Near-field light focusing by wavelength-sized dielectric spheroids for photovoltaic applications

We explore the near-field concentration properties of dielectric spheroidal scatterers with sizes close to the wavelength, using an analytical separation-of-variables method. Such particles act as mesoscopic lenses whose physical parameters are optimized here for maximum scattered light enhancement in photovoltaic applications.

Influence of laser wavelength on Laser-Fired contacts for crystalline silicon solar cells

In the Laser-Fired Contact (LFC) process, a laser beam fires a metallic layer through a dielectric passivating layer into the silicon wafer to form an electrical contact with the silicon bulk [1]. This laser technique is an interesting alternative for the fabrication of both laboratory and industrial scale high efficiency passivated emitter and rear cell (PERC). One of the principal characteristics of this promising technique is the capability to reduce the recombination losses at the rear surface in crystalline silicon solar cells. Therefore, it is crucial to optimize LFC because this process is one of the most promising concepts to produce rear side point contacts at process speeds compatible with the final industrial application. In that sense, this work investigates the optimization of LFC processing to improve the back contact in silicon solar cells using fully commercial solid state lasers with pulse width in the ns range, thus studying the influence of the wavelength using the three first harmonics (corresponding to wavelengths of 1064 nm, 532 nm and 355 nm). Previous studies of our group focused their attention in other processing parameters as laser fluence, number of pulses, passivating material [2, 3] thickness of the rear metallic contact [4], etc. In addition, the present work completes the parametric optimization by assessing the influence of the laser wavelength on the contact property. In particular we report results on the morphology and electrical behaviour of samples specifically designed to assess the quality of the process. In order to study the influence of the laser wavelength on the contact feature we used as figure of merit the specific contact resistance. In all processes the best results have been obtained using green (532 nm) and UV (355 nm), with excellent values for this magnitude far below 1 mΩcm2.

Band gap control via tuning of inversion degree in CdIn2S4 spinel

Based on theoretical arguments, we propose a possible route for controlling the band-gap in the promising photovoltaic material CdIn2S4. Our ab initio calculations show that the experimental degree of inversion in this spinel (fraction of tetrahedral sites occupied by In) corresponds approximately to the equilibrium value given by the minimum of the theoretical inversion free energy at a typical synthesis temperature. Modification of this temperature, or of the cooling rate after synthesis, is then expected to change the inversion degree, which in turn sensitively tunes the electronic band-gap of the solid, as shown here by screened hybrid functional calculations.

Top-Hat HELLISH-VCSOA for optical amplification and wavelength conversion for 0.85 to 1.3ìm operation

The Top-Hat hot electron light emission and lasing in semiconductor heterostructure (HELLISH)-vertical cavity semiconductor optical amplifier (VCSOA) is a modified version of a HELLISH-VCSOA device. It has a shorter p-channel and longer n-channel. The device studied in this work consists of a simple GaAs p-i-n junction, containing 11 Ga0.35In0.65 N0.02As0.08/GaAs multiple quantum wells in its intrinsic region; the active region is enclosed between six pairs of GaAs/AlAs top distributed Bragg reflector (DBR) mirrors and 20.5 pairs of AlAs/GaAs bottom DBR mirrors. The operation of the device is based on longitudinal current transport parallel to the layers of the GaAs p-n junction. The device is characterised through I-V-L and by spectral photoluminescence, electroluminescence and electro-photoluminescence measurements. An amplification of about 25 dB is observed at applied voltages of around V = 88 V.

Nondestructive quantification of chemical and physical properties of fruits by time-resolved reflectance spectroscopy in the wavelength range 650-1000 nm

Time-resolved reflectance spectroscopy can be used to assess nondestructively the bulk (rather than the superficial) optical properties of highly diffusive media. A fully automated system for time-resolved reflectance spectroscopy was used to evaluate the absorption and the transport scattering spectra of fruits in the red and the near-infrared regions. In particular, data were collected in the range 650-1000 nm from three varieties of apples and from peaches, kiwifruits, and tomatoes. The absorption spectra were usually dominated by the water peak near 970 nm, whereas chlorophyll was detected at 675 nm. For ail species the scattering decreased progressively with increasing wavelength. A best fit to water and chlorophyll absorption line shapes and to Mie theory permitted the estimation of water and chlorophyll content and the average size of scattering centers in the bulls; of intact fruits.

