Anisotropy-driven reshaping and diagnostic limits of high-charge perfect optical vortices.

Perfect optical vortices (POVs) are annular beams designed such that their radii are, in principle, independent of topological charge, making them attractive for structured illumination and optical manipulation. We present a systematic experimental and numerical study of POVs generated using a phase-only spatial light modulator and investigate how controlled angular anisotropy reshapes their structure across a wide range of charges. Three distinct regimes are identified. In the absence of anisotropy, charge-invariant annuli persist only for moderate charges, while higher charges exhibit multi-ring, Bessel-like structure accompanied by a gradual increase in effective radius. At moderate anisotropy, these multi-ring profiles consolidate into single opened annuli with tunable azimuthal asymmetry. In this regime, speckle cross-correlation remains structured even for widely separated charges that exhibit weak correlations under isotropic encoding. At extreme anisotropy, annular intensity profiles converge across all charges, forming pseudo-POVs that remain annular in intensity but exhibit pronounced redistribution of OAM-dependent signatures and a collapse of charge-dependent cross-correlation signatures within the sensitivity of intensity-only measurements. Non-interferometric speckle analysis supports these findings. Autocorrelation rules out trivial ellipticity as the origin of radius convergence, while cross-correlation reveals sensitivity to charge ordering at low anisotropy and an effective loss of charge distinguishability within intensity-only diagnostics at extreme anisotropy. Together, these results clarify the robustness limits of POVs under angular deformation and establish angular anisotropy as a practical control parameter for engineering and diagnosing annular vortex beams.