Random nonlinear layered structures as sources of photon pairs for quantum-information processing

Random nonlinear layered structures have been found to be a useful source of photon pairs with perfectly indistinguishable un-entangled photons emitted into a very narrow spectral range. Localization of the interacting optical fields typical for random structures gives relatively high photon-pair fluxes. Superposing photon-pair emission quantum paths at different emission angles, several kinds of two-photon states (including states with coincident frequencies) useful in quantum-information processing can easily be generated.Comment: 4 pages, 5 figure

Second harmonic generation from ZnO films and nanostructures.

Zinc oxide ZnO is a n-type semiconductor having a wide direct band gap (3.37 eV) as well as a non-centrosymmetric crystal structure resulting from hexagonal wurtzite phase. Its wide transparency range along with its second order nonlinear optical properties make it a promising material for efficient second harmonic generation processes and nonlinear optical applications in general. In this review, we present an extensive analysis of second harmonic generation from ZnO films and nanostructures. The literature survey on ZnO films will include some significant features affecting second harmonic generation efficiency, as crystalline structure, film thickness, surface contributes, and doping. In a different section, the most prominent challenges in harmonic generation from ZnO nanostructures are discussed, including ZnO nanowires, nanorods, and nanocrystals, to name a few. Similarly, the most relevant works regarding third harmonic generation from ZnO films and nanostructures are separately addressed. Finally, the conclusion part summarizes the current standing of published values for the nonlinear optical coefficients and for ZnO films and nanostructures, respectively

Chiral near-field manipulation in Au-GaAs hybrid hexagonal nanowires

We demonstrate the control of enhanced chiral field distribution at the surface of hybrid metallo-dielectric nanostructures composed of self-assembled vertical hexagonal GaAs-based nanowires having three of the six sidewalls covered with Au. We show that weakly-guided modes of vertical GaAs nanowires can generate regions of high optical chirality that are further enhanced by the break of the symmetry introduced by the gold layer. Changing the angle of incidence of a linearly polarized plane wave it is possible to tailor and optimize the maps of the optical chirality in proximity of the gold plated walls. The low cost feasibility of the sample combined to the simple control by using linearly polarized light and the easy positioning of chiral molecules by functionalization of the gold plates make our proposed scheme very promising for enhanced enantioselective spectroscopy applications

Self-Phase-Matched Second-Harmonic and White-Light Generation in a Biaxial Zinc Tungstate Single Crystal

Second-order nonlinear optical materials are used to generate new frequencies by exploiting second-harmonic generation (SHG), a phenomenon where a nonlinear material generates light at double the optical frequency of the input beam. Maximum SHG is achieved when the pump and the generated waves are in phase, for example through birefringence in uniaxial crystals. However, applying these materials usually requires a complicated cutting procedure to yield a crystal with a particular orientation. Here we demonstrate the first example of phase matching under the normal incidence of SHG in a biaxial monoclinic single crystal of zinc tungstate. The crystal was grown by the micro-pulling-down method with the (102) plane perpendicular to the growth direction. Additionally, at the same time white light was generated as a result of stimulated Raman scattering and multiphoton luminescence induced by higher-order effects such as three-photon luminescence enhanced by cascaded third-harmonic generation. The annealed crystal offers SHG intensities approximately four times larger than the as grown one; optimized growth and annealing conditions may lead to much higher SHG intensities

Optimization of highly circularly polarized thermal radiation in α\alpha-MoO3_3/β\beta-Ga2_2O3_3 twisted layers

We investigate a bi-layer scheme for circularly polarized infrared thermal radiation. Our approach takes advantage of the strong anisotropy of low-symmetry materials such as $\beta$-Ga$_2$O$_3$ and $\alpha$-MoO$_3$. We numerically report narrow-band, high degree of circular polarization (over 0.85), thermal radiation at two typical emission frequencies related to the excitation of $\beta$-Ga$_2$O$_3$ optical phonons. Optimization of the degree of circular polarization is achieved by a proper relative tilt of the crystal axes between the two layers. Our simple but effective scheme could set the basis for a new class of lithography-free thermal sources for IR bio-sensing.Comment: 11 pages, 6 figure

Resonant second harmonic generation in random dielectric structures

International audience; We show that resonant second harmonic generation can be obtained in random dielectric structures. The scheme is based on internal resonances due to the optical counterpart of Anderson localization. By making use of different localization lengths at the fundamental and at the second harmonic frequencies, we predict a conversion efficiency that is four orders of magnitude higher than a bulk material and even one order of magnitude higher than an ideal phase matched slab of the same size. The method is highly insensitive to fabrication tolerances, and provides excellent angle tunability. [DOI:10.2971/jeos.2006.06021

Free-standing plasmonic nanoarrays for leaky optical waveguiding and sensing

Flat optics nanogratings supported on thin free-standing membranes offer the opportunity to combine narrowband waveguided modes and Rayleigh anomalies for sensitive and tunable biosensing. At the surface of high-refractive index Si3N4 membranes we engineered lithographic nanogratings based on plasmonic nanostripes, demonstrating the excitation of sharp waveguided modes and lattice resonances. We achieved fine tuning of these optical modes over a broadband Visible and Near-Infrared spectrum, in full agreement with numerical calculations. This possibility allowed us to select sharp waveguided modes supporting strong near-field amplification, extending for hundreds of nanometres out of the grating and enabling versatile biosensing applications. We demonstrate the potential of this flat-optics platform by devising a proof-of-concept nanofluidic refractive index sensor exploiting the long-range waveguided mode operating at the sub-picoliter scale. This free-standing device configuration, that could be further engineered at the nanoscale, highlights the strong potential of flat-optics nanoarrays in optofluidics and nanofluidic biosensing. (C) 2022 Optica Publishing Group under the terms of the Optica Open Access Publishing Agreemen

Properties of entangled photon pairs generated in one-dimensional nonlinear photonic-band-gap structures

We have developed a rigorous quantum model of spontaneous parametric down-conversion in a nonlinear 1D photonic-band-gap structure based upon expansion of the field into monochromatic plane waves. The model provides a two-photon amplitude of a created photon pair. The spectra of the signal and idler fields, their intensity profiles in the time domain, as well as the coincidence-count interference pattern in a Hong-Ou-Mandel interferometer are determined both for cw and pulsed pumping regimes in terms of the two-photon amplitude. A broad range of parameters characterizing the emitted down-converted fields can be used. As an example, a structure composed of 49 layers of GaN/AlN is analyzed as a suitable source of photon pairs having high efficiency.Comment: 14 pages, 23 figure

Midinfrared thermal emission properties of finite arrays of gold dipole nanoantennas

We studied the far-field thermal emission properties of finite arrays of resonant gold dipole nanoantennas at equilibrium temperature. We numerically investigated the transition from the super-Planckian emission of the single resonant antenna to the sub-Planckian emission inherent to infinite periodic arrays. Increasing the number of unit cells of the array, the overall size of the system increases, and the relative emissivity quickly converges to values lower than the unity. Nevertheless, if the separation between nanoantennas in the array is small compared to the wavelength, the near-field interaction makes the emission of each unit cell multipolar. This opens the doors for additional tailoring of the emitted power and directionality of thermal radiation