Photonic mode solver with a nice interface and output.
The documentation for this project can be found here.
It is recommend to install modesolverpy either via:
pip3 install modesolverpy
apt install gnuplotyaourt -S python-modesolverpyIf installing using the Arch Linux AUR package or pip, dependencies will be automatically downloaded and installed, if not, one should ensure the following dependencies are installed:
Either Gnuplot or Matplotlib can be used for plotting; I am a Gnuplot user to the code was written with it in mind. If both Gnuplot and Matplotlib are installed, the code will default to Gnuplot.
EITHER:
OR:
The main reasons to consider this library include:
- semi-vectorial and fully vectorial options,
- simple structure drawing,
- automated data saving and plotting via Gnuplot,
- some limited (at this stage) data processing (finding MFD of fundamental mode), and
- easily extensible library.
The following example finds the first two modes of a waveguide with the following, arbitrary, parameters:
- thin-film thickness: 500nm
- waveguide height: 400nm,
- waveguide width: 500nm,
- refractive index of waveguide: 3,
- refractive index of substrate: 1.4,
- refractive index of cladding: 1, and
- wavelength: 1550nm.
importmodesolverpy.mode_solverasmsimportmodesolverpy.structureasstimportnumpyasnp# All units are relative. [um] were chosen in this case.x_step=0.02y_step=0.02wg_height=0.4wg_width=0.5sub_height=0.5sub_width=2.clad_height=0.5n_sub=1.4n_wg=3.n_clad=1.film_thickness=0.5wavelength=1.55angle=75.structure=st.RidgeWaveguide(wavelength,
x_step,
y_step,
wg_height,
wg_width,
sub_height,
sub_width,
clad_height,
n_sub,
n_wg,
angle,
n_clad,
film_thickness)
structure.write_to_file('example_structure_1.dat')
mode_solver=ms.ModeSolverSemiVectorial(2, semi_vectorial_method='Ey')
mode_solver.solve(structure)
mode_solver.write_modes_to_file('example_modes_1.dat')
The following looks at a contrived ridge waveguide in Z-cut KTP.
The simulation outputs:
- 5 plots for each refractive index axis (n_xx, n_xy, n_yx, n_yy and n_zz),
- 48 plots for Ex, Ey, Ez, Hx, Hy and Hz,
- 8 effective index values, one for each mode,
- a wavelength sweep of the waveguide (plotting n_eff vs wavelength for each mode),
- whether a mode is qTE or qTM and the percentage overlap with TE and TM, and
- the group velocity of the mode.
The waveguide parameters are:
- thin-film thickness: 1.2um,
- waveguide height: 800nm,
- waveguide width: 1.2um,
- refractive index of waveguide: used Sellmeier equations to get n_xx, n_yy, n_zz at 1550nm,
- refractive index of substrate: used Sellmeier equation to get SiO2 at 1550nm,
- refractive index of cladding: 1, and
- wavelength: 1550nm.
importmodesolverpy.mode_solverasmsimportmodesolverpy.structureasstimportopticalmaterialspyasmatimportnumpyasnpwl=1.55x_step=0.06y_step=0.06wg_height=0.8wg_width=1.8sub_height=1.0sub_width=4.clad_height=1.0film_thickness=1.2angle=60.defstruct_func(n_sub, n_wg, n_clad):
returnst.RidgeWaveguide(wl, x_step, y_step, wg_height, wg_width,
sub_height, sub_width, clad_height,
n_sub, n_wg, angle, n_clad, film_thickness)
n_sub=mat.SiO2().n(wl)
n_wg_xx=mat.Ktp('x').n(wl)
n_wg_yy=mat.Ktp('y').n(wl)
n_wg_zz=mat.Ktp('z').n(wl)
n_clad=mat.Air().n()
struct_xx=struct_func(n_sub, n_wg_xx, n_clad)
struct_yy=struct_func(n_sub, n_wg_yy, n_clad)
struct_zz=struct_func(n_sub, n_wg_zz, n_clad)
struct_ani=st.StructureAni(struct_xx, struct_yy, struct_zz)
struct_ani.write_to_file()
solver=ms.ModeSolverFullyVectorial(8)
solver.solve(struct_ani)
solver.write_modes_to_file()
solver.solve_ng(struct_ani, 1.55, 0.01)
solver.solve_sweep_wavelength(struct_ani, np.linspace(1.501, 1.60, 21))The group velocity at 1550nm for each mode is:
# modes_full_vec/ng.dat
# Mode idx, Group index
0,1.776
1,1.799
2,1.826
3,1.847
4,1.841
5,1.882
6,1.872
7,1.871
Only the first 4 (out of 8) modes are shown, and only the E-fields are shown (not H-fields). For the rest of the images, look in the example folder or run the script.
A_{x,y,z} give the percentage power of that particular E-field component with respect to the total of all components.
Mode types:
# modes_full_vec/mode_info
# Mode idx, Mode type, % in major direction, n_eff
0,qTE,97.39,1.643
1,qTM,92.54,1.640
2,qTE,90.60,1.576
3,qTM,91.41,1.571
4,qTE,89.48,1.497
5,qTM,86.70,1.475
6,qTE,89.47,1.447
7,qTM,68.35,1.437
Analytic calculation of the grating coupler period for various duty-cycles in SOI.
