Bruno Piccirillo

Hypergeometric-Gaussian modes

We studied a novel family of paraxial laser beams forming an overcomplete yet nonorthogonal set of modes. These modes have a singular phase profile and are eigenfunctions of the photon orbital angular momentum. The intensity profile is characterized by a single brilliant ring with the singularity at its center, where the field amplitude vanishes. The complex amplitude is proportional to the degenerate (confluent) hypergeometric function, and therefore we term such beams hypergeometric-Gaussian (HyGG) modes. Unlike the recently introduced hypergeometric modes [Opt. Lett. 32, 742 (2007)], the HyGG modes carry a finite power and have been generated in this work with a liquid-crystal spatial light modulator. We briefly consider some subfamilies of the HyGG modes as the modified Bessel Gaussian modes, the modified exponential Gaussian modes, and the modified Laguerre-Gaussian modes.

Efficient generation and sorting of orbital angular momentum eigenmodes of light by thermally tuned q-plates

We present methods for generating and for sorting specific orbital angular momentum (OAM) eigenmodes of a light beam with high efficiency, using a liquid crystal birefringent plate with unit topological charge known as “q-plate.” The generation efficiency has been optimized by tuning the optical retardation of the q-plate with temperature. The measured OAM m=±2 eigenmodes generation efficiency from an input TEM00 beam was of 97%. Mode sorting of the two input OAM m=±2 eigenmodes was achieved with an efficiency of 81%.

Photon spin-to-orbital angular momentum conversion via an electrically tunable q-plate

Exploiting electro-optic effects in liquid crystals, we achieved real-time control of the retardation of liquid-crystal-based q-plates through an externally applied voltage. Electro-optic q-plates can be operated as electrically driven converters of photon spin into orbital angular momentum, enabling a variation of the orbital angular momentum probabilities of the output photons over a time scale of milliseconds.

Optical angular momentum transfer to transparent isotropic particles using laser beam carrying zero average angular momentum

The torque exerted by an astigmatic optical beam on small transparent isotropic particles was dynamically measured observing the angular motion of the particles under a microscope. The data confirmed that torque was originated by the transfer of orbital angular momentum associated with the spatial changes in the phase of the optical field induced by the moving particle. This mechanism for angular momentum transfer works also with incident light beams with no net angular momentum.

Polarization-controlled evolution of light transverse modes and associated Pancharatnam geometric phase in orbital angular momentum

We present an easy, efficient, and fast method to generate arbitrary linear combinations of light orbital angular-momentumeigenstates � =± 2startingfromalinearlypolarizedTEM00 laserbeam.Themethodexploits the spin-to-orbital angular-momentum conversion capability of a liquid-crystal-based q plate and a Dove prism inserted into a Sagnac polarizing interferometer. The nominal generation efficiency is 100%, being limited only by reflection and scattering losses in the optical components. When closed paths are followed on the polarization Poincar´ e sphere of the input beam, the associated Pancharatnam geometric phase is transferred unchanged to the orbital angular momentum state of the output beam.

Two-dimensional photonic quasicrystals by single beam computer-generated holography

Recently important efforts have been dedicated to the realization of a new kind of photonic crystals, known as photonic quasicrystals, in which the lack of the translational symmetry is compensated by rotational symmetries not achievable by the conventional periodic crystals. Here we show a novel approach to their fabrication based on the use of a programmable Spatial Light Modulator encoding Computer-Generated Holograms. Using this single beam technique we fabricated Penrose-tiled structures possessing rotational symmetry up to 23-fold, and a two-dimensional Thue-Morse structure, which is an aperiodic structure not achievable by multiple beam holography.

Detection of Zak phases and topological invariants in a chiral quantum walk of twisted photons.

Topological insulators are fascinating states of matter exhibiting protected edge states and robust quantized features in their bulk. Here we propose and validate experimentally a method to detect topological properties in the bulk of one-dimensional chiral systems. We first introduce the mean chiral displacement, an observable that rapidly approaches a value proportional to the Zak phase during the free evolution of the system. Then we measure the Zak phase in a photonic quantum walk of twisted photons, by observing the mean chiral displacement in its bulk. Next, we measure the Zak phase in an alternative, inequivalent timeframe and combine the two windings to characterize the full phase diagram of this Floquet system. Finally, we prove the robustness of the measure by introducing dynamical disorder in the system. This detection method is extremely general and readily applicable to all present one-dimensional platforms simulating static or Floquet chiral systems.

The Polarizing Sagnac Interferometer: a tool for light orbital angular momentum sorting and spin-orbit photon processing

In this paper we show that an optical setup based on a polarizing Sagnac interferometer combined with a Dove prism can be used as a convenient general-purpose tool for the generation, detection and sorting of spin-orbit states of light. This device can work both in the classical and in the quantum single-photon regime, provides higher sorting efficiency and extinction ratio than usual hologram-fiber combinations, and shows much higher stability and ease of alignment than Mach-Zehnder interferometer setups. To demonstrate the full potential of this setup, we also report some demonstrative experiments of several possible applications of this setup.

Guiding light via geometric phases

A mechanism for confining and guiding light that relies on spin–orbit interactions of light is presented.

Statistical moments of quantum-walk dynamics reveal topological quantum transitions.

Many phenomena in solid-state physics can be understood in terms of their topological properties [1, 2]. Recently, controlled protocols of quantum walks are proving to be effective simulators of such phenomena [3–6]. Here we report the realization of a photonic quantum walk showing both the trivial and the non-trivial topologies associated with chiral symmetry in one-dimensional periodic systems, as in the SuSchrieffer-Heeger model of polyacetylene [7]. We find that the probability distribution moments of the walker position after many steps behave differently in the two topological phases and can be used as direct indicators of the quantum transition: while varying a control parameter, these moments exhibit a slope discontinuity at the transition point, and remain constant in the non-trivial phase. Extending this approach to higher dimensions, different topological classes, and other typologies of quantum phases may offer new general instruments for investigating quantum transitions in such complex systems.Many phenomena in solid-state physics can be understood in terms of their topological properties. Recently, controlled protocols of quantum walk (QW) are proving to be effective simulators of such phenomena. Here we report the realization of a photonic QW showing both the trivial and the non-trivial topologies associated with chiral symmetry in one-dimensional (1D) periodic systems. We find that the probability distribution moments of the walker position after many steps can be used as direct indicators of the topological quantum transition: while varying a control parameter that defines the system phase, these moments exhibit a slope discontinuity at the transition point. Numerical simulations strongly support the conjecture that these features are general of 1D topological systems. Extending this approach to higher dimensions, different topological classes, and other typologies of quantum phases may offer general instruments for investigating and experimentally detecting quantum transitions in such complex systems.