I can’t find any examples on the Knowledge Base. Is there a fundamental limitation?
A simple answer to this questions is that varFDTD is not designed for non-planar structure. The varFDTD solver is based on collapsing a 3D geometry into a 2D set of effective indices that can be solved with 2D FDTD, and this works best with waveguides made from planar structures. For more information of the varFDTD physics, please visit this page.
Indeed, depends on what physical quantities you are trying to extract from a simulation, you might be able to make use of other solvers to meet your needs, such as the FDE and EME solver in MODE Solutions. We do have a section in the KB for fiber simulation and there are examples to run some simulation for fibers using FDE, EME solver. We are happy to continue the discussion if users have questions about a specific simulation in mind.