Determining Vortex-Beam Superpositions by Shear Interferometry

Abstract

Optical modes bearing optical vortices are important light systems in which to encode information. Optical vortices are robust features of optical beams that do not dissipate upon propagation. Thus, decoding the modal content of a beam is a vital component of the process. In this work, we present a method to decode modal superpositions of light beams that contain optical vortices. We do so using shear interferometry, which presents a simple and effective means of determining the vortex content of a beam, and extract the parameters of the component vortex modes that constitute them. We find that optical modes in a beam are easily determined. Its modal content can be extracted when they are of comparable magnitude. The use of modes of well-defined topological charge, but not well-defined radial-mode content, such as those produced by phase-only encoding, are much easier to diagnose than pure Laguerre–Gauss modes.

Splitting, generation, and annihilation of phase singularities in non-coaxial interference of Bessel–Gaussian beams

“…Because vortex beams possess a spiral phase term, the phase changes l 2p when the beam propagates by the unit wavelength. Consequently, beam interference patterns vary according to beam position (manifested as a separation angle b along line y x tan b = ) [39], with such differences amplified when the TCs are opposite. When the magnitudes and signs are both equal, the interferogram is a simple angular rotation, with only the relative position changing and the number of singularities equal to 0. b = However, when the TCs of the two beams are opposite, the vortex singularities may transform into edge dislocations at different separation angles.…”

“…Studies involving the superposition of two offaxis optical vortices with orthogonal polarization states have revealed rich light-field structures comprising polarization singularities and different polarization morphologies [34][35][36]. Moreover, the application of off-axis interference in experiments has yielded several breakthroughs, including off-center spiral zone plates [37], selfreferenced interference [38], shear interferometry [39][40][41][42], and Young's three-pinhole experiment [43,44].…”

Characteristics of Spiral Patterns Formed by Coaxial Interference between Two Vortex Beams with Different Radii of Wavefront Curvatures

“…The most commonly used TC detection method is based on Mach-Zehnder interferometer (MZI) [19][20][21][22][23][24], which uses beam splitters in combination with mirrors to interfere two beams passing through two arms of different paths, and allows their phase structure to be compared with each other. For off-axis interference between two plane wave vortex beams of different TCs, fork-shaped fringes form, and the sign and magnitude of TCs' difference can be determined by analyzing these interferograms and the orientation between two vortex beams [13][14][15][16][17][18][19][20][21]. For coaxial interference between two plane wave vortex beams of different TCs, a petal-shaped pattern forms, and the petal number is just the magnitude of TCs' difference [23][24][25][26][27].…”

Generation and detection of optical vortices superposition by using interferometer setups

“…sagnac interferometry (Some figures may appear in colour only in the online journal) Optical vortices superpositions have attracted a great deal of attention in terms of research and technological applications [1]. A few studies have been done on the generation and detection of the optical vortex superpositions by the simple freespace optics recipe [2][3][4]. The generation of optical vortices is one of the most extensively studied subjects in optical technologies.…”

“…By using vortex lens, four types of vector vortex beams by using a modified polarization Sagnac interferometer have been generated [3]. Recetnly, a method to decode modal superpositions of optical vortex beams by using shear interferometry setup has been demonstrated [2].…”