Multiplexed Generation of Generalized Vortex Beams with On‐Demand Intensity Profiles Based on Metasurfaces

Abstract

Optical vortex beams (VB) have provided a new degree of freedom for carrying optical information due to the unbounded number of orthogonal orbital angular momentum (OAM) channels. Due to the presence of phase singularity, VBs possess a dark zone in the center surrounded by a bright ring whose radius is directly related to the OAM carried by the beam. Here multiplexed generalized vortex beams (GVB) are demonstrated with various custom‐defined closed‐loop beam profiles, including polygons, star and windmill, by tailoring the local phase gradient along the azimuthal direction. By utilizing different polarization channels of metasurfaces, multiple GVBs with independent intensity profiles are generated. This approach provides a playground for realizing various optical modulating capabilities, such as precise particle manipulation, optical source, and OAM encryption.

Basis function approach for diffractive pattern generation with Dammann vortex metasurfaces

“…Thus, the complex amplitude of the GVB can be expressed as e i φ(θ) . For GVB, the radius R of beam intensity profile in k space is proportional to the phase gradient as Rfalse(θkfalse)∝dnormalφfalse(normalθfalse)dnormalθ with θ k = θ + π/2, which determines the intensity profile ( 41 ).…”

“…Here, we propose and demonstrate a previously unexplored approach for diffraction-multiplexed generation of generalized vortex beams (GVBs) based on the linear combination of a few custom-defined basis patterns, by using Dammann vortex metasurface (DVM). As shown previously (41), GVBs have a custom-defined angular phase distribution, i.e., the local angular phase gradient is no longer a constant like the conventional vortex beams. The angular phase distribution directly controls the intensity profiles of the vortex beams.…”

Metasurface‐Assisted Indirect‐Observation Cryptographic System

“…By contrast, multichannel metasurfaces, which is implemented by multiplexing, can encrypt the information in different working modes, thus further enhancing the information security and capacity. For example, different information can be obtained by changing the incident beam's wavelength, [22][23][24] polarization, [25][26][27][28] incident angle, [29] or topological number. [30,31] In addition, some multiplexing works have showcased by encrypting information into different observation spaces [32,33] or spatial frequency.…”

Terahertz Near‐Field Vortex Beams with Variable Intensity Profiles Based on Geometric Metasurfaces

“…Recently, generalized vortex beams, in which the corresponding intensity profiles have C N -fold discrete rotational symmetry instead of continuous rotational symmetry for conventional vortices, have been demonstrated in free space, because of unique properties in intensity and phase distribution, extending the study of vortex beam and providing a new perspective on controlling the properties of EM waves. For example, Yang et al, [58] have designed geometric metasurfaces encoded with noncanonical vortex phase profile to realize the free-space optical vortex with variable intensity profile, and Zhang et al, [59] have developed metasurfaces for generating multiplexed vortex beams with generated intensity profiles. However, these previous studies focus on the vortex with variable intensity profile in the far field, and the intensity profiles of these generalized vortices are limited to the C N -fold discrete rotational symmetry.…”

“…Recently, generalized vortex beams, in which the corresponding intensity profiles have C N− fold discrete rotational symmetry instead of continuous rotational symmetry for conventional vortices, have been realized in free space, extending the study of vortex beam and providing a new perspective on controlling the properties of EM waves. [ 58,59 ] However, these previous studies focus on the vortex with variable intensity profiles in the far field, and the intensity profiles of these generalized vortices are limited to the C N− fold discrete rotational symmetry. Near‐field vortices (that are surface plasmonic vortices) generated by metal‐based structures enable an unprecedented capability in confining, manipulating, and enhancing EM fields at subwavelength mode volumes, and thus, they open a new avenue to significantly reduce the vortex size that can be applied in integrated nanophotonics.…”