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I am not sure if I need Lumerical FDTD or Lumerical MODE. We know Lumerical MODE has a Var-FDTD solver. What are the cases when Var-FDTD cannot be used?
In the following case you can not use Var-FDTD:
1- Fiber optics cannot be simulated since the structure is not planar.
2- Structures with graded refractive index in the x or y directions cannot be simulated since smoothly varying refractive index within the propagation plane, which is the xy plane,
is not supported, although if the refractive index is graded along the z-dimension, this
can be simulated.
3- Waveguides with sloped sidewalls, also cannot be simulated as the structure cross section
is smoothly-varying in the propagation plane.
4- Grating couplers which couple light into or out of the xy plane in the vertical direction
cannot be simulated since the light should be travelling in-plane.
5- Nanoparticles which scatter light in 3 dimensions cannot be simulated for the same reason that the method does not support light propagating out of the xy plane.
6- Grid attributes, such as permittivity rotation, np density or temperature grid attributes
imported from DEVICE simulations are also not supported.