OAM Light for Communications

Structured light” refers to the exquisite tailoring of the spatial distribution of an optical beam’s amplitude and phase front to exhibit fascinating properties (see “Structured Light: Tailored for Purpose,” OPN, June 2020). One class of structured light that has gained particular interest in the optics community is beams carrying orbital angular momentum (OAM). These are often referred to as vortex beams, since they typically have a ring amplitude shape with a central intensity null. Moreover, the phase front “twists” in a helical fashion as it propagates; the amount of OAM (that is, the mode number) carried by the beam is the number of 2π phase changes in the azimuthal direction; and the twisting can be clockwise or counterclockwise. Interestingly, even a single photon can carry OAM.