Nonlinear Time-Reversal of Classical Waves: Experiment and Model

TL;DR

This paper demonstrates nonlinear time-reversal of electromagnetic waves in a passive system, enabling secure communication and providing a model that replicates experimental results in a wave-chaotic environment.

Contribution

It introduces a passive nonlinear time-reversal method and develops a star-graph model to simulate and interpret experimental findings.

Findings

Passive nonlinear objects can be used for time-reversal.

The system enables high-rate secure communication.

Model simulations match experimental observations.

Abstract

We consider time-reversal of electromagnetic waves in a closed, wave-chaotic system containing a discrete, passive, harmonic-generating nonlinearity. An experimental system is constructed as a time-reversal mirror, in which excitations generated by the nonlinearity are gathered, time-reversed, transmitted, and directed exclusively to the location of the nonlinearity. Here we show that such nonlinear objects can be purely passive (as opposed to the active nonlinearities used in previous work), and develop a high-rate secure communication system based on nonlinear time-reversal. A model of the experimental system is developed, using a star-graph network of transmission lines, with one of the lines terminated by a model diode. The model simulates time-reversal of linear and nonlinear signals, demonstrates features seen in the experimental system, and supports our interpretation of the experimental results.