RSoft Enewsletter

January/February 2018

Creating Custom PDK Models with the S-Matrix/Custom PDK Generation Utility

Although photonic foundries continue to enhance support for wider arrays of active and passive photonic PDKs based on different technologies, there are times when the ability to generate custom & proprietary PDKs and to use them in circuit simulations and mask generation are important. Whether the motive is to generate intellectual property (IP), or to supplement an existing PDK, OptSim Circuit together with RSoft’s device modeling tools offer virtually limitless ways to create custom components and PDKs and deploy them in PICs. 

This article illustrates a step-by-step process for using the S-Matrix/PDK Generation Utility of RSoft device modeling tools to create the data file to be used in OptSim Circuit. For illustration, we consider a case of a half ring component simulated with FullWAVE as shown in Figure 1, and use it in OptSim Circuit as custom PDK model to create and simulate a full ring resonator circuit. We will calculate both S-Matrix data as well as a mask layout using the new S-Matrix and PDK Generation Utility.

Fig.1: FullWAVE layout of a half-ring component used to
calculate S-matrix data

To run the S-Matrix/PDK Generation Utility for the layout in Figure 1, a valid license for RSoft FullWAVE is required. 

The ring structure is built from standard silicon wire waveguides and can be found in the examples/Utilities/SMatrix folder for v2017.09. FullWAVE’s simulation options set the grid size, simulation domain, boundary condition, etc. A pulse temporal excitation is used. The S-Matrix Utility requires that port monitors are set up at each measurement position. Port monitors are overlap monitors with specified port numbers. They can be easily created via the CAD tree or by converting a normal monitor to a port. The launch field is automatically moved to each port by the S-Matrix/PDK Generation Utility to generate the respective transfer function data in a format that can be used in OptSim Circuit. Figure 2 shows the half ring structure with ports labeled for clarity.

Fig.2: The half ring structure with ports labeled for clarity

Figure 3 shows the setup options for the S-Matrix and PDK Generation Utility. The “Output Mode” is set to “S-Matrix + PDK” to generate an S-matrix data file, an OptSim Circuit *.dta file, a GDS II mask file, and an *.spt file for PhoeniX Software’s OptoDesigner. The S-Matrix Utility automatically alternates the input ports and initial necessary CW scan or pulse simulations to obtain spectra data at each port. 

Fig. 3: Setup options for the S-Matrix and PDK Generation Utility

To learn more about this utility and its options, refer to Chapter 12 of the RSoft CAD User Guide, accessed in the Help menu of the RSoft CAD Environment program. Note that only two simulations will be needed because of structure symmetry. 

Figure 4 shows output files generated by the S-Matrix and PDK Generation Utility.

Fig. 4 shows output files generated by the S-Matrix and PDK Generation Utility. 

The files with *.pcs extension are WinPLOT files created by the utility to view FullWAVE’s simulation outputs in RSoft’s DataBROWSER and are not necessary for creating custom PDKs in OptSim Circuit.

To convert the output of the S-Matrix and PDK Generation Utility into an OptSim Circuit custom PDK, launch OptSim Circuit’s User Libraries Organizer and select the *.dta file to be added as a custom PDK entity as shown in Figure 5.

Fig. 5: User Libraries Organizer in OptSim Circuit

The PDK entity will show up in OptSim Circuit’s models’ library (Figure 6) as a custom PDK element that can be dragged and dropped into the schematic like any other OptSim Circuit model in the models’ tree.

Fig. 6: Custom PDK available in the OptSim Circuit GUI for use in schematic like any other Circuit model

To use the half-ring custom PDK in OptSim Circuit as a building block to make a full ring resonator circuit, we start by creating a compound component, placing two half-ring PDKs and making connections as shown in Figure 7.

Fig. 7: An OptSim Circuit compound component using two half-ring PDKs to create a ring resonator circuit

Each half-ring PDK element uses S-Matrix data automatically generated by the S-Matrix and PDK Generation Utility in FullWAVE (Figure 8).

Fig. 8: Parameter window of the half-ring PDK showing S-matrix data file name

The S-matrix data file format follows the file format of OptSim Circuit’s bi-directional optical multiport device model.

