Increasing the information capacity per unit bandwidth has been a perennial goal of scientists and engineers1. Multiplexing of independent degrees of freedom, such as wavelength, polarization and more recently space, has been a preferred method to increase capacity2,3 in both radiofrequency and optical communication. Orbital angular momentum, a physical property of electromagnetic waves discovered recently4, has been proposed as a new degree of freedom for multiplexing to achieve capacity beyond conventional multiplexing techniques5,6,7,8,9, and has generated widespread and significant interest in the scientific community10,11,12,13,14. However, the capacity of orbital angular momentum multiplexing has not been established or compared to other multiplexing techniques. Here, we show that orbital angular momentum multiplexing is not an optimal technique for realizing the capacity limits of a free-space communication channel15,16,17 and is outperformed by both conventional line-of-sight multi-input multi-output transmission and spatial-mode multiplexing.
Subscribe to Journal
Get full journal access for 1 year
only $14.08 per issue
All prices are NET prices.
VAT will be added later in the checkout.
Rent or Buy article
Get time limited or full article access on ReadCube.
All prices are NET prices.
Shannon, C. E. A mathematical theory of communication. Bell Syst. Tech. J. 23, 45 (1948).
Ng, S. X., Hanzo, L. L., Keller, T. & Webb, W. Quadrature Amplitude Modulation: From Basics to Adaptive Trellis-Coded, Turbo-Equalised and Space–Time Coded OFDM, CDMA and MC-CDMA Systems (Wiley-IEEE, 2004).
Evangelides, S. G. Jr, Mollenauer, L. F., Gordon, J. P. & Bergano, N. S. Polarization multiplexing with solitons. J. Lightw. Technol. 10, 28–35 (1992).
Allen, L., Beijersbergen, M. W., Spreeuw, R. J. C. & Woerdman, J. P. Orbital angular momentum of light and the transformation of Laguerre–Gaussian laser modes. Phys. Rev. A 45, 8185–8189 (1992).
Fabrizio, T. et al. Encoding many channels on the same frequency through radio vorticity: first experimental test. New J. Phys. 14, 033001 (2012).
Willner, A. E., Wang, J. & Huang, H. A different angle on light communications. Science 337, 655–656 (2012).
Wang, J. et al. Terabit free-space data transmission employing orbital angular momentum multiplexing. Nature Photon. 6, 488–496 (2012).
Yan, Y. et al. High-capacity millimetre-wave communications with orbital angular momentum multiplexing. Nature Commun. 5, 4876 (2014).
Bozinovic, N. et al. Terabit-scale orbital angular momentum mode division multiplexing in fibers. Science 340, 1545–1548 (2013).
Cartiledge, E. Adding a twist to radio technology: spiralling radio waves could revolutionize telecommunications. Nature http://dx.doi.org/10.1038/news.2011.114 (2011).
Edfors, O. & Johansson, A. J. Is orbital angular momentum (OAM) based radio communication an unexploited area? IEEE Trans. Antennas Propag. 60, 1126–1131 (2012).
Michele, T., Christophe, C. & Julien, P.-C. Comment on ‘Reply to Comment on “Encoding many channels on the same frequency through radio vorticity: first experimental test” ’. New J. Phys. 15, 078001 (2013).
Tamburini, F. et al. Reply to Comment on “Encoding many channels on the same frequency through radio vorticity: first experimental test”. New J. Phys. 14, 118002 (2012).
Kish, L. B. & Nevels, R. D. Twisted radio waves and twisted thermodynamics. PLoS ONE 8, e56086 (2013).
Mair, A., Vaziri, A., Weihs, G. & Zeilinger, A. Entanglement of the orbital angular momentum states of photons. Nature 412, 313–316 (2001).
Molina-Terriza, G., Torres, J. P. & Torner, L. Twisted photons. Nature Phys. 3, 305–310 (2007).
