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Open AccessArticle

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

1
College of Optical Science and Engineering, Zhejiang University, Hangzhou 310027, China
2
Central Research Laboratory, Hamamatsu Photonics K. K., Hamamatsu 434-8601, Japan
*
Authors to whom correspondence should be addressed.
Appl. Sci. 2019, 9(19), 3956; https://doi.org/10.3390/app9193956
Received: 30 August 2019 / Revised: 16 September 2019 / Accepted: 17 September 2019 / Published: 20 September 2019
A generalized contour-sum method has been proposed to measure the topological charge (TC) of an optical vortex (OV) beam using a Shack–Hartmann wavefront sensor (SH-WFS). Moreover, a recent study extended it to be workable for measuring an aberrated OV beam. However, when the OV beam suffers from severe distortion, the closed path for circulation calculation becomes crucial. In this paper, we evaluate the performance of five closed path determination methods, including watershed transformation, maximum average-intensity circle extraction, a combination of watershed transformation and maximum average-intensity circle extraction, and perfectly round circles assignation. In the experiments, we used a phase-only spatial light modulator to generate OV beams and aberrations, while an SH-WFS was used to measure the intensity profile and phase slopes. The results show that when determining the TC values of distorted donut-shaped OV beams, the watershed-transformed maximum average-intensity circle method performed the best, and the maximum average-intensity circle method and the watershed transformation method came second and third, while the worst was the perfect circles assignation method. The discussions that explain our experimental results are also given. View Full-Text
Keywords: wavefront sensor; spatial light modulator; contour-sum method; topological charge; orbital angular momentum wavefront sensor; spatial light modulator; contour-sum method; topological charge; orbital angular momentum
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Wang, D.; Huang, H.; Toyoda, H.; Liu, H. Topological Charge Detection Using Generalized Contour-Sum Method from Distorted Donut-Shaped Optical Vortex Beams: Experimental Comparison of Closed Path Determination Methods. Appl. Sci. 2019, 9, 3956.

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