1. A computer-implemented method for simulating an electromagnetic property of a medium, the medium being meshed to define a plurality of mesh elements in an initial reference frame, the method comprising, for each mesh element: determining a unitary transformation at a transformation module having a processor configured for transforming an initial permittivity tensor in the initial reference frame into a transformed permittivity tensor in a transformed reference frame, the transformed permittivity tensor being diagonal; using a standard finite-difference time-domain (FDTD) process for simulating the electromagnetic property of the medium; while modifying the standard FDTD process by: applying the unitary transformation at the transformation module to an initial electric displacement field tensor in the initial reference frame to generate a transformed electric displacement field tensor in the transformed reference frame; communicating the transformed permittivity tensor, the transformed electric displacement field tensor and a transformed electric field tensor to an update generation module; generating an updated transformed electric field tensor at the update generation module according to the standard FDTD process, using the transformed permittivity tensor, the transformed electric displacement field tensor, and the transformed electric field tensor; communicating the updated transformed electric field tensor to the transformation module; and applying an inverse unitary transformation at the processor of the transformation module to the updated transformed electric field tensor to generate an updated initial electric field tensor in the initial reference frame; and using the updated electric field tensor in the initial reference frame in an update of the standard FDTD process while running the simulation.