Fadi I. Baida

Light transmission by subwavelength annular aperture arrays in metallic films

We study the spectral response of a metallic film with an engraved 2D periodic structure of annular apertures. We show that an enhanced transmission can be obtained and can reach 90%. The variation of the spectral response as a function of the film thickness from 150 nm to a value of 1.8 μm is also studied. We show that a guided mode in the subwavelength coaxial structure is responsible for this large transmission. A wavelength cut-off exists. We study the transmission characteristics on the optical and geometrical parameters of the array (period, coaxial radii, incident polarization and dielectric constants) using a 3D-FDTD algorithm.

Experimental and theoretical characterization of a lithium niobate photonic crystal

In this letter, we investigate the feasibility of tunable lithium niobate (LiNbO3) photonic crystals. The optical response through a LiNbO3 photonic structure is theoretically determined in order to obtain a photonic band gap with optimal tunability. We show by means of a finite difference time domain simulation that the optimal lattice parameters can provide a Δλ=7nm shift in the photonic band gap for a Δn=0.01 variation of the refractive index with an extinction ratio of −22.5dB. The fabrication process and the optical characterization of these novel photonic crystal structures are also reported. The extinction ratio of the measured photonic band gap is lower than −12dB.

Enhanced confined light transmission by single subwavelength apertures in metallic films

The diffraction of light that emerges from a metallic circular aperture is studied. Near- and far-field results are presented. Spectral angular transmitted intensities are performed versus the incident wavelength for four kinds of aperture. It is shown that, for a definite configuration, a large enhancement of transmission--compared with the basic case of a single hole--occurs combined with a spectacular angular confinement of light. Such effects are, for example, of great interest in optical near-field microscopy for which the probe is a nanosource.

Experimental and theoretical observations of the slow-light effect on a tunable photonic crystal

We describe how the susceptibility of a nonlinear material, such as lithium niobate, can change when the material is nanostructured. Indeed, we show, by the calculation of the local-field factor inside a photonic crystal, a significant augmentation of the susceptibility, especially at the edges of the photonic bandgap. In addition, and for the case of lithium niobate, we observe an increase of the second-order nonlinear coefficient. The experimental realization of an electro-optic tunable photonic crystal, based on a square lattice of holes, shows that the measured phenomenon completely agrees with the theoretical predictions.

Optical characterization of nanosources used in scanning near-field optical microscopy

We propose an optical method to characterize tips used in scanning near-field optical microscopy (SNOM). The tip is a nanosource, and its optical emission is studied by an inverted scanning tunneling optical microscopy (also called photon scanning tunneling microscopy) apparatus. Then we can obtain information about the spatial Fourier spectrum of the source. We give the formulas connecting the detected intensity to the properties of the nanosource and to geometric parameters of the apparatus. Our discussion is illustrated by a simple approximation for the nanosource: the Bethe–Bouwkamp model.

Numerical study of the displacement of a three-dimensional Gaussian beam transmitted at total internal reflection. Near-field applications

Longitudinal and transverse shifts of a light beam at total internal reflection was experimentally studied by far-field measurements on the reflected field. We propose to use a scanning tunneling optical microscope (STOM) to study these shifts in transmission, and we present a theoretical model of this proposed experiment to obtain a numerical estimation of these shifts. We study the reflection and the transmission of a three-dimensional polarized incident beam. We verify the validity of our formalism by studying the Goos-Hanchen shift in reflection and by comparing our results with published ones. Then we calculate STOM images of the transmitted field distribution. On the images the well-known Goos-Hanchen shift is easily observed. But we also encounter a smaller shift, perpendicular to the plane of incidence. This transverse shift was also observed in reflection by Imbert and Levy [Nouv. Rev. Opt. 6, 285 (1975)]. We study the variations of the two shifts versus various parameters such as the angle of incidence, the optical index, and the incident polarization. Then we discuss the feasibility of the near-field observation of these shifts.

Theoretical study of near-field surface plasmon excitation, propagation and diffraction

Surface plasmons have been extensively studied by using far field techniques. Today, new experiments can be developed by using scanning probe microscopes. In optics, the tip of a scanning near-field optical microscope has been used to detect or to excite the surface plasmon in the near-field region. In this paper, we propose a theoretical study of one of these optical experiments. A 3D model of excitation and detection by scanning tunneling optical microscope (STOM) of the surface plasmon is developed. The surface plasmon is excited by a 3D polarized gaussian beam in the Kretschmann configuration. We determine its propagation length. We also present a preliminary study of the interaction of the surface plasmon with the edge of a surface defect. Our results are in good accordance with experimental ones and show new effects.

Lithium niobate photonic crystal wire cavity: Realization of a compact electro-optically tunable filter

We report an electro-optically tunable filter using a lithium niobate photonic crystalcavity configuration with an efficient optical guiding geometry. The compact device (5.5u2009μmu2009×u20092.8u2009μm) was made on a hybrid waveguide combining an annealed proton exchange waveguide and a ridge waveguide realized by focused ion beam with vertically deposited electrodes. Due to the slow light and nonlinear effect in lithium niobate photonic crystal, experimental results show an enhanced tunability of ∼0.56u2009nm/V. This compact tunable photonic crystalcavity demonstration opens the path for the development of micro and nano-scale low-power driving active photonic devices.

Propagation and diffraction of locally excited surface plasmons

With the use of optical near-field techniques, it is now possible to excite or observe surface plasmons with high lateral resolution. A theoretical study is presented of surface plasmon excitation by near-field optical probes and the influence of well-defined structures on surface plasmon propagation and surface plasmon detection in the far field. The generation and the diffraction of the surface plasmon is calculated by using a theoretical scheme founded upon a first-order perturbation expansion of the Rayleigh-Fano method. A very good agreement is obtained between numerical and experimental results. The theoretical tools used should prove a useful guideline for future experiments of nanooptics with surface plasmons.

Conical optics: the solution to confine light

We compare the performances in terms of confinement and depth of field of spherical and conical optics. It turns out that, if the spherical optics is adapted to the usual parallel imaging, conical optics seems to be the optimized solution for systems based on scanning (sequential imaging). It is shown that the optimized confinement capability of conical optics is due to the ability of conical components to generate a single Bessel beam with high efficiency. The calculations are based on Weyl formulas.