A Magnetically Switchable Bifocal Metasurface

TL;DR

This paper presents a numerical study of a magneto-optical metasurface that can dynamically switch its focal length using an external magnetic field, enabling tunable flat reflective optics.

Contribution

It introduces a magneto-optical metasurface design with tunable focal length controlled by magnetic fields, demonstrated through full-wave simulations.

Findings

Switching magnetic field from +0.2 T to -0.2 T doubles the focal length.

The metasurface operates at a wavelength of 1.550 μm with distinct focusing properties.

Focal length varies from 7.16 mm to 13.76 mm depending on magnetic field direction.

Abstract

Tunable flat optics are essential for advancing compact photonic devices. Here we show a numerical study of a reflective magneto-optical metasurface with a dynamically tunable focal length. The structure comprises bismuth iron garnet nanodisks in a Gires-Tournois resonator configuration. The magneto-optical properties of the garnet modulate the reflected phase response via an external magnetic field, allowing focusing at different focal lengths. Full-wave simulations demonstrate that the metasurface exhibits distinct focusing characteristics depending on the applied magnetic field direction for a fixed right circularly polarized incident wave at 1.550 {\mu}m. Specifically, switching the external field from +0.2 T to -0.2 T changes the focal length by a factor of approximately two (from 7.16 mm to 13.76 mm). These findings demonstrate that magneto-optical metasurfaces offer a flexible, viable approach for non-mechanical, tunable focusing in compact reflective optical components.