Enhanced transmission beyond the cut-off through sub-Lambda Annular Aperture Arrays

A cascaded structure of annular aperture arrays perforated in silver films is shown to act as a high quality Fabry-Pérot interferometer (quality factor up to 200). The transmission of a single nanostructured layer exhibits a cut-off wavelength beyond which there is no transmission. It is demonstrated, here, that the double structure permits to overcome this cut-off. It is also found that transmission is enhanced by a factor of 150 for certain wavelengths. This kind of cascaded nanostructured metallic layers offers many promising applications as well as for optical wavelengths than for THz-waves because this effect still exists for perfect metals. It opens up the path for the conception of a new generation of integrated components based on metallo-dielectric structures that can be easily tailored as tunable devices

Quantification of the Transmission Properties of Anisotropic Metasurfaces Illuminated by Finite-Size Beams

The aim of this paper is to present an analytical method to quantitatively address the influence of a focusing illumination on the optical response properties of a metasurface illuminated by a finite-size beam. Most theoretical and numerical studies are performed by considering an infinite periodic structure illuminated by a plane wave. In practice, one deals with a finite-size illumination and structure. The combination of the angular spectrum expansion with a monomodal modal method is used to determine the beam size needed to acquire efficient properties of a metasurface that behaves as an anisotropic plate. Interesting results show that the beam-size can be as small as 5 × 5 periods to recover the results of a plane wave. Other results also show that the beam-size can be used as an extrinsic parameter to enhance the anisotropic metasurface performance and to adjust its expected properties finely (birefringence and/or transmission coefficient). These findings are important for the design of real (finite) structures and can be adapted for experimental conditions to achieve optimized results and take full advantage of the metamaterial properties

spectres.mp4

The movie shows the temporal evolution of the optical transmission spectrum through a nanophotonic periodic structure that is being deformed as a function of time by an acoustic resonance at 500 MHz. The vibrating pillars are made of silver and the piezoelectric substrate is made of lithium niobate. The period of the structure is 640 nm

lfixe.mp4

The movie shows the temporal evolution of the optical transmission through a nanophotonic periodic structure that is being deformed as a function of time by an acoustic resonance at 500 MHz. The optical wavelength is fixed. The vibrating pillars are made of silver and the piezoelectric substrate is made of lithium niobate. The period of the structure is 640 nm

Simultaneous photonic and phononic band gaps in a two-dimensional lithium niobate crystal

International audienceThe possibility to obtain hypersonic phononic band gaps in artificial crystals presenting submicron lattice parameters has shown that phononic and photonic crystals can be made of comparable dimensions, hence opening the way to simultaneous elastic and electromagnetic band gaps. We here focus on the theoretical investigation of air/lithium niobate 2D phoxonic crystals. The conditions for the existence of a full photonic band gap in this material are demanding, due to its relatively low refractive index and its elastic anisotropy which slightly hinders the opening of large phononic band gaps. The most commonly used singleatom lattices, i.e. square and hexagonal, as well as multipleatom hexagonal lattices were considered. In each case, photonic and phononic band structures were computed independently. 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 1.55 μm are given. The corresponding phononic frequencies are in the Gigahertz range

Towards phoXonic crystals

International audienceThe simultaneous existence of photonic and phononic band gaps opens up many possibilities for enhancing acousto-optical interactions at a common wavelength scale. In this paper, we will give a brief review of the current state of the art dedicated to these structures, before focusing on theoretical investigations of the band diagrams of such 'phoxonic' crystals. We will more particularly focus on air/lithium niobate crystals in view of designing integrated phoxonic devices relying on surface acoustic waves. A comparison with a silicon based solution, in particular with slab structures, will also be drawn