Vagharshak Hakobyan

Structured light offers a promising solution for the increasing data demands of modern optical networks, opening up degrees of freedom that can be leveraged for greater channel capacity and more bits per photon. However, its implementation is hindered by real-world distortions, for example, atmospheric turbulence in free space, with severe and rapidly evolving phase perturbations that alter the amplitude, phase, and vectorial polarization structure of the beam. Here, we demonstrate that optical topologies in the form of skyrmions are highly resilient to the effects of real-world atmospheric turbulence. We create and transmit these particle-like topologies of light through a 270-meter free-space optical link, revealing their robustness across a wide variety of conditions and turbulence strengths. While we observe severe distortion in the states’ underlying degrees of freedom, we show that the topological numbers are preserved in all cases. We account for fast changes to the medium, where the channel produces statistically averaged outcomes, by probing the state’s decoherence, showing that while the degree of polarization consequently decays, the topology remains intact. Using topology, we show that information can be transmitted through the channel with almost perfect fidelity (>98%) in most cases, only decreasing to 86% in the most severe conditions tested. This work idemonstrates the potential for optical topologies as reliable and robust information carriers in a real-world environment and points to the potential for other complex channels too, offering attractive features for classical and quantum communication alike.

Mise en forme de la lumière par interaction spin-orbite optique: L'interaction spin-orbite pour la lumière permet le couplage entre les degrés de liberté associés à l'état de polarisation de la lumière et ceux associés à l'espace. Ce couplage est particulièrement important dans les milieux qui sont à la fois inhomogènes et anisotropes. Dans ce travail, nous exploitons la mise en forme des propriétés de biréfringence artificielle ou naturelles de matériaux optiques tels que la silice, le nitrure de silicium, le silicium ou les cristaux liquides pour façonner différentes propriétés d'un faisceau lumineux. En particulier, nous démontrons la réalisation d'éléments optiques originaux permettant la transformation d'un faisceau gaussien en un faisceau de Laguerre-Gauss. En exploitant la superposition de tels modes générés par le couplage spin-orbite optique, nous montrons qu'il est possible de façonner des textures de polarisation de type skyrmion. Enfin, en tirant parti de la dépendance en longueur d'onde du niveau d'interaction spin-orbite, des dispositifs électro-optiques à base de cristaux liquides sont proposés pour moduler spectralement la topologie de la distribution de phase spatiale du champ lumineux, ce qui ouvre un champ d'applications dans la mise en forme d'impulsions optiques ultra-brèves.

Spatially structured light has enabled advanced topological and vectorial control, while spatiotemporal manipulation has so far remained largely restricted to scalar phase engineering. Here, we introduce a geometric-phase method for shaping spatiotemporal vectorial beams using q-plates of arbitrary topological charge. We develop an analytical framework describing the polarization-controlled generation of vector beams and polarization skyrmions in the space-time or momentum-time domain and experimentally validate it using an electrically tunable liquid-crystal q-plate. Our results establish q-plates as compact and reconfigurable platforms for vectorial topological shaping of ultrashort pulses, opening directions in spatiotemporal photonics.

We propose a spin-orbit strategy for generating dual-wavelength quantum skyrmions realized either as entangled photon pairs at dual wavelengths or as heralded single-photon states at a given wavelength-regimes neither previously conceptualized nor demonstrated. By coupling a two-photon entangled state to an electrically tunable liquid crystal topological defect, we engineer both nonlocal and local skyrmionic topologies in a reconfigurable platform. We highlight with examples how this approach may open new directions for engineered topological quantum states that exploit the topological richness of liquid crystals.

Here we propose the use of an adjustable liquid crystal spin–orbit device (SOD) to shape bi-colour structured light to create bimodal states. We demonstrate the proof-of-principle for two individual wavelengths in a nonlinear optics framework. The SOD has an inhomogeneous optical axis orientation and birefringence, allowing it to modulate two wavelengths of light with pre-selected transmission functions by simply tuning a voltage. We combine this bi-colour functionality in a nonlinear optical experiment by employing three-wave mixing in a periodically poled crystal to show how the combined effect of linear spin–orbit transformation rules and nonlinear selection rules gives rise to novel approaches for light to modulate light, and light to unravel light. We show that the roles of the nonlinear crystal and SOD can be switched to either characterise the device with known light, or unravel unknown light with the device. This synergy between spin–orbit and nonlinear optics offers a novel paradigm where light manipulates and reveals its own structure across spectral domains.

We report on the extension of the q-plate concept, a hallmark of spin-orbit optical vortex generation since its introduction in 2006, to the generation of optical skyrmions. Stokes skyrmions of arbitrary order with polarization-controlled Skyrme number and reconfigurable multiskyrmions are obtained. This is done by endowing q-plates with a winding number associated with the radial degree of freedom that adds to the usual one associated with the azimuthal degree of freedom.

We report on the design, fabrication and performance of novel flat-optical spin-orbit modal beam shapers made from silica glass by femtosecond laser nanostructuring technology, choosing the Laguerre-Gauss basis as a case study. The basic design principle involves endowing a transparent dielectric material, initially isotropic and homogeneous, with doubly inhomogeneous anisotropic characteristics (optical axis orientation and birefringence). The quantitative structural characterization of the fabricated devices is achieved by Stokes polarimetric analysis and the modal beam shaping performance is assessed via modal decomposition. The modal beam shaping capabilities obtained outperform those of previously produced spin-orbit beam shapers based on the same fabrication technology. Also, current challenges and perspectives associated with high-order and spectrally broadband modal beam shaping are discussed. More generally, the proposed approach extends the scope of spin-orbit optical elements to any situation where complex field amplitude shaping is required in a single stage.

Shaping the orbital angular momentum of optical pulses in the spectral domain is a means of managing light in space and time that offers many possible applications. However, these are limited by the small number of techniques available, whose flexibility does not yet rival that of the continuous regime. We propose here to implement a tunable hyperspectral management of the orbital angular momentum of a polychromatic light field. The main idea is to exploit the dispersive nature of geometric phase optical elements by intentionally choosing to work in a regime of high anisotropic optical retardance. An experimental proof of principle is demonstrated in the visible range using a supercontinuum laser and an optically thick, electrically controllable, liquid crystal structured wave plate.