Nonreciprocal Negative Refraction Enabled by Photonic Time Crystals

TL;DR

This paper introduces a theoretical framework for achieving nonreciprocal negative refraction using time-varying photonic structures, demonstrated through two designs in optical and microwave regimes that exhibit high isolation.

Contribution

It presents the first general approach to nonreciprocal negative refraction via photonic time crystals, expanding the design possibilities for time-varying metasurfaces.

Findings

Achieved over 46 dB isolation in optical design.

Demonstrated ~11 dB isolation in microwave design.

Validated designs with a customized harmonic-balance finite-element solver.

Abstract

We propose and theoretically demonstrate nonreciprocal negative refraction enabled by time-varying photonic structures. By engineering temporal modulations at the interfaces of hyperbolic media, we achieve isolation between forward and backward beams while preserving the hallmark property of negative refraction. Two complementary approaches are developed: in the optical regime, a multilayer AZO/ZnO hyperbolic slab is sandwiched between permittivity-modulated dielectric layers (3D time crystals); in the microwave regime, a wire medium is sandwiched between time-modulated resistive metasurfaces (2D time crystals). Both designs exploit Floquet harmonic expansions and are validated with a customized harmonic-balance finite-element solver. We report isolation exceeding 46 dB in the optical device and ~11 dB in the microwave counterpart. This work introduces a general framework for nonreciprocal negative refraction across frequency regimes, expanding the design space of time-varying metasurfaces and photonic time crystals.