Frequency conversion cascade by crossing multiple space and time interfaces

TL;DR

This paper introduces a novel space-time cascade method for wave frequency conversion that achieves large shifts with high efficiency using non-commutative interfaces, avoiding complex metamaterials.

Contribution

The authors propose a new space-time cascade concept enabling arbitrary large frequency shifts through iterative elementary cycles with non-commutative interfaces.

Findings

Achieved 4-octave frequency conversion cascade with water waves.

Demonstrated 100% efficiency in upward and downward frequency conversions.

Avoided the need for high-frequency or sub-wavelength metamaterials.

Abstract

Time varying media recently emerged as promising candidates to fulfill the dream of controlling the wave frequency without nonlinear effects. However, frequency conversion remains limited by the dynamics of the variations of the propagation properties. Here we propose a new concept of space-time cascade to achieve arbitrary large frequency shifts by iterated elementary transformation cycles. These cycles use an intermediate medium in which wave packets enter and exit through non-commutative space and time interfaces. This concept avoids high frequency or sub-wavelength demanding metamaterials. Upward and downward frequency conversions are performed with 100% efficiency regardless of impedance matching. As an example, we implement this concept with water waves controlled by electrostriction and achieve frequency conversion cascades over a range of 4 octaves.