Mickaël Février

Giant coupling effect between metal nanoparticle chain and optical waveguide.

We demonstrate that the optical energy carried by a TE dielectric waveguide mode can be totally transferred into a transverse plasmon mode of a coupled metal nanoparticle chain. Experiments are performed at 1.5 μm. Mode coupling occurs through the evanescent field of the dielectric waveguide mode. Giant coupling effects are evidenced from record coupling lengths as short as ~560 nm. This result opens the way to nanometer scale devices based on localized plasmons in photonic integrated circuits.

Observation of Near-Field Dipolar Interactions Involved in a Metal Nanoparticle Chain Waveguide

We present near-field measurements of transverse plasmonic wave propagation in a chain of gold elliptical nanocylinders fed by a silicon refractive waveguide at optical telecommunication wavelengths. Eigenmode amplitude and phase imaging by apertureless scanning near-field optical microscopy allows us to measure the local out-of-plane electric field components and to reveal the exact nature of the excited localized surface plasmon resonances. Furthermore, the coupling mechanism between subsequent metal nanoparticles along the chain is experimentally analyzed by spatial Fourier transformation on the complex near-field cartography, giving a direct experimental proof of plasmonic Bloch mode propagation along array of localized surface plasmons. Our work demonstrates the possibility to characterize multielement plasmonic nanostructures coupled to a photonic waveguide with a spatial resolution of less than 30 nm. This experimental work constitutes a prerequisite for the development of integrated nanophotonic devices.

Integration of short gold nanoparticles chain on SOI waveguide toward compact integrated bio-sensors

We demonstrate the integration of short metal nanoparticle chains (L ≈700 nm) supporting localized surface plasmons in Silicon On Insulator (SOI) waveguides at telecom wavelengths. Nanoparticles are deposited on the waveguide top and excited through the evanescent field of the TE waveguide modes. Finite difference time domain calculations and waveguide transmission measurements reveal that almost all the TE mode energy can be transferred to nanoparticle chains at resonance. It is also shown that the transmission spectrum is very sensitive to the molecular environment of nanoparticles, thus opening the way towards ultra-compact sensors in guided plasmonics on SOI. An experimental demonstration is reported with octadecanthiol molecules for a detection volume as small as 0.26 attoliter.

Theoretical analysis of Bloch mode propagation in an integrated chain of gold nanowires

The eigenmodes analysis of Bloch modes in a chain of metallic nanowires (MNWs) provides a significant physical understanding about the light propagation phenomena involved in such structures. However, most of these analyses have been done above the light line in the dispersion relation, where the Bloch modes can only be excited with radiative modes. By making use of the Fourier modal method, in this paper we rigorously calculate the eigenmode and mode excitation of a chain of MNWs via the fundamental transverse magnetic (TM) mode of a dielectric waveguide. Quadrupolar and dipolar transversal Bloch modes were obtained in an MNW chain embedded in a dielectric material. These modes can be coupled efficiently with the fundamental TM mode of the waveguide. Since the eigenmodes supported by the integrated plasmonic structure exhibit strong localized surface plasmon (LSP) resonances, they could serve as a nanodevice for sensing applications. Also, the analysis opens a direction for novel nanostructures, potentially helpful for the efficient excitation of LSPs and strong field enhancement.

Numerical analysis of tip-localized surface plasmon resonances in periodic arrays of gold nanowires with triangular cross section

In this contribution, we numerically study the tip enhancement of localized surface plasmons in periodic arrays of gold nanowires with triangular cross section under different illumination configurations. We found that the plasmonic resonance in a single nanowire is excited with a transverse magnetic (TM) plane wave impinging from the substrate at the critical angle, whereas grazing angles are required for the excitation of resonant propagating modes in periodic arrays of triangular-shaped nanowires. Moreover, we found that resonant plasmonic quasi-Bloch modes are efficiently excited with the fundamental TM mode of a dielectric waveguide placed underneath the array. The integrated plasmonic structure allows a strong enhancement of the electromagnetic field at the tip of the nanowires, hence its potential application in the development of new nanophotonic devices.

Bloch mode spatial harmonic decomposition in integrated localized surface plasmon chain

We consider a gold nanoparticle chain integrated on a dielectric waveguide. With appropriate geometrical parameters, such a chain behaves as a waveguide. We show that the spatial harmonics generated in the sub-wavelength periodic structure can be locally separated or extracted. This is done by playing with the phase matching condition of the coupling with the dielectric waveguide: only the fundamental component is locally cancelled in the periodic structure, resulting in a non-monotone phase evolution along the structure. Additionnally we show that the analysis of spatial harmonics allows extracting more information on the localized surface plasmon mode generation.

Optical near field imaging of localized surface plasmons modes in metallic nanostructures integrated on dielectric waveguides

The study of surface plasmon-polaritons interactions in metallic nanostructures has been a topic of interest during last years due to their use in various areas such as the photonics, chemistry and biology. Example of use is found in biosensors for the efficient detection of biological analyte and in nanophotonic elements for on-chip photonics. Here, we study the interactions properties of localized surface plasmons in a hybrid waveguiding structure made of bi-dimensional array of gold nanowires vertically integrated on silicon-on-insulator waveguides across the near infrared spectrum. With the use of near-field scanning optical microscopy (NSOM) in perturbation mode, we qualitatively obtained the spectral response of such hybrid structure through intensity near field maps of the light propagation. These experimental results demonstrate that metallic nanostructures integrated on silicon are suitable for the development of localized surface plasmon integrated devices or metallic metamaterials.

Modal analysis of LSP propagation in an integrated chain of gold nanowires

Light propagation in an integrated chain of metallic nanowires (MNW) is theoretically investigated by means of rigorous coupled wave analysis. First, we analyze the nanowires chain immersed in a dielectric homogeneous medium and we compute the eigenmodes dispersion relation and their field profiles. Depending on the nanowire aspect ratio, in addition to the longitudinal and the transversal chain modes, we found a new mode characterized by quadrupolar-like localized surface plasmons resonances well identified at the edge of the first Brillouin zone. We then consider the vertical coupling of the MNW chain with the fundamental TM0 mode of a planar dielectric waveguide. We demonstrate that high energy transfer can be obtained, by computing near field maps and spectral responses (transmission, reflection, and absorption) of the structure consisting in a finite number of nanowires. The coupling mechanism between the dielectric waveguide and the MNW chain is rigorously explained through the analysis of the eigenmodes dispersion relation.

Light propagation in metallic nanoparticle chains on SOI waveguide

In this work, we demonstrate successful interfacing between metallic nanoparticle (MNP) chain supporting localized surface plasmons (LSP) and silicon-on-insulator (SOI) waveguides. We show that the optical energy carried by a TE SOI waveguide mode at telecom wavelengths can be efficiently transferred into MNP chains deposited on the waveguide top, whatever the number of metallic particles (from 5 to 50). Especially in short chains, most of the energy can be transferred into the fourth or fifth MNP of the chains. Predictions from theoretical models are fully corroborated by transmission and near-field measurements.