Free space optical communication using orbital angular momentum multiplexing - presentation
Free space optical communication usingorbital angular momentum multiplexingEmma Yann ZhangHong Kong University of Science and TechnologyMay 11, 2013
History of Orbital Angular Momentum1932 – C. Darwin identified another part of angular momentumin photons besides spin.• Angular momentum of photons has external part due to motion of thecenter of gravity and intrinsic part due to spin.During high order atomic transitions,photon emits at a distance r from atom. Theproduct of linear momentum of photon andradial distance contributes to an angularmomentum independent of spin.C.G. Darwin. (1932). “Notes on the Theory of Radiation,” Proceedings of the Royal Society of London.
History of Orbital Angular Momentum1992 – L. Allen found all helically phased beams have OAM,and can be generated using cylindrical lenses• OAM is a natural property in helically phased beams• LG modes (helical beams) can be easily produced using cylindrical lensesmode converters from HG modes.L. Allen et al. (1992). “Orbital angular momentum of light and the transformation of Laguerre-Gaussian lasermodes,” Physical Review AHelical light beams with OAM = +ħ Cylindrical lenses mode converter
History of Orbital Angular Momentum1992 – Helical beams with optical vortex generated using forkeddiffraction grating.• More lines at the bottom, light diffracts at different angle• Changing the number of split lines changes the mode produced.V. Yu. Bazhenov et al. 1992."Screw dislocations in light wavefronts." Journal of Modern Optics 39.5Forked diffraction grating produces screwed wavefrontswith optical vortex at the center
History of Orbital Angular Momentum1995 – OAM can be transferred and rotate microscopic particles• Direction of rotationdetermined by the sign of theOAM state.• A laser beam of a few mWgives a rotation speed of 1-10Hz.He, H., et al. 1995. "Direct observation of transfer of angular momentum to absorptive particles from a laser beamwith a phase singularity." Physical Review Letters, 75.5The rotation of a trapped red bloodcell under (i)15ħ, (ii)−15ħ.Dasgupta et al. 2011.Optics Express, Vol. 19, Issue 8
History of Orbital Angular Momentum2004 – Gibson et al. demonstrated free-space opticalcommunication with OAM-carrying light beams• Information encoded in OAM states,transmitted in air over 15m.• Computer generated hologram onspatial light modulators (SLM)Gibson, Graham, et al. 2004. "Free-space information transfer using light beams carrying orbital angularmomentum." Opt. Express 12.22
History of Orbital Angular Momentum2012 – Terabit data transfer rate using OAM multiplexing.• Data rate of 2.56Tbit/s over 1meter in free space• Combining OAM multiplexingand polarization multiplexing toincrease capacity and spectralefficiencyWang, Jian, et al. 2012."Terabit free-space data transmission employing orbital angular momentummultiplexing." Nature Photonics.
Laguerre-Gaussian Mode LGpl p – number of radial nodes l – azimuthal index
Orbital and spin angular momentumAngular momentum Orbital SpinWave fronts: Helically phased waves Circularly polarized wavesAM per photon l ħ σħNo. of states ±1, 2, 3, 4….. ±1Each photon has unlimited OAM states that can carry information without interference!
OAM Multiplexing in FSO Communication SystemLaser resonatorGenerating LGbeamsMultiplexingLG beamsPropagating infree spaceDemultiplexingLG beamsRecover dataHologramsusing SLM
Advantages of OAM MultiplexingAdvantages Limitations High data capacity Higher when combinedwith other multiplexingmethods Enhanced security Capacity limited byatmospheric turbulence Unable to use in long haulfiber communication systems Mode coupling in waveguide Wong, KLGG, et al. 2012. "Quantization oforbital angular momentum in helically twistedphotonic crystal fiber." Frontiers in Optics.
Applications Deep space and near-Earthoptical communications LAN to LAN connectionsin campus / city areanetworkDjordjevic, I. B. (2011). Deep-space and near-Earth optical communications by coded orbital angular momentum(OAM) modulation. Opt. Express, 19
Interesting videos on OAM Talk by Miles Padgett at SPIE Photonic West: Miles J.Padgett Photonics West 2013 plenary talk: Light in aTwist: Optical Angular Momentumhttp://www.youtube.com/watch?v=5yyTEUYY8o8 Short introductory on OAM and optical tweezers:Miles Padgett: Optical tweezers and twisted beams oflight http://www.youtube.com/watch?v=2hdKXMRKSY8