To generate a PDAFlow *.spt file for use with PhoeniX Software OptoDesigner, with the schematic of Figure 7 open, from the OptSim Circuit GUI, click on Utilities > Generate PDAFlow Netlist (Figure 9).

Fig. 9: Generating a PDAFlow netlist (*.spt file) for the schematic of Fig. 7

Sections 1.1 and 1.2 of OptSim Circuit Interfaces to Mask Layout Tool manual (which is optsim-maskref.pdf file in C:\RSoft\docs\ folder) describe the interface and setup options in details in order to create a mask in OptoDesigner from the OptSim Circuit PDAFlow netlist. Figure 10 shows the mask in OptoDesigner of the OptSim Circuit schematic of Figure 7.

Fig. 10: Mask in OptoDesigner from OptSim Circuit PDAFlow netlist (*.spt file) for the schematic of Fig. 7

To carry out circuit simulation of the custom PDK-based ring resonator, create a new project file and load the compound component of Figure 7. The schematic is shown in Figure 11. 

Fig. 11: Schematic of the example project file

A wideband source launches light to the input port 1. Analyzers at all four ports are used to measure power spectra. Of particular interest in case of a ring resonator are the spectra at the through and drop ports, as shown on the top and bottom respectively in Figure 12. To validate OptSim Circuit’s custom PDK-based approach, a comparison was made to the spectra at through and drop ports obtained from FullWAVE’s FDTD-based simulation of the entire ring. As shown in Figure 12, the results match very well. In terms of simulation time, the custom PDK-based OptSim Circuit simulations run approximately 10-times faster than the FDTD simulations for this small, 2D ring resonator. For larger structures with symmetries and repeated sub-structures, OptSim Circuit can computationally be even more efficient when compared to the rigorous FDTD-based simulations. The Circuit approach can especially be helpful for modeling large, bi-direction devices, where FDTD can be computationally prohibitive. 

(a)

(b)

 

Fig. 12: Power spectra at the (a) through and (b) drop ports of the ring resonator circuit of Fig. 11

The procedure described in this article can be applied to passive, linear photonic components modeled in RSoft device modeling tools. Circuit level behavior of such components can be fully described by their S-parameters. The S-Matrix/PDK Generation Utility from the RSoft device modeling tools automates the task of measuring transfer matrix and creating necessary output files that the User Libraries Organizer of OptSim Circuit uses to create and organize custom PDKs. The custom PDKs, as shown in this application note, can be used in OptSim Circuit to build and simulate photonic circuits, and to create PDAFlow netlist for generating mask via interface to the third-party tool, PhoeniX Software OptoDesigner. 

Join Us for PIC International Training

April 9-10
Sheraton Brussels Airport Hotel
Brussels, Belgium

 

The PIC International conference team is pleased to announce the launch of PIC International Training. The training event will be organized in partnership with PhoeniX Software and Synopsys.

Synopsys and PhoeniX Software will present a two-day workshop on electro-photonic design automation (EPDA) for photonic integrated circuits (PICs). The workshop is aimed at application and R&D engineers as well as managers interested in understanding the development of PICs and the role of software automation in their design, simulation, and fabrication.

During the first half of the workshop, Synopsys and PhoeniX Software will provide an overview of their software tools and their role in integrated photonics design and manufacturing. Synopsys will describe its photonic tool chain, which features OptSim Circuit for schematic-driven PIC design, as well as the RSoft Photonic Component Design Suite for device design and custom generation of PDK components that can be used in OptSim Circuit and PhoeniX Software OptoDesigner. PhoeniX Software will describe OptoDesigner, a comprehensive tool for PIC design and mask generation that naturally interfaces with OptSim Circuit for full PDK-driven and custom PIC design.

The second half of the workshop will feature live training and hands-on demonstration of the Synopsys and PhoeniX Software tools for PDK-driven PIC design. The top-down training will demonstrate OptSim Circuit for PIC schematic entry and simulation, PhoeniX Software OptoDesigner for PIC layout and mask generation (including its interface with OptSim Circuit), and the RSoft Photonic Component Design Suite for custom PDK development and device design. During the hands-on session, attendees will have the opportunity to work directly with the software under the guidance of technical staff from both companies.