Optical vortex position detection with Shack-Hartmann wavefront sensor using extended closed contour method

摘要

We propose a new method, based on Shack-Hartmann wavefront sensor (SH-WFS), to achieve high-accuracy position detection of phase singular points of optical vortex (OV) beam. The method calculates evaluation values related to phase slopes of incoming wavefront from Hartmanngram recorded by SH-WFS, and then determines precisely the position of the singular points by calculating the centroid of the 3x3-evaluation-value distribution centered at peak position. A main point is that, in evaluation-value calculation, we use a closed contour connecting the centers of 8-connected, instead of 2x2, lenslet apertures. Theoretical analysis shows that the measurement errors can be greatly reduced in comparison to that of 2x2 closed contour. Proof experiments were performed to confirm its accuracy by measuring singular points of OV beams generated by a liquid crystal on silicon spatial light modulator. The root-mean-square error of the measured position of singular points was approximately 0.052, in units of the lens size of lenslet array used in the SH-WFS. The method achieves fast-speed and sub-lens size spatial resolution detection, is suitable for real-time control applications.