Linear Polarization Independent Planar Retro-reflectors Based on Anisotropic Binary Coding Theory

With the theoretical support of generalized Snell’s laws, coding metasurfaces can control electromagnetic (EM) waves flexibly. In this paper, we propose an anisotropic binary coding method, which can flexibly control transverse electric (TE) and transverse magnetic (TM) linear polarized waves, realizing a linear polarization independent retroreflector flat device. The binary coding metasurface is composed of a single-layer Jerusalem cross structure, having a well performance of anisotropy for linear polarized EM waves, which means that the two kinds of linear polarized EM waves can be freely and flexibly controlled independently. Different from the previous gradient metafurface whose structural elements need to form a characteristic phase profile to realize single angle retro-reflections utilizing multiple structure elements, the binary coding metasurface is composed of just two structure units. This is the reason that why it is called a binary coding metasurface. For two kinds of linear polarized EM waves, the $0- \pi$ phase profile is formed at the same frequency under the same oblique incident angle. In addition, the phase distribution of binary code is symmetrical, which means that the metasurface can achieve the performance of retro-reflections at the same time for two oblique angles of symmetry discovery. When the electromagnetic wave is vertically incident on the binary coding metasurface, the specular reflection occurs due to the phase profile of the structural unit disappears, which can also be regarded as the retro-reflection when it is vertically incident. As an example, a metasurface working around 10.0 GHz under vertical and oblique incidences is designed and simulated. The simulation results denote that the binary coding metasurface can achieve efficient TE and TM polarization retroreflections around 10.0 GHz with normal and oblique incident angles of ±50.0°. Utilizing binary coding metasurface to realize retro-reflections can control the diffraction directions for incident EM waves more flexibly. This strategy can also be extended to THz or even optical realms, and has potential application value in integrated and miniaturized devices.