  We propose a basic mechanism for isochronal synchrony and communication with
mutually delay-coupled chaotic systems. We show that two Ikeda ring oscillators
(IROs), mutually coupled with a propagation delay, synchronize isochronally
when both are symmetrically driven by a third Ikeda oscillator. This
synchronous operation, unstable in the two delay-coupled oscillators alone,
facilitates simultaneous, bidirectional communication of messages with chaotic
carrier waveforms. This approach to combine both bidirectional and
unidirectional coupling represents an application of generalized
synchronization using a mediating drive signal for a spatially distributed and
internally synchronized multi-component system.
