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2020-11-05
Research Status and Prospects of Orbital Angular Momentum Technology in Wireless Communication
By
Progress In Electromagnetics Research, Vol. 168, 113-132, 2020
Abstract
It becomes more and more challenging to satisfy the long-term demand of transmission capacity in wireless networks if we limit our research within the frame of traditional electromagnetic wave characteristics (e.g., frequency, amplitude, phase and polarization). The potential of orbital angular momentum (OAM) for unleashing new capacity in the severely congested spectrum of commercial communication systems is generating great interest in wireless communication field. The OAM vortex wave/beam has different topological charges, which are orthogonal to each other. It provides a new way for multiplexing in wireless communications. Electromagnetic wave or synthetic beam carrying OAM has a spiral wavefront phase structure, which may provide a new degree of freedom or better orthogonality in spatial domain. In this paper, we introduce the fundamental theory of OAM. Then, OAM generation and reception methods are equally demonstrated. Furthermore, we present the latest development of OAM in wireless communication. We further discuss the controversial topic ``whether OAM provides a new degree of freedom'' and illustrate our views on the relationship between OAM and MIMO. Finally, we suggest some open research directions of OAM.
Citation
Feng Zheng, Yijian Chen, Siwei Ji, and Gaoming Duan, "Research Status and Prospects of Orbital Angular Momentum Technology in Wireless Communication," Progress In Electromagnetics Research, Vol. 168, 113-132, 2020.
doi:10.2528/PIER20091104
References

1. Allen, L., M. W. Beijersbergen, R. J. C. Spreeuw, and J. P. Woerdman, "Orbital angular momentum of light and the transformation of Laguerre-Gaussian laser modes," Physical Review, Vol. 45, No. 11, 8185-8189, 1992.

2. Jackson, J. D., "Classical electrodynamics," American Journal of Physics, Vol. 67, No. 9, 78-78, 1999.

3. McMorran, B. J., A. Agrawal, I. M. Anderson, et al. "Electron vortex beams with high quanta of orbital angular momentum," Science, Vol. 331, No. 6014, 192-195, 2011.

4. Drevinskas, R., M. Gecevicius, M. Beresna, and P. G. Kazansky, "Femtosecond laser nanostructuring for high-topological charge vortex tweezers with continuously tunable orbital angular momentum," The European Conference on Lasers and Electro-Optics. Optical Society of America, 2015.

5. Vaziri, A., G. Weihs, and A. Zeilinger, "Superpositions of the orbital angular momentum for applications in quantum experiments," Journal of Optics B: Quantum and Semiclassical Optics, Vol. 4, S47-S51, 2002.

6. Liu, K., Y. Cheng, X. Li, and Y. Gao, "Microwave-sensing technology using orbital angular momentum: Overview of its advantages," IEEE Veh. Technol. Mag., Vol. 14, No. 2, 112-118, 2019.

7. Liu, H., K. Liu, Y. Cheng, and H. Wang, "Microwave vortex imaging based on dual coupled OAM beams," IEEE Sensors Journal, Vol. 20, No. 2, 806-815, 2020.

8. Uchida, M. and A. Tonomura, "Generation of electron beams carrying orbital angular momentum," Nature, Vol. 464, No. 7289, 737-739, 2010.

9. Verbeeck, J., H. Tian, and P. Schattschneider, "Production and application of electron vortex beams," Nature, Vol. 467, No. 7313, 301-304, 2010.

10. Beijersbergen, M. W., M. Kristensen, and J. P. Woerdman, "Spiral phaseplate used to produce helical wavefront laser beams," Conference on Lasers and Electro-Optics Europe, 1994.

11. Liang, J. and S. Zhang, "Orbital Angular Momentum (OAM) generation by cylinder dielectric resonator antenna for future wireless communications," IEEE Access, Vol. 4, 9570-9574, 2016.

