Eight-connected contour method for accurate position detection of optical vortices using Shack–Hartmann wavefront sensor

Abstract

Abstract. We propose a simple method of realizing an accurate position detection of phase singularities in an optical vortex (OV) beam using a Shack-Hartmann wavefront sensor (SH-WFS). The method calculates circulations which are the discrete contour integrals of phase slope vectors measured by the SH-WFS and then determines the accurate positions of the singular points by calculating the centers-of-gravity with a fixed window size around the local peak of the circulation distribution. We use closed paths that connect the centers of eightconnected, instead of 2 × 2-neighboring lenslet apertures for calculating the circulations. Both the numerical analysis and proof-of-principle experiment were performed to confirm the measurement accuracy. In experiments, the positions of singular points in OV beams generated by a liquid-crystal-on-silicon spatial light modulator were measured. The root-mean-square error of the position measurement was approximately 0.09 in units of the lens size of the lenslet array used in the SH-WFS. We also estimated the topological charges of the singular points being detected based on the peak circulations, and the results agreed well with theoretical ones. The method achieves both rapid implementation and sublens-size spatial resolution detection and is suitable for applications that require real-time control of OV beams.

Vortex position detection using a scanning triangular aperture in a digital micromirror device

“…However, the practical application of this method is limited due to extensive training requirements. There is also a vast use of Shack-Hartmann wavefront sensor [42] and its modifications [43,44] to locate vortices. The slopes of the acquired wavefront are used in an algorithm to generate a branch point potential map, with peaks and valleys displaying the locations and polarities of the OVs.…”

Topological Charge Detection Using Generalized Contour-Sum Method from Distorted Donut-Shaped Optical Vortex Beams: Experimental Comparison of Closed Path Determination Methods

“…As one of the key devices used in adaptive optics systems [19], Shack-Hartmann wavefront sensors (SH-WFS) have also been utilized to determine the TC value of OV beams [12,[20][21][22][23]. An SH-WFS consists of a lenslet array and an image sensor, and directly measures the phase slope of the incident wavefront at each lenslet position.…”

“…The basic form of the contour-sum method uses the pre-assigned closed paths, e.g., the closed path associated with the central 2 × 2 or 3 × 3 lenslet area to calculate the discrete line integral, which is employed to determine the TC value of an OV beam [20,22]. This approach is successful in measuring OV beams with nearly uniform or quasi-uniform intensity distribution.…”