Generation of an asymmetric optical vortex array with tunable singularity distribution.

Abstract

Light beams with multiple phase singularities, namely, optical vortex arrays (OVAs), can be generated via coherent superpositions of symmetric laser modes, e.g., the combination of a circular vortex beam and a Gaussian beam. Further, a non-trivial evolution of the singularity structure can be obtained when the system's symmetry is broken. In this paper, we propose an asymmetric OVA (AOVA) with a highly tunable structure. The AOVA is generated by the coaxial superposition of a vortex beam and an elliptical Gaussian beam in the waist plane. After the interference of the two beams, the original high-order phase singularity residing on the beam axis breaks up into multiple +1 and -1 order vortices. The vortices are located at discrete azimuthal angles and different distances from the beam center. Unlike previous OVAs with annular shapes, the AOVA can present various singularity structures devoid of rotational symmetry, which are decided by the radii of the elliptical Gaussian beam and the topological charge of the vortex beam. Furthermore, we theoretically show that the number, sign, and distribution of local singularities can be modulated by defining two azimuthal discriminant functions. Numerical simulations and visualizations are also carried out. This work provides a new perspective for designs of connected OVAs and may find potential applications, especially in particle manipulation, optical communication, and optical metrology.