DTE - GDAF - Comunicaciones en Congresos y otros eventos

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Characterization of high-power white leds for VLC applications
(Elsevier B.V., 2021-12-01) Betancourt, Juan S.; Torres Zafra, Juan Carlos; Morales Céspedes, Máximo; Martínez Sarriegui, Iñaki; Valle, Carlos del; Sánchez Pena, José Manuel; Comunidad de Madrid; European Commission; Ministerio de Ciencia e Innovación (España); Universidad Carlos III de Madrid
During the last years, visible light communications (VLC) have been proposed for providing connectivity while ensuring satisfactory illumination in both indoor environments and also specific outdoor scenarios without the need of deploying complex infrastructures for that purpose. Transmission for VLC is carried out through lightemitting diodes (LEDs), which correspond to semiconductors based on PN-junction materials with a direct gap. In this sense, the current flow plays a major role in the behavior and performance of these devices for VLC. Therefore, characterizing the electrical response of high-power white LED results mandatory for the successful implementation of VLC. At this point, it is worth noting that the electrical characterization is usually not available for high-power LEDs since, in fact, determining these characterization results challenging. In this sense, there exist some measurement instruments such as LCRs or impedance analyzers typically employed for characterizing materials and passive electrical components. However, these kinds of instruments are subject to a limited input impedance and a maximum value of forwarding current. In this work, the electrical characterization of the LED LXHL-BW02 of Luxeon is analyzed to show that typically commercial instrumentation for characterizing these devices is limited for high-power LEDs, which may provide polluted results when these limitations are not considered. After that, the characterization of the LXHL-BW02 based on a lock-in amplifier is proposed.
Friction during earthquakes: 25 years of experimental studies
(IOP Science, 2021-10-27) Di Toro, Giulio; Aretusini, Stefano; Cornelio, C; Nielsen, S; Spagnuolo, Elena; Nuñez Cascajero, Arantzazu; Tapetado Moraleda, Alberto; Vázquez García, María Carmen
Dynamic fault strength τ (rock friction in the broad sense) and its evolution with seismic slip and slip rate are among the most relevant parameters in earthquake mechanics. Given the large slip rate (1 m s−1 on average), displacement (up to tens of meters), effective stress (tens of MPa), typical of seismic faulting at depth, thermo-mechanical effects become outstanding: dynamic fault strength is severely affected by fluid and rock phase changes, extreme grain size reduction, and the production of amorphous and unstable materials in the slipping zone. Here, first we will summarize the most relevant findings about dynamic fault strength during seismic slip mainly obtained thanks to the exploitation of dedicated experimental machines (i.e., rotary shear apparatus). However, the interpretation of this experimental dataset remains debated because of technical limitations which impede us to measure fundamental parameters such as temperature, strain rate, pore fluid pressure and grain size in the slipping zone. Without a sound estimate of these physical parameters, any constitutive law proposed to describe the evolution of dynamic fault strength during simulated seismic slip remains speculative. Then, we will discuss the results of some recent experiments which exploit new technical approaches to overcome the main limitations of the previous studies. The experimental approach, together with field studies of the geometry and architecture of exhumed faults and modelling, remains our most powerful tool to investigate seismic-related deformation mechanisms in both natural and human-induced earthquakes.
Theoretical performance of the PF-GIPOF transfer function under different W-shaped refractive index profile designs
(International Cooperative of Plastic Optical Fibers, 2015) Sánchez Montero, David Ricardo; Ponce Hernández, Wendy; Pinzón Castillo, Plinio Jesús; Vázquez García, María Carmen; Comunidad de Madrid; Ministerio de Economía y Competitividad (España)
The frequency response of PF-GIPOF with W-shaped refractive index profile is theoretically investigated. The proposed index profile incorporates a trench in the cladding region to tune the modal dispersion of outer groups.We focus on the effect of this design on the PF-GIPOF baseb and band width. The relationship between new index profiles and a high-bandwidth fiber condition is highlighted in order to increase the maximum achievable aggregated transmission capacity over PF-GIPOFs.
