High-precision detection of topological charge of integral and fractional vortices based on metasurface

High-precision detection of topological charge is significant for the practical applications of vortex beams. In view of the existing evaluation with low resolution of topological charge and more complexity to judge simultaneously integer and fraction, this paper proposes the double judgment method for topological charge based on the designed metasurface. The inner and outer diffraction patterns of metasurface can judge the value and sign of topological charge. The detection precision of the proposed method reaches 0.05. The theoretic and simulated results give the solid verification for the effectiveness of the proposed method. This method has outstanding advantages including planer structure design without additional elements, direct judgment without data processing and high precision over the existing methods. We think this work is benefit to the detection of topological charge and the applications of optical vortices.