Nonreciprocal metasurfaces with epsilon-near-zero materials

TL;DR

This paper presents a nanoscale nonreciprocal metasurface using epsilon-near-zero materials that achieves ultra-fast optical nonreciprocity with control over amplitude and phase, enabling advanced wavefront manipulation.

Contribution

It introduces a novel nonreciprocal metasurface based on indium tin oxide in its epsilon-near-zero regime with ultra-fast response and dual amplitude-phase nonreciprocity.

Findings

Operates in 1200-1300 nm spectral range

Uses incident power densities of 40-70 GW/cm²

Achieves nonreciprocal control of both amplitude and phase

Abstract

Nonreciprocal optics enables asymmetric transmission of light when its sources and detectors are exchanged. A canonical example -- optical isolator -- enables light propagation in only one direction, similar to how electrical diodes enable unidirectional flow of electric current. Nonreciprocal optics today, unlike nonreciprocal electronics, remains bulky. Recently, nonlinear metasurfaces opened up a pathway to strong optical nonreciprocity at the nanoscale. However, demonstrations to date were based on optically slow nonlinearities involving thermal effects or phase transition materials. In this work, we demonstrate a nonreciprocal metasurface with an ultra-fast optical response based on indium tin oxide in its epsilon-near-zero regime. It operates in the spectral range of 1200-1300 nm with incident power densities of 40-70 GW/cm$^2$. Furthermore, the nonreciprocity of the metasurface extends to both amplitude and phase of the forward/backward transmission opening a pathway to nonreciprocal wavefront control at the nanoscale.