Measuring the orbital angular momentum of a vortex beam under extremely low coherence

Author:

Zhang Zhao12ORCID,Liu Zhenzhen12,Liu Xin12,Gbur Greg3ORCID,Liang Chunhao12,Cai Yangjian12,Zeng Jun12ORCID

Affiliation:

1. Shandong Provincial Engineering and Technical Center of Light Manipulation & Shandong Provincial Key Laboratory of Optics and Photonic Devices, School of Physics and Electronics, Shandong Normal University 1 , Jinan 250358, China

2. Collaborative Innovation Center of Light Manipulation and Applications, Shandong Normal University 2 , Jinan 250358, China

3. Department of Physics and Optical Science, The University of North Carolina at Charlotte 3 , Charlotte, North Carolina 28223, USA

Abstract

Due to carrying orbital angular momentum (OAM), vortex beams are also known as OAM beams. Coherence, as another controllable parameter of the beam, and its joint control with the vortex phase greatly promote the applications of the vortex beam such as particle manipulation and anti-atmospheric turbulence. However, the OAM information, quantified by the topological charge (TC), hidden in the second-order electric field statistical function of a partially coherent vortex beam is not easily extracted experimentally. In addition, the existing TC measurement schemes for the partially coherent vortex beams are limited to the detection of the near focal plane. The above-mentioned difficulties and limitations undoubtedly limit the application of vortex beams. Here, we achieve OAM measurement of a partially coherent Laguerre Gaussian (PCLG) beam under different coherence conditions, especially at extremely low coherence, by coupling the cross phase. The cross phase can separate the original concentric dark rings in the degree of coherence function of a PCLG beam. The number of separated dark rings is equal to the magnitude of the TC which determines the OAM carried by each photon in the vortex beam. The sign of TC is determined by the arrangement direction of separated dark rings, which determines the direction of rotation of the spiral wavefront of the vortex beam. In addition, we verify the accuracy of our method experimentally, especially under the condition of extremely low coherence and during propagation. Our results can find application in OAM-based free space optical communication and information encryption.

Funder

National Key Research and Development Program of China

National Natural Science Foundation of China

Local Science and Technology Development Project of the Central Government

China Postdoctoral Science Foundation

Natural Science Foundation of Shandong Province

Publisher

AIP Publishing

Subject

Physics and Astronomy (miscellaneous)

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