Tunable full-space metasurfaces for multiple terahertz wavefront manipulation and holographic imaging

Full-space metasurfaces are attracting much attention for their capability to concomitantly manipulate transmitted and reflected waves of incident waves. In this thesis, a tunable full-space metasurface based on Pancharatnam-Berry (PB) phase modulation and InSb temperature characteristics is proposed. After the circularly polarized (CP) waves pass through the metasurface, the incident CP waves are converted into cross- polarized CP waves at 0.56 THz, which has an effective transmission amplitude of 80%, and the transmission amplitude can be adjusted by raising the temperature of InSb from 200K to 330K, which can reduce the transmission amplitude to about 20%; it is capable of reflecting co-polarized CP waves over a wide bandwidth of 1.6-1.75 THz and the reflection amplitude is up to 92%. The wavefronts of CP waves in transmission and reflection modes are modulated independently of each other at two terahertz frequencies by PB phase without interfering with each other, and by altering the geometrical parameters corresponding to the transmission or reflection modes of the unit structure, phase coverage of 0 similar to 2 pi in the corresponding modes can be obtained independently. As proof of concept, a series of terahertz wavefront modulation devices, such as single-focus tunable metalens and dual-channel point focusing reflective metalens, full-space deflective vortex beams and full-space holographic imaging via the (Gerchberg-Saxton) GS algorithm, are designed through the combinantion of the PB phase with the theory of metasurface scattering in two modes. Our work significantly expands the ability of full-space metasurfaces to control electromagnetic waves, and the proposed metasurfaces have the property of simultaneously and independently modulating transmitted and reflected wavefronts, which show promising applications in full-space terahertz high-resolution imaging and high-speed broadband communications.