In this example, we calculate the gain spectrum and Free Spectral Range (FSR) of a Mach-Zehnder interferometer designed in Siemens EDA Tanner L-Edit Photonics as part of the layout-driven flow.
This example requires the GPIC CML to be installed.
Overview
Understand the simulation workflow and key results
We are considering a Layout-driven workflow where the circuit layout is designed in Siemens EDA Tanner L-Edit Photonics and the circuit is simulated in INTERCONNECT.
The circuit is an imbalanced Mach-Zehnder interferometer, composed of waveguides, directional couplers, grating couplers and terminator elements.
| Note: The GPIC compact model library (CML) used here is intended for demonstration purpose only. The models are intended to be representative of typical component behavior, however, they are not calibrated to a foundry process. Lumerical cannot provide and guarantee with respect to the model accuracy and completeness. |
Step 1: Layout design and netlist extraction (Siemens EDA Tanner L-Edit Photonics)
The circuit layout is designed in Siemens EDA Tanner L-Edit Photonics using the GPIC iPDK, a generic photonic process design kit. The netlist is then extracted for two different path length differences, 50 microns and 100 microns.
The example files (layout, GPIC iPDK, etc.) are provided with Siemens EDA Tanner installation package.
Step 2: Circuit simulation (INTERCONNECT)
We import the netlist in an INTERCONNECT test-bench simulation file. The test-bench is composed of an Optical Network Analyzer (ONA) that is used to obtain the gain spectrum as well as the free spectral range (FSR) for the two path length differences.
Run and results
Instructions for running the model and discussion of key results
Step 1: Layout and netlist extraction (Siemens EDA Tanner L-Edit Photonics)
- Open the interferometer example (.../TannerEDA/TannerTools_vxxxx.x/Designs/Interferometer/lib.defs)
- Open the desired layout cell, interferometer_50u or interferometer_100u, corresponding to \(50\mu m\) and \(100\mu m\) path length differences
- Export the netlist using the Lumerical header file (GPIC/models/lumerical/headerFile.spi)
This example is part of the Siemens EDA Tanner installation package. In the “Taking the model further” section, we cover how to extract the netlist with the Ansys macro. We will not cover here the layout design or netlist extraction directly with the L-Edit Photonic Tools . Please refer to the documentation provided with Siemens EDA Tanner for more information.
Step 2: Circuit simulation (INTERCONNECT)
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Open the simulation file, Mentor_Interoperability_Interferometer.icp
Note: users will get the "Error loading reference" errors if the GPIC CML is not installed at this point. Users can manually install this CML or, run the script in the next step to get it installed automatically. - Open the script file, Mentor_Interoperability_Interferometer.lsf
- Click the run script button
- Results are plotted automatically and can be accessed from the result view and the script workspace
This Application Gallery example is provided with two netlists:
- Mentor_Interoperability_Interferometer_50u.spi (\(50\mu m\) path length difference)
- Mentor_Interoperability_Interferometer_100u.spi (\(100\mu m\) path length difference)
We use an Optical Network Analyzer (ONA) to calculate the gain spectrum (transmission in dB) for the TE mode.
The ONA can also extract the Free Spectral Range (FSR), representing the spacing between each peak of the transmission spectrum.
The script will output the mean FSR for the two path length differences in the script prompt.
For such Mach-Zehnder interferometer, the FSR is given by:
$$FSR = \frac{\lambda^2}{\Delta L n_g}$$
where \(\Delta L\) is the path length difference, and \(n_g\) is the group index of the waveguide.
As we could expect, we can see that doubling the path length difference will reduce the FSR by a factor of 2.
Important model settings
Description of important objects and settings used in this model
This example requires the GPIC compact model library (CML) to be installed before running the example files. This example is provided with the CML file GPIC_v2.0.cml.
See the Install Compact Model Library page on the Knowledge Base for more information on how to install the CML.
Updating the model with your parameters
Instructions for updating the model based on your device parameters
Optical Network Analyzer (ONA) settings
The ONA settings allow you to control:
- Input power (0dBm)
- Simulation bandwidth (start and stop frequency, 1565nm to 1530nm)
- Number of points (1000)
- Plot kind (frequency or wavelength)
- Polarization (orthogonal identifier, 1 for TE, 2 for TM)
| Note: This circuit is designed to operate in the C-band (1530nm to 1565nm), TE mode. Care should be taken if you modify the ONA settings to make sure your stay in the operating domain of the components. |
Some models of the GPIC CML include temperature sensitivity. The simulation temperature (300K) is set in the "Root Element" properties.
Taking the model further
Information and tips for users that want to further customize the model
Use updated/new netlist
You can modify the circuit layout in Siemens EDA Tanner L-Edit Photonics, export the new netlist and import it back to your INTERCONNECT test-bench circuit to verify how the modifications affect the behavior of the circuit.
Import netlist from user interface :
- Select the compound element
- Import the netlist (*.spi) from File-Import-Import SPICE netlist
Import netlist from script :
- Use the " importnetlist " command
importnetlist("COMPOUND_NAME", "new_netlist.spi");
where COMPOUND_NAME is the name of the compound element hosting the circuit, and new_netlist.spi, the new netlist to be imported.
Note: The same methodology can be applied to other circuits designed in Siemens EDA Tanner L-Edit Photonics.
Use other test-bench circuits
In this example, the interferometer is connected to an ONA to calculate its transmission spectrum and FSR.
Other circuits can be used. You can create different test-bench simulation files that you can use depending on the results you want to extract.
Automated netlist extraction and test bench simulation with Ansys Lumerical macro for Tanner L-Edit Photonics
The Ansys Lumerical macro automates the following process:
- Exporting netlist from Tanner
- Opening INTERCONNECT testbench
- Importing netlist into INTERCONNECT compound
- Running simulation
To install and run the macro:
- Open a single Tanner L-Edit session
- In your file explorer, navigate to ...\TannerEDA\TannerTools_vxxxx.x\ThirdParty\lumerical\installLumericalMacros.tbc"
- Run the file by dragging and dropping into the Command Line
- Close your Tanner session
- Open a new session
- Open a layout file
- Go to “Ansys” tool bar menu item and select “Run INTERCONNECT Test”
- Fill in the fields and then hit “Run”. Alternatively, hit “Export” to extract the netlist, without opening a test bench.
Macro fields:
- PDK headerfile: Locate this file within the PDK. For GPIC it is found at: ...\TannerEDA\TannerTools_vxxxx.x\Process\GPIC\Production\GPIC\models\lumerical\headerFile.spi
- Netlist location: Choose a location/name to save the netlist file.
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Project file: You can do one of the following:
- Select an existing testbench project file (.icp). For this example choose …\TannerEDA\TannerTools_vxxxx.x\Designs\Interferometer\simulations\lumerical\Lumerical_INTERCONNECT_Interferometer_Test_Bench.icp
- Define new project file. The project file will be automatically generated and the netlist will be imported into a compound element. You can then build your test bench around this and save the file for future use.
- Select a script file (.lsf). A variable “netlistPath” will be added to the INTERCONNECT workspace, which can be used in the script file to load the netlist.
- Compound name: Name of the compound in the test bench. Typically this should be the same as the circuit layout name.
Additional resources
Additional documentation, examples and training material
See also
- Install a Compact Model Library
- Optical Network Analyzer (ONA)
- Mentor and Lumerical partner with Towerjazz to advance Photonic IC design
Related Ansys Innovation Courses