Transmission Continuous Meta-Grating for Generating Wide-Band Low-to-High Order OAM With Extremely High Mode Purity

This article presents a novel continuous dielectric meta-grating array (DMGA) for generating wide-band, high-performance transmission orbital angular momentum (OAM) vortex beams with high mode purity. A broadband meta-grating unit (MGU) was designed and modeled theoretically, including a detailed analysis of its design process. Simulations and theoretical calculations show that, in the 26–39 GHz (40%), the unit achieves a 180° transmission phase and a transmission coefficient over 0.9. The array patterning was determined using a grating function. The DMGA is composed of continuously spatially varying grating strips, effectively preventing issues caused by array discontinuity such as interatom coupling and discontinuous step phase changes, which could lead to vortex beam distortion and low purity. Simulations show that the DMGA generates broadband, high-performance vortex beams with high mode purity for mode orders
$l =2$
, 3, 4, 5, 6, 7, 8, 9, and 10, exhibiting advantages in generating high-quality, high-order OAM beams. Additionally, it exhibits frequency-aperture size insensitivity, enabling miniaturization and customization of aperture sizes. Finally, the measurement confirms the effectiveness.