Electrical phase shifter workflow

1. Run templates/ps_pn_te_c/run_electrical_PS_collection.lsf in CHARGE. 

• If you have configured the workflow to run simulations to extract modeling parameters, then it will create plots to show the key results.

• The first figure plots the junction capacitance as a function of applied voltage using both the electron and hole density variations. The final capacitance value saved in the output data file is the average of these. However, the two lines should be very close to each other. If they deviate a lot then it indicates that the simulation mesh has not been refined enough near the depletion region.

• The second figure plots the perturbation to the effective index of the active waveguide as a function of applied voltage. Verify that both the real and imaginary parts of the perturbation are physically accurate.

• Besides creating the two plots, the workflow also creates (up to) three text files in the “output_data” folder. These files record the electrical bandwidth, junction capacitance and the perturbation to the effective index of the active waveguide as a function of applied voltage. The user can copy these files to the “input_data” folder to be used an input data and skip re-running the simulations a second time (see “Updating the model with your parameters” section below for more detail).

After the data required for the compact model is successfully collected by the workflow, you can use CML Compiler to easily generate the compact model needed for your design. Here we briefly describe the steps involved for compact model generation using CML Compiler. For more details about each step, please visit Creating a Custom CML with CML Compiler.

1. Prepare the foundry directory. You can use the lumfoundry template if you don’t have an existing directory structure for your library.
2. Create a sub folder within the “source” folder called “ps_pn_te_c” and copy the output .json file generated by the workflow (in the “templates/ps_pn_te_c/output_data” folder).
3. [optional] Copy a .svg file into the “ps_pn_te_c” folder to be used as the icon for your compact model. To keep things simple, name the .svg file “ps_pn_te_c.svg”.
4. Add the necessary lines in the element_list of the .XML file. You can simply copy the lines for the “ps_pn_te_c” element from the lumfoundry_template.xml file. Note that you will have to change the file extension of the “parameter_filename” to .json from .lsf.
5. Open the Lumerical launcher and Launch a new project with CML Compiler

6. Follow steps in Building a Compact Model Library to have CML Compiler build your library.
7. Once CML Compiler is done running, open INTERCONNECT and check the newly created and installed compact model library. It should contain the element you created in the previous steps.

1. Navigate to templates/ps_pn_te_c/input_data. Here you will find the following files:

1. Open templates/ps_pn_te_c/input_data/ps_pn_te_c_input_data.lsf in any Ansys Lumerical tool. This one file contains all the possible input data that can be provided to the workflow (and are necessary to build the compact model). Every parameter defined in the script file are optional and the user should update the file with whatever information is available and remove the rest (you can also simply choose to comment out missing data).
2. The user can choose to get any missing data either from simulation or use default (dummy) data instead. If the missing data is something that cannot be achieved from simulation then the workflow uses dummy data from the “ps_pn_te_c” lumfoundry template by default.
3. For a statistically enabled compact model, "stat_parameters" cell should be provided as described in Electrical Phase Shifter (Statistical) - Lumfoundry Template under the "Statistical Data" section. FOMs such as Vpi_Lpi and IL can be set as statistical parameters. For an example please see ps_pn_stat_te_c template. Also please see Statistical Data Collection for more information.
4. For more information about all the parameters included in the input data file, please visit Electrical Phase Shifter – Lumfoundry Template and phase_shifter_electrical – CML Compiler Model.

1. Open templates/ps_pn_te_c/working_dir/PN_phase_shifter.ldev file in CHARGE. Edit the geometry, material definitions, simulation objects and boundary conditions to match your process.
2. Alternatively, you can create your own CHARGE project file for the electrical simulation of the active waveguide.
3. Irrespective of whether you are editing the project file in the template to meet your process or creating a project file from scratch, the following conditions must be met:

• The boundary conditions are called “anode” and “cathode” and the bias is always applied to “anode” with “cathode” grounded (set to zero Volt).
• There is a charge density monitor in the object tree called “charge_monitor” that records the charge density of the entire waveguide.
• The “save data” option in the charge monitor must be enabled and the filename should be set to “charge.mat”.
• The “integrate total charge” option in the charge density monitor must be enabled if simulating for junction capacitance. Note that the workflow uses the change in total charge as a function of bias voltage to calculate the DC capacitance of the pn junction.
• If simulating for slab resistance, a metallic geometry (called “wg_contact”) must be placed over the entire depletion region at zero bias. The mesh order must be such that if enabled, it takes priority over the overlapping silicon and gets included in the simulated geometry. A corresponding boundary condition named “wg_contact” must also be defined and assigned to the “wg_contact” geometry object.

