488 research outputs found
Nonlinear dielectric epsilon near-zero hybrid nanogap antennas
High-index Mie-resonant dielectric nanostructures provide a new framework to
manipulate light at the nanoscale. In particular their local field confinement
together with their inherently low losses at frequencies below their band-gap
energy allows to efficiently boost and control linear and nonlinear optical
processes. Here, we investigate nanoantennas composed of a thin indium-tin
oxide layer in the center of a dielectric Gallium Phosphide nanodisk. While the
linear response is similar to that of a pure GaP nanodisk, we show that the
second and third-harmonic signals of the nanogap antenna are boosted at
resonance. Linear and nonlinear finite-difference time-domain simulations show
that the high refractive index contrast leads to strong field confinement
inside the antenna's ITO layer. Measurement of ITO and GaP nonlinear
susceptibilities deliver insight on how to engineer nonlinear nanogap antennas
for higher efficiencies for future nanoscale devices.Comment: main: 18 pages, 4 figues, supplemental: 8 pages, 4 figures, 1 tabl
Turbulence Hierarchy in a Random Fibre Laser
Turbulence is a challenging feature common to a wide range of complex
phenomena. Random fibre lasers are a special class of lasers in which the
feedback arises from multiple scattering in a one-dimensional disordered
cavity-less medium. Here, we report on statistical signatures of turbulence in
the distribution of intensity fluctuations in a continuous-wave-pumped
erbium-based random fibre laser, with random Bragg grating scatterers. The
distribution of intensity fluctuations in an extensive data set exhibits three
qualitatively distinct behaviours: a Gaussian regime below threshold, a mixture
of two distributions with exponentially decaying tails near the threshold, and
a mixture of distributions with stretched-exponential tails above threshold.
All distributions are well described by a hierarchical stochastic model that
incorporates Kolmogorov's theory of turbulence, which includes energy cascade
and the intermittence phenomenon. Our findings have implications for explaining
the remarkably challenging turbulent behaviour in photonics, using a random
fibre laser as the experimental platform.Comment: 9 pages, 5 figure
Recommended from our members
3D-nanoprinted on-chip antiresonant waveguide with hollow core and microgaps for integrated optofluidic spectroscopy
Here, we unlock the properties of the recently introduced on-chip hollow-core microgap waveguide in the context of optofluidics which allows for intense light-water interaction over long lengths with fast response times. The nanoprinted waveguide operates by the antiresonance effect in the visible and near-infrared domain and includes a hollow core with defined gaps every 176 ”m. The spectroscopic capabilities are demonstrated by various absorption-related experiments, showing that the Beer-Lambert law can be applied without any modification. In addition to revealing key performance parameters, time-resolved experiments showed a decisive improvement in diffusion times resulting from the lateral access provided by the microgaps. Overall, the microgap waveguide represents a pathway for on-chip spectroscopy in aqueous environments
Metafiber transforming arbitrarily structured light
Structured light has proven useful for numerous photonic applications.
However, the current use of structured light in optical fiber science and
technology is severely limited by mode mixing or by the lack of optical
elements that can be integrated onto fiber end-faces for complex wavefront
control, and hence generation of structured light is still handled outside the
fiber via bulky optics in free space. We report a metafiber platform capable of
creating arbitrarily structured light on the hybrid-order Poincar\'e sphere.
Polymeric metasurfaces, with unleashed height degree of freedom and a greatly
expanded 3D meta-atom library, were laser nanoprinted and interfaced with
polarization-maintaining single-mode fibers. Multiple metasurfaces were
interfaced on the fiber end-faces, transforming the fiber output into different
structured-light fields, including cylindrical vector beams, circularly
polarized vortex beams, and an arbitrary vector field. Our work provides a new
paradigm for advancing optical fiber science and technology towards
fiber-integrated light shaping, which may find important applications in fiber
communications, fiber lasers and sensors, endoscopic imaging, fiber
lithography, and lab-on-fiber technology
The Interactive Sphere for Three-Dimensional Control in Games and Virtual Reality
In electronic games, the controller is the mean through which the player can interact with the gameâs virtual world, being an essential factor in all of the user experience. New controllers may, therefore, completely modify the player experience, also serving as a tool to investigate new ways of interacting with interactive systems of various purposes. In this context, this paper presents the Interactive Sphere, a spherical device to be employed specially with games and virtual reality environments. This novel device combines the pressing of certain regions of the sphere with gestural interaction, in addition to providing haptic, auditive and visual feedback. The paper describes all of the rationale behind the decisions taken during the design and development process of the device, in addition to the techniques employed for implementing the detection of the acts of pressing and moving the Interactive Sphere. In this project, accessible, low-cost materials and techniques were prioritized, which could be more easily adapted to other contexts. We envision that the lessons learned and the guidelines derived from its design and development process may assist in the idealization and construction of new ways of interacting, by providing a set of methods, techniques and technologies that were employed in the development of a new physical artifact of interaction presented in this work
Physico-chemical characterization of inclusion complex between hydroxymethylnitrofurazone and hydroxypropyl-beta-cyclodextrin
Hydroxymethylnitrofurazone (NFOH) is a prodrug that is active against Trypanosoma cruzi. It however presents low solubility and high toxicity. Hydroxypropyl-beta-cyclodextrin (HP-beta-CD) can be used as a drug-delivery system for NFOH modifying its physico-chemical properties. The aim of this work is to characterize the inclusion complex between NFOH and HP-beta-CD. The rate of NFOH release decreases after complexation and thermodynamic parameters from the solubility isotherm studies revealed that a stable complex is formed (deltaGÂș= 1.7 kJ/mol). This study focuses on the physico-chemical characterization of a drug-delivery formulation that comes out as a potentially new therapeutic option for Chagas disease treatment.FAPESPCoordenacao de Aperfeicoamento de Pessoal de Nivel Superior (CAPES
Permittivity-asymmetric quasi-bound states in the continuum
Broken symmetries lie at the heart of nontrivial physical phenomena. Breaking
the in-plane geometrical symmetry of optical systems allows to access a set of
electromagnetic states termed symmetry-protected quasi-bound states in the
continuum (qBICs). Here we demonstrate, theoretically, numerically and
experimentally, that such optical states can also be accessed in metasurfaces
by breaking the in-plane symmetry in the permittivity of the comprising
materials, showing a remarkable equivalence to their geometrically-asymmetric
counterparts. However, while the physical size of atoms imposes a limit on the
lowest achievable geometrical asymmetry, weak permittivity modulations due to
carrier doping and electro-optical Pockels and Kerr effects, usually considered
insignificant, open up the possibility of infinitesimal permittivity
asymmetries for on-demand, and dynamically tuneable optical resonances of
extremely high quality factors. We probe the excitation of
permittivity-asymmetric qBICs (-qBICs) using a prototype
Si/TiO metasurface, in which the asymmetry in the unit cell is provided
by the refractive index contrast of the dissimilar materials, surpassing any
unwanted asymmetries from nanofabrication defects or angular deviations of
light from normal incidence. -qBICs can also be excited in 1D
gratings, where quality-factor enhancement and tailored interference phenomena
via the interplay of geometrical and permittivity asymmetries are numerically
demonstrated. The emergence of -qBICs in systems with broken
symmetries in their permittivity may enable to test time-energy uncertainties
in quantum mechanics, and lead to a whole new class of low-footprint optical
and optoelectronic devices, from arbitrarily narrow filters and topological
sources, biosensing and ultrastrong light-matter interaction platforms, to
tuneable optical switches.Comment: Manuscript and Supplementary Information, 27 pages, 4 Figures
manuscript + 4 Supplementary Figure
- âŠ