Tuning the properties of carbon fiber-reinforced poly (phenylene sulphide) laminates via incorporation of inorganic fullerene-like WS2 nanoparticles

Novel carbon fiber (CF)-reinforced poly(phenylene sulphide) (PPS) laminates incorporating inorganic fullerene-like tungsten disulfide (IF-WS2) nanoparticles were prepared via melt-blending and hot-press processing. The influence of the IF-WS2 on the morphology, thermal, mechanical and tribological properties of PPS/CF composites was investigated. Efficient nanoparticle dispersion within the matrix was attained without using surfactants. A progressive rise in thermal stability was found with increasing IF-WS2 loading, as revealed by thermogravimetric analysis. The addition of low nanoparticle contents retarded the crystallization of the matrix, whereas concentrations equal or higher than 1.0 wt% increased both the crystallization temperature and degree of crystallinity compared to those of PPS/CF. Mechanical tests indicated that with only 1.0 wt% IF-WS2 the flexural modulus and strength of PPS/CF improved by 17 and 14%, respectively, without loss in toughness, ascribed to a synergistic effect between the two fillers. A significant enhancement in the storage modulus and glass transition temperature was also observed. Moreover, the wear rate and coefficient of friction strongly decreased, attributed to the lubricant role of the IF-WS2 combined with their reinforcing effect. These inorganic nanoparticles show great potential to improve the mechanical and tribological properties of conventional thermoplastic/CF composites for structural applications.

Sentence selection for improving the tuning process of a statistical machine translation system

Este artículo describe una estrategia de selección de frases para hacer el ajuste de un sistema de traducción estadístico basado en el decodificador Moses que traduce del español al inglés. En este trabajo proponemos dos posibilidades para realizar esta selección de las frases del corpus de validación que más se parecen a las frases que queremos traducir (frases de test en lengua origen). Con esta selección podemos obtener unos mejores pesos de los modelos para emplearlos después en el proceso de traducción y, por tanto, mejorar los resultados. Concretamente, con el método de selección basado en la medida de similitud propuesta en este artículo, mejoramos la medida BLEU del 27,17% con el corpus de validación completo al 27,27% seleccionando las frases para el ajuste. Estos resultados se acercan a los del experimento ORACLE: se utilizan las mismas frases de test para hacer el ajuste de los pesos. En este caso, el BLEU obtenido es de 27,51%.

Two-wavelength switching with a distributed-feed back semiconductor optical amplifier (DFBSOA)

Switching of a signal beam by another control beam at different wavelength is demonstrated experimentally using the optical bistability occurring in a 1.55 mm-distributed feedback semiconductor optical amplifier (DFBSOA) working in reflection. Counterclockwise (S-shaped) and reverse (clockwise) bistability are observed in the output of the control and the signal beam respectively, as the power of the input control signal is increased. With this technique an optical signal can be set in either of the optical input wavelengths by appropriate choice of the powers of the input signals. The switching properties of the DFBSOA are studied experimentally as the applied bias current is increased from below to above threshold and for different levels of optical power in the signal beam and different wavelength detunings between both input signals. Higher on-off extinction ratios, wider bistable loops and lower input power requirements for switching are obtained when the DFBSOA is operated slightly above its threshold value.

