Aloyse Degiron

The role of localized surface plasmon modes in the enhanced transmission of periodic subwavelength apertures

After reviewing the present understanding of the transmission properties of single apertures and the enhanced transmission through hole arrays, experimental results are presented which show how localized surface plasmon (LSP) modes of individual apertures contribute to the transmission peaks associated with the periodic arrays. In particular, it is shown that the surface plasmon polaritons (SPPs) of the periodic structure dominate the spectral signature of the arrays. The results also indicate that the LSP of each hole can interact and that this can be controlled by appropriate arrangement of the apertures in the array.

Implementation of PT symmetric devices using plasmonics: principle and applications

The so-called PT symmetric devices, which feature ε((-x)) = ε((x))* associated with parity-time symmetry, incorporate both gain and loss and can present a singular eigenvalue behaviour around a critical transition point. The scheme, typically based on co-directional coupled waveguides, is here transposed to the case of variable gain on one arm with fixed losses on the other arm. In this configuration, the scheme exploits the full potential of plasmonics by making a beneficial use of their losses to attain a critical regime that makes switching possible with much lowered gain excursions. Practical implementations are discussed based on existing attempts to elaborate coupled waveguide in plasmonics, and based also on the recently proposed hybrid plasmonics waveguide structure with a small low-index gap, the PIROW (Plasmonic Inverse-Rib Optical Waveguide).

Holes with very acute angles: a new paradigm of extraordinary optical transmission through strongly localized modes.

It is shown that submicrometer holes with very acute angles present extraordinary optical transmission peaks associated to strongly localized modes. The positions of these peaks are: (i) strongly redshifted with respect to the peak position that could be expected if the considered hole were in a film made of perfect electric conductor, (ii) independent on the angle of incidence for a large range of angles and (iii) strongly dependent on the direction of the incident electric field. In addition, it is demonstrated that these properties are linked to the mechanisms leading to the existence of channel-plasmon-polaritons.

Subwavelength metallic waveguides as a tool for extreme confinement of THz surface waves

Research on surface waves supported by metals at THz frequencies is experiencing a tremendous growth due to their potential for imaging, biological sensing and high-speed electronic circuits. Harnessing their properties is, however, challenging because these waves are typically poorly confined and weakly bound to the metal surface. Many design strategies have been introduced to overcome these limitations and achieve increased modal confinement, including patterned surfaces, coated waveguides and a variety of sub-wavelength geometries. Here we provide evidence, using a combination of numerical simulations and time-resolved experiments, that shrinking the transverse size of a generic metallic structure always leads to solutions with extreme field confinement. The existence of such a general behavior offers a new perspective on energy confinement and should benefit future developments in THz science and technology.

Sub-diffraction-limit semiconductor resonators operating on the fundamental magnetic resonance

We demonstrate semiconductor terahertz (THz) resonators with sub-wavelength dimensions in all three dimensions of space. The maximum confinement is obtained for resonators with a diameter of 13 μm, which operate at a wavelength of ≈272 μm. This corresponds to a λeff/6 confinement, where λeff is the wavelength inside the material (or λ/20, if the free space wavelength is considered). These highly sub-wavelength devices operate on the fundamental magnetic resonance, which corresponds to the fundamental oscillation mode of split-ring resonators and is usually inactive in purely optical resonators. In this respect, these resonators are another step towards the hybridization of optics and electronics at THz frequencies. As a proof of principle for cavity quantum electrodynamics experiments, we apply these resonators to THz intersubband polaritons.

3D opticall metamaterials

This work focuses on the fabrication of 3D infrared metamaterials. We characterize the sample and provide useful guidelines for the design of these structures