Low-loss 7-channel visible WDM scheme for implementing efficient data transmission systems over SI-POF
(2015) Pinzón Castillo, Plinio Jesús; Vázquez García, María Carmen; Pérez Garcilópez, Antonia Isabel; Zubia, J.; Comunidad de Madrid; Ministerio de Economía y Competitividad (España)
In this work, the design of a visible wavelength division multiplexing (WDM) scheme of 7 channels is presented, The multiplexing is performed using a fiber bundle based multiplexer with insertion losses (ILs) lower than 2.2 dB, including the lossesb y LDs' coupling. The channelss eparationi s performed by using a compact demultiplexer based on a reflective diffraction grating. This demultiplexer is optimized to accommodate up to 8 channels in the range from 430 to 655 nm, with ILs lower than 4.5 dB per channel. The analysis done on the proposed WDM scheme shows that the total ILs included by multiplexing and demultiplexing are lower than 7 dB. This is enough to obtain a real improvement in the performance of commercial and experimental transmission systems based on visible WDM over SI-POF.
Efficient real-time multi-gigabit Ethernet data transmission system based on visible WDM over SI-POF
(International Cooperative of Plastic Optical Fibers, 2015) Pinzón Castillo, Plinio Jesús; Vázquez García, María Carmen; Pérez Garcilópez, Antonia Isabel; López, A.; Comunidad de Madrid; Ministerio de Economía y Competitividad (España)
A real-time data communication system based on a step-index polymer optical fiber (SI-POF) link of more than 50 m based on a 3-channel visible wavelength division multiplexing (visible WDM) scheme is presented.S pecial care on implementingl ow insertion loss multiplexers/demultiplexeriss carried out to allow for greener solutions in terms of power consumption. The system performance has been tested using the first and last channels ofthe 3-channel available grid. The results show that the proposed system can establish a real-time Ethernet link with connection speed of up to 2 Gb/s with bit error rate <1x10-10, and having the potential for expanding its data transmission speed up to 3 Gb/s.
A novel liquid crystal temperature sensor based on modal control principle
(2013-09-22) Algorri Genaro, José Francisco; Urruchi del Pozo, Virginia; Sánchez Pena, José Manuel; Bennis, Noureddine; Comunidad de Madrid; Ministerio de Economía y Competitividad (España)
The well-known electrically-controlled anisotropic properties of liquid crystals not only have been valued in displays applications, but also have led to the conception of innovative approaches for a wide and diversified field of applications, such as optical communications, imaging, metamaterials, microwaves, biomedical, etc. Also, the fact that liquid crystals parameters have a strong dependence with temperature, has allowed researchers to extend the design of liquid crystal devices into the field of sensors. The simultaneous effect of both dependences, on voltage and temperature, has been recently exploited in a novel frequency-temperature liquid crystal transducer [1]...
Assessment of optical aberrations of tunable liquid crystal cylindrical microlenses
(2013-09-15) Algorri Genaro, José Francisco; Urruchi del Pozo, Virginia; Romero, B.; Sánchez Pena, José Manuel; Bennis, Noureddine; Comunidad de Madrid; Ministerio de Economía y Competitividad (España)
Cylindrical lenses are promising devices for a wide range of applications [1-3]. This kind of lenses can be used in some novel applications such as light-sheet microscopy, line illumination microscopy or autostereoscopic devices. However, as any kind of lens, the main drawback is the generation of optical aberrations. These aberrations determine the image quality of an optical system. Interferometrists often like to represent wavefronts as Zernike polynomials. Zernike polynomials have been widely used because, unlike other polynomial set, they are orthogonal over a unit circle and represent balanced classical optical aberrations, yielding minimum variance over a circular pupil [4]. These characteristics are lost when non circular pupils are employed. Some research works have developed new coefficients for different pupils [5]. Notwithstanding that, they were targeted for rotational symmetric optics [6]. In the referred paper, 2D Chebyshev polynomials related to some Seidel aberrations are described. These ones form a useful orthogonal basis for optics of rectangular apertures, making them an attractive option for cylindrical lenses. In this work, optical aberrations in a liquid crystal (LC) cylindrical lens have been modeled and measured, for the first time. We have developed our own application specifically to extract the 3D wavefront from an interference pattern. This software tool also allows us to obtain the optical aberrations based on Chebyshev polynomials. A tunable LC cylindrical lens has been designed and manufactured. Optical aberrations have been assessed by adjusting the control voltage applied to the device.
