Using INTERCONNECT, one can incorporate sophisticated PIC element descriptions by incorporating highly-accurate physical designs from Lumerical’s electromagnetic simulator products. In this chapter, we will showcase two examples of circuits in INTERCONNECT where the compact model parameters come from component-level simulations using FDTD, MODE and CHARGE.
In this example, INTERCONNECT is used to demonstrate how the grating coupler performs in a larger scale circuit. INTERCONNECT is a photonic integrated circuit simulator and works with a schematic representation of circuits. S-parameters extracted from the FDTD calculation (from Grating coupler) and the mode data from MODE solution file, waveguide_gc.lms is used for this example.
Calculate waveguide properties using MODE
To characterize the waveguide (ie. mode profiles, dispersion, etc), open the waveguide_gc.lms project file in MODE. Run the basic mode eigensolver to find the support modes of the waveguide. Next, switch to the frequency analysis tab and click the Frequency sweep button to calculate the dispersion of the mode. Finally, in the 'Options' property of the frequency sweep tab, select the Data Export option and click the 'Export for INTERCONNECT' button. This will export all required data from MODE to a file that will be loaded into the 'MODE waveguide' object within INTERCONNECT. The file should be named 'waveguide.ldf'.
Calculate overall device performance with INTERCONNECT
The s-parameters of the overall device is calculated. Open the simulation file, gratingCoupler_sparameter.icp, and run the simulation. The simulation will not run without the 'waveguide.ldf' file created by MODE in the previous step.
The below plots were generated using the script file plot_INTERCONNECT_result.lsf. The ripples that are observed in the plots are related to the length of the waveguide.
DPSK receiver with MMI couplers
The simulation of a differential phase shift keying (DPSK) receiver in INTERCONNECT is presented here. The S parameters of the MMI coupler are calculated from MODE Solutions varFDTD solver and are used to build a MMI coupler model in Lumerical INTERCONNECT. This MMI coupler model is used to design a DPSK receiver in INTERCONNECT. The DPSK receiver's bit error rate (BER) is calculated by varying the received power. As the S parameter of the MMI coupler is generated at different MMI coupler geometries, the simulation method described here can be used to test the degradation in the DPSK receiver’s sensitivity for the mismatch in the targeted MMI coupler design parameters.
In this example, we will look at variations in the following MMI design parameters:
- Width of the MMI coupler access waveguide (wa)
- Width of the MMI coupler (w)
- Length of the MMI core waveguide (L)
- Open the file MMI_varFDTD.lms, and run the parameter sweep. This will generate 12 varFDTD simulation files with 3 variations for the MMI access waveguide width, 2 variations for the MMI width and 2 variations for the MMI length.
- In the same MMI_varFDTD.lms, run the script file MODE_to_INTERCONNECT_MMI.lsf. This script will generate 12 text files, each containing the S parameter values for each variation of the MMI coupler. This script will also generate an xml file, which will map the name of the text files to each variation of the MMI coupler. These files will be used to create the MMI coupler compact model in INTERCONNECT.
- Copy the files generated in step 2 to the directory where the .icp files are located.
- (Optional) Verify the behavior of the MMI compact model using MMI_S_param.icp. Here, the compact model is a S parameters element which will read the S parameter results from steps 1 and 2. An optical network analyzer will utilize the SPS solver in INTERCONNECT to calculate the frequency response of the compact model. Run the parameter sweep and under "Result View", select the S parameter elements, and visualize the results. Using the “line” plot type option, the transmission gain can be viewed for different variations. Verify that the S parameter results here are the same as the results from the varFDTD simulation.
5. The dpsk_tranceiver.icp files contains the DPSK receiver circuit based on  using the MMI coupler compact model generated from steps 1-3. Here, we will use the TSM solver in INTERCONNECT to calculate the time domain response of the DPSK circuit. The parameter sweep section of this file contains different variations of the MMI coupler design as well as variations in the attenuation of one of the attenuators. Run the parameter sweep followed by BER_plot.lsf. This will generate the BER vs received power plots for different MMI coupler design variation. Two example plots are shown below:
Component-level simulations of photonic components can be used to calculate accurate transmission gain or loss values for the component. However, in order to understand how variations in the design of the component (ex. due to fabrication effects) will impact the performance of a photonic integrated circuit, one must use a combination of component-level simulations as well as circuit-level simulations. In this example, we demonstrated how to extract the S parameters of a MMI coupler using component-level varFDTD simulations, and use the S parameters to create a circuit-level compact model in INTERCONNECT. In INTERCONNECT, one can easily access how variations in the geometry of the component will effect the BER sensitivity of the DPSK receiver.
 Mohammed Shafiqul Hai, Meer Nazmus Sakib, and Odile Liboiron-Ladouceur, "A 16 GHz silicon-based monolithic balanced photodetector with on-chip capacitors for 25 Gbaud front-end receivers," Opt. Express 21, 32680-32689 (2013)