Multimode interferometer

SiFab contains three multimode interferometers (MMI):

  • MMI1x2: a fully parametric MMI, with one input and two outputs.

  • MMI1x2Optimized1310: an 1x2 MMI with locked properties optimized for 1310 micrometers.

  • MMI1x2Optimized1550: an 1x2 MMI with locked properties optimized for 1550 micrometers.

The section Simulation and regeneration of the data files explains how to simulate and regenerate the simulation data of an MMI. The section Creating a new optimized MMI explains how to create a new optimized MMI with different layout parameters.

MMI1x2

This is an MMI with fully customisable layout. This class has a circuit model where the following parameters can be provided to perform a circuit simulation of the MMI: center_wavelength, transmission, reflection_in and reflection_out.

Reference

Click on the name of the component below to see the complete PCell reference.

si_fab.all.MMI1x2

MMI with 1 input and 2 outputs.

Example

from si_fab import all as pdk

mmi = pdk.MMI1x2(
    trace_template=pdk.SiWireWaveguideTemplate(),
    width=5.0,
    length=15.0,
    taper_width=1.5,
    taper_length=4.0,
    waveguide_spacing=2.5,
)
mmi_lv = mmi.Layout()
mmi_lv.visualize(annotate=True)
../../../../../../../../_images/example_mmi_1x2.png

MMI Model

For the 1x2 MMI, we use the following model:

\[\begin{split}\begin{array}{c} S[in_1, out_1] &=& S[out_1, in_1] &=& t \\ S[in_1, out_2] &=& S[out_2, in_1] &=& t \\ S[in_1, in_1] &=& r_1 &=& r_1 \\ S[out_1, out_1] &=& S[out_2, out_2] &=& r_1 &=& r_2 \end{array}\end{split}\]

where \(t\) is the transmission (through), \(r_1\) is the reflection at the input and \(r_2\) is the reflection at the output. \(t\), \(r_1\), \(r_2\) are dispersive with respect to wavelength.

MMI1x2Optimized1550

This MMI inherits from MMI1x2. All the properties are locked, because the layout has been optimized to obtain maximum transmission at 1550 nm wavelength. The optimization and simulation of this component have been performed using CAMFR, the built-in 2D solver of IPKISS. After the simulation, a fitting is performed of the transmission and reflections as a function of wavelength. The fitting coefficients for \(t\), \(r1\), \(r2\) are stored and used by Caphe to calculate the S-matrix and perform a circuit simulation.

Reference

Click on the name of the component below to see the complete PCell reference.

si_fab.all.MMI1x2Optimized1550

MMI1x2 with layout parameters optimized for maximum transmission at 1550 nm.

Example

from si_fab import all as pdk
from ipkiss3 import all as i3
import numpy as np
import pylab as plt

mmi = pdk.MMI1x2Optimized1550()
mmi_lv = mmi.Layout()
mmi_lv.visualize(annotate=True)

mmi_cm = mmi.CircuitModel()

wavelengths = np.linspace(1.5, 1.6, 51)
S = mmi_cm.get_smatrix(wavelengths=wavelengths)
plt.figure()
plt.title("MMI transmission")
plt.plot(wavelengths, i3.signal_power_dB(S["out1", "in1"]), "-", linewidth=2.2, label="T(out1)")
plt.plot(wavelengths, i3.signal_power_dB(S["out2", "in1"]), "-", linewidth=2.2, label="T(out2)")
plt.plot(wavelengths, i3.signal_power_dB(S["in1", "in1"]), "-", linewidth=2.2, label="R(in1)")
plt.ylim(-60, 5)
plt.xlabel("Wavelength [um]", fontsize=16)
plt.ylabel("Transmission [dB]", fontsize=16)
plt.legend(fontsize=14, loc=5)
plt.show()
../../../../../../../../_images/example_mmi_1x2_optimized_1550_00.png
../../../../../../../../_images/example_mmi_1x2_optimized_1550_01.png

MMI1x2Optimized1310

Same as MMI1x2Optimized1550 but optimized at 1310.

Reference

Click on the name of the component below to see the complete PCell reference.

si_fab.all.MMI1x2Optimized1310

MMI1x2 with layout parameters optimized for maximum transmission at 1310 nm.

Example

from si_fab import all as pdk
import numpy as np
import pylab as plt
import ipkiss3.all as i3

mmi = pdk.MMI1x2Optimized1310()
mmi_lv = mmi.Layout()
mmi_lv.visualize(annotate=True)

mmi_cm = mmi.CircuitModel()

wavelengths = np.linspace(1.26, 1.36, 1001)
S = mmi_cm.get_smatrix(wavelengths=wavelengths)
plt.figure()
plt.title("MMI transmission")
plt.plot(wavelengths, i3.signal_power_dB(S["out1", "in1"]), "-", linewidth=2.2, label="T(out1)")
plt.plot(wavelengths, i3.signal_power_dB(S["out2", "in1"]), "-", linewidth=2.2, label="T(out2)")
plt.plot(wavelengths, i3.signal_power_dB(S["in1", "in1"]), "-", linewidth=2.2, label="R(in1)")
plt.ylim(-70, 5)
plt.xlabel("Wavelength [um]", fontsize=16)
plt.ylabel("Transmission [dB]", fontsize=16)
plt.legend(fontsize=14, loc=5)
plt.show()
../../../../../../../../_images/example_mmi_1x2_optimized_1310_00.png
../../../../../../../../_images/example_mmi_1x2_optimized_1310_01.png

Simulation and regeneration of the data files

The simulation data of MMI1x2Optimized1550 and MMI1x2Optimized1310 are obtained with CAMFR can be regenerated. This can be done with the regenerate_mmi() function using the script example_mmi_1x2_optimized_1550.py contained in si_fab/components/mmi/regeneration. The user can specify the following options:

  • mmi_class: the mmi to regenerate. The name should not contain parentheses ().

  • wavelengths: list of wavelengths at which the simulation should be run.

  • center_wavelength: the center wavelength of the component.

  • resimulate: boolean. If True, the MMI will be simulated at all the wavelengths. A fitting of the transmission as a function of wavelength is performed and the results are stored in a file in data/component_name.z.

  • plot: boolean. If True, it plots the results of the simulation.

For a complete tutorial on how to design and optimize the 1x2 MMI, check out Multi-mode interferometer (MMI).

Reference

Click on the name of the functions below to see the complete API reference of the simulation and regeneration recipes.

si_fab.components.mmi.simulation.simulate_camfr.simulate_splitter_by_camfr

It simulates a symmetric splitter and returns the transmission and reflection.

si_fab.components.mmi.regeneration.regen_utils.regenerate_mmi

It regenerates the simulation fitting data and/or the plots of the optimized MMI.

Creating a new optimized MMI

The user has the possibility of exploring the MMI and creating a new optimized component with different optimized parameters. The optimization can be performed by running the script optimize_mmi_1x2_1550.py contained in si_fab/components/mmi/optimization. Some layout parameters are kept fixed (taper_width, taper_length, width), while the length of the MMI (length) and the spacing between the output waveguides (wg_spacing) are optimized to obtain maximum transmission. The new layout parameters can be used to create an optimized MMI with new default values. The simulation data of this new component can be generated by running the regeneration script and should be used to perform circuit simulations of this new component.

For a complete tutorial on how to design and optimize the 1x2 MMI, check out Multi-mode interferometer (MMI).

Reference

Click on the name of the function below to see the complete API reference of the optimization recipe.

si_fab.components.mmi.optimization.opt_utils.optimize_mmi

Optimizes the length and waveguide spacing of a 1x2 MMI at fixed wavelength, taper_length and width.