The Full-space Bessel Beam Modulator Based on Pancharatnam-Berry Metasurface

Bessel beam has the exotic property of non-diffraction and self-healing effect. In microwave frequency range, various modulation methods, such as metasurface, binary hologram, axicon, have been widely studied for the generation of Bessel beam with different orders. Zero-order Bessel beam could be modulated with circular polarization (CP, also known as the spin angular momentum, SAM) and higher-order Bessel beams carry orbital angular momentum (OAM). In this paper, three different types of Bessel beam modulator (zero-order, first-order, second order) based on Pancharatnam-Berry metasurface are designed and optimized. The proposed ultrathin metasurface, excited by a SAM (right-handed circularly polarized, RCP) wave, simultaneously generate two beams with two opposite SAM modes (LCP and RCP) in transmission and reflection direction. The magnitude and phase of meta-unit are carefully designed and optimized along the transmission and reflection direction and three distinctive types of Bessel beam modulaters are designed. Besides, when a PEC sphere is allocated in the non-diffraction zone of the Bessel beam, the electric field distribution demonstrates that the beam scatters by the existence of the PEC obstacle and then refocuses into a new narrow beam-width beam, which prove the validity of the self-healing property. The near-field scan measurement results of Bessel beam modulator show that the Bessel beam with SAM and OAM characteristics can be simultaneously generated in both transmission and reflection directions, and the measurement results are in good agreement with the full-wave simulation results. This result has potential application value in microwave imaging, target detection, wireless power transmissions, etc.