Seems to match well with the periods in Taillaert et al., Grating Couplers for Coupling between Optical Fibers and Nanophotonic Waveguides, IOP Science, 2006.
importmodesolverpy.mode_solverasmsimportmodesolverpy.structureasstimportmodesolverpy.designasdeimportopticalmaterialspyasmatimportnumpyasnpwls= [1.5, 1.55, 1.6]
x_step=0.05y_step=0.05etch_depth=0.07wg_width=10sub_height=0.5sub_width=14.clad_height=0.5film_thickness=0.22polarisation='TE'dcs=np.linspace(20, 80, 61) /100ed1=etch_depthft1=film_thicknessed2=ft1-ed1ft2=ed2periods= []
periods.append(dcs)
forwlinwls:
ngc= []
fored, ftin [(ed1, ft1), (ed2, ft2)]:
defstruct_func(n_sub, n_wg, n_clad):
returnst.RidgeWaveguide(wl, x_step, y_step, ed, wg_width,
sub_height, sub_width, clad_height,
n_sub, n_wg, None, n_clad, ft)
n_sub=mat.SiO2().n(wl)
n_wg_xx=3.46n_wg_yy=3.46n_wg_zz=3.46n_clad=mat.Air().n()
struct_xx=struct_func(n_sub, n_wg_xx, n_clad)
struct_yy=struct_func(n_sub, n_wg_yy, n_clad)
struct_zz=struct_func(n_sub, n_wg_zz, n_clad)
struct_ani=st.StructureAni(struct_xx, struct_yy, struct_zz)
#struct_ani.write_to_file()solver=ms.ModeSolverFullyVectorial(4)
solver.solve(struct_ani)
#solver.write_modes_to_file()ifpolarisation=='TE':
ngc.append(np.round(np.real(solver.n_effs_te), 4)[0])
elifpolarisation=='TM':
ngc.append(np.round(np.real(solver.n_effs_tm), 4)[0])
period=de.grating_coupler_period(wl, dcs*ngc[0]+(1-dcs)*ngc[1], n_clad, 8, 1)
periods.append(period)
filename='dc-sweep-%s-%inm-etch-%i-film.dat'% (polarisation, etch_depth*1000, film_thickness*1000)
np.savetxt(filename, np.array(periods).T, delimiter=',', header=','.join([str(val) forvalinwls]))
print(np.c_[periods])
Simulation of mode hybridisation in 220nm thick fully-etched SOI ridge waveguides.
Results look the same as those found in Daoxin Dai and Ming Zhang, "Mode hybridization and conversion in silicon-on-insulator nanowires with angled sidewalls," Opt. Express 23, 32452-32464 (2015).
importmodesolverpy.mode_solverasmsimportmodesolverpy.structureasstimportopticalmaterialspyasmatimportnumpyasnpwl=1.55x_step=0.02y_step=0.02etch_depth=0.22wg_widths=np.arange(0.3, 2., 0.05)
sub_height=1.sub_width=4.clad_height=1.film_thickness=0.22n_sub=mat.SiO2().n(wl)
n_clad=mat.Air().n(wl)
n_wg=3.476r= []
forwinwg_widths:
r.append(st.RidgeWaveguide(wl, x_step, y_step, etch_depth, w,
sub_height, sub_width, clad_height,
n_sub, n_wg, None, n_clad, film_thickness))
solver=ms.ModeSolverFullyVectorial(6)
solver.solve_sweep_structure(r, wg_widths)
solver.write_modes_to_file()
Analytic calculation of 3dB coupling length into two parallel SOI waveguides with a varying gap at 3 different TE wavelengths.
An example refractive index profile for the two waveguides spaced 200nm is shown.
importmodesolverpy.mode_solverasmsimportmodesolverpy.structureasstimportmodesolverpy.designasdeimportopticalmaterialspyasmatimportnumpyasnpimporttqdmwls= [1.5, 1.55, 1.6]
x_step=0.02y_step=0.02etch_depth=0.22wg_width=0.44sub_height=0.5sub_width=2.clad_height=0.5film_thickness=0.22gaps=np.linspace(0.1, 0.5, 11)
forwlinwls:
lengths= []
n_sub=mat.SiO2().n(wl)
n_clad=mat.Air().n(wl)
n_wg=3.476forgapintqdm.tqdm(gaps):
r=st.WgArray(wl, x_step, y_step, etch_depth, [wg_width, wg_width], gap,
sub_height, sub_width, clad_height, n_sub, n_wg, None)
#r.write_to_file()solver=ms.ModeSolverFullyVectorial(2)
solver.solve(r)
n1=solver.n_effs_te[0]
n2=solver.n_effs_te[1]
lengths.append(de.directional_coupler_lc(wl*1000, n1, n2)/2)
filename='dc-sweep-%inm-%s-%inm-etch-%i-film.dat'% (wl*1000, 'TE', etch_depth*1000, film_thickness*1000)
np.savetxt(filename, np.c_[gaps, lengths], delimiter=',', header='Coupling lengths (50\%)')
If you add functionality, please send me a pull request.
This finite difference mode solver is based on a modified version of EMpy.
Thank you to Inna Krasnokutska for testing.