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.
In this work, we revisit the operation principles of Bragg reflectors assisted directional couplers. We show that an
efficient narrow band forward coupling operation can be achieved by an appropriate engineering of the Bragg grating
waveguides dispersion properties.
Our theoretical analysis reveals the existence of a minimum Bragg grating coupling strength for co-directional phase
matching. This threshold coupling condition is an essentially new aspect of Bragg grating asymmetric directional
couplers as compared to conventional co-directional couplers and Bragg reflectors. The threshold condition is
analytically determined, and a coupled mode theory four-wave model is successfully applied to describe the behavior of
the investigated device.
It is shown that the optimal operation is achieved with only one Bragg grating distributed along one of the two
waveguides. A numerical validation of the results of coupled mode theory is performed for the case of shallow-etched
Silicon on Insulator (SOI) ridge waveguides with Bragg grating assisted coupling. The selectivity is a factor of 5.5 higher
than that obtained in the conventional approach of asymmetric directional couplers where III-V waveguides with
different alloy compositions are coupled vertically. The proposed design is shown to be compatible with existing micronano-
fabrication technology.
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.
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).
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.
Magneto photonic crystals exhibit unique combination of
magneto-optical nonreciprocity and resonant behavior
originating from periodic structure. Modeling of magneto photonic structures requires inclusion of magnetic induced
anisotropy and description of medium using a permittivity tensor. On the other hand, differential theory of periodic
gratings based on Fourier expansion of permittivity tensor and electromagnetic field is recently frequently applied. In
this paper we propose an approach of effective propagation constant calculation from scattering matrix of the waveguide
consisting of the anisotropic magneto-optical lamellar grating. The structure is modeled using Rigorous Coupled Wave
Analysis (RCWA) extended by Fourier factorization method. The approach is applied to optimize parameters of
integrated magneto-optic waveguide isolator with lamellar grating from magneto-optic medium at transverse geometry.
Silicon is the basic material for the microelectronics industry. The predicted limits for electrical interconnects in electronic circuits favor the development of alternative solutions such as optical interconnects to transfer information. The silicon-based components are an alternative to realise these interconnections, providing that high speed and high efficiency integrated optoelectronic devices can be realized. In this work, we have fabricated two-dimensional photonic crystal (PC) microcavities on silicon-on-insulator (SOI). The samples contain self-assembled Ge/Si islands deposited in the upper silicon layer by chemical vapor deposition. The silicon layer thickness measures 0.3 mm. The photonic crystals consist of triangular lattices of air holes etched in the upper silicon layer of the SOI substrate. The period lattice measures 0.5 μm and the drilled holes had diameters between 0.3 and 0.45 μm. These structures exhibit a forbidden band around 1.3 - 1.5 μm in TE polarisation. Different photonic crystal hexagonal microcavities were processed and the optical properties are probed at room temperature with the Ge/Si island photoluminescence. Quality factors larger than 200 are measured for hexagonal microcavities. On the one hand, the presence of the PC improves the vertical extraction of light, and on the other hand, we show that a significant enhancement of the Ge/Si island photoluminescence (x 100) can be achieved in the 1.3 - 1.55 μm spectral region using the microcavities. These attractive results should allow to realise efficient light emitting-diodes in the near infrared.
Due to its very short carrier lifetime and its absorption window in the 1550nm spectral range, ion-irradiated InGaAs is a material of choice for opto-electronic telecommunication systems. Ion irradiated-InGaAs is a well adapted material for realizing fast saturable absorbers and fast photoconductive antennas. However, to our knowledge, no detailed experimental study has been reported on the thermal stability of ion-irradiated InGaAs. Post-irradiation annealing of such a material is required to enhance opto-electrical response, and the thermal stability of irradiated devices. Moreover, the study of annealing kinetics provides useful information about the nature of defects and their initial distribution. The carrier lifetime, the mobility and the residual carrier concentration versus anneal in heavy(Au+) and light(H+) ion-irradiated InGaAs samples have been measured. The defect annealing kinetics observed in proton-irradiated samples is described well by a Frenkel pair recombination model, thereby indicating the dominance of isolated point defects. In contrast, the model is not adapted to describe the thermal behavior of Au+-irradiation-induced defects that are clusters of point defects as observed via Transmission Electronic Microscopy. A higher thermal stability for the components based on Au+-irradiated InGaAs than on H+-irradiated ones is then expected.
The far infrared behavior of doped semiconductors is dominating by the free carrier response and it is well described by the simple Drude model. As the free carriers can be photogenerated in high resistivity semiconductors, the electromagnetic response of these semiconductors can be changed, via laser excitation, from a dielectric behavior to a metallic one. Using terahertz time-domain spectroscopy, we have checked this Drude-like behavior with several silicon wafers of different doping, and with a high resistivity silicon sample photo-excited by a Ti:Sa laser beam. Then we benefited of this effect to photo-modify the transmission of a photonic band-gap crystal in the terahertz range. The photonic band-gap crystal is a woodpile structure, which exhibits a complete forbidden band around 265 GHz. Silicon- made defects are introduced in interstitial sites of the lattice of the photonic crystal in order to create a defect mode inside the photonic band-gap of the crystal. This defect mode then acts as a narrow bandpass filter at the frequency of 253 GHz. Under 400-mW laser excitation power, the resonance peak associated to the defect mode completely vanishes.
We report a low cost and material independent fabrication technique to reproduce sub-millimeter 3D photonic crystals. The crystal is made by stacking mechanically machine dielectric substrates. Interstitial defects can be introduced in the structures. This technique is illustrated by experimental studies with highly resistive silicon based crystals with and without defects. A terahertz time-domain spectroscopy set-up is used for broad band transmission characterization of the crystals. Systematic measurements of the transmission characteristics for different crystal thicknesses and incident angles were performed. A wide compete photonic band gap centered at 265 GHz with a 19 percent band-gap to mid-gap frequency ratio, and excellent filtering properties are observed with only six crystal periods. The influence of the defects was experimentally studied and an external control of their mode's transmission coefficients is demonstrated. The transmission coefficient of the defect modes is controlled by illuminating the interstitial silicon defects with a 330 mW laser beam. Numerical simulations reproduce this behavior by modeling the illumination as an increase of the defect absorption.
A new type of semiconductor unipolar laser operating in the mid-infrared spectral region, the Quantum Fountain intersubband laser, is demonstrated. It is based on optical pumping of a three-bound-state coupled quantum well structure in the GaAs/AlGaAs material system. The lasing transition occurs between the two excited states. Population inversion can be achieved by benefitting from LO-phonon resonance between the two lower subbands. The optical pumping scheme enables a simpler design of the active region than electrically pumped intersubband lasers. Moreover, because doped layers and metallic contacts are not necessary for the operation of the Quantum Fountain laser, free-carrier and plasmon absorptions can be minimised, thus allowing long- wavelength operation. Large optical gains are measured using pump-probe experiments with a free-electron laser. Lasing action under optical pumping by a pulsed CO2 laser has been achieved at a record long wavelength of 15.5 micrometer with an output peak power of the order of 0.6 W at low temperatures.
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