Phase space description of nonlinear directional couplers

A comprehensive analysis of the symmetric nonlinear directional coupler as a function of the excitation conditions is reported. The analysis is based on a coupled-mode technique in normalized (dimensionless) parameters, using the linear supermodes of the guiding structure, most of the results being derived from the Hamiltonian of the resulting nonlinear equations. The exchange of power between the branches in the coupler is graphically described by means of the trajectories of the motion in the phase space. The effect of saturation of the nonlinear index has been included.Peer Reviewe

Supermode analysis of the three-waveguide nonlinear directional coupler: the critical power

The three-waveguide nonlinear directional coupler switching characteristic is studied using the eigenmodes of the structure (i.e. supermodes). This model, which is more exact than the one used in previous works, has allowed to confirm the three waveguide configuration as an alternative to the two waveguide nonlinear coupler. Moreover, an analytical expression for the critical power at which the switching between the output branches occurs has been found.Peer Reviewe

Nonlinear resonant conversion of modes in optical waveguides

A new class of resonant exchange of power among three co-propagating modes in dielectric optical waveguides exhibiting Kerr-like nonlinearity is reported. Unlike the coupling of modes travelling in different, spatially separated channels as in the directional coupler (Jensen, IEEE J. Quantum Electron. QE-18 (1982) 1580; Chen, Snyder and Mitchell, Electron. Lett. 26 (1990) 77; Schmidt-Hattenberger, Trutschel and Lederer, Optics Lett. 16 (1991) 294) this paper points out the possibility of obtaining an efficient coupling of modes travelling in one single channel. The key point here is the imposition of a geometrical resonance between modes, to improve the coupling process. Due to this resonance condition, which is related with the wavelength through the propagation constants, the power exchange process is very sensitive to the wavelength.Peer Reviewe

Proyecto de Innovación docente: Making novel researchers. Poster Session

Ponencia presentada en la Jornada de Innovación Docente 2019: metodologías activas en el aula, celebrada el 17 de junio de 2019 en la Universidad Carlos III de Madrid

Bandgap widening in macroporous silicon photonic crystals by multiperiodic structures

Large bandgaps with low transmission in 3D macroporous silicon photonic crystals have been proved as an interesting technology for the development of optical filters and spectroscopic MIR gas sensors. The aim of this study is the investigation of different bandgap widening methods based on multiperiodic structures for 3D macroporous silicon photonic crystals. To do so, chirped modulations and structures with different periodicity groups have been modelled and theoretically analysed by means of 3D FDTD simulations. They have revealed that by using different decreasing periodicity groups, bandgaps with null transmission and widths as high as 1800 nm, 4 times the original single periodicity photonic crystal bandgap, can be obtained. Furthermore, it has been shown that a resonant cavity with a 20% transmission can be placed in a 1 µm wide bandgap. The results open a way to use this type of structures not only for gas sensing but also for other purposes such as wide stop-band filters, selective filters or broadband mirrors.Peer ReviewedPostprint (published version

Sphingosine-1-phosphate activates chemokine-promoted myeloma cell adhesion and migration involving α4β1 integrin function

51 p.-7 fig.-1 tab.-2 fig.supl.Myeloma cell adhesion dependent on α4β1 integrin is crucial for the progression of multiple myeloma (MM). The α4β1-dependent myeloma cell adhesion is up-regulated by the chemokine CXCL12, and pharmacological blockade of the CXCL12 receptor CXCR4 leads to defective myeloma cell homing to bone marrow (BM). Sphingosine-1-phosphate (S1P) regulates immune cell trafficking upon binding to G-protein-coupled receptors. Here we show that myeloma cells express S1P1, a receptor for S1P. We found that S1P up-regulated the α4β1-mediated myeloma cell adhesion and transendothelial migration stimulated by CXCL12. S1P promoted generation of high-affinity α4β1 that efficiently bound the α4β1 ligand VCAM-1, a finding that was associated with S1P-triggered increase in talin-β1 integrin association. Furthermore, S1P cooperated with CXCL12 for enhancement of α4β1-dependent adhesion strengthening and spreading. CXCL12 and S1P activated the DOCK2-Rac1 pathway, which was required for stimulation of myeloma cell adhesion involving α4β1. Moreover, in vivo analyses indicated that S1P contributes to optimizing the interactions of MM cells with the BM microvasculture and for their lodging inside the bone marrow. The regulation of α4β1-dependent adhesion and migration of myeloma cells by CXCL12-S1P combined activities might have important consequences for myeloma disease progressionThis study was supported by the Ministerio de Ciencia e Innovación (Grant Nos SAF2011-24022 to JT, SAF2009-07035 to AGP, SAF2009-11037 to AH, RD06/0020/0011 to JT and AGP, RD06/0020/0006 to NCG and MG and PI081825 to MG), the Comunidad de Madrid (Grant No. P2010/BMD-2314 to AGP, JT and AH) and the Fundación de Investigación Médica Mutua Madrileña (to AGP and MG). AH was also funded by the FP7-People-2009-RG (Grant No. 246655), a Ramón y Cajal Fellowship (Grant No. RYC-2007-00697) and the Pro-CNIC Foundation.Peer reviewe

Medida del perfil de velocidad de un líquido en un tubo de sección circular mediante un radar láser

In this paper we present the measures of the profile or velocity gradient of a liquid (water) across a circular section pipe in laminar state, by means of a two-dimension laser radar system (2D-LDA) designed by the EEF-TSC group of UPC. The measurement instrument is build with an optical system that outputs three laser beams that are focused on the target, two acoustic-optical modulators, a set of lenses and mirrors, and two beam splitters. The dispersed signal, produced by particles introduced in the liquid, is captured by means of a set of lenses that focus it on a photodetector (APD). By means of an electronic subsystem and an acquisition and processing subsystem (in Visual C++) we obtain the results and they are compared to the theoretical model (essentially parabolic profile).Peer ReviewedPostprint (author’s final draft

Análisis del proteoma del exudado estigmático

Comunicaciones a congreso

Manuel Vázquez Montalbán. Guías didácticas y de lectura para ESO y Bachillerato

Podeu consultar la versió en català a: http://hdl.handle.net/2445/11088