Satyajit Maji | Searcharxiv

arXiv2019

Common-path generation of stable cylindrical perfect vector vortex beams with arbitrary order

A Highly flexible and efficient method of generating stable radially and Azimuthally polarized perfect optical vortex beams and all higher-order cylindrical vector vortex beams are proposed and demonstrated. The method is the most convenient implementation of the superposition of two orthogonally circularly polarized optical vortex beams of arbitrary integer topological charges. By simply controlling the relative amplitude and phase between vertical and horizontal polarization component of an input perfect vortex beam on a phase-sensitive Spatial Light Modulator (SLM) and using a common-path interferometry, all arbitrary order Poincaré beams are prepared. Calibration curve of relative phase vs grey-scale of the phase function on the SLM is drawn to facilitate the determination of required phase-offset using pre-calculated grey-scale colour-map. Generated beams states of polarization are uniformly distributed throughout the beam cross-section. The interference pattern of the two-beam in a projected linear polarization state also gives the cylindrically symmetric petal beams with control over the number and orientation of petals.

physics.optics↗

arXiv2019

Geometric phase associated with Poincaré beams due to unfolding of fractional optical vortex beams

Optical vortex beam of fractional order 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 inside a birefringent crystal 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) across the beam 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 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. This study can be useful for different geometric phase based application of optical vortex beams.

physics.optics↗