Saleh, M. F., Di Giuseppe, G., Saleh, B. E. A. & Teich, M. C. Photonic circuits for generating modal, spectral, and polarization entanglement. IEEE Photon. J. 2, 736–752 (2010).
Karimi, E. et al. Generating optical orbital angular momentum at visible wavelengths using a plasmonic metasurface. Light Sci. Appl. 3, e167 (2014).
Xinlu, G. et al. Generating, multiplexing/demultiplexing and receiving the orbital angular momentum of radio frequency signals using an optical true time delay unit. J. Opt. 15, 105401 (2013).
Cai, X. et al. Integrated compact optical vortex beam emitters. Science 338, 363–366 (2012).
Strain, M. J. et al. Fast electrical switching of orbital angular momentum modes using ultra-compact integrated vortex emitters. Nature Commun. 5, 4856 (2014).
Mirhosseini, M., Malik, M., Shi, Z. & Boyd, R. W. Efficient separation of the orbital angular momentum eigenstates of light. Nature Commun. 4, ( 2013).
Genevet, P., Lin, J., Kats, M. A. & Capasso, F. Holographic detection of the orbital angular momentum of light with plasmonic photodiodes. Nature Commun. 3, 1278 (2012).
Phillips, R. L. & Andrews, L. C. Spot size and divergence for Laguerre Gaussian beams of any order. Appl. Opt. 22, 643–644 (1983).
O'Sullivan, M. N., Mirhosseini, M., Malik, M. & Boyd, R. W. Near-perfect sorting of orbital angular momentum and angular position states of light. Opt. Express 20, 24444 (2012).
Lavery, M. P. J. et al. The efficient sorting of light's orbital angular momentum for optical communications. Proc. SPIE 8542, 85421R (2012).
Berkhout, G. C. G., Lavery, M. P. J., Courtial, J., Beijersbergen, M. W. & Padgett, M. J. Efficient sorting of orbital angular momentum states of light. Phys. Rev. Lett. 105, 153601 (2010).
Richardson, D. J., Fini, J. M. & Nelson, L. E. Space-division multiplexing in optical fibres. Nature Photon. 7, 354–362 (2013).
Foschini, G. J. Layered space–time architecture for wireless communication in a fading environment when using multi-element antennas. Bell Labs Tech. J. 1, 41–59 (1996).
Goodman, J. W. Introduction to Fourier Optics (McGraw Hill, 1996).
Wells, D. The Penguin Book of Curious and Interesting Numbers Revised Edition (Penguin, 1986).
Ren, Y. et al. Atmospheric turbulence effects on the performance of a free space optical link employing orbital angular momentum multiplexing. Opt. Lett. 38, 4062–4065 (2013).
Li, G., Bai, N., Zhao, N. & Xia, C. Space-division multiplexing: the next frontier in optical communication. Adv. Opt. Photon. 6, 413–487 (2014).
Cover, T. & Thomas, J. A. Elements of Information Theory (Wiley, 2012).
Shiu, D.-S., Foschini, G. J., Gans, M. J. & Kahn, J. M. Fading correlation and its effect on the capacity of multielement antenna systems. IEEE Trans. Commun. 48, 502–513 (2000).
This work was supported in part by the National Key Basic Research Program of China (973), project #2014CB340104/3, NSFC projects 61377076, 61307085 and 61431009.
The authors declare no competing financial interests.
About this article
Cite this article
Zhao, N., Li, X., Li, G. et al. Capacity limits of spatially multiplexed free-space communication. Nature Photon 9, 822–826 (2015). https://doi.org/10.1038/nphoton.2015.214
Evaluation of the Laguerre–Gaussian mode purity produced by three-dimensional-printed microwave spiral phase plates
Royal Society Open Science (2020)
Optics Express (2020)
Journal of the Optical Society of America B (2020)
High-dimensional communication on etchless lithium niobate platform with photonic bound states in the continuum
Nature Communications (2020)
IEEE Photonics Journal (2020)