Tunable and switchable polarization rotation with non-reciprocal plasmonic thin films at designated wavelengths

We experimentally demonstrate an ultra-thin plasmonic optical rotator in the visible regime that induces a polarization rotation that is continuously tunable and switchable by an external magnetic field. The rotator is a magneto-plasmonic hybrid structure consisting of a magneto-optical EuSe slab and a one-dimensional plasmonic gold grating. At low temperatures, EuSe possesses a large Verdet constant and exhibits Faraday rotation, which does not saturate over a regime of several Tesla. By combining these properties with plasmonic Faraday rotation enhancement, a large tuning range of the polarization rotation of up to 8.4° for a film thickness of 220 nm is achieved. Furthermore, through experiments and simulations, we demonstrate that the unique dispersion properties of the structure enable us to tailor the wavelengths of the tunable polarization rotation to arbitrary spectral positions within the transparency window of the magneto-optical slab. The demonstrated concept might lead to important, highly integrated, non-reciprocal, photonic devices for light modulation, optical isolation, and magnetic field optical sensing. The simple fabrication of EuSe nanostructures by physical vapor deposition opens the way for many potentially interesting magneto-plasmonic systems and three-dimensional magneto-optical metamaterials. A tunable and switchable ultrathin-film optical rotator with a variable working wavelength is experimentally realized by a team in Germany. Scientists at the University of Stuttgart and the Max Planck Institute for Solid State Research fabricated a plasmonic optical rotator for visible light whose polarization rotation can be continuously tuned and switched by applying a magnetic field. They realized this by combining a magneto-optical EuSe slab having a high Verdet constant and a high saturation magnetic flux density with a one-dimensional plasmonic gold grating. The unique dispersion properties of the structure enable free tuning of the working wavelength by varying the grating parameters. The team anticipates that the concept will lead to highly integrated non-reciprocal photonic devices for actively controlled light modulation, magnetic field sensing and optical isolation. Furthermore, the simple fabrication of EuSe nanostructures by physical vapour deposition opens the way for a wide range of magneto-plasmonic systems and three-dimensional magneto-optical metamaterials.