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• Chinese Optics Letters
• Vol. 20, Issue 2, 020601 (2022)
Lin Zhao1、2, Yuan Hao1, Li Chen1, Wenyi Liu1, Meng Jin1, Yi Wu1, Jiamin Tao1, Kaiqian Jie1, and Hongzhan Liu1、*
Author Affiliations
• 1Guangdong Provincial Key Laboratory of Nanophotonic Functional Materials and Devices, Guangzhou 510006, China
• 2School of Electronics and Information Technology, Sun Yat-sen University, Guangzhou 510275, China
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Abstract

Vortex optical communication has been a hot research field in recent years. A key step is mode recognition in the orbital angular momentum (OAM) free-space optical (FSO) communication system. In this article, we propose an OAM mode recognition method based on image recognition technology, which uses the interferogram between the vortex beam and the Gaussian beam to identify the OAM mode. In order to resist the influence of atmospheric turbulence on the recognition accuracy, we added a Gaussian smoothing filter into the recognition process. Moreover, we used random phase screens to generate interferogram sets at distances of 1 km and 2 km. The verification result shows that the proposed scheme produces high identification accuracy for the distorted optical field. The average accuracy can reach 100% and 87.78% under the conditions of medium- and strong-turbulence levels, respectively. It is anticipated that these results might be helpful for improving the reliability of the OAM-FSO communication system in the future.
 $E=ELG+ETEM00.$(1)

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 $ELG(r,φ,z)=2p!π(p+|l|)!1ω2(z)[2rω2(z)]|l|Lp|l|[2r2ω2(z)]×exp[i(2p+|l|+1)arctan(zzR)]×exp[−r2ω(z)−ikr2z2 R(z)]exp(ilφ).$(2)

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 $ETEM00(r,φ,z)=1ω2(z)exp[−r2ω(z)−ikr2z2 R(z)]×exp[iarctan(zzR)].$(3)

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 $0<Δr<2π·R(z)/(k·z).$(4)

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 $ϕ(kx,ky)=0.033Cn2[1+1.802kx2+ky2kl2−0.254(kx2+ky2kl2)7/12]×exp(kx2+ky2kl2)(kx2+ky2+1L02)−11/6,$(5)

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 $ψ2(kx,ky)=2πΔz·(kx2+ky2)·ϕ(kx,ky)·(2πNΔx)2,$(6)

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 $θ(x,y)=F{Cψ(kx,ky)},$(7)

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 $y¯j=1k∑i=−mmexp[−(xi−xj)22σ2]yi,0(8)

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 $k=∑i=−mmexp[−(xi−xj)22σ2],$(9)

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Copy Citation Text
Lin Zhao, Yuan Hao, Li Chen, Wenyi Liu, Meng Jin, Yi Wu, Jiamin Tao, Kaiqian Jie, Hongzhan Liu. High-accuracy mode recognition method in orbital angular momentum optical communication system[J]. Chinese Optics Letters, 2022, 20(2): 020601