This posts presents simulation files of a Y splitter example shown in Inverse Design webinar from February 19
The example expands the existing Y branch Inverse design example by optimizing not only the splitter taper, but also the arms of the splitter. This allows us to achieve smaller footprint while maintaining very low insertion loss.
Both 2D and 3D base simulation and optimization files are included.
Step 1: Define base simulation parameters
The goal for this initial step is to define the basic parameters of the FDTD simulation that will be used for the adjoint optimization. Key simulation settings for the input/output waveguides, monitors for field gradient and figure of merit (FOM) calculations, source and mesh are parametrized for ease of running optimization routine. It is required that the base simulation setup is fully scripted in lumerical script (.lsf format). The script is later used as an input into the optimization routine.
Step 2: Define the optimizable geometry
The second step is to define a parametrized polygon geometry that will represent the body of the Y branch connecting the input and output waveguide (the optimized geometry). This is defined as a python function that accepts a set of optimization parameters and generates corresponding polygon geometry in the base FDTD simulation geometry defined in step 1. Initial parameter values and their limits will also get defined in this step.
Step 3: Run the parametric optimization in 2D
Run the optimization python script with the base simulation script and parametrized polygon object as an input. This will be a 2D simulation for fast delivery of a near optimal design which can be used as the initial guess for the 3D optimization in the next step. To find the best set of parameters that define the optimal Y branch shape, the optimization routine will use the specified field monitors to calculate:
•the field gradients: the gradients of the field due to perturbation of permittivity resulting from slight changes in geometry of the optimized region
•the gradient of the figure of merit (FOM): the gradient of the mode overlap to the fundamental TE mode of the waveguides as a result of the shape changes
After optimization, the optimized Y branch component shape will be exported into GDS II format which can be used for further simulation and/or fabrication (mask design).
Step 4: Run the parametric optimization in 3D [optional]
As an optional step, the best solution found by the 2D optimization can be used as an initial guess for a 3D optimization for a more realistic simulation and to further improve the performance of the design.