KEYWORDS: Nanostructures, Waveguides, Radio propagation, Geometrical optics, Near field optics, Silicon, Near field scanning optical microscopy, Surface plasmons, Wave propagation, Nanowires
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.
The transformation optics was introduced by J. Pendry and U. Leonhardt in 2006 [1,2]. In this method an initial space is transformed into a new space and this transformed space can be materialized by a material, which the electromagnetic parameters can be deduced from the metric of the transformed space. In the general case the electromagnetic parameters are anisotropic tensors. At microwave frequencies these materials can be realized using classical metamaterials like SRR form J. Pendry or ELC from D. Smith [3]. At infrared wavelengths this realization is a challenge because the dimensions of the metamaterials are much smaller than the wavelength and become nanometric. Then the design of these metamaterials must be simplified and original methods must be developed to allow the realization of these metamaterials with controlled electromagnetic properties. In this paper we describe the realization of a multilayer metamaterial working at infrared wavelength, which the permittivity and the permeability can be adjusted separately. We give some examples of realized multilayer materials operating around 150THz, with a comparison between the results of full wave simulations of these materials and their characterizations using a Fourier Transform Infrared Spectrometer.
KEYWORDS: Waveguides, Metamaterials, Near field scanning optical microscopy, Silicon, Near field optics, Dielectric polarization, Light wave propagation, Dielectrics, Interfaces
We address the experimental validation of the technological feasibility and operation of the metamaterials in a guided wave configuration in the spectral domain around 1.5μm. For our experiments we considered a 2D array of 200×50×50nm gold cut wires placed on the top of a 10μm wide and 200nm thick silicon waveguide. The transmission spectral measurements performed in the spectral range between 1.25 and 1.64μm using an end-fire coupling setup, revealed a marked dip for TE polarized light, corresponding to the cut wires resonance frequency obtained by numerical modeling. No such a dip in transmission was observed for TM polarized light, i.e. when the electric filed is perpendicular to the layers interface and the orientation of the cut wires. The scanning near field optical microscopy experiments (SNOM), performed in the same spectral range, revealed for TE polarized light a strong enhancement of the electric field confined in the region between the ends of the adjacent cut wires. These results confirm the efficient excitation of the cut wires resonance in a guided wave configuration for the TE polarization. The ability for local engineering of the field interaction with the metamaterial layer and thus the control in such a way of the light flow in a guiding slab, paves the way to a novel class of photonic devices.
We investigate the potential of metallic metamaterials (MM) for integrated optic applications in the
near-infrared (λ=1.5μm). Specifically we consider a composite guiding structure made of a MM layer
over a high index slab waveguide such as silicon. In this configuration only the evanescent tail
interacts with the MM layer which acts essentially as a perturbation. Our numerical simulations show
that an array of gold coupled cut wires over a slab waveguide leads to a significant variation of the slab
effective index in the vicinity of the resonance and thus can serve as building blocks for implementing
optical functions. This geometry is compatible with current nano-fabrication technologies.
Metamaterials building blocks, from microwave to optical range are mainly based on metal-dielectric
composite. In almost all structures with true negative index (not coming from
losses) two kind of meta-atoms (electric and magnetic) are mixed in order to drive
simultaneously the effective permittivity and permeability to negative values and thus to
obtain a negative index of refraction. In this paper we show that two coupled structures with
localized plasmons modes (e.g. Cut wires or Split-Ring-Resonators) can exhibit negative
refractive index by their own, by appropriately controlling the hybridization scheme of the so
called plasmons modes. As a result, the metallic filling factor is drastically reduced and low
losses especially at optical frequencies may allow realistic applications of metamaterials.
