Generating Orbital Angular Momentum Terahertz Radiation Based on Spoof Surface Plasmon

Abstract

Since orbital angular momentum (OAM) holds many promises in various advanced applications, such as the wireless communication, it has been investigated widely in recent years. The generation of the OAM mode based on the spoof surface plasmon (SSP) is presented in this paper. The SSP on the helical grating is introduced and the dispersion characteristic is analyzed. The phase of SSP in this system changes along the angular direction and carries OAM mode, which is different from the SSP generated from the cylindrical grating. When the free electron passes over the helical grating, the SSP can be excited effectively. However, as the wavenumber of the SSP is far larger than the wavenumber in the free space, the SSP is confined in the surface of the helical grating. By loading an asynchronous ring array, the SSP wave can be converted into the OAM mode. The operating frequency and the radiation can be tailored by the energy of the free electron. Moreover, the rotation of the OAM mode can be changed by the direction of the helical grating. The method introduced in this paper may provide an efficient way to generate the OAM and boost the applications of the OAM in the communication system.