  Finite-difference time-domain (FDTD) is an effective algorithm for resolving
Maxwell equations directly in time domain. Although FDTD has obtained
sufficient development, there still exists some improvement space for it, such
as ultra-wide-band response and frequency-dependent nonlinearity. In order to
resolve these troubles, a modified version of FDTD called complex-field
frequency-decomposition (CFFD) FDTD method is introduced, in which the
complex-field is adopted to eliminate pseudo-frequency components when
computing nonlinearity and the frequency-decomposition is adopted to transform
an ultra-wide-band response into a series of narrow-band responses when
computing the interaction of ultra-short pulse with matters. Its successful
applications in several typical situations and comparison with other methods
sufficiently verify the uniqueness and superiority in processing
ultra-wide-band response and frequency-dependent nonlinearity.
