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Benefiting from the unprecedented superiority of coding metasurfaces at manipulating electromagnetic waves in the microwave band, in this paper, we use the Pancharatnam-Berry (PB) phase concept to propose a high-efficiency reflectivetype coding metasurface that can arbitrarily manipulate the scattering pattern of terahertz waves and implement many novel functionalities. By optimizing the coding sequences, we demonstrate that the designed 1-, 2-, and 3-bit coding metasurfaces with specific coding sequences have the strong ability to control reflected terahertz waves. The two proposed 1-bit coding metasurfaces demonstrate that the reflected terahertz beam can be redirected and arbitrarily controlled. For normally incident x-and y-polarized waves, a 10 dB radar cross-section (RCS) reduction can be achieved from 2.1 THz to 5.2 THz using the designed 2-bit coding metasurface. Moreover, two kinds of orbital angular momentum (OAM) vortex beams with different moduli are generated by a coding metasurface using different coding sequences. Our research provides a new degree of freedom for the sophisticated manipulation of terahertz waves, and contributes to the development of metasurfaces towards practical applications.

Metamaterial perfect absorbers play an essential role in many optoelectronic devices. In this paper, a dual-band tunable metamaterial perfect absorber based on graphene is proposed. The simulation results present that under normal incidence two absorption peaks of 99.9% and 99.9% occur at the frequencies 1.69 THz and 4.30 THz, respectively. Impedance matching theory is employed to elaborate this dual-band perfect absorption phenomenon. While at oblique incidence, the absorption of the absorber remains more than 90% over a wide incident angle from 0° to 75° for the transverse electric (TE) polarization and 60° for the transverse magnetic (TM) polarization separately. Furthermore, it is also independent to the polarization angles. In addition, the effects of different geometrical parameters and the chemical potential of graphene on the resonant frequencies are investigated in detail. The two peaks of the absorber can be dynamically tuned by the variation of the chemical potential of graphene. Due to its good performances, the designed metamaterial perfect system has great potential applications in biosensing, photodetectors, stealth, and imaging devices.

A surface plasmon polarized structure consisting of two metal-insulator-metal (MIM) waveguide coupled with clockwork spring-shaped resonators are constructed in this paper, and its geometric parameters are controlled within a few hundred nanometers. The finite element method (FEM) and multimode interference coupled mode theory (MICMT) are used to simulate and theoretically calculate the optical response of the designed structure. By modifying the structural parameters of the system, the influence on the asymmetry of the Fano resonance line is studied. The changes of the transmission spectra at different refractive indexes are also investigated. Based on this asymmetric resonant line, the sensitivity and FOM* (figure of merit) value of the cavity with different parameters are measured. The sensitivity and FOM* under the best parameters are 1200 nm/RIU and 191.6, respectively. The surface plasmon structure proposed and the results in this paper are promising for applications in the field of high-performance sensing and micro-nano optical devices.

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