Alternative method for measuring phase retardation of birefringent elements

This study proposes an alternative method for measuring the phase retardation of birefringent elements. The technique employs vortex modulation to control the spatial phase of two orthogonally polarized beams, establishing a linear relationship between the measured phase retardation and the inclination angle of the central dark fringe in the interference pattern. The inclination angle of the central dark fringe can be accurately determined through image processing and centroid analysis of the interference pattern, allowing for the inference of the phase retardation. The feasibility of our method was demonstrated with a measurement uncertainty of nearly 0.12° over a range from -180^∘ to 180°.