71 research outputs found
Phase recovery by using optical fiber dispersion and pulse pre-stretching
No full textIn this work, the applicability of a recently proposed phase recovery technique is extended, by using temporal pulse pre-stretching. As a proof of concept, the light pulses emitted by a two-stage laser system consisting of a sub-picosecond passively mode-locked fiber laser followed by an erbium-doped fiber amplifier were experimentally analyzed. These results were successfully compared with two indirect phase recovery techniques, both based on the Gerchberg–Saxton recursive algorithm and with the intensity autocorrelation when sub-picosecond light pulses were analyzed.Fil: Cuadrado Laborde, Christian Ariel. Universidad de Valencia. Departamento de Física Aplicada y Electromagnetismo; España. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Rosario. Instituto de Física de Rosario (i); ArgentinaFil: Brotons Gisbert, M.. Universidad de Valencia. Departamento de Física Aplicada y Electromagnetismo; EspañaFil: Serafino, G.. Scuola Superiore Sant’Anna. TeCIP Institute; ItaliaFil: Bogoni, A.. Inter-university National Consortium for Telecommunications. National Laboratory of Photonic Networks; ItaliaFil: Pérez Millán, P.. Universidad de Valencia. Departamento de Física Aplicada y Electromagnetismo; España. FYLA LASER SL.; EspañaFil: Andres, M. V.. Universidad de Valencia. Departamento de Física Aplicada y Electromagnetismo; Españ
An Impact Study of the Economic Partnership Agreements (EPAs) in the Six ACP Regions
No full textThis article intends to present a very detailed analysis of the trade-related aspects of Economic Partnership Agreements (EPAs) negotiations. We use a dynamic partial equilibrium model – focusing on the demand side – at the HS6 level (covering 5,113 HS6 products). Two alternative lists of sensitive products are constructed, one giving priority to the agricultural sectors, the other focusing on tariff revenue preservation. In order to be WTO compatible, EPAs must translate into 90 percent of bilateral trade fully liberalised. We use this criterion to simulate EPAs for each negotiating regional block. ACP exports to the EU are forecast to be 10 percent higher with the EPAs than under the GSP/EBA option. On average ACP countries are forecast to lose 70 percent of tariff revenues on EU imports in the long run. Yet imports from other regions of the world will continue to provide tariff revenues. Thus when tariff revenue losses are computed on total ACP imports, losses are limited to 26 percent on average in the long run and even 19 percent when the product lists are optimised. The final impact on the economy depends on the importance of tariffs in government revenue and on potential compensatory effects. However this long term and less visible effect will mainly depend on the capacity of each ACP country to reorganise its fiscal base.Preferential Trade Agreements, Africa, EPAs, Partial Equilibrium Simulations, International Relations/Trade,
Magnetic Characterization Of The Mechanically Induced Thermite Reaction Between Fe2o3 And Al
No full textWe have investigated the mechanically induced self-propagating reaction between Fe2O3 and Al. In this reaction the final phases, Al2O3 and Fe, are formed by an in situ chemical reaction. The evolution of the system was characterized as a function of the milling time using X-ray diffraction, magnetometry (300 and 5 K) and Mössbauer spectroscopy (300 and 77 K). After reaction, Fe particles in a crystalline Al2O3 matrix have been formed. At larger milling times, a rather wide Fe grain size distribution of around 20 nm was obtained according to the diffraction patterns. Mössbauer spectra were constituted of both paramagnetic and ferromagnetic contributions. The former was attributed to small grains of superparamagnetic Fe (within the Mössbauer characteristic time τM ≈ 10-8s) and FeAl2O4, whereas the latter was associated to larger Fe grains. Saturation magnetization, coercivity field and remanent magnetization rapidly reached a stationary value with the milling time. A correlation between the microstructural characteristics of the sample and its magnetic properties before and after reaction is described. © 2004 Elsevier B.V. All rights reserved.3541-4 SPEC. ISS.125128Pardavi-Horvath, M., (1992) IEEE Trans. Magn., 28, p. 3186Meiklejohn, W.H., (1953) Rev. Mod. Phys., 25, p. 302Giri, A.K., (1997) Mater. Res. Bull., 32, p. 523Cuadrado-Laborde, C., (2001) Hyperfine Interactions, 134, p. 131Stewart, S.J., (2003) J. Magn. Magn. Mater., 260, p. 447Raming, T.P., (2002) J. Colloid. Interf. Sci., 249, p. 346C. Cuadrado-Laborde, et al., submittedMurad, E., (1981) Mössbauer Spectroscopy Applied to Inorganic Chemistry: Iron Oxides and Oxyhydroxides, pp. 507-582. , G.J. Long (Ed.), Plenum, Netherland
Introductory Chapter: Application of Optical Fiber for Sensing
No full text1. Introduction
The history of the use of optical fiber for sensing applications began with two
different, but interrelated, discoveries: laser light and optical fibers. The first laser
was built in 1960 by T. H. Maiman at Hughes Research Laboratories, based on the
theoretical work by C. H. Townes and A. L. Schawlow. A laser provides a source
of an intense coherent light, highly collimated, and quasi-monochromatic; its
potential for data transfer was immediately envisaged. Naturally, first experiments
involved the transmission of the laser beam through the air. However, a communication
channel cannot be practically sustained propagating freely through
the air, owing to atmospheric attenuation and weather influence. Researchers also
conducted experiments by transmitting the laser beam through glass fibers, which
soon became the preferred medium for transmission of light. First, optical fibers
were not practical to sustain a communication channel mainly due to the presence
of impurities in the fiber material, resulting in very high transmission losses
(>1000 dB/km), until Corning presented at the beginning of the 1970s optical
fibers with (in comparison) very lower transmission losses, with only a few dB/km.
