F. I. Baida

Electro-optic effect exaltation on lithium niobate photonic crystals due to slow photons

The authors demonstrate how slow group velocities that are easily attainable at the band edge of photonic crystals can drastically enhance the electro-optical effect on tunable photonic crystal components. This property opens up the possibility of microsized nonlinear devices with low power requirement. In this letter we show how these possibilities for enhancement of nonlinear effects have been used to fabricate a 13×13μm2 sized lithium niobate photonic crystal intensity modulator that shows an enhanced electro-optic effect 312 times bigger than the one predicted by the classical Pockels effect for an equivalent device in bulk material.

Tailoring simultaneous photonic and phononic band gaps

The simultaneous existence of photonic and phononic band gaps opens up many possibilities for enhancing acousto-optical interactions at a common wavelength scale. We term such structures phoxonic crystals. By computing the existence and dependence of phoxonic band gaps on the choice of lattice and unit cell, we obtain a hierarchy of two-dimensional phoxonic crystal structures. The single-atom hexagonal and square lattices, and some multiple-atom hexagonal lattices, including honeycomb and heterometric lattices, are investigated. For definiteness, arrays of air holes in lithium niobate are considered in the computations. It is observed that decreasing the symmetry of the lattice by adding atoms of different sizes inside the unit cell leads to larger phoxonic band gaps. Examples of designs for operation at an optical wavelength of 1550 nm are given. The corresponding phononic frequencies are in the gigahertz range.

90% Extraordinary optical transmission in the visible range through annular aperture metallic arrays

We demonstrate what we believe to be the first experimental extraordinary optical transmission (EOT) of up to 90%, thanks to a well-identified guided mode that propagates through annular apertures engraved into an optically thick silver layer. In spite of the metal losses, high transmission can be obtained by adjusting the geometrical parameters of the fabricated structure, as was already theoretically demonstrated. To our knowledge, this is the first study showing such a large transmission in the visible range.

Transmission properties of slanted annular aperture arrays. Giant energy deviation over sub-wavelength distance.

This paper is devoted to the study of the transmission properties of Slanted Annular Aperture Arrays made in perfectly conducting metal. More precisely, we consider the transmission based on the excitation of the cutoff-less guided mode, namely the TEM mode. We numerically and analytically demonstrate some intrinsic properties of the structure showing a transmission coefficient of at least 50% of an unpolarized incident beam independently of the illumination configuration (angle and plane of incidence). The central symmetry exhibited by the structure is analytically exploited to demonstrate the existence of a polarization state for which all the incident energy is transmitted through the sub-wavelength apertures when the eigenmode is excited, whatever are the illumination and the geometrical parameters. For this state of polarization, the laminar flow of the energy through the structure can exhibit giant deviation over very small distances. An example of energy flow deviation of 220° per wavelength is presented for illustration. The results presented in this paper could be considered as an important contribution to the understanding of the enhanced transmission phenomenon based on the excitation of guided modes.

Enhanced electro-optical lithium niobate photonic crystal wire waveguide on a smart-cut thin film.

We report an electro-optically tunable photonic crystal linear cavity etched on a 200 nm lithium niobate waveguide ridge. The photonic crystal cavity and the ridge are both fabricated on a 1 μm thin film of lithium niobate obtained by smart-cut technology. The photonic crystal, of area 4x0.8 μm2, has been engineered to work in a slow light configuration so that the electro-optic effect is 20 times more important than in bulk material.

An angle-independent Frequency Selective Surface in the optical range

We suggest and numerically demonstrate a design for Frequency Selective Surfaces (FSS) operating in the optical (visible and near-infrared) range. The position and width of the FSS bandpass do not depend on the angle of incidence and polarization state of the incoming light, allowing high transmission at any angle. The FSS is formed by annular apertures perforated in a metal film and arranged in a square array. Angle- and polarization-independent transmission properties are demonstrated for silver. These results can be extended to other metals as well as to other frequency domains.

Annular aperture arrays: study in the visible region of the electromagnetic spectrum

Baida and Van Labeke recently proposed a structure that exhibits a supertransmission of light through an array of nanometric coaxial apertures in a metallic film that has been named an annular aperture array (AAA) [Opt. Commun. 209, 17 (2002); Phys. Rev. B 67, 155314 (2003); J. Microsc. 213, 140 (2003)]. We present the first experimental study, to our knowledge, of an AAA structure in the visible region. For technological reasons, the structure under study does not produce a supertransmission of 80% as in Baida and Van Labeke [Opt. Commun. 209, 17 (2002)]. We built the nanostructure and experimentally recorded its far-field spectral response. This transmission shows only one broad band with a maximum around lambda = 700 nm, giving a maximum efficiency around 17%. A finite-difference time-domain simulation reproduces quite well the obtained transmission spectrum.

A theoretical model for the Inverse Scanning Tunneling Optical Microscope (ISTOM)

Abstract Recently experiments have been performed with a new kind of Scanning Near-field Microscope. The apparatus is derived from a Scanning Tunneling Optical Microscope by simply inverting the direction of light propagation: it is thus an Inverted Scanning Tunneling Optical Microscope (ISTOM) where the tip is used in emission mode and where detection can be mediated via homogeneous or evanescent waves. We propose a theoretical calculation of the detected intensity measured in ISTOM experiments. In this model, the sample is a relief on the hemisphere surface and the source is an aperture tip described within the Bethe-Bouwkamp approximation. The use of plane wave expansions of the various fields and of a perturbation method for matching the boundary conditions lead to concise analytical formulas. The discussion of the influence of the various parameters on the detected intensity is thus quite easy. We illustrate the formulas by some examples showing the variations of the detected signal versus tip-surface distance, tip radius and detection angle.

Fiber-integrated optical nano-tweezer based on a bowtie-aperture nano-antenna at the apex of a SNOM tip

We propose a new concept of fiber-integrated optical nano-tweezer on the basis of a single bowtie-aperture nano-antenna (BNA) fabricated at the apex of a metal-coated SNOM tip. We demonstrate 3D optical trapping of 0.5 micrometer latex beads with input power which does not exceed 1 mW. Optical forces induced by the BNA on tip are then analyzed numerically. They are found to be 10(3) times larger than the optical forces of a circular aperture of the same area. Such a fiber nanostructure provides a new path for manipulating nano-objects in a compact, flexible and versatile architecture and should thus open promising perspectives in physical, chemical and biomedical domains.

Bowtie nano-aperture as interface between near-fields and a single-mode fiber

We present the development and study of a single bowtie nano-aperture (BNA) at the end of a monomode optical fiber as an interface between near-fields/nano-optical objects and the fiber mode. To optimize energy conversion between BNA and the single fiber mode, the BNA is opened at the apex of a specially designed polymer fiber tip which acts as an efficient mediator (like a horn optical antenna) between the two systems. As a first application, we propose to use our device as polarizing electric-field nanocollector for scanning near-field optical microscopy (SNOM). However, this BNA-on-fiber probe may also find applications in nanolithography, addressing and telecommunications as well as in situ biological and chemical probing and trapping.