An ultra-thin optical polarizer based on weyl semimetals.

• We numerically show that an ultra-thin Weyl semimetal film can achieve an excellent performance of a high polarization extinction ratio (more than 40 dB) and a low insertion loss (less than 0.07 dB). • Monolayer polarizer shows that the optimum insertion loss is not achieved in the band with the highest PER. An isotropic substrate has little effect on the TM mode, while effectively adjusts the position of TE mode transmission peak. Thus, the proposed sandwich structure can further reduce insertion loss (from 0.06 dB to 0.03 dB) and obtain wider acceptances range of angle (from 49. 5 ∘ to 71 ∘). • Due to the high reflectivity of the two interfaces inside the WSM layer, the incident light is reflected several times in the single-layer structure, forming a structure similar to the Fabry-Perot cavity, which seriously affects the polarizer's performance. To overcome the challenges above, the proposed a gradient Fermi level structure eliminates the interference peak, thus resulting a wider bandwidth (approximately 60 % improvement). This method can be generalized to larger thickness cases. • With the increasing demand for on-chip integrated devices, our work can be helpful for the integration of a range of potential optical applications in optical communication and omnidirectional polarization detectors. Recently, Weyl semimetals have been extensively studied due to their unique optical responses, especially in the mid-infrared region. However, the possibility of developing optical polarizers based on Weyl semimetals remains unexplored. In this paper, under the Voigt geometry, we numerically show that an ultra-thin Weyl semimetal film with thickness L = 100 nm can achieve an impressive polarization extinction ratio (more than 40 dB) with a wide acceptance angle. Further, the proposed sandwich structure can effectively adjust the position of the TE mode transmission peak alone, thus obtaining lower insertion loss (from 0.06 dB to 0.03 dB) and wider acceptance range of angle (from 49. 5 ∘ to 71 ∘). The proposed gradient Fermi level structure eliminates the Fabry-Perot cavity resonance, thus resulting a wider bandwidth (approximately 60 % improvement). Our proposed ultra-thin and wide-angle polarizer may have potential applications in optical communication and omnidirectional polarization detectors. [ABSTRACT FROM AUTHOR]