Multilevel Spiral Axicon for High-Order Bessel-Gauss Beams Generation.

This paper presents an efficient method to generate high-order Bessel-Gauss beams carrying orbital angular momentum (OAM) by using a thin and compact optical element such as a multilevel spiral axicon. This approach represents an excellent alternative for diffraction-free OAM beam generation instead of complex methods based on a doublet formed by a physical spiral phase plate and zero-order axicon, phase holograms loaded on spatial light modulators (SLMs), or the interferometric method. Here, we present the fabrication process for axicons with 16 and 32 levels, characterized by high mode conversion efficiency and good transmission for visible light (λ = 633 nm wavelength). The Bessel vortex states generated with the proposed diffractive optical elements (DOEs) can be exploited as a very useful resource for optical and quantum communication in free-space channels or in optical fibers.

Influence of Random Plasmonic Metasurfaces on Fluorescence Enhancement.

One of the strategies employed to increase the sensitivity of the fluorescence-based biosensors is to deposit chromophores on plasmonic metasurfaces which are periodic arrays of resonating nano-antennas that allow the control of the electromagnetic field leading to fluorescence enhancement. While artificially engineered metasurfaces realized by micro/nano-fabrication techniques lead to a precise tailoring of the excitation field and resonant cavity properties, the technological overhead, small areas, and high manufacturing cost renders them unsuitable for mass production. A method to circumvent these challenges is to use random distribution of metallic nanoparticles sustaining plasmonic resonances, which present the properties required to significantly enhance the fluorescence. We investigate metasurfaces composed of random aggregates of metal nanoparticles deposited on a silicon and glass substrates. The finite difference time domain simulations of the interaction of the incident electromagnetic wave with the structures reveals a significant enhancement of the excitation field, which is due to the resonant plasmonic modes sustained by the nanoparticles aggregates. We experimentally investigated the role of these structures in the fluorescent behaviour of Rhodamine 6G dispersed in polymethylmethacrylate finding an enhancement that is 423-fold. This suggests that nanoparticle aggregates have the potential to constitute a suitable platform for low-cost, mass-produced fluorescent biosensors.

Cyclic permutations for qudits in d dimensions.

One of the main challenges in quantum technologies is the ability to control individual quantum systems. This task becomes increasingly difficult as the dimension of the system grows. Here we propose a general setup for cyclic permutations Xd in d dimensions, a major primitive for constructing arbitrary qudit gates. Using orbital angular momentum states as a qudit, the simplest implementation of the Xd gate in d dimensions requires a single quantum sorter Sd and two spiral phase plates. We then extend this construction to a generalised Xd(p) gate to perform a cyclic permutation of a set of d, equally spaced values {|[Formula: see text]〉, |[Formula: see text] + p〉, …, |[Formula: see text] + (d - 1)p〉} [Formula: see text] {|[Formula: see text] + p〉, |[Formula: see text] + 2p〉, …, |[Formula: see text]〉}. We find compact implementations for the generalised Xd(p) gate in both Michelson (one sorter Sd, two spiral phase plates) and Mach-Zehnder configurations (two sorters Sd, two spiral phase plates). Remarkably, the number of spiral phase plates is independent of the qudit dimension d. Our architecture for Xd and generalised Xd(p) gate will enable complex quantum algorithms for qudits, for example quantum protocols using photonic OAM states.

Independent and combined information transfer from axicon and helical phase distributions.

Helical phase distributions used for optical information transfer increase its capacity by offering a characteristic spatial intensity arrangement for the diffracted beam. Here we propose the superposition between helical phase distribution with an axicon type. They form a composed object placed in the object arm to generate holographic masks. The diffracted patterns from these masks exhibit asymmetric shapes and peaks along the optical axis, with two kinds of spots, which contain independent or combined information from both phase distribution constructive parameters. To read these parameters based only on the diffraction patterns analysis, we generate the match reading masks (RMs) to be inserted in the optical path. In this proof-of-concept experiment, we demonstrate that one can sort constructive parameter values of each phase distribution, from both kinds of spots, using specific RMs.

Method of determination of light-scatterer distribution in edge-lit backlight units using an analytical approach.

We present a method to find the optimum distribution of scatterers in an edge-lit lightguide plate (LGP) for rendering a uniform distribution of the outcoupled light. We propose a simple mathematical model describing the light propagation in a waveguide with a distribution of scattering elements located on the lower surface of the waveguide. We have found a differential equation giving the distribution of scattering elements leading to a uniform irradiance along the LGP, and we propose a method to determine the value of the outcoupling coefficient of an individual scattering element from the irradiance (or radiance) measurements. We have verified the validity of this model by performing ray tracing simulations on an LGP with the scattering elements distributed according to the solution of the proposed differential equation, and we have found a quantitative agreement between the analytical results and the simulated ones. Also this model has been used to directly calculate the output power of a given embossed LGP.