Vanadium dioxide-assisted broadband tunable terahertz metamaterial absorber.

Tunable terahertz (THz) functional devices have exhibited superior performances due to the use of active materials, such as liquid crystals, graphene, and semiconductors. However, the tunable range of constitutive parameters of materials is still limited, which leads to the low modulation depth of THz devices. Here, we demonstrate a broadband tunable THz absorber based on hybrid vanadium dioxide (VO) metamaterials. Unlike other phase change materials, VO exhibits an insulator-to-metal transition characteristic and the conductivity can be increased by 4-5 orders of magnitude under external stimulus including electric fields, optical, and thermal pumps. Based on the unique transition character of VO, the maximum tunable range of the proposed absorber can be realized from 5% to 100% by an external thermal excitation. Meanwhile, an absorption greater than 80% in a continuous range with a bandwidth about 2.0  THz can be obtained when VO is in its metal phase at high temperature. Furthermore, the absorber is insensitive to the incident angle up to 50° and such a broadband THz absorber can be used in applications including imaging, modulating, cloaking, and so on.