An analytical approach to the design of liquid crystal microlenses
(2013-03-20) Algorri Genaro, José Francisco; Urruchi del Pozo, Virginia; Sánchez Pena, José Manuel; Otón Sánchez, J.M.; Comunidad de Madrid; Ministerio de Educación, Cultura y Deporte (España)
New analytical expressions for designing liquid crystal microlenses have been proposed. Equations involved, based on a novel equivalent electric circuit, lead to optimum designs of liquid crystal lenses which lens diameter ranges from few micrometers to one millimeter. A particular mathematical relationship between the microlens thickness and diameter is the key parameter to achieving a quasi-parabolic phase distribution across the microlens diameter. Frank-Oseen equations have been used for modeling and solving the problem. A solution for the elastic constants of a hypothetic liquid crystal, proper for a microlens device, is proposed. Manufacturing parameters of the lenses have been designed for fulfilling focal length and diameter requirements. Some of them are the thickness, the electrode configuration, and the driving scheme (modal or hole patterned). A set of liquid crystal microlenses has been manufactured and an electrooptic characterization has been carried out in order to compare the measurements with the analytical approach.
Simulations on distribution of phase retardation through liquid crystal lenses
(2012-08-19) Algorri Genaro, José Francisco; Urruchi del Pozo, Virginia; Sánchez Pena, José Manuel; Oton Sanchez, Jose Manuel
For this research work, a simulation programa for simulate liquid crystal lens electrooptical behaviour, based on Frank-Oseen's free energy formulation, has been developed and the results have been compared to previous experimental data...
Polymer stabilized blue phase beam steering
(2019-09-13) Algorri Genaro, José Francisco; Urruchi del Pozo, Virginia; García Cámara, Braulio; Sánchez Pena, José Manuel; Ministerio de Economía y Competitividad (España)
Nematic liquid crystal (LC) based beam steering have been reported for wide applications. However, for conventional nematic LC beam steering the thickness is of several microns in order to have a wider deflection angle. The response time is relatively slow and the diffraction efficiency is low. The aim of this work has been focused on designing and theoretically analyzing a novel beam steering based on polymer stabilized blue phase liquid crystal (PSBPLC). This special mesophase of the chiral doped nematic LC has several advantageous characteristics. For example, a microsecond response time (approximately ten times faster than NLC) due to the double-twist cylinder diameter and short coherence length. A simulation program estimates the electrical field inside the structure solving the Gauss' law by FEM. An isotropic initial state is considered. The induced birefringence, and the ordinary and extraordinary refractive indices, are calculated in each mesh point. Orientation of the electrical field vector determines the optical axis orientation. The induced optical anisotropy of the PS-BPLC is considered. With this information and adopting the extended Jones matrix, the related electro-optical properties are estimated.
Optical vortices by a modal liquid crystal spiral phase plate
(2015-09-13) Algorri Genaro, José Francisco; Torres Zafra, Juan Carlos; Urruchi del Pozo, Virginia; Sánchez Pena, José Manuel; Ministerio de Economía y Competitividad (España)
An ideal spiral phase plate based on liquid crystal and high resistivity layers is proposed and theoretically analyzed. The proposed structures generates a spiral-like voltage with simple voltage control...
