Theoretical method for the analysis and design of tunable terahertz graphene-based Faraday polarization rotators

A theoretical method is presented that facilitates the analysis and design of graphene-based tunable terahertz polarization rotators. Most previous designs are based on a three-dimensional (3-D) full-wave electromagnetic simulation; thus, it is time-consuming to get well-tuned structural parameters. Using the proposed method, the transmission response of the polarization rotator is directly calculated for a given set of structural parameters. Hence, the need of the electromagnetic simulation is lifted. The accuracy of the proposed method is rigorously validated, as excellent agreement between the theoretical and simulation results is observed. Using the method, a rotator of 12 THz central frequency with a small magnetic bias field of 0.5 T and a small unit cell of 0.5 by 0.5(µm)² is designed. It is shown that the center frequency can be increased to any desired frequency, without the need of a large magnetic bias, by reducing the unit cell size. The method presented in this work can be extended for the analysis and design of other tunable terahertz nonreciprocal devices, such as isolators, circulators, phase shifters, and switches.