12. Lei, X. Y. and Y. J. Cheng, "High-efficiency and high-polarization separation reflectarray element for OAM-folded antenna application," IEEE Antennas and Wireless Propagation Letters, Vol. 16, 1357-1360, 2017.

13. Tamburini, F., E. Mari, B. Thide, et al. "Experimental verification of photon angular momentum and vorticity with radio techniques," Applied Physics Letters, Vol. 99, No. 20, 204102, 2011.

14. Singh, R. P. and P. G. Poonacha, "Survey of techniques for achieving topological diversity," 2013 National Conference on Communications (NCC), 2013.

15. Wu, H., Y. Yuan, Z. Zhang, and J. Cang, "UCA-based orbital angular momentum radio beam generation and reception under different array configurations," 2014 Sixth International Conference on Wireless Communications and Signal Processing (WCSP), 2014.

16. Li, L., et al., "Intelligent metasurface imager and recognizer," Light Science and Applications, Vol. 8, No. 97, 1-9, 2019.

17. Ma, Q., et al., "Smart metasurface with self-adaptively reprogrammable functions," Light Science and Applications, Vol. 8, No. 98, 2019.

18. Li, L., et al., "Machine-learning reprogrammable metasurface imager," Nature Commun., Vol. 10, No. 1082, 1-8, 2019.

19. Han, J., L. Li, H. Yi, and Y. Shi, "1-bit digital orbital angular momentum vortex beam generator based on a coding reflective metasurface," Optical Materials Express, Vol. 8, No. 11, 3470, 2018.

20. Shuang, Y., H. Zhao, W. Ji, T. J. Cui, and L. Li, "Programmable high-order OAM-carrying beams for direct-modulation wireless communications," IEEE Journal on Emerging and Selected Topics in Circuits and Systems, Vol. 10, No. 1, 29-37, 2020.

21. Yu, S., L. Li, G. Shi, et al. "Design, fabrication, and measurement of reflective metasurface for orbital angular momentum vortex wave in radio frequency domain," Applied Physics Letters, Vol. 108, No. 12, 121903, 2016.

22. Yu, S., L. Li, G. Shi, et al. "Generating multiple orbital angular momentum vortex beams using a metasurface in radio frequency domain," Applied Physics Letters, Vol. 108, No. 24, 241901, 2016.

23. Xu, B. J., C. Wu, Z. Wei, et al. "Generating an orbital-angular-momentum beam with a metasurface of gradient reflective phase," Optical Materials Express, Vol. 6, No. 12, 3940-3945, 2016.

24. Guo, K., Q. Zheng, Z. Yin, and Z. Guo, "Generation of mode-reconfigurable and frequencyadjustable OAM beams using dynamic reflective metasurface," IEEE Access, Vol. 8, 75523-75529, 2020.

25. Maccalli, S., G. Pisano, S. Colafrancesco, et al. "Q-plate for millimeter-wave orbital angular momentum manipulation," Applied Optics, Vol. 52, No. 4, 635-639, 2013.

26. Chen, M. L. N., L. J. Jiang, and W. E. I. Sha, "Artificial perfect electric conductor-perfect magnetic conductor anisotropic metasurface for generating orbital angular momentum of microwave with nearly perfect conversion efficiency," J. Appl. Phys., Vol. 119, No. 6, 064506, 2016.

27. Menglin, C., J. Li, and S. Wei, "Orbital angular momentum generation and detection by geometric-phase based metasurfaces," Applied Sciences, Vol. 8, No. 3, 362, 2018.

28. Karimi, E., S. A. Schulz, I. De Leon, et al. "Generating optical orbital angular momentum at visible wavelengths using a plasmonic metasurface," Light Science and Applications, Vol. 3, No. 5, 167, 2014.

29. Chen, M. L. N., L. J. Jiang, and W. E. I. Sha, "Orbital Angular Momentum (OAM) generation by composite PEC-PMC metasurfaces in microwave regime," 2016 IEEE International Symposium on Antennas and Propagation (APSURSI), 2016.

