Twisted Focusing of Optical Vortices with Broadband Flat Spiral Zone Plates

Recent developments have shown that light's orbital angular momentum (OAM) can be harnessed for a diversity of emerging applications and generated by miniaturized OAM generators. Nanostructured flat logarithmic‐spiral zone plates (LSZPs) are proposed to produce as well as focus optical vortices with a long focal depth in the broadband visible range. Topologically breaking the in‐plane symmetry, this nanoengineered LSZP continuously modulates both amplitude and phase in the diffraction field to shape twisted focusing of the optical vortex beam, which is microscopically confined and spatially spiraling with variant crescent‐shaped transverse intensity profiles. Owing to its rich structural degree of freedom upon aperiodic and continuously variant features, the LSZP provides a compact solution to generate and control optical vortices carrying scalable OAM and highly concentrated photons with a high transmission efficiency of ∼22%. This can offer new opportunities for 3D light shaping, optical manipulation, flat optics, and photonics miniaturization and integration. Topologically breaking in‐plane symmetry, the nanoengineered flat logarithmic spiral zone plates (LSZPs) continuously modulate both amplitude and phase of the diffracted field to form twisted focusing of optical vortices spatially spiraling with variant transverse intensity profiles. Owing to its rich structural degree of freedom upon aperiodic and continuously variant features, the LSZP exhibits polarization‐insensitive and broadband behaviors.