Generation of Optical Vortex Arrays Using Single-Element Reversed-Wavefront Folding Interferometer

Optical vortex arrays have been generated using simple, novel, and stable reversed-wavefront folding interferometer. Two new interferometric configurations were used for generating a variety of optical vortex lattices. In the first interferometric configuration one cube beam splitter (CBS) was used in one arm of Mach-Zehnder interferometer for splitting and combining the collimated beam, and one mirror of another arm is replaced by second CBS. At the output of interferometer, three-beam interference gives rise to optical vortex arrays. In second interferometric configuration, a divergent wavefront was made incident on a single CBS which splits and combines wavefronts leading to the generation of vortex arrays due to four-beam interference. It was found that the orientation and structure of the optical vortices can be stably controlled by means of changing the rotation angle of CBS. 1. Introduction Optical vortices (OVs) are point phase defects, also called phase singularities in the distribution of optical wave-fields where both real and imaginary values of the optical fields are zero [1]. An interesting peculiarity of point phase defects is the helicoidal structure of the wave front around the defect axis and is described as exp( Φ), where l is the topological charge and Φ is the azimuthal angle around the defect axis. The magnitude of topological charge determines the degree of circulation, that is, the number of 2π cycles of phase accumulation around the vortex point. The sign of topological charge defines the handedness or helicity of the phase singular beam along the propagation direction of the -axis. An interesting aspect of a vortex beam is that it possesses orbital angular momentum (OAM). Optical vortices play significant role for studying OAM of light fields [2, 3] and have been widely used in the area of optical tweezers [4], singular optics [5], optical solitons [6], and optical metrology [7, 8]. The most commonly used methods for generating OVs with single or multiple charge are synthetic holograms [9], spiral phase plates [10], liquid-crystal cells [11], dielectric wedge [12], and higher-order laser beams [13]. An alternative method for generating OVs efficiently is the use of optical fibers [14] such as, a hollow-core optical fiber for generating doughnut-shaped beam and a holey fiber for generating hollow beam. Recently, there has been great interest for generating optical vortex arrays (OVAs) also called vortex lattices using multiple beam interference [15, 16]. It has been demonstrated that when three or more plane waves overlap in