e-3) max(data.values*1e-3)]);
ylim([0 100]);
%% Plot final design for 100 % coupler
em.section('name', 'coupler', 'length', 180e3);
em.EME();
em.plot();
%% Close EMode
em.close();
Console output:
EMode 0.1.1 - email
Solving S-matrices...
Solving section: sbend... completed in 1 min 47.8 sec
Solving section: coupler... completed in 0.6 sec
Solving section: 1... completed in 24.3 sec
completed in 2 min 13.9 sec
Sweeping section parameter 'length'... completed in 26.3 sec
Solving S-matrices...
Solving section: sbend... completed in 0.1 sec
Solving section: coupler... completed in 0.0 sec
Solving section: 1... completed in 0.0 sec
completed in 0.7 sec
Exited EMode
Figures:
