This video is taken from the FDE Learning Track on Ansys Innovation Courses.
Convergence testing is a procedure where you vary the simulation settings and find the
required settings for accurate results.
Parameters that commonly require convergence testing are simulation region span, and mesh
In this bent waveguide example, we are sweeping the x span of the simulation region and track
the effective index.
The goal is to find the x span where the result converges.
You can use the sweep object for the convergence test.
Note that you first need to run the modal analysis to make sure that the result you
are tracking is available from the Result dropdown menu of the sweep object.
After finding the modes, create a sweep object and add the parameter to sweep, in this case
the x span of FDE and the result, neff.
Once the sweep has run, you can visualize the result by right-clicking the sweep object.
You can see that the neff is gradually converging as you increase the x span of FDE.
Next example is a straight Si waveguide embedded in SiO2.
We use a mesh override over the Si waveguide to ensure that mesh lines fall at structure
This will help reduce the oscillations in your result as you increase the number of
We fix the mesh override and increase the number of mesh cells in FDE, starting from
100 in x and y directions, respectively.
The test result shows that you can get a converged result at around 600 mesh cells.
See the links below this video to see more examples of convergence testing on simple
waveguide systems that have an analytic solution.