Millimeter-Wave Nondiffracting Circular Airy OAM Beams

Abstract

We demonstrate using theoretical analysis and full-wave numerical simulations nondiffracting circular Airy beams modulated with different orbital angular momenta (OAM) at millimeter wavelengths. It is shown that applying an azimuthal spiral phase component to the circular Airy beam results in a circular Airy OAM beam. These beams are radially symmetric with a null at the center and experience an inward radial shift within a certain propagation distance. Such propagation dynamics are contrary to that of a conventional OAM beam where the vortex radius increases, and the beam intensity decreases as the beam propagates due to diffraction effects. Thus, the circular Airy OAM beam can be nondiffracting over an appreciable distance of few tens of meters (i.e., few thousand wavelengths) and open the door for high data-rate communications. Phase only spatial wave modulators of aperture 20 cm $\times20$ cm with $40 \times 40$ pixels are designed for generating the circular Airy OAM beams with OAM of order 0, 1, and 2. These spatial wave modulators when illuminated with Gaussian beams generate the corresponding circular Airy OAM beam. Full-wave numerical simulation results showing the generation and propagation of circular Airy OAM beams at millimeter wavelengths that are nondiffracting up to 50 m are presented.