Evaluation of the Laguerre-Gaussian mode purity produced by 3D-printed microwave spiral phase plates

Computer-aided design software and additive manufacturing provide flexibility in the direct fabrication of multi-material devices. This design and fabrication versatility has been investigated for the manufacture of dielectric spiral phase plates (SPP) to generate electromagnetic waves with helical wave-fronts. Three types of SPPs designed to produce an orbital angular momentum (OAM) mode number l=|1| were additively manufactured using multi-material extrusion and multijet fabrication methods. The phase mode and mode characteristics of transformed helical microwaves as a function of the SPP geometrical features was investigated experimentally in the 12 to 18 GHz frequency range, providing high purity at characteristic frequencies. The SPPs were further combined with an additively manufactured dielectric lens that provided a marked improvement in OAM mode purity. Finally, multiplexing and de-multiplexing of two OAM modes were demonstrated successfully using the optimum SPP geometry and d...