Maite Volatier

Optical modes at the interface between two dissimilar discrete meta-materials

We have studied theoretically and experimentally the properties of optical surface modes at the hetero-interface between two meta-materials. These meta-materials consisted of two 1D AlGaAs waveguide arrays with different band structures.

Second harmonic generation in AlGaAs photonic wires using low power continuous wave light

We report modal phase matched (MPM) second harmonic generation (SHG) in high-index contrast AlGaAs sub-micron ridge waveguides, by way of sub-mW continuous wave powers at telecommunication wavelengths. We achieve an experimental normalized conversion efficiency of ~14%/W/cm2, obtained through a careful sub-wavelength design supporting both the phase matching requirement and a significant overlap efficiency. Furthermore, the weak anomalous dispersion, robust fabrication technology and possible geometrical and thermal tuning of the device functionality enable a fully integrated multi-functional chip for several critical areas in telecommunications, including wavelength (time) division multiplexing and quantum entanglement.

OBSERVATION OF ONE- AND TWO-DIMENSIONAL DISCRETE SURFACE SPATIAL SOLITONS

The recent theoretical predictions and experimental observations of discrete surface solitons propagating along the interface between a one- or two-dimensional continuous medium and a one- or two-dimensional waveguide array are reviewed. These discrete solitons were found in second order (periodically poled lithium niobate) and third order nonlinear media, including AlGaAs, photorefractive media and glass, respectively.

Optical spatial solitons at the interface between two dissimilar periodic media: theory and experiment

Discrete spatial solitons traveling along the interface between two dissimilar one-dimensional arrays of waveguides were observed for the first time. Two interface solitons were found theoretically, each one with a peak in a different boundary channel. One evolves into a soliton from a linear mode at an array separation larger than a critical separation where-as the second soliton always exhibits a power threshold. These solitons exhibited different power thresholds which depended on the characteristics of the two lattices. For excitation of single channels near and at the boundary, the evolution behavior with propagation distance indicates that the solitons peaked near and at the interface experience an attractive potential on one side of the boundary, and a repulsive one on the opposite side. The power dependence of the solitons at variable distance from the boundary was found to be quite different on opposite sides of the interface and showed evidence for soliton switching between channels with increasing input power.

Tuneable four-wave mixing in AlGaAs nanowires.

We have experimentally demonstrated broadband tuneable four-wave mixing in AlGaAs nanowires with the widths ranging between 400 and 650 nm and lengths from 0 to 2 mm. We performed a detailed experimental study of the parameters influencing the FWM performance in these devices (experimental conditions and nanowire dimensions). The maximum signal-to-idler conversion range was 100 nm, limited by the tuning range of the pump source. The maximum conversion efficiency, defined as the ratio of the output idler power to the output signal power, was -38 dB. In support of our explanation of the experimentally observed trends, we present modal analysis and group velocity dispersion numerical analysis. This study is what we believe to be a step forward towards realization of all-optical signal processing devices.

Through cell vias contacts for multijunction solar cells

The efficiency of multijunction solar cells used in concentrated photovoltaic systems is limited by shading from the grid line top electrode and electrical losses in the top epilayers. We propose to use through cell vias contacts to suppress the top electrode. Simulations show that the combination of through cell vias contacts with thin fingers has a potential absolute efficiency gain of 2 to 3% for concentration factors between 500 and 2000x. In addition, bus bars suppression improves by more than 20% the power extracted from a 6” wafer. Such an architecture requires additional technological steps. We discuss the challenges associated with via etching and report promising etching results for III-V heterostructures and germanium.

Plasma etching applications in concentrated photovoltaic cell fabrication

Photovoltaic cells are conventionally electrically isolated (isolation) and then separated from the wafer (singulation) by saw dicing at the end of the fabrication process. However, saw dicing presents limitations in terms of cell shapes and causes excessive material losses. We propose isolation and singulation by plasma etching as an alternative to saw dicing. The etching process proposed also allows via hole etching for through cell via contacts (TCVC) [1]. This technology uses isolated metallized vias to carry front-side generated carriers to the backside. This new architecture could increase the efficiency and increase the energy production per wafer for concentrated photovoltaic (CPV) cells. In this paper, those two plasma etching applications for CPV cell fabrication are discussed. More precisely, triple junction solar cells have been fabricated with either a plasma singulation or with via holes and compared with reference cells (without via hole and saw dicing singulation). One sun IV measurements,...

Nonlinear scattering and trapping by local photonic potentials

We experimentally study nonlinear scattering by local photonic potentials embedded in continuous Kerr media, and demonstrate nonlinear trapping in guiding potentials and resonant transmission in anti-guiding potentials. The results are verified by numerical simulations.

Impact of Via Hole Integration on Multijunction Solar Cells for Through Cell Via Contacts and Associated Passivation Treatment

The impact of via etching on triple junction solar cell performance has been investigated for through cell via contact architectures. Triple junction solar cells with standard top and back contacts have been fabricated and vias have been etched through the subcells to investigate the new geometry proposed. The external quantum efficiency, the open-circuit voltage (Voc), the fill factor (FF), and the ideality factor have been measured and compared to those of standard triple junction solar cells without vias. In this way, we evaluate the losses attributable to via etching. Small performance losses from via integration are observed, but performance can be partially restored with an ammonium sulfide passivation treatment. Furthermore, the results show that the V oc losses are almost absent at the high sun concentration that the new architecture is designed for. The source of the performance degradation is correlated with a larger total surface recombination at the edges of the device. The passivation treatment allows an effective surface passivation of the via holes.

Permanent bonding process for III-V/Ge multijunction solar cell integration

In this paper, we propose a process to permanently bond multi-junction solar cells (MJSCs) front side to a transparent superstrate using polydimethylsiloxane (PDMS). This process could allow for substrate handling during several fabrication schemes such as thin MJSCs, substrate lift-off /recycling or through cell via contacts (TCVC) solar cells. The developed process is compatible with standard microfabrication processes such as photolithography, etching or metallization. Permanent bonding of III-V/Ge triple junction solar cell on quartz superstrate has been used to handle the solar cell and to demonstrate a 20 µm thick TCVC device. No significant performance loss was observed on I-V characteristics for a bonded triple junction solar cell.In this paper, we propose a process to permanently bond multi-junction solar cells (MJSCs) front side to a transparent superstrate using polydimethylsiloxane (PDMS). This process could allow for substrate handling during several fabrication schemes such as thin MJSCs, substrate lift-off /recycling or through cell via contacts (TCVC) solar cells. The developed process is compatible with standard microfabrication processes such as photolithography, etching or metallization. Permanent bonding of III-V/Ge triple junction solar cell on quartz superstrate has been used to handle the solar cell and to demonstrate a 20 µm thick TCVC device. No significant performance loss was observed on I-V characteristics for a bonded triple junction solar cell.