Emulating Faraday Rotation With Nonmagnetic Time-Modulated Metasurface

A nonmagnetic cascaded architecture is proposed to emulate the Faraday rotation effect for various polarization rotation angles, comprising a double-layer time-modulated nonreciprocal metasurface and a specifically oriented polarization grating. The metasurface layers are loaded with varactors and modulated in time via biasing voltages to break Lorentz reciprocity. By tailoring the modulation signal on each layer, independent control over the nonreciprocal transmissions of both orthogonal polarizations is achieved. The polarization grating is utilized to selectively filter the desired linear polarization components, thereby enhancing the isolation and purity of the rotated polarization states. A theoretical model of the double-layer metasurface is developed to guide the design of the nonreciprocal transmissive meta-atoms. Full-wave electromagnetic field and circuit cosimulations closely match the theoretical predictions, validating the effectiveness of the time-modulation scheme and the nonreciprocal transmission. Finally, an experimental test on the double-layer time-modulated metasurface has been carried out in a TEM-cell, which showcases nonreciprocal transmission with a nonreciprocity of up to 6.8 dB, confirming the practical feasibility of the proposed method. This work introduces a magnet-free approach to Faraday rotation, offering enhanced integrability and design flexibility compared to conventional magneto-optical implementations.