Active metasurface at THz based on liquid crystals
(2018-09) Algorri Genaro, José Francisco; Zografopoulos, Dimitrios; Bennis, Noureddine; Morawiak, Przemyslaw; Urruchi del Pozo, Virginia; Beccherelli, Romeo; Comunidad de Madrid; Ministerio de Economía y Competitividad (España)
The THz range has gained great attention in recentyears. Due to the long wavelength of THz rays,conventional scaling of LC devices from the visible tothe THz range results in thicker devices with theunderlying disadvantages. A further option to overcomethese drawbacks is to use metamaterials.In this study, an active fishnet metamaterial based onhigh birefringence liquid crystal materials, is proposedand theoretically analyzed. Low absorption and lowrefractive index substrates (HDPE) coated with thicklayers of ITO (acting as a reflective layer at THz) areused. Apart from providing the electromagneticresonances that lead to negative refractive index, theITO layers also serve as the electrodes for theapplication of the control voltage. The latter allows forthe tuning of the metamaterial key parameters, suchas transmittance and effective permittivity orpermeability.
An all optical nanometric switch
(2015-10) García Cámara, Braulio; Algorri Genaro, José Francisco; Cuadrado, Alexander; Urruchi del Pozo, Virginia; Sánchez Pena, José Manuel; Serna, Rosalia; Vergaz Benito, Ricardo; Comunidad de Madrid; Ministerio de Economía y Competitividad (España)
Current requirements on information transfer, computation and storage demand new counterparts to the electronic components. In particular, full-optical components are currently explored. Different phenomena observed in the interaction of light with nanoparticles allow the development of this concept. In this work, we explored the possibility of creating a full optical nanometric switch to be the simplest part of the future family of components in optical nanocircuits. In 80's, Kerker et al [1] showed that the scattering of sub-wavelength particles can be directed under certain conditions. In fact, a nanoparticle can accomplish a zero backscattering (ZB) or minimum forward scattering (MF) depending on the relationship between its material, size and incident wavelength. We have demonstrated that the Kerker conditions can be found in the visible range for several usual semiconductor materials, as Silicon, Germanium, TiO2, GaAs, etc [2]. Playing with sizes, it is possible to obtain nanoparticles satisfying either the ZB or the MF at the same wavelength. Then, we have proposed a dimer of silicon nanoparticles [3] presenting such combination of directional scattering in the visible range. This set can produce either a maximum or a minimum of the scattered field in the area between the nanoparticles. As Kerkers' conditions are very dependent on the wavelength, we propose that a modulation of the incident wavelength can be used as switching parameter (Fig. 1). We have searched the optimum parameters of the dimer setup, in wavelength, distance between particles and their sizes, in order to make easier the fabrication for the Research Community to get an experimental Proof of Technology of these simple designs.
Micro-optical phase modulators based on liquid crystal technology
(2015-10-23) Algorri Genaro, José Francisco; Urruchi del Pozo, Virginia; Bennis, Noureddine; Sánchez Pena, José Manuel; Oton, J.M.; Comunidad de Madrid; Ministerio de Economía y Competitividad (España)
An optical phase modulator is an optical element used to control the phase of light. They have multiple applications, for example ophthalmological applications, tunable zooms, beam steering, correction of aberrations, astronomy, 3D vision applications, etc. The displays and photonics application group (GDAF) of Carlos III university of Madrid (UC3M) in collaboration with CEMDATIC of Polytechnic University of Madrid (UPM) have extended the knowledge in this field by the proposal of several advanced micro-optical phase modulators. These, obtain with simply topologies either common optical elements, e.g. microlenses for autostereoscopic devices [1], aberration controllers for rectangular micro-optical elements [2] and microlenses with reduced aberrations and tunable rotation [3], or singular optical elements, e.g. micro-axicon arrays [3] and tunable optical vortices [5].