1. Open templates/ps_pn_te_c/working_dir/PN_phase_shifter.lms file in MODE. Edit the geometry, material definitions, simulation objects, boundary conditions and parameter sweep to match your process.
2. Alternatively, you can create your own MODE project file for the optical simulation of the active waveguide.
3. Regardless of whether you are editing the project file in the template to meet your process or creating a project file from scratch, the following conditions must be met:

• The np density grid attribute object is called “np”.
• The parameter sweep object name is consistent with the “mode_sweep_name” parameter defined in the “workflow driver file” as explained below in Step 6.
• The parameter sweep object is pointing towards the right np density grid attribute object for its sweep parameter.
• The parameter sweep object has a result called neff1 to record the first mode and neff2 to record the second mode (the latter is required only if building the compact model for two modes).

1. Open templates/ps_pn_te_c/working_dir/PN_phase_shifter_passive_WG.lms file in MODE. Edit the geometry, material definitions, simulation objects and boundary conditions to match your process.
2. Alternatively, you can create your own MODE project file for the optical simulation of the passive waveguide.

1. Open templates/ps_pn_te_c/run_electrical_PS_collection.lsf in Ansys Lumerical CHARGE. Note that if you do not intend to run any electrical simulations using the workflow then you can open the file in any Ansys Lumerical tool. However, if available, we recommend using CHARGE to open the file to avoid any unexpected error.
2. Start by defining the folder names for the input data, output data and simulation files (working directory) followed by the file names for the input and output data files along with the CHARGE and MODE project files (if applicable).
3. Update the data control flags to match your preferences. The flags are as follows:
   ps_data_control: Controls the source of the index perturbation data of the active waveguide. Options are: 1 = dummy_data (from lumfoundry template), 2 = experimental or user provided data from the input data file, 3 = run simulations to get data.
   Cj_data_control: Controls the source of the junction capacitance (Cj) data of the phase shifter. Options are: 1 = dummy_data (from lumfoundry template), 2 = experimental or user provided data from the input data file, 3 = run simulation to get data.
   Rj_data_control: Controls the source of the slab resistance (Rj) data of the phase shifter. Options are: 1 = dummy_data (from lumfoundry template), 2 = experimental or user provided data from the input data file, 3 = run simulation to get data.
   BW_data_control: Controls the source of the electro-optical bandwidth data of the phase shifter. Options are: 1 = experimental or user provided data from the input data file, 2 = calculate using the RC time constant from Rj and Cj.
   IL_data_control: Controls the source of the insertion loss data of the phase shifter. Options are: 1 = experimental or user provided data from the input data file, 2 = calculate using the waveguide loss data.
   VpiLpi_data_control: Controls the source of the pi phase shift voltage (VpiLpi) data of the phase shifter. Options are: 1 = experimental or user provided data from the input data file, 2 = calculate using the index perturbation data of the active waveguide.
   active_wg_data_control: Controls the source of the waveguide data for the active waveguide. Options are: 1 = dummy_data (from lumfoundry template), 2 = experimental or user provided data from the input data file, 3 = run simulations to get data.
   passive_wg_data_control: Controls the source of the waveguide data for the passive waveguides. Options are: 1 = dummy_data (from lumfoundry template), 2 = experimental or user provided data from the input data file, 3 = run simulations to get data.
4. Update the simulation settings (if you are running simulations). The available settings are listed below:
   sim_wavelength: Wavelength value to run the MODE simulations for either the active or the passive waveguides in units of meter. Must match with the “wavelength_data” parameter provided in the input data file.
   sim_temp: Simulation temperature for CHARGE and MODE simulations in units of Kelvin. Must match with the “temperature_data” parameter provided in the input data file.
   bias_voltage: Vector defining the bias voltage sweep for active waveguide simulation. Providing this parameter is optional as the sweep can be directly defined in the CHARGE project file as well.
   bias_sweep_type: If the bias sweep is directly defined in the CHARGE project file, the sweep type used in the file must be defined using this parameter. Options are “range” or “values”.
   active_wg_excess_loss: Additional waveguide losses (e.g. loss due to surface roughness) to be added to the active waveguide loss from MODE simulation in units of dB/m.
   passive_wg_excess_loss: Additional waveguide losses (e.g. loss due to surface roughness) to be added to the passive waveguide loss from MODE simulation in units of dB/m.
   passive_wg_dneff_dT: Temperature dependence of passive waveguide effective index in units of 1/K. The workflow currently does not support simulations to extract this parameter. So if running simulations for passive waveguides, this parameter value has to be provided directly. If not provided, then this value will be set to zero in the output data file.
   active_wg_dneff_dT: Temperature dependence of active waveguide effective index in units of 1/K. The workflow currently does not support simulations to extract this parameter. So if running simulations for active waveguides, this parameter value has to be provided directly. If not provided, then this value will be set to zero in the output data file.
   mode_sweep_name: Name of the sweep object in the MODE project file for the active waveguide simulation.
   VpiLpi_voltage: Bias range to calculate the large-signal VpiLpi (required if ‘VpiLpi_data_control’ is set to 2).
   bias_R_slab: Bias voltage for slab resistance (Rj) simulation (required if ‘Rj_data_control’ is set to 3).