Conference Agenda

Vector light beams feature a spatially varying optical polarisation and can exhibit localised structures reminiscent of the skyrmions familiar from the study of magnetic media. We present a theory and experimental measurements of such skyrmions in both paraxial and non-paraxial optics. A key feature for our analysis is the skyrmion field which determines the properties of the skyrmions and traces out field lines. In paraxial optics these field lines are lines of constant polarisation, but in non-paraxial optics, the fact the polarisation ellipses are no longer restricted to the transverse plane, makes it necessary to introduce several different skyrmion fields, each representing a different aspect of the three-dimensional optical polarisation.

The fabrication of Diffractive Optical Elements (DOEs) involves the analog patterning of material surfaces on the scale of light wavelength. This typically requires multi-step lithographic processes. Differently from the photoresists of standard lithography, thin films of amorphous azobenzene-containing polymers (azopolymers) can directly produce a structured surface using a single irradiation step with structured light. The resulting surface reliefs can be used directly as planar phase-modulating DOEs without the need for any post-exposure process. Additionally, the surface geometry and its optical functionality can be reconfigured at will. Here, we demonstrate reprogrammable and ready-to-use azopolymer diffractive gratings, lenses, and holographic projectors, produced by grayscale digital holographic patterns. By exploiting the all-optical scheme based of computer-generated holography, the diffraction behavior of the DOEs is optimized during the developing of structured surfaces. Full all-optical reconfigurability of the fabricated devices is also achieved. Our approach provides a versatile, efficient, and all-optical reversible fabrication framework for DOEs, making it a promising option to overcome the demanding, cumbersome, and irreversible fabrication processes typically involved in the realization of planar diffractive optical devices.

Polarization structured heralded single photons have been generated through spontaneous parametric down-conversion in a type-I dual crystal pumped by an inhomogeneously polarized beam in a general Poincaré mode, i.e. an inseparable superposition of two orthogonally polarized states through two orthogonal orbital angular momentum modes. The polarization structure of the signal photons can be controlled by manipulating the polarization state of their idler photon sisters with zero orbital angular. Due to the separate conservations of spin and orbital angular momenta in a type-I dual crystal SPDC process, any projection of the idler polarization state turns into a unitary transformation of the polarization basis of the signal photons, while preserving the orbital angular momentum modes originally included in the pump. We demonstrate, in this way, the ability to toggle between direct and basis-switched pump-single photon transfer by selectively projecting the polarization of the heralding photon before detection.

A method for the generation of structured laser beams (SLB) and hollow structured laser beams (HSLB) whose transverse profiles are invariant and can propagate to infinity is described. SLBs are formed after passing through an optical system that generates a special waveform as a combination of rotationally symmetric optical aberrations. Transverse profile consists of concentric circles with a very bright central core and a bounding outer-ring. The divergence of the central core 0.01 millirad has been experimentally confirmed. When the system was illuminated with a special vector beam, a hollow SLB (HSLB) beam was generated. Its central part is very narrow and completely dark. Unlike conventional hollow beams, where the electric field strength is zero in the dark areas, an electromagnetic field with the zero Poynting vector is present in this part of the beam. By varying the illumination parameters of the vector beam, it is possible to obtain situations where there is a longitudinal component of the electric field or/and magnetic field in the central core. The simulation results are in good agreement with the SLB profile measurements using a polarization camera.

We analyze polarization diffractive elements with the Fourier transform Jones (FTJ) matrix integrated with the beam coherence-polarization (BCP) matrix. Analytical derivations and experimental results are presented of the intensity, state and degree of polarization and coherence properties of the diffracted field generated by a simple diffractive element consisting in double polarizer rectangular aperture.