609 research outputs found
Inhomogeneous Gain Saturation in EDF: Experiment and Modeling
Erbium-Doped Fiber Amplifiers can present holes in spectral gain in
Wavelength Division Multiplexing operation. The origin of this inhomogeneous
saturation behavior is still a subject of controversy. In this paper we present
both an experimental methods and a gain's model. Our experimental method allow
us to measure the first homogeneous linewidth of the 1.5 m erbium emission
with gain spectral hole burning consistently with the other measurement in the
literature and the model explains the differences observed in literature
between GSHB and other measurement methods
Photonic crystal-driven spectral concentration for upconversion photovoltaics
International audienceThe main challenge for applying upconversion (UC) to silicon photovoltaics is the limited amount of solar energy harvested directly via erbium-based upconverter materials (24.5 W m(-2)). This could be increased up to 87.7 W m(-2) via spectral concentration. Due to the nonlinear behavior of UC, this could increase the best UC emission by a factor 13. In this paper, the combined use of quantum dots (QDs)for luminescent down-shiftingand photonic crystals (PCs)for reshaping the emissionto achieve spectral concentration is shown. This implies dealing with the coupling of colloidal QDs and PC at the high-density regime, where the modes are shifted and broadened. In the first fabricated all-optical devices, the spectral concentration rises by 67%, the QD emission that matches the absorption of erbium-based upconverters increases by 158%, and the vertical emission experiences a 680% enhancement. Remarkably, the PC redshifts the overall emission of the QDs, which could be used to develop systems with low reabsorption losses. In light of this, spectral concentration should be regarded as one of the main strategies for UC photovoltaics
Photonic crystals and optical mode engineering for thin film photovoltaics
International audienceIn this paper, we present the design, analysis, and experimental results on the integration of 2D photonic crystals in thin film photovoltaic solar cells based on hydrogenated amorphous silicon. We introduce an analytical approach based on time domain coupled mode theory to investigate the impact of the photon lifetime and anisotropy of the optical resonances on the absorption efficiency. Specific design rules are derived from this analysis. We also show that, due to the specific properties of the photonic crystal resonances, the angular acceptance of such solar cells is particularly high. Rigorous Coupled Wave Analysis simulations show that the absorption in the a-Si:H active layers, integrated from 300 to 750nm, is only decreased from 65.7% to 60% while the incidence angle is increased from 0 to 55°. Experimental results confirm the stability of the incident light absorption in the patterned stack, for angles of incidence up to 50°
Absorption control in pseudodisordered photonic-crystal thin film
The positive effects of various perturbations introduced in a bidimensional
photonic-crystal patterned membrane on its integrated absorption are
investigated numerically and theoretically. Two phenomena responsible for the
enhanced absorption observed are identified: an increase of the spectral
density of modes, obtained thanks to folding mechanisms in the reciprocal
lattice, and a better coupling of the modes with the incident light. By
introducing a proper pseudodisordered pattern, we show that those two effects
can be exploited so as to overcome the integrated absorption obtained for an
optimized and single pattern unit cell photonic crystal
- …