Encoding terahertz metasurface reflectors based on Geometrical phase Modulation

Multi-dimension and freedom modulation of polarization state based on the geometrical-phase periodic encoding metasurface has important application prospects. Here, terahertz metasurfaces composed of specially shaped metal pattern coded particles are proposed. When the coded particles are normally incident, the amplitude reflectivity of the terahertz wave is above 80% in the range of 0.50-1.80 THz. Combined with the Pancharatnam-Berry (P-B) phase theory, 8 kinds of coded particles are designed by rotating the angle of the designed unit. Three kinds of 1-bit, 2-bit, and 3-bit periodic encoding metasurfaces with different encoding sequences are used to manipulate the reflected terahertz waves splitting into multiple-beam with different deflection angles. In addition, both reflection characteristics (including amplitude, phase, phase coverage, etc) of all coded particles and the angle deflection of the designed 2-bit periodic metasurface have been measured by normal incidence and variable angle THz time-domain spectrometers, respectively. The reason for the deviation between theoretical and experimental values has been further analyzed based on generalized Snell law and experimental results, which can provide a reference for reverse design of the coded metasurfaces to aim at various practical needs.