▎ 摘　　要

We numerically demonstrate a switchable metamaterial absorber with two states (i.e., ultra-broadband and narrowband) in the terahertz region. Such switchable functionalities are accomplished by using a simple absorption system consisting of a hybrid metamaterial with vanadium dioxide (VO2) and graphene. Theoretical calculations show that when VO2 is in the metal state, the absorption system without a graphene ring can act as a broadband absorber. For the broadband absorber, the absorption bandwidth of 5.05 THz (i.e., 93%) can be obtained under the condition of over 90% absorption rate, covering a frequency range of 2.91-7.96 THz. Meanwhile, the absorber exhibits tunable characteristics, whose absorption rate can be continuously adjusted from 1% to 99% by controlling the conductivity of VO2 from 2 x 10(2) to 2 x 10(5) S/m. It is polarization-insensitive with a large angle tolerance in both transverse electric and transverse magnetic waves. Multiple interference theory is used to analyze the mechanism of the broadband absorber, and the theoretical results are in good agreement with simulations. When the VO2 is changed to the insulator state, the absorber system with a graphene ring can be switched to a narrowband absorber. This work will have great potential applications in the terahertz regime, such as tunable broadband absorbers, dynamic sensing, cloaking, and photodetectors. (C) 2021 Optical Society of America