30. Chen, M. L. N., L. J. Jiang, and W. E. I. Sha, "Quasi-continuous metasurfaces for orbital angular momentum generation," IEEE Antennas and Wireless Propagation Letters, Vol. 18, No. 3, 477-481, 2019.

31. Chen, M. L. N., L. J. Jiang, and W. E. I. Sha, "Ultrathin complementary metasurface for orbital angular momentum generation at microwave frequencies," IEEE Transactions on Antennas and Propagation, Vol. 65, No. 1, 396-400, 2017.

32. Guan, L., Z. He, D. Ding, Y. Yu, W. Zhang, and R. Chen, "Polarization-controlled shared-aperture metasurface for generating a vortex beam with different modes," IEEE Transactions on Antennas and Propagation, Vol. 66, No. 12, 7455-7459, 2018.

33. Chen, M. L. N., L. J. Jiang, and W. E. I. Sha, "Detection of orbital angular momentum with metasurface at microwave band," IEEE Antennas and Wireless Propagation Letters, Vol. 17, No. 1, 110-113, 2018.

34. Yi, J., X. Cao, R. Feng, et al. "All-dielectric transformed material for microwave broadband orbital angular momentum vortex beam," Physical Review Applied, Vol. 12, No. 2, 024064, 2019.

35. Li, W., J. Zhu, Y. Liu, B. Zhang, Y. Liu, and Q. H. Liu, "Realization of third order OAM mode using ring patch antenna," IEEE Transactions on Antennas and Propagation, Early Access Article, 2020.

36. Feng, P., S. Qu, and S. Yang, "OAM-generating transmitarray antenna with circular phased array antenna feed," IEEE Transactions on Antennas and Propagation, Vol. 68, No. 6, 4540-4548, 2020.

37. Ming, J. and Y. Shi, "A mode reconfigurable orbital angular momentum water antenna," IEEE Access, Vol. 8, 89152-89160, 2020.

38. Stegenburgs, E., et al., "Near-infrared OAM communication using 3D-printed microscale spiral phase plates," IEEE Communications Magazine, Vol. 57, No. 8, 65-69, 2019.

39. Wu, G., K. F. Chan, S. Qu, K. F. Tong, and C. H. Chan, "Orbital Angular Momentum (OAM) mode-reconfigurable discrete dielectric lens operating at 300 GHz," IEEE Transactions on Terahertz Science and Technology, Vol. 10, No. 5, 480-489, 2020.

40. Wu, G., Y. Zeng, K. F. Chan, S. Qu, and C. H. Chan, "3-D printed terahertz lens with circularly polarized focused near field," 13th European Conference on Antennas and Propagation (EuCAP), 2019.

41. Wu, G. B., Y. Zeng, K. F. Chan, S. Qu, and C. H. Chan, "High-gain circularly plarized lens antenna for terahertz applications," IEEE Antennas and Wireless Propagation Letters, Vol. 18, No. 5, 921-925, 2019.

42. Dieylar Diallo, C., D. K. Nguyen, A. Chabory, and N. Capet, "Estimation of the orbital angular momentum order using a vector antenna in the presence of noise," The 8th European Conference on Antennas and Propagation (EuCAP 2014), 2014.

43. Nguyen, D. K., J. Sokoloff, O. Pascal, A. Chabory, B. Palacin, and N. Capet, "Local estimation of orbital and spin angular momentum mode numbers," IEEE Antennas and Wireless Propagation Letters, Vol. 16, 50-53, 2017.

44. Yan, Y., et al., "High-capacity millimetre-wave communications with orbital angular momentum multiplexing," Nature Communications, Vol. 5, 4876, 2014.

45. Allen, B., A. Tennant, Q. Bai, and E. Chatziantoniou, "Wireless data encoding and decoding using OAM modes," Electronics Letters, Vol. 50, No. 3, 232-233, 2014.

