Internet data traffic capacity is rapidly reaching the limits of conventional fiber technologies. To combat this issue there has been a growing interest in Orbital Angular Momentum (OAM) multiplexing, a form of multiplexing that is based on distinguishing orthogonal signals using the OAM of electromagnetic waves. OAM multiplexing promises huge potential for growth in signal bandwidth through optical fibers; terabit transmission rates have been achieved using only a few OAM channels , and as the number of OAM quantum states is unbounded, OAM multiplexing can theoretically access a near-infinite number of channels that is subject only to the constraints of real-world optics.
A common OAM configuration is the so-called optical vortex. An optical vortex is a beam of light in which the light is twisted like a corkscrew around its axis of travel, with a zero of the optical field at the axis itself. Thus, when projected onto a flat surface, an optical vortex looks like a ring of light with a dark hole in the center. In addition to telecommunications, optical vortices offer potential applications in a wide variety of areas such as astrophysical optics and the detection of extrasolar planets, optical tweezers, optical trapping, laser beam shaping, and quantum computing.
An optical vortex is created by a complex phase-front structure, and carries an orbital angular momentum (OAM) in addition to its spin angular momentum (SAM). OAM carrying beams can be produced using different devices like spiral phase plates, computer generated holograms, spatial light modulators, or inhomogeneous birefringent devices called "q-plates". To date, most theoretical and experimental optical vortex work has been done in the visible region of the spectrum, however, the radio domain is also very important and more efficient devices are needed for these frequencies. In this application example, we describe the simulation of a q-plate working at millimeter wavelengths.