Today, typical transmission losses are below 0.2 dB/km. This represents an extraordinary
improvement as compared with electrical signal transmission through
coaxial cables, not to mention the wider bandwidth available, which is several
orders of magnitudes higher
Long-period fiber gratings in active fibers
No full textTraditionally, long period fiber gratings (LPG) are made in passive optical fibers that have negligible loss. However, loss or gain that can be controlled via optical pumping adds a new degree of freedom and - as will be shown in this chapter - brings many new and interesting properties. From the historical perspective, the first attempt to combine the fiber gain and LPG filtering characteristics was for gain flattening of an Erbium-doped fiber (EDF) amplifier by inscribing LPG directly into the active fiber [1]. At the same time, theoretical studies [2,3] showed that a proper level of loss/gain in the fiber core or cladding can modify the LPG transmission characteristics. Significant theoretical and experimental body of work has been published since with new emerging applications appearing. In this chapter, we investigate the new phenomena brought by the presence of the loss/gain [2,3]. Following this, we look on practical possibilities how to obtain required gain in active optical fibers and show how to analyze such structures, in which (incoherent) noise from an amplifying fiber is simultaneously generated and diffracted at the LPG [4]. Finally, we discuss possible application of the LPG in active fibers
Yb-doped strictly all-fiber laser actively Q-switched by intermodal acousto-optic modulation
No full textWe show an actively Q-switched ytterbium-doped strictly all-fiber laser. Cavity loss modulation is achieved in a tapered optical fiber by core-to-cladding mode-coupling induced by travelling flexural acoustic waves. When the acoustical signal is switched-off, the optical power losses within the cavity are reduced, and then a laser pulse is emitted. Trains of Q-switched pulses were successfully obtained at repetition rates in the range 1-10 kHz, with pump powers between 59 and 88 mW, at the optical wavelength of 1064.1 nm. Best results were for laser pulses of 118 mW peak power, 1.8 μs of time width, with a pump power of 79 mW, at 7 kHz repetition rate.Fil: Villegas García, Irma Lorena. Universidad de Valencia; España. Centro de Investigaciones en Optica; MéxicoFil: Cuadrado Laborde, Christian Ariel. Universidad de Valencia; España. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - La Plata. Centro de Investigaciones Ópticas. Provincia de Buenos Aires. Gobernación. Comisión de Investigaciones Científicas. Centro de Investigaciones Ópticas. Universidad Nacional de La Plata. Centro de Investigaciones Ópticas; ArgentinaFil: Díez, Antonio. Universidad de Valencia; EspañaFil: Cruz, Jose Luis. Universidad de Valencia; EspañaFil: Martínez Gámez, M. A.. Centro de Investigaciones en Óptica; MéxicoFil: Andrés Bou, Miguel Vicente. Universidad de Valencia; Españ
Bragg grating based integrated photonic Hilbert transformers
No full textPlanar Bragg grating based photonic Hilbert transformers are experimentally demonstrated in this work. Planar Bragg gratings are utilized to implement a general Hilbert transform, a fractional order Hilbert transform and terahertz bandwidth Hilbert transforms, using a direct UV grating writing technique in a silica-on-silicon platform. The design, fabrication and integration of the proposed devices are discussed and presented. The photonic Hilbert transformers could be further monolithically integrated with flat top reflectors and interferometric structures, implementing all-optical single-sideband filter
Proposal of time-resolved chirp-measurement through all-optical in-fiber mathematical operators
No full textWe propose a simple technique to measure in the time domain the magnitude of frequency chirp of high-speed temporal complex waveforms. The technique relies in the properties of three time-domain chirp-sensitive operations: the Hilbert transform, the integration, and the differentiation, all of them analyzed in its integer and fractional counterpart. The implementation of these operations through fiber Bragg gratings is also discussed. We numerically prove the viability of this technique.Facultad de Ingenierí
Ball milling sound statistical analysis and its relationship with the mechanical work intensity
No full text- …
