Encoding terahertz metasurface reflectors based on geometrical phase modulation

Abstract

Multi-dimension and multi-freedom modulation of polarization state based on the geometrical-phase periodic encoding metasurface has important application prospects. Here, terahertz metasurface composed of specially shaped metal pattern coded particles is proposed. When the coded particles are normally incident, the amplitude reflectivity of the terahertz wave is above 80% in a 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, and phase coverage) of all coded particles and the angle deflection of the designed 2-bit periodic metasurface are measured by normal incidence THz time-domain spectrometer and variable incident angle THz time-domain spectrometer, respectively. Based on generalized Snell law and experimental results, the reason for the discrepancy between theoretical value and experimental value is further analyzed, which can provide a reference for the reverse design of the coded metasurfaces to meet various practical needs.