Terahertz metasurface with absorption of both linearly and circularly polarized waves

In recent years, the development of ultrafast laser technology has provided a stable and reliable terahertz source for the generation of terahertz wave pulses, which has made great progress in terahertz wave research. As a new type of two-dimensional artificial metamaterial, metasurface can effectively control the transmission, reflection and polarization of electromagnetic waves, which has attracted the attention of researchers all over the world. Most of the reported terahertz absorbers so far are based on metasurfaces with linear polarization incidence, and few studies have been conducted on terahertz metasurfaces that can produce efficient absorption at both linear and circular polarization incidence, which limits the practical application scenarios. Therefore, it is necessary to explore an efficient absorber which can satisfy both linear polarization and circular polarization. We propose a vanadium dioxide composite metasurface structure, vanadium dioxide is a typical temperature-controlled phase change material, and its conductivity will undergo a huge mutation during the phase change process. When the temperature is lower than the critical temperature(68°C), vanadium dioxide has high resistivity and good insulation performance. When the temperature is higher than the critical temperature, the resistance changes from high resistance state to low resistance state and shows metal characteristics. By changing the external temperature to change the phase of vanadium dioxide, to achieve free switching frequency, to meet the linear polarization and circular polarization incident efficient absorption. When vanadium dioxide is insulated, its conductivity is 0S/m, the metasurface can absorb left-handed circularly polarized wave at 1.30 THz and reflect the incident right-handed circularly polarized wave, and the circular dichroism is 0.85. When vanadium dioxide is metallic, its conductivity is 2×105S/m and linearly polarized incident metasurface, the absorption rate of TE linearly polarized incident wave by metasurface reaches 98.5 % at 1.95 THz, realizing perfect absorption of terahertz wave. The structure has good wide-angle absorption performance for both TE polarization wave and left-handed circularly polarized wave. This composite metasurface structure can achieve good absorption effect of terahertz waves with different frequencies and different polarization states. Therefore, the design concept of the composite metasurface structure can be used for the design of other metasurface terahertz devices, and can be used for terahertz imaging and sensing systems due to different response characteristics to different polarization signals.