Radially-Coupled-Spiral Phase-Shift Zone Plate: A Compact Diffractive Element for Helico-Conical Beam Generation

We present a novel diffractive optical element, the Radially-Coupled-Spiral Phase-Shift Zone Plate (RCS-PZP), for generating helico-conical vortex beams with non-separable radial--azimuthal phase coupling. Unlike classical optical vortices with a simple helical phase dependence, the RCS-PZP incorporates an additional radial coupled spiral phase term, which breaks cylindrical symmetry and forms a single well-defined spiral-like intensity arm. The radial phase component determines the focusing of the beam, while angular coupling generates spatially varying orbital angular momentum. The radial position and stretch length of the generated single spiral-like intensity pattern are also determined by the phase-shift parameter and topological charge value. Furthermore, Numerical simulations demonstrate that these beams exhibit complex vortex structures, radially modulated angular momentum, and self-healing properties. In turn, the RCS-PZP provides an economic and efficient platform for high-level beam shaping, which has the potential to be used in optical tweezer and manipulation. Experimental confirmation is underway to confirm the simulation outcomes.