Magnetic modulation of light using a Gires-Tournois Nanocavity and metasurface

We experimentally demonstrate the enhancement of magneto-optical properties in the visible and near infrared spectral regime by employing Gires-Tournois (GT) resonant architectures based on cobalt. Two distinct systems are investigated: a planar GT cavity composed of a thin Co layer, a silica spacer, and another thin cobalt layer coating a thick aluminium substrate; and a GT metasurface with the same multilayer architecture, but where the top continuous cobalt layer is replaced by a periodic array of cobalt disk-shaped meta-atoms. Through a careful sample realization and characterization, we experimentally demonstrate that both structures achieve an order of magnitude increase in the polar Magneto-Optical Kerr Effect (p-MOKE) to 200 nm cobalt film. This result is analyzed by means of a combination of analytical models and numerical simulations. This enhancement is mainly attributed to constructive interference within the GT cavity and to the synergistic effects of localized surface plasmon resonances, surface lattice resonances and optical cavity modes in the metasurface. These results establish a promising platform for the development of compact, magneto-optically tunable nanophotonic devices with potential applications in nonreciprocal photonics, active optical modulation, and sensing technologies.