46. Cano, E. and B. Allen, "Multiple-antenna phase-gradient detection for OAM radio communications," Electronics Letters, Vol. 51, No. 9, 724-725, 2015.

47. Vourch, C. J., B. Allen, and T. D. Drysdale, "Planar millimetre-wave antenna simultaneously producing four orbital angular momentum modes and associated multi-element receiver array," IET Microwaves, Antennas & Propagation, Vol. 10, No. 14, 1492-1499, 2016.

48. Zhang, C. and L. Ma, "Detecting the orbital angular momentum of electro-magnetic waves using virtual rotational antenna," Scientific Reports, Vol. 7, No. 1, 4585, 2017.

49. Yao, Y., X. Liang, W. Zhu, J. Geng, and R. Jin, "Experiments of orbital angular momentum phase properties for long-distance transmission," IEEE Access, Vol. 7, 62689-62694, 2019.

50. Knutson, E. M., S. Lohani, O. Danaci, S. D. Huver, and R. T. Glasser, "Deep learning as a tool to distinguish between high orbital angular momentum optical modes," Proc. SPIE, Vol. 9970, No. 997013, 2016.

51. Doster, T. and A. T. Watnik, "Machine learning approach to OAM beam demultiplexing via convolutional neural networks," Applied Optics, Vol. 56, No. 12, 3386-3396, 2017.

52. Rostami, S., W. Saad, and C. S. Hong, "Deep learning with persistent homology for Orbital Angular Momentum (OAM) decoding," IEEE Communications Letters, Vol. 24, No. 1, 117-121, 2020.

53. Tamburini, F., E. Mari, A. Sponselli, B. Thide, and F. Romanato, "Encoding many channels in the same frequency through radio vorticity: first experimental test," New Journal of Physics, Vol. 14, No. 3, 033001, 2012.

54. Yuri, K., N. Honma, and K. Murata, "Mode selection method suitable for dual-circular-polarized OAM transmission," IEEE Transactions on Antennas and Propagation, Vol. 67, No. 7, 4878-4882, 2019.

55. Zheng, S., X. Hui, X. Jin, H. Chi, and X. Zhang, "Transmission characteristics of a twisted radio wave based on circular traveling-wave antenna," IEEE Transactions on Antennas and Propagation, Vol. 63, No. 4, 1530-1536, 2015.

56. Chen, Y., S. Zheng, H. Chi, X. Jin, and X. Zhang, "Half-mode substrate integrated waveguide antenna for generating multiple orbital angular momentum modes," Electronics Letters, Vol. 52, No. 9, 684-686, 2016.

57. Pan, Y., et al., "Generation of orbital angular momentum radio waves based on dielectric resonator antenna," IEEE Antennas and Wireless Propagation Letters, Vol. 16, 385-388, 2017.

58. Zhang, W., et al., "Four-OAM-mode antenna with traveling-wave ring-slot structure," IEEE Antennas and Wireless Propagation Letters, Vol. 16, 194-197, 2017.

59. Zheng, S., et al., "Realization of beam steering based on plane spiral orbital angular momentum wave," IEEE Transactions on Antennas and Propagation, Vol. 66, No. 3, 1352-1358, 2018.

60. Zheng, S., X. Hui, J. Zhu, et al. "Orbital angular momentum mode-demultiplexing scheme with partial angular receiving aperture," Optics Express, Vol. 23, No. 9, 12251-12257, 2015.

61. Yao, Y., X. Liang, W. Zhu, J. Geng, and R. Jin, "Phase mode analysis of radio beams carrying orbital angular momentum," IEEE Antennas and Wireless Propagation Letters, Vol. 16, 1127-1130, 2017.

62. Yao, Y., X. Liang, W. Zhu, J. Geng, and R. Jin, "Experiments of orbital angular momentum phase properties for long-distance transmission," IEEE Access, Vol. 7, 62689-62694, 2019.

