Probing Optical Vortex Beams via a Controllable Anisotropic Diffractive Phase Element

In this work, we investigate the diffraction of optical vortex beams through a tunable elliptical Fresnel phase mask (TEFPM). The resulting diffraction patterns are influenced by both the topological charge of the beam and the ellipticity of the mask, exhibiting characteristic intensity distributions that allow direct determination of the magnitude and sign of the topological charge. Requiring only a single controllable parameter, the TEFPM offers a simple and adaptable approach for vortex charge characterization, with a reduced detection distance that supports optical system compactness. The experimental results are confirmed by the exact analytical solutions.