Coding Metasurface Beam Modulation Based on Phase Change Materials

Electromagnetic metasurface is a synthetic surface composed of sub-wavelength unit particles, which can freely regulate the amplitude, phase, and polarization direction of electromagnetic waves. The optical properties of the metasurface can be dynamically adjusted by the phase change material. In this paper, phase change material of Ge₂Sb₂Te₅ (GST) is utilized to dynamically change the refractive index of the unit structure. Using the amorphous phase, semi-crystalline phase, and crystalline phase of GST material, we can construct three different coding unit particles. Based on the Pancharatnam-Berry phase principle, one can obtain the phase change by rotating different angles of the anisotropic element structure under the incident condition of circularly polarized light. In order to realize the free control of the beam in mid-infrared band, the Fourier convolution principle in digital signal processing is introduced, and the Fourier convolution addition or subtraction is carried out on different coded sequences to realize the free control of beam deflection direction. In other words, we combine physical encoded particles with digital encoded particles to construct a 3-bit encoded metasurface to regulate the scattering angle of the transmitted beam. We combine two kind of GST encoded particles in the same state but with different geometric parameters to form composite structure, and the metasurface in different crystal states produces different deflection effects to achieve tunable phase change encoded metasurface. The dynamic coded metasurface designed by us has a wide application prospect in communication, radar, antenna, and other fields.