Nonlinear Time-Reversal in a Wave Chaotic System
  Exploiting the time-reversal invariance and reciprocal properties of the lossless wave equation enables elegantly simple solutions to complex wave-scattering problems, and is embodied in the time-reversal mirror. A time-reversal mirror operates by recording the wave disturbance as a function of time at one or more points in a medium, broadcasting a time-reversed version of the signal(s) in the opposite direction, and allowing the waves to reverse-propagate back to their origin. Here we demonstrate the implementation of an electromagnetic time-reversal mirror in a wave chaotic system containing a discrete nonlinearity, and, as an example of its utility, we have used it to demonstrate a new form of secure communication. 
Matthew Frazier, Biniyam Taddese, Thomas Antonsen, and Steven M.   Anlage
nlin.CD