The low intensity regions existed around the singular point of optical vortex (OV) beams influence the position detection accuracy of phase singular points, especially for OVs of large topological charge. A new method using Shack-Hartmann wavefront sensor (SH-WFS) is proposed to solve this problem. In the method, we combine several phase slopes obtained at individual lenses of a lens array into one to avoid the influence of the low intensity region and use correlation matching with pre-calculated simulation data to get the accurate singular point position. The experimental results show that the position detection precision of this method is maintained less than 0.2 in unit of lens-size for OVs of charges -20 to 20.
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 eight-connected, 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.
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.
Access to the requested content is limited to institutions that have purchased or subscribe to SPIE eBooks.
You are receiving this notice because your organization may not have SPIE eBooks access.*
*Shibboleth/Open Athens users─please
sign in
to access your institution's subscriptions.
To obtain this item, you may purchase the complete book in print or electronic format on
SPIE.org.
INSTITUTIONAL Select your institution to access the SPIE Digital Library.
PERSONAL Sign in with your SPIE account to access your personal subscriptions or to use specific features such as save to my library, sign up for alerts, save searches, etc.