63. Yao, Y., X. Liang, M. Zhu, W. Zhu, J. Geng, and R. Jin, "Analysis and experiments on reflection and refraction of orbital angular momentum waves," IEEE Transactions on Antennas and Propagation, Vol. 67, No. 4, 2085-2094, 2019.

64. Cheng, W., W. Zhang, H. Jing, S. Gao, and H. Zhang, "Orbital angular momentum for wireless communications," IEEE Wireless Communications, Vol. 26, No. 1, 100-107, 2019.

65. Qin, F., S. Gao, W. Cheng, Y. Liu, H. Zhang, and G. Wei, "A high-gain transmitarray for generating dual-mode OAM beams," IEEE Access, Vol. 6, 61006-61013, 2018.

66. Cheng, W., H. Zhang, L. Liang, H. Jing, and Z. Li, "Orbital-angular-momentum embedded massive MIMO: Achieving multiplicative spectrum-efficiency for mmwave communications," IEEE Access, Vol. 6, 2732-2745, 2018.

67. Yang, Y., W. Cheng, W. Zhang, and H. Zhang, "Mode modulation for wireless communications with a twist," IEEE Transactions on Vehicular Technology, Vol. 67, No. 11, 10704-10714, 2018.

68. Wang, L., X. Ge, R. Zi, and C. Wang, "Capacity analysis of orbital angular momentum wireless channels," IEEE Access, Vol. 5, 23069-23077, 2017.

69. Ge, X., R. Zi, X. Xiong, Q. Li, and L. Wang, "Millimeter wave communications with OAM-SM scheme for future mobile networks," IEEE Journal on Selected Areas in Communications, Vol. 35, No. 9, 2163-2177, 2017.

70. Zhang, C. and L. Ma, "Millimetre wave with rotational orbital angular momentum," Scientific Reports, Vol. 6, No. 1, 31921, 2016.

71. Zhang, C. and L. Ma, "Detecting the orbital angular momentum of the electro-magnetic waves with orbital angular momentum," Scientific Reports, Vol. 7, No. 1, 4585, 2017.

72. Zhang, C. and L. Ma, "Trellis-coded OAM-QAM union modulation with single-point receiver," IEEE Communications Letters, Vol. 21, No. 4, 690-693, 2017.

73. Zhang, C., J. Jiang, and Y. Zhao, "Euclidean space with orbital angular momentum," 2019 IEEE International Conference on Communications Workshops (ICC Workshops), 2019.

74. Lee, D., et al., "An experimental demonstration of 28 GHz band wireless OAM-MIMO (Orbital Angular Momentum Multi-Input and Multi-Output) multiplexing," 2018 IEEE 87th Vehicular Technology Conference (VTC Spring), 2018.

75. Doohwan, L., S. Hirofumi, et al. "An evaluation of orbital angular momentum multiplexing technology," Applied Sciences, Vol. 9, No. 9, 1729-1741, 2019.

76. Yuan, Y., Z. Zhang, J. Cang, H. Wu, and C. Zhong, "On the capacity of an orbital angular momentum based MIMO communication system," 2017 9th International Conference on Wireless Communications and Signal Processing (WCSP), 2017.

77. Hirano, T., "Equivalence between orbital angular momentum and multiple-input multiple-output in uniform circular arrays: Investigation by eigenvalues," Microwave and Optical Technology Letters, Vol. 60, No. 5, 1072-1075, 2018.

78. Chen, R., H. Zhou, and J. Li, "Constant envelope multi-mode OAM communication system with UCA antennas," 2019 IEEE Global Communications Conference (GLOBECOM), 2019.

79. Zhao, L., H. Zhang, and W. Cheng, "Fractal uniform circular arrays based multi-orbital-angular-momentum-mode multiplexing vortex radio MIMO," China Communications, Vol. 15, No. 9, 118-135, 2018.