Electron temperature versus laser intensity times wavelength squared: a comparison of theory and experiments

The peak temperature in the corona of plasma ejected by a laser-irradiated slab is discussed in terms of a one-electron-temperature model. Both heat-flux saturation and pulse rise-time effects are considered;the intensity in the rising half of the pulse is approximated by a linear function of time, I(t) = Iot/r. The temperature is found to be proportional to (IQX2)273 and a function of I0X4/r. Above a certain value of I0X4/T, the plasma presents two characteristic temperatures (at saturation and at the critical surface) which can be identified with experimentally observed cold- and hot-electron temperatures. The results are compared with extensive experimental data available for both nd and CO2 lasers, I0(W'cnf2) X2 (/um) starting around 1012. The agreement is good if substantial flux inhibition is assumed (flux-limit factor f = 0.03), and fails for I0X2 above 1O1S. Results for both ablation pressure and mass ablation rate are also given.

Wavelength monitoring with semiconductor laser amplifiers

The semiconductor laser diodes that are typically used in applications of optical communications, when working as amplifiers, present under certain conditions optical bistability, which is characterized by abruptly switching between two different output states and an associated hysteresis cycle. This bistable behavior is strongly dependent on the frequency detuning between the frequency of the external optical signal that is injected into the semiconductor laser amplifier and its own emission frequency. This means that small changes in the wavelength of an optical signal applied to a laser amplifier causes relevant changes in the characteristics of its transfer function in terms of the power requirements to achieve bistability and the width of the hysteresis. This strong dependence in the working characteristics of semiconductor laser amplifiers on frequency detuning suggest the use of this kind of devices in optical sensing applications for optical communications, such as the detection of shifts in the emission wavelength of a laser, or detect possible interference between adjacent channels in DWDM (Dense Wavelength Division Multiplexing) optical communication networks

Tuning the current ratio of a CPV system to maximize the energy harvesting in a particular location

A method based on experimental data is proposed to optimize the energy harvesting of a silicone-on-glass Fresnel-lens based CPV system. It takes into account the spectral variations along the year in a particular location as well as the thermal and spectral sensitivities of the optics and solar cell. In addition, different alternatives to tune the top/middle subcells current ratio in a CPV module are analyzed and their capacity to maximize the annually produced energy is quantified.

Self-Tuning PID controller for autonomous car tracking in urban traffic

In this paper an on line self-tuned PID controller is proposed for the control of a car whose goal is to follow another one, at distances and speeds typical in urban traffic. The bestknown tuning mechanism is perhaps the MIT rule, due to its ease of implementation. However, as it is well known, this method does not guarantee the stability of the system, providing good results only for constant or slowly varying reference signals and in the absence of noise, which are unrealistic conditions. When the reference input varies with an appreciable rate or in presence of noise, eventually it could result in system instability. In this paper an alternative method is proposed that significantly improves the robustness of the system for varying inputs or in the presence of noise, as demonstrated by simulation.

Proposal for a Wavelength Multiplexed Quantum Metropolitan Area Network

Quantum Key Distribution (QKD) is maturing quickly. However, the current approaches to its network use require conditions that make it an expensive technology. All the QKD networks deployed to date are designed as a collection of dedicated point-to-point links that use the trusted repeater paradigm. Instead, we propose a novel network model in which QKD systems use simultaneously quantum and conventional signals that are wavelength multiplexed over a common communication infrastructure. Signals are transmitted end-to-end within a metropolitan area using optical components. The model resembles a commercial telecom network and takes advantage of existing components, thus allowing for a cost-effective and reliable deployment.

Quantum metropolitan optical network based on wavelength division multiplexing

Quantum Key Distribution (QKD) is maturing quickly. However, the current approaches to its application in optical networks make it an expensive technology. QKD networks deployed to date are designed as a collection of point-to-point, dedicated QKD links where non-neighboring nodes communicate using the trusted repeater paradigm. We propose a novel optical network model in which QKD systems share the communication infrastructure by wavelength multiplexing their quantum and classical signals. The routing is done using optical components within a metropolitan area which allows for a dynamically any-to-any communication scheme. Moreover, it resembles a commercial telecom network, takes advantage of existing infrastructure and utilizes commercial components, allowing for an easy, cost-effective and reliable deployment.