Hindawi Publishing Corporation International Journal of Optics Volume 2012, Article ID 689612, 7 pages doi:10.1155/2012/689612 Research Article Generation of Optical Vortex Arrays Using Single-Element Reversed-Wavefront Folding Interferometer Brijesh Kumar Singh, 1 G. Singh, 2 P. Senthilkumaran, 1 and D. S. Mehta 2 1 Department of Physics, Indian Institute of Technology Delhi, Hauz Khas, New Delhi 110016, India 2 Laser Applications and Holography Laboratory, Instrument Design Development Centre, Indian Institute of Technology Delhi, Hauz Khas, New Delhi 110016, India Correspondence should be addressed to Brijesh Kumar Singh, brijeshsingh831@gmail.com Received 15 April 2011; Revised 7 June 2011; Accepted 8 June 2011 Academic Editor: Shunichi Sato Copyright © 2012 Brijesh Kumar Singh et al. This is an open access article distributed under the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited. 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(il 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 z-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 demon- strated that when three or more plane waves overlap in space, complete destructive interference occurs on nodal lines, also called phase singularities or optical vortices leading to the generation of regular net of vortex lattices. Various optical interferometric configurations have been implemented for generating vortex lattices. Generation of OVAs by three-, four- and five- plane wave interference [17], interferometric optical vortex array generator [18, 19], creation of OV lattices by wavefront division [20], using couple of Wollaston prisms [21, 22], and lateral shearing interferometers [23] have been reported. Such periodic arrays of optical vortices have been used as phase markers [22], in optical metrology for the measurements of small-angular rotations, tilt, ori- entation [24–26], and birefringence [27]. But most of the aforementioned interferometric techniques used for gener- ating vortex lattices are based on modified Mach-Zehnder