With the rapid develop of information era, there is an increasing demand on the transmission capacity of communication systems. The existing fiber optical communication systems face great challenge. Lots of new techniques are emerging to overcome the capacity crunch of optical communications, among which fiber-based orbital angular momentum (OAM) communications may provide a possible solution.
Jian Wang’s group at Wuhan National Laboratory for Optoelectronics (WNLO), Multi-Dimensional Photonics Laboratory (MDPL), has been devoted to the research of fiber OAM communications for many years and achieved a series of progress:
Firstly, in long-distance OAM fiber transmission, Jian Wang’s group analyzed the OAM mode transmission performance. By using LDPC codes to mitigate the influence of mode crosstalk and DMD for long-distance fiber OAM modes transmission, PhD candidate Andong Wang from MDPL demonstrated OAM modes transmission and multiplexing in 50-km fiber (Optics Express Vol. 24, PP. 11716-11726, 2016).
Figure 1 Concept and principle of strong mode coupling in long-distance OAM transmission.
Moreover, Jian Wang’s group also achieved a series of progress in fiber OAM communication. Directed by Prof. Jian Wang, PhD candidates Chen Si and Jun Liu cooperating with Dr. Cheng Du and Mr. Qi Mo in Fiberhome Telecommunication Technologies Co. Ltd, demonstrated full-duplex bidirectional data transmission link using twisted lights multiplexing over 1.1-km orbital angular momentum fiber (Optics Express 24 16934-16944, 2016). In addition, by using the supported modes in optical fiber, PhD candidates Long Zhu et al., realized image transfer by employing mode encoding/decoding in km-scale fiber (Optics Letters 41, 1969, 2016). Furthermore, PhD candidate Jun Liu from MDPL, directed By Prof. Wang, cooperated with Sun Yatsen University, University of Glasgow and Fiberhome Telecommunication Technologies, has demonstrated and evaluated the performance of analog signal transmission system with photonic integrated optical vortex emitter and 3.6-km few-mode fiber (FMF) link using OAM modes (Optics Letters 41, 1969-1972, 2016).
Figure 2 Concept of full-duplex bidirectional data transmission using twisted lights multiplexing over 1.1-km OAM fiber.
Figure 3 Concept of image transfer using mode encoding/decoding in km-scale fiber.
Figure 4 Experimental setup of an analog signal transmission system with photonic integrated optical vortex emitter and 3.6-km FMF link.
In addition, Prof. Jian Wang’s group designed two kinds of fiber converter to realize low-cost, versatile all-fiber OAM conversion. PhD candidate Liang Fang proposed fiber helical gratings (HGs) for flexible generation, conversion, and exchange of fiber guided OAM modes (IEEE Journal of Quantum Electronics 52, 6600306, 2016). It is expected that the proposed scheme is a promising method for fiber-based generation, date exchange, and spectra processing of OAM modes, and may have some potential applications in OAM multiplexing in fiber communications. Moreover, directed by Prof. Jian Wang, cooperating with Dr. Cheng Du and Mr. Qi Mo in Fiberhome Telecommunication Technologies Co. Ltd, PhD candidate Jun Liu, demonstrated all fiber pre- and post-data exchange in km-scale fiber-based twisted lights multiplexing (Optics Letters 41, 3896-3899, 2016).
Figure 5 (a) Scheme of helical gratings (HGs) OAM converter. (b) Concept of all-fiber pre- and post-data exchange functions in an OAM-SDM network.
These works are partially supported by the National Basic Research Program of China (973Program) (2014CB340004), the National Natural Science Foundation of China (NSFC) (11274131, 11574001, 61222502), the Program for New Century Excellent Talents in University (NCET-11-0182), and the Wuhan Science and Technology Plan Project (2014070404010201).
Links of the published papers:
 Andong Wang, Long Zhu, Shi Chen, Cheng Du, Qi Mo, and Jian Wang*, “Characterization of LDPC-coded orbital angular momentum modes transmission and multiplexing over a 50-km fiber,” Optics Express 24(11), 11716-11726 (2016).
 Shi Chen, Jun Liu, Yifan Zhao, Long Zhu, Andong Wang, Shuhui Li, Jing Du, Cheng Du, Qi Mo and Jian Wang*, “Full-duplex bidirectional data transmission link using twisted lights multiplexing over 1.1-km orbital angular momentum fiber,” Scientific Reports 6, 38181 (2016).
 Long Zhu, Jun Liu, Qi Mo, Cheng Du, and Jian Wang, “Encoding/decoding using superpositions of spatial modes for image transfer in km-scale few-mode fiber,” Opt. Express 24(15), 16934-16944 (2016).
 Jun Liu, Shimao Li, Jing Du, Charalambos Klitis, Cheng Du, Qi Mo, Marc Sorel, Siyuan Yu, Xinlun Cai, and Jian Wang*, “Performance evaluation of analog signal transmission in an integrated optical vortex emitter to 3.6-km few-mode fiber system,” Optics Letters 41(9), 1969-1972 (2016).
 Liang Fang and Jian Wang*, “Mode conversion and orbital angular momentum transfer among multiple modes by helical gratings,” IEEE Journal of Quantum Electronics, 52(8), 6600306 2016.
 Jun Liu, Long Zhu, Andong Wang, Shuhui Li, Shi Chen, Cheng Du, Qi Mo, and Jian Wang*, “All fiber pre- and post-data exchange in km-scale fiber-based twisted lights multiplexing,” Opt. Lett. 41(16), 3896 (2016).