Topological transformation of fractional optical vortex beams using computer generated holograms

Maji, Satyajit; Brundavanam, Maruthi M.

doi:10.1088/2040-8986/aab1da

Cited by 16 publications

(14 citation statements)

References 30 publications

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“…Vortex trajectories with the help of topological manifolds, leading to formation of knots, links, and loops, were studied [170,171,[178][179][180][181][182][183][184]. Other types of phase defects such as edge and mixed-type phase defects [32,34], anisotropic vortices [185], and perfect [76,[186][187][188][189][190][191][192][193][194] and fractional vortices came under study [195][196][197][198][199][200][201][202][203][204]. Some of the earliest optical elements capable of producing phase singularities were reported [58,59,61].…”

Section: Literature Survey Of Phase and Polarization Singularitiesmentioning

confidence: 99%

Phase Singularities to Polarization Singularities

Ruchi

Senthilkumaran

Pal

2020

International Journal of Optics

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Polarization singularities are superpositions of orbital angular momentum (OAM) states in orthogonal circular polarization basis. The intrinsic OAM of light beams arises due to the helical wavefronts of phase singularities. In phase singularities, circulating phase gradients and, in polarization singularities, circulating ϕ12 Stokes phase gradients are present. At the phase and polarization singularities, undefined quantities are the phase and ϕ12 Stokes phase, respectively. Conversion of circulating phase gradient into circulating Stokes phase gradient reveals the connection between phase (scalar) and polarization (vector) singularities. We demonstrate this by theoretically and experimentally generating polarization singularities using phase singularities. Furthermore, the relation between scalar fields and Stokes fields and the singularities in each of them is discussed. This paper is written as a tutorial-cum-review-type article keeping in mind the beginners and researchers in other areas, yet many of the concepts are given novel explanations by adopting different approaches from the available literature on this subject.

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Section: Literature Survey Of Phase and Polarization Singularitiesmentioning

confidence: 99%

Phase Singularities to Polarization Singularities

Ruchi

Senthilkumaran

Pal

2020

International Journal of Optics

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“…The optical field of an integer TC (m) vortex generated by the diffraction of a Gaussian beam from a computer generated Hologram (CGH) with point screw dislocation can be written as [25,47],…”

Section: Theorymentioning

confidence: 99%

“…The scalar to polarization singularity transformation is demonstrated by the evolution of the C-points and L-lines across the Poincaré beam. The effect of the determining parameters like phase morphology described by the TC [25,45], beam separation and relative phases of the eigen-polarization components are exclusively studied and discussed. The GP associated with the spatial polarization around the C-point singularities due to unfolding of different fractional vortex beams are measured.…”

Section: Introductionmentioning

confidence: 99%

“…The strength of the singularity is characterized by signed numbers called topological charge (TC) for scalar singularities and topological index (TI), Poincaré-Hopf index for ellipse and vector singularities [3]. Scalar OV beams generated from fractional helicoidal phase steps have exclusive topological features which have been theoretically and experimentally investigated [23][24][25]. The fractional OV (FOV) beams have intricate optical current flow across the beam and both extrinsic and intrinsic OAM [25][26][27][28].…”

Section: Introductionmentioning

confidence: 99%

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Localized geometric phase analogue associated with Poincaré beams due to unfolding of fractional optical vortex beams through a birefringent crystal

Maji¹,

Pattanayak²,

Brundavanam³

2020

J. Opt.

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Fractional optical vortex beam is generated by the diffraction of a Gaussian beam using computer generated hologram embedded with mixed screw-edge dislocation. Unfolding of the generated fractional vortex beam into eigen-polarization components with orthogonal polarization results in the conversion of scalar phase singularity to vector polarization singularities in the beam cross-section. The evolution of the singularities of the ellipse field namely C-points (points of undefined major axis) and L-lines (lines of undefined handedness) in the state of polarization distribution on a transverse plane quantifies the transformation. The effect of the phase morphology dictated by the fractional order of the dislocation, transverse spatial separation and longitudinal relative phase of the two eigen-polarization components on determining the complex transverse polarization structure is investigated. The nature of the generated Poincaré beam is also indicated by projecting the states of polarization on to the Poincaré sphere. With increasing order of dislocation from 0.0 to 1.0 in fractional steps and with increasing relative phase, the partial Poincaré beam is transformed to a full Poincaré beam. The transformation of the local structure around the C-points is measured through the geometric phase due to the Poincaré sphere contour around the C-points for different dynamic phase difference of the unfolded FOV beams generated from different fractional order of dislocation. This study can be useful for different geometric phase based application of optical vortex beams.

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“…This unwrapping of the phase-front is associated with the formation of chains of smaller vortices with alternating signs located along the binary phase dislocations, as marked by '+' and '-' signs. Note that chains of vortices with alternating signs are typically a signature of fractional (non-integer) vortex beams [49][50][51], and are experienced here during the topological inversion. Third, the vortices with '-' sign approach the beam center, guided along the path of phase dislocation, and coalesce into one large vortex that replaces the = 2 vortex, thus reversing its topology.…”

Section: B Mechanism Of Topological Charge Inversionmentioning

confidence: 99%

Evolution of orbital angular momentum in three-dimensional structured light

et al. 2018

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Light beams with an azimuthal phase dependency of e i φ have helical phase fronts and thus carry orbital angular momentum (OAM), a strictly conserved quantity with propagation. Here, we engineer quasi three-dimensional (3D) structured light fields and demonstrate unusual scenarios in which OAM can vary locally in both sign and magnitude along the beam's axis, in a controlled manner, under free-space propagation. To reveal the underlying mechanisms of this phenomenon, we perform full modal decomposition and reconstruction of the generated beams to describe the evolution of their intrinsic OAM and topological charge with propagation. We show that topological transition and the associated variation in local OAM rely on the creation, movement, and annihilation of local vortex charges without disturbing the global net charge of the beam, thus conserving the global OAM while varying it locally. Our results may be perceived as an experimental demonstration of the Hilbert Hotel paradox, while advancing our understanding of topological deformations in general.

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Topological transformation of fractional optical vortex beams using computer generated holograms

Cited by 16 publications

References 30 publications

Phase Singularities to Polarization Singularities

Phase Singularities to Polarization Singularities

Localized geometric phase analogue associated with Poincaré beams due to unfolding of fractional optical vortex beams through a birefringent crystal

Evolution of orbital angular momentum in three-dimensional structured light

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