Autostereoscopic displays based on liquid crystal microlenses
(2016-10-20) Algorri Genaro, José Francisco; Urruchi del Pozo, Virginia; Sánchez Pena, José Manuel; Oton Sanchez, Jose Manuel; Comunidad de Madrid; Ministerio de Economía y Competitividad (España)
Three-diqensional vision has acquired great importance in audiovisual industry in the past ten years. Despite this, the first generation of autostereoscopic displays failed to generate enough consumer excictement. Sime reasons are few 3D content and performance issues...
Towards a polarization control of the directional scattering of semiconductor nanoparticles
(2016-10) García Cámara, Braulio; Algorri Genaro, José Francisco; Cuadrado, Alexander; Sánchez Pena, José Manuel; Vergaz Benito, Ricardo; Comunidad de Madrid; Ministerio de Economía y Competitividad (España)
In this work we analyze the sensitivity of the directional scattering conditions in semiconductor nanodisks with the polarizationof the incident light. The possibility to reach or not this directional scattering as a function of the polarization of the incidentbeam could be very interesting for the design of new all-optical devices for optical communications and circuitry.
Tuning and enhancement of the magneto-dielectric behavior ofsemiconductor nanoparticles
(2015-08) García Cámara, Braulio; Algorri Genaro, José Francisco; Urruchi del Pozo, Virginia; Sánchez Pena, José Manuel; Vergaz Benito, Ricardo; Ministerio de Economía y Competitividad (España)
Magneto-dielectric response of semiconductor nanoparticles has been recently shown asa useful phenomenon for several applications, e.g. sensors. The enhancement and spectral tuning ofthis behavior is a keynote aspect for some of these approaches. In this work, we show that the Mieresonances of nanoparticles composed of AlxGa1-xAs can be enhanced and tuning in a fine way bycontrolling the relation between the particle size and the concentration of Al atoms (x).
Thermo-optical properties of polydimethylsiloxane (PDMS) doped with metallic nanoparticles
(2015-08) Algorri Genaro, José Francisco; García Cámara, Braulio; Podereux, D.; Vergaz Benito, Ricardo; Urruchi del Pozo, Virginia; Sánchez Pena, José Manuel; Comunidad de Madrid; Ministerio de Economía y Competitividad (España)
The thermo-optical response of polydimethylsiloxane (PDMS) doped with metallic nanoparticles is theoretically studied. The temperature dependence of the effective refractive index of the mixture has been analyzed through the spectral evolution of the output power ratio of a beam crossing a sample. Both the nanoparticle size and the concentration effects have been analyzed to design a potential temperature sensor.
Towards the polarization control of the directional scattering of semiconductor nanodisks
(CentraleSupelec, Laboratoire Génie Électrique et Électronique de Paris, 2016-07) Vergaz Benito, Ricardo; Algorri Genaro, José Francisco; Cuadrado, A.; Sánchez Pena, José Manuel; García Cámara, Braulio; Comunidad de Madrid; Ministerio de Economía y Competitividad (España)
In this work we analyze the sensitivity of the directional scattering conditions in semiconductor nanodisks with the polarization of the incident light. The possibility to reach or not this directional scattering as a function of the polarization of the incident beam could be very interesting for the design of new all-optical devices for optical communications and computing.
Studying light concentration in a dimer of semiconductor nanoparticles for all-optical devices
(Centralesupelec, Laboratoire Génie Électrique et Électronique de Paris, 2016-07) Vergaz Benito, Ricardo; Algorri Genaro, José Francisco; Cuadrado, A.; Urruchi del Pozo, Virginia; Sánchez Pena, José Manuel; García Cámara, Braulio
Scattering by subwavelength dielectric nanospheres can have interesting directionaleffects in the case of accomplishing Kerker's conditions. We have taken advantage of theseconditions to design a dimer of semiconductor nanoparticles where an important contrast can beachieved in their gap, due to the directionality and the interferential interaction of the scatteredfields.

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