3-D Printed Terahertz Lens to Generate Higher Order Bessel Beams Carrying OAM
Geng‐Bo Wu, Ka Fai Chan, Chi Hou Chan
Abstract
Conventional vortex beams carrying orbital angular momentum (OAM) suffer from the limitation of beam divergence in wireless communications applications. This article proposes novel 3-dimensional (3-D) printed discrete dielectric lenses (DDLs) for generation of nondiffractive OAM beams operating at 300 GHz. By virtue of its arbitrary aperture phase control capability, a terahertz (THz) DDL combining the functionalities of three conventional bulky refractive hyperbolic, spiral phase plane, and aixcon lenses is proposed to generate nondiffractive Bessel vortex beam carrying OAM. An aperture field analysis method is also developed to evaluate the radiation performance of the DDL antennas. Furthermore, to cover the OAM signal in an intended longitudinal region, two DDL synthesis methods are explored to generate extended higher order Bessel beams carrying OAM. The first approach is based on geometric optics, while the second uses the alternating projection method (APM) to optimize the aperture phase distribution of the DDL. Two THz DDLs are conveniently fabricated by 3-D printing technology. Measured results demonstrate that THz nondiffractive OAM beams can be successfully generated by the designed DDLs. The generated THz OAM beam with attractive nondiffractive characteristic may open new opportunities for next-generation ultra-high-speed wireless communications.