80. Cheng, W., Y. Liu, and H. Zhang, "Space-frequency-mode multidimensional hybrid modulation in OAM based MIMO-OFDM systems," Proc. 23rd Asia-Pacific Conf. Commun., 2017.

81. Yan, Y., et al., "OFDM over mm-wave OAM channels in a multipath environment with intersymbol interference," Proc. IEEE Global Communiation Conference, 2016.

82. Hu, T., Y. Wang, J. Zhang, and Q. Song, "OFDM-OAM modulation for future wireless communications," IEEE Access, Vol. 7, 59114-59125, 2019.

83. Liang, L., W. Cheng, W. Zhang, and H. Zhang, "Joint OAM multiplexing and OFDM in sparse multipath environments," IEEE Transactions on Vehicular Technology, Vol. 69, No. 4, 3864-3878, 2020.

84. Chen, Y., X. Xiong, Z. Zhu, S. Zheng, and X. Zhang, "Orbital angular momentum mode-group based spatial field digital modulation: Coding scheme and performance analysis," 2020 IEEE International Conference on Communications Workshops (ICC Workshops), IEEE, 2020.

85. Xiong, X., S. Zheng, Z. Zhu, X. Yu, X. Jin, and X. Zhang, "Performance analysis of plane spiral OAM mode-group based MIMO system," IEEE Communications Letters, Vol. 24, No. 7, 1414-1418, 2020.

86. Xiong, X., S. Zheng, Z. Zhu, Y. Chen, Z. Wang, X. Yu, X. Jin, and X. Zhang, "OAM mode-group generation method: Partial arc transmitting scheme," Signal Processing, 2020.

87. Tamagnone, M., C. Craeye, et al. "Comment on encoding many channels on the same frequency through radio vorticity: First experimental test," New Journal of Physics, Vol. 14, No. 11, 118001, 2012.

88. Tamburini, F., E. Mari, et al. "Radio beam vorticity and orbital angular momentum," Phys. Lett., Vol. 99, 204102-3, 2011.

89. Tamagnone, M., et al., "Comment on ‘Reply to comment on “Encoding many channels on the same frequency through radio vorticity: First experimental test”’," New Journal of Physics, Vol. 15, 078001, 2013.

90. Andersson, M., et al., "Orbital angular momentum modes do not increase the channel capacity in communication links," New Journal of Physics, Vol. 17, 043040, 2015.

91. Edfors, O. and A. J. Johansson, "Is Orbital AngularMomentum (OAM) based radio communication an unexploited area?," IEEE Transactions on Antennas and Propagation, Vol. 60, No. 2, 1126-1131, 2012.

92. Oldoni, M., et al., "Space-division demultiplexing in orbital-angular-momentum-based MIMO radio systems," IEEE Transactions on Antennas and Propagation, Vol. 63, No. 10, 4582-4587, 2015.

93. Chen, R., H. Xu, X. Wang, and J. Li, "On the performance of OAM in keyhole channels," IEEE Wireless Communications Letters, Vol. 8, No. 1, 313-316, 2019.

94. Chen, R., H. Xu, M. Moretti, and J. Li, "Beam steering for the misalignment in UCA-based OAM communication systems," IEEE Wireless Communications Letters, Vol. 7, No. 4, 582-585, 2018.

95. Zhang, K., et al., "Phase-engineered metalenses to generate converging and non-diffractive vortex beam carrying orbital angular momentum in microwave region," Optics Express, Vol. 26, No. 2, 1351-1360, 2018.

96. Liu, T., et al., "All-dielectric transformation medium mimicking a broadband converging lens," Optics Express, Vol. 26, No. 16, 20331-20341, 2018.

97. Liu, K., Y. Cheng, H. Wang, et al. "Generation of unconventional OAM waves by a circular array," The Journal of Engineering, Vol. 11, No. 21, 7962-7965, 2019.