Geometric-Phase Waveplates for Free-Form Dark Hollow Beams

Abstract

We demonstrate the possibility to create optical beams with phase singularities engraved into exotic intensity landscapes imitating the shapes of a large variety of diverse plane curves. To achieve this aim, we have developed a method for directly encoding the geometric properties of some selected curve into a single azimuthal phase factor without passing through indirect encryption methods based on lengthy numerical procedures. The outcome is utilized to mould the optic axis distribution of a liquid-crystal-based inhomogeneous waveplate. The latter is finally used to sculpt the wavefront of an input optical gaussian beam via Pancharatnam-Berry phase.

Spatial mode analysis of optical beams carrying monstar disclinations

“…However, equation ( 2) is likely to describe only the most basic disclinations and going beyond would require adding even more modes to the mix. In [20], in order to encompass a larger variety of disclinations, possibly having a higher degree of asymmetry, a different approach has been proposed in which a light beam embedding a complex disclination pattern can be obtained by superposing the fundamental TEM 00 mode, in a circular polarization state, with a Free-From Helical (FFH) mode of integer order m in an orthogonal circular polarization state [9]…”

“…which belongs to the recently introduced class of the Modulated Poincaré Beams (MPBs) [2,9]. An FFH m q mode of order m is defined as…”

“…If a circularly polarized beam with a definite helicity is fed to a multimode fiber with a stepped index profile and a circularly polarized beam with opposite helicity is extracted at the output, the transmitted beam will exhibit an isolated wavefront dislocation, and a sign change in the helicity at the fiber input together with a corresponding sign change in the helicity of the selected output will result in a change in the sign of the screw dislocation [5]. Highly efficient control of the polarization degrees of freedom, as well as controllable shaping of the intensity and phase distributions have been recently demonstrated by combining dielectric media anisotropy and inhomogeneities [2,9]. The propagation of the optical fields bearing PSs is associated with some novel phenomena, in particular in 3D space.…”

“…Compared to phase singularities, the generation of PSs typically requires a larger set of control parameters and tailoring optical beams with a specified topological structure is a difficult task. We have recently introduced a general method for engineering inhomogeneously polarized beams (IPBs) in which the rotation rate of the local polarization azimuth around a C-or a V-point can be set as desired [2,9], based on a geometric approach that enables shaping the wavefronts of the spatial modes required to generate the target polarization map without passing through the direct manipulation of the OAM spectrum. In a recent paper, Free-Form Hollow (FFH) beams have been introduced [9].…”

“…We have recently introduced a general method for engineering inhomogeneously polarized beams (IPBs) in which the rotation rate of the local polarization azimuth around a C-or a V-point can be set as desired [2,9], based on a geometric approach that enables shaping the wavefronts of the spatial modes required to generate the target polarization map without passing through the direct manipulation of the OAM spectrum. In a recent paper, Free-Form Hollow (FFH) beams have been introduced [9]. An FFH beam carries non-circular screw phase dislocations generated by imparting to a TEM 00 mode, in the beam waist, a periodical purely-azimuthal phase that reflects the symmetry properties of a suitable generating plane curve.…”