Fully optically tunable and flexible composite films for enhanced terahertz control and multifunctional terahertz devices

Flexible terahertz (THz) devices that incorporate with active media can effectively manipulate THz waves and thus hold a high position for the next generation of THz devices. Here, we propose a fully optically tunable and soft composite film based on vanadium dioxide nanowires/poly- (vinylpyrrolidone) (VO2/PVP), which presents a NIR light-driven THz modulation. The modulation mechanism and multifunctional properties of the VO2/PVP composite film are investigated; it exhibits a large modulation depth of ∼65%, a very low-power NIR light-driven THz modulation, and excellent mechanical flexibility. The experimental results are shown to be in good agreement with numerical simulations. Further, the VO2/PVP composite film is utilized as an optically active medium to implement an optically tunable and highly flexible THz polarizer; the device possesses multifunctional capabilities for manipulating THz wave polarization and modulating THz wave amplitude. Considering the simple preparation process of the proposed composite film by the spin-coating method and its convenient implementation in THz systems, this work provides an alternative strategy to develop actively tunable and flexible THz compact devices.