M. A. Rebolledo

Bio: M. A. Rebolledo is an academic researcher from University of Zaragoza. The author has contributed to research in topics: Laser & Photonic-crystal fiber. The author has an hindex of 12, co-authored 40 publications receiving 378 citations.

Prospects of new planar optical waveguides based on eutectic microcomposites of insulating crystals: The ZrO2(c)-CaZrO3 erbium doped system

Abstract: A new approach to produce structured optical materials is described. The method relies on the capability of growing eutectic crystals of wide optical band gap materials by directional solidification procedures. The laser float zone technique was used to produce ordered arrays of alternate lamellae with thickness of the order of microns of erbium doped CaZrO3 and calcia stabilized zirconia single crystals. The later, having a higher refractive index, exhibited planar waveguiding effects as it has been proved experimentally. The possibility of producing waveguides from eutectic crystals promises the fabrication of hundreds of planar waveguides integrated into a crystal grown at a speed of several tenths of cm/h.

In situ assessment and minimization of nonlinear propagation effects for femtosecond-laser waveguide writing in dielectrics

Abstract: The effect of nonlinear propagation on the shape of the focal volume has been assessed by in situ plasma emission imaging during the subsurface processing of a commercial phosphate glass. The sample was processed with an elliptically shaped femtosecond-laser beam at 1 kHz repetition rate and scanned transversely with respect to the writing beam axis. As a consequence, optimal conditions for minimizing undesirable nonlinear propagation effects during the production of optical waveguides by direct laser writing have been determined. Under these conditions, it is possible to induce structural transformations and still preserve the focal volume shape associated with the linear propagation regime. While at low pulse energy a single scan laser-written structure does not support a guided mode, the use of multiple scans with minimized nonlinear propagation effects enables the production of optical waveguides. The latter show a significantly improved performance in terms of the refractive index change and propagation losses when compared to single scan waveguides.

In situ measurement of absorption and emission cross sections in Er/sup 3+/-doped waveguides for transitions involving thermalized states

Abstract: An application to transitions involving thermalized states of a procedure based on the McCumber theory to determine emission and absorption cross sections in waveguides from transversal fluorescence spectra is presented. The procedure is tested in Er-doped Ti:LiNbO/sub 3/ waveguides to provide accurate cross-section values for the recently attractive 550-nm band. We also study the excited-state absorption transition around 860 nm and present, to our knowledge, the first published cross-section values for this transition.

Femtosecond laser written 16.5?mm long glass-waveguide amplifier and laser with 5.2?dB?cm?1 internal gain at 1534?nm

Abstract: A 16.5?mm long, heavily doped erbium?ytterbium phosphate glass-waveguide amplifier was fabricated by the femtosecond laser (fs-laser) inscription technique. The femtosecond laser inscription of waveguides was carried out at 500?kHz repetition rate using a 0.68?NA aspheric lens. The energy deposition profile in the dielectric material was initially simulated using a generalized adaptive fast-Fourier evolver (GAFFE) algorithm. The size and shape of the guiding structures were carefully controlled by the slit shaping technique to reduce the coupling losses, with achievable values down to less than 0.1?dB. Rigorous simulations of the response of the active waveguides were carried out to optimize their performance as optical amplifiers. A maximum of 8.6?dB internal gain at 1534?nm was obtained upon bidirectional laser pumping at 976?nm, leading to a gain per unit length of 5.2?dB?cm?1. Laser action was also achieved for both ring and linear cavity configurations.

Determination of emission and absorption cross sections of in waveguides from transversal fluorescence spectra

Abstract: A procedure for the determination of emission and absorption cross sections in integrated waveguides from transversal fluorescence spectra is presented. It is based on an approximate treatment of McCumber's theory, which was demonstrated to provide accurate values for -doped silica fibres. Results on the transition of in waveguides pumped by a 980 nm laser diode are shown and compared to results from attenuation measurements. Advantages over other procedures for waveguide characterization (less dependence on experimental inaccuracies, all measurements are made on the waveguide, consideration of codoping influence and no pump interference around ) are discussed in detail.

Multiphase solidification in multicomponent alloys

Abstract: Multiphase solidification in multicomponent alloys is pertinent to many commercial materials and industrial processes, while also raising challenging questions from a fundamental point of view. Within the past few years, research activities dedicated to multiphase solidification of ternary and multicomponent alloys experienced considerable amplification. This paper gives an overview of our present understanding in this field and the experimental techniques and theoretical methods research relies on. We start with an introduction to thermodynamic databases and computations and emphasize the importance of thermophysical property data. Then, we address pattern formation during coupled growth in ternary alloys and cover microstructure evolution during successive steps of phase formation in solidifying multicomponent alloys. Subsequently, we review advances made in phase field modeling of multiphase solidification in binary and multicomponent alloys, including various approaches to crystal nucleation and growth. Concluding, we address open questions and outline future prospects on the basis of a close interaction among scientists investigating the thermodynamic, thermophysical and microstructural properties of these alloys.