  The timestep of the Finite-Difference Time-Domain method (FDTD) is
constrained by the stability limit known as the Courant-Friedrichs-Lewy (CFL)
condition. This limit can make FDTD simulations quite time consuming for
structures containing small geometrical details. Several methods have been
proposed in the literature to extend the CFL limit, including implicit FDTD
methods and filtering techniques. In this paper, we propose a novel approach
which combines model order reduction and a perturbation algorithm to accelerate
FDTD simulations beyond the CFL barrier. We compare the proposed algorithm
against existing implicit and explicit CFL extension techniques, demonstrating
increased accuracy and performance on a large number of test cases, including
resonant cavities, a waveguide structure, a focusing metascreen and a
microstrip filter.
