Millimeter-Wave Transmit-Arrays for High-Capacity and Wideband Generation of Scalar and Vector Vortex Beams

Vector vortex beams, which can be described by higher-order Poincaré spheres, are generalized forms of waves carrying orbital angular momentum with inhomogeneous states-of-polarization on their wavefronts. Conventional approaches for vector vortex beam generation are primarily constrained by a restricted channel capacity with low efficiency and mode number. In this chapter, the fundamentals of scalar and vector vortex beams are introduced first. Then, a non-interleaved vortex multiplexing approach is presented that enables ultrahigh-capacity, high-efficiency, and flexible generation of massive structured scalar and vector vortex beams. A series of proof-of-concept prototypes, implemented by sub-wavelength-thick transmit-arrays at millimeter-wave frequencies, are demonstrated experimentally. Methods that can break the mode symmetry due to the inherent property of Berry phase elements are further illustrated, which enables a much larger degree of freedom in massive vector vortex beam generation. The demonstrated methodology holds great promises for structured wavefront shaping, which may have profound impacts in a variety of fields including spin-Hall photonics, compressive imaging, electromagnetic communication, and so on.