  Backflow, or retropropagation, is a counterintuitive phenomenon whereby for a
forward-propagating wave the energy locally propagates backward. In this study,
energy backflow has been examined in connection with (a) (2+1)-dimensional
unidirectional scalar and vector-valued monochromatic waves; (b) a (2+1)D
scalar spatiotemporal wavepacket constructed by using an appropriate temporal
frequency spectrum; (c) a scalar closed-form analytical unidirectional version
of the Focus Wave Mode -- a localized pulse propagating luminally and without
spread. Furthermore, an extended class of (2+1)D and (3+1)D finite-energy
unidirectional spatiotemporally localized wave packets has been derived.