Man made artificial materials or metamaterials have attracted in the recent years a huge amount of
interest owing to their potentials applications. Among these, we can cite perfect lens [1], hyper lens
[2], electromagnetic cloak [3-7] and applications in non linear and/or guided optics [9-10]. In this
paper we present and review some applications of infrared metallo- dielectric metamaterials
developed in our group including the design of novel low loss negative index metamaterials, realistic
cloaking in the infrared [7], sensing [8-9] and applications in non linear and/or guided optics [9-10]
The basic physics of each presented application is reviewed and the use of these applications on
functional photonic device is discussed.
Metamaterials in infrared and optical domain are mainly based on metal-dielectric composite.
Collective excitations also called surface plasmons are thus the main mechanism in infrared
metamaterials structures. Taking profit of the plasmonic interpretation instead of LC circuit
approaches (better suited for microwave experiment) new approaches in understanding and
engineering resonances is possible. In this paper we show numerically and experimentally
how certain metamaterials can open opportunities in the engineering of plasmonic modes at
the nanoscale for application including sensing and SERS (surface enhanced Raman
Spectroscopy).
Metamaterials have attracted much interest since their realization by Smith et al. [2]. A few research teams all other the
world are making them a reality in the infrared and optical regime. Following the theoretical study of C. Rockstuhl et al.
[4], we have fabricated various metamaterial structures derived from the combination of SRR (Split Ring Resonators)
and nano-continuous wires by diminishing the size of the legs of the SRR perpendicular to the gap. This geometrical
transformation shown in the SEM (scanning electron microscope) pictures of figure 1 allows an experimental
understanding of the origin of resonances in metamaterials under normal incidence. The fabrication was performed by e-beam
lithography, gold on silicon. Simulations were performed using a Drude model of the electromagnetic permittivity
of gold. Both measurement and simulation results lead to an accurate analyze of the plasmonic resonances of the
metamaterial and open the way to their control in infrared metamaterials under normal to plane propagation.
Since the event of metamaterials, a considerable effort has been performed to fabricate them in the infrared and optical
regimes. However, apart from the experimental demonstration and observation of H. J. Lezec et al based on surface
plasma polariton, direct visualisation of negative refraction based on metal-dielectric resonances have not been
performed experimentally so far in the infrared or visible regime (photonic crystals with periodicity on the order of the
wavelength are not considered here). Very often only simulations have given the needed phase information for the
retrieval methods in optical experiments. In this paper, a metamaterial composed of SRR (Split Ring Resonators) and a
continuous wire is considered. We extract the phase information from the transmission and the reflection measurements
through a diffraction grating made of the metamaterial to be characterized and silicon or gold. This retrieval allows a
unambiguous retrieval of the effective parameters under conditions discussed in the paper at IR and visible wavelengths.
Dielectric substrates supporting planar periodic subwavelength metamaterial-based metallic arrays and presenting
frequency dispersive phase characteristics are applied to ultra-compact high-gain and high-directivity planar antennas. In
this paper, different models of metamaterial-based surfaces introducing a zero degree reflection phase shift to incident
waves are firstly studied numerically using finite-element method analysis where the bandwidth and operation frequency
are predicted. These surfaces are then applied in a resonant Fabry-Perot type cavity and a ray optics analysis is used to
design different models of ultra-compact high-gain microstrip printed antennas. Firstly, a cavity antenna of thickness
&lgr;/60 based on the use of a microstrip patch antenna and two bidimensional metamaterial-based surfaces, the first one
acting as a High Impedance Surface (HIS) and the second one acting as a Partially Reflecting Surface (PRS) is designed.
This cavity is then optimized for easier fabrication process and loss reduction by the use of only one bidimensionnal
composite metamaterial-based surface acting as a PRS. Secondly, another surface presenting a variable phase by the use
of a non periodic metamaterial-based metallic strips array is designed for a passive low-profile steering beam antenna
application. Finally, a switchable operation frequency cavity by the implementation of varicap diodes is designed and
fabricated. All these cavity antennas operate on subwavelength modes, the smallest cavity thickness being of the order of &lgr;/60.
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