Jean-Yves Laluet

Channel plasmon subwavelength waveguide components including interferometers and ring resonators

Photonic components are superior to electronic ones in terms of operational bandwidth, but the diffraction limit of light poses a significant challenge to the miniaturization and high-density integration of optical circuits. The main approach to circumvent this problem is to exploit the hybrid nature of surface plasmon polaritons (SPPs), which are light waves coupled to free electron oscillations in a metal that can be laterally confined below the diffraction limit using subwavelength metal structures. However, the simultaneous realization of strong confinement and a propagation loss sufficiently low for practical applications has long been out of reach. Channel SPP modes—channel plasmon polaritons (CPPs)—are electromagnetic waves that are bound to and propagate along the bottom of V-shaped grooves milled in a metal film. They are expected to exhibit useful subwavelength confinement, relatively low propagation loss, single-mode operation and efficient transmission around sharp bends. Our previous experiments showed that CPPs do exist and that they propagate over tens of micrometres along straight subwavelength grooves. Here we report the design, fabrication and characterization of CPP-based subwavelength waveguide components operating at telecom wavelengths: Y-splitters, Mach–Zehnder interferometers and waveguide–ring resonators. We demonstrate that CPP guides can indeed be used for large-angle bending and splitting of radiation, thereby enabling the realization of ultracompact plasmonic components and paving the way for a new class of integrated optical circuits.

Optical chirality without optical activity: How surface plasmons give a twist to light

Light interacts differently with left and right handed three dimensional chiral objects, like helices, and this leads to the phenomenon known as optical activity. Here, by applying a polarization tomography, we show experimentally, for the first time in the visible domain, that chirality has a different optical manifestation for twisted planar nanostructured metallic objects acting as isolated chiral metaobjects. Our analysis demon-strate how surface plasmons, which are lossy bidimensional electromagnetic waves propagating on top of the structure, can delocalize light information in the just precise way for giving rise to this subtle effect.

Optical transmission in perforated noble and transition metal films

Optical transmission through arrays of subwavelength apertures is studied systematically in different metals over the optical spectral range in comparable conditions. The results provide an absolute comparison and thereby highlight the influence of the dielectric constants, surface excitations, interband transitions and different loss mechanisms. Only noble metals such as Ag, Au and Cu give rise to significant transmission in the optical regime. Hole arrays in W transmit very poorly, as expected, since W cannot sustain surface plasmons in the optical range.

Optimization of surface plasmons launching from subwavelength hole arrays: modelling and experiments

The launching of surface plasmons by micro-gratings of subwavelength apertures milled in a thick metal film is important for the development of surface plasmon based circuits. By comparing the near-field optical images of such surface plasmon sources with the results of a Huygens-Fresnel principle based scattering model, we show that the properties of the locally launched SP beams such as divergence or uniformity can be tuned by adjusting the shape of the micro-gratings. This allows us to propose an optimized source array well adapted for providing a narrow, collimated and uniform beam.

Refractive micro-optical elements for surface plasmons: from classical to gradient index optics.

Controlling the propagation of surface plasmons along a metal-dielectric interface is a key feature for the development of surface plasmon based circuits. We have designed various two-dimensional refractive dielectric optical elements for surface plasmons (SP) and characterized their capacity to route SP, using near- or far-field techniques. We first present basic devices analogous to usual optical components and the associated challenges for SP optics. We then use a metamaterial approach to locally vary the refractive index and fabricate gradient index structures for SP circuitry.

Nanophotonic components utilizing channel plasmon polaritons

Channel plasmon polaritons (CPPs) propagating along the bottom of subwavelength grooves cut into a metal surface were recently shown to exhibit strong confinement combined with low propagation loss, a feature that makes this guiding configuration very promising for the realisation of ultra-compact photonic components. Here, the results of our investigations of CPP guiding by V-grooves cut into gold are presented, demonstrating efficient large-angle bending and splitting of radiation as well as waveguide-ring resonators and Bragg grating filters.

Tailoring Polarization States of Visible Light through Metallic Nanostructures

We focus on the possibility offered through the control of surface plasmons by metallic nanostructures (in particular chiral structures) to design optical devices with specific polarization properties. Our systems operate in the visible range.