Flexible THz Carrier-Envelope Phase Shifter Based on Metamaterials

The ability to manipulate terahertz (THz) waveform is important for its applications. Despite rapid progress in metamaterials (MMs), the carrier-envelope phase (CEP) control for THz pulse is still challenging due to its broadband feature. THz scanning tunneling microscope (THz-STM), as an emerging technique combining both high temporal and spatial resolution, imposes additional requirements. Here, an ultra-thin and flexible THz CEP shifter with five groups of different MM arrays is proposed. The CEP shifter is based on a specified split-ring resonator with a pair of cross-oriented gratings to enhance transmission efficiency. Simulation and experimental results show that the CEP of the THz pulse is modulated by passing through different MM arrays in turn, which can be shifted as high as 2 pi. The CEP shifter has good tolerance to wide-angle oblique incidence and structural bending, which is expected to be used as a key component for THz-STM. The structure of the CEP shifter has many potential applications, including THz wave focusing, beam-steering, spatial phase modulation, and structured light generation.