Broadband linear-to-circular polarization converter based on phosphorene metamaterial

We propose a broadband reflective linear-to-circular (LTC) polarization converter in a mid-infrared regime based on monolayer black phosphorus (phosphorene) metamaterial. The proposed converter consists of periodic unit cells, each cell of which is formed by multiple phosphorene layers, a dielectric layer, and a fully reflective gold mirror. In the frequency range of 14.20 and 23.10 THz, the magnitudes of the reflection coefficients are approximately equal and the phase difference value between the two orthogonal electric field components of the reflected wave is close to π/2 or −3π/2, which indicates the reflective wave can be deemed the circular polarization with the incidence of linearly polarized wave. The simulation results show that the relative bandwidth of LTC polarization conversion reaches 58% and 47.8%, respectively, when the pucker ridge alignment of the phosphorene is perpendicular to the y-direction and x-direction. Finally, the physical mechanism is revealed via the field decomposition and current distribution. This polarization converter has great potential for future applications in electronic measurement, photonic design, and in some other optoelectronic systems.