DTE - GDAF - Artículos de Revistas

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Experimental demonstration of a silicon-slot quasi-bound state in the continuum in near-infrared all-dielectric metasurfaces
(Elsevier Ltd, 2023-06-01) Algorri Genaro, Jose Francisco; Sánchez Pena, José Manuel; Zografopoulos, Dimitrios; DELL'OLIO, F.; DING, Y.; F. LABBÉ,; DMITRIEV, V.; LOPEZ HIGUERA, J. M.; ANDREANI, L. C.; GALLI, M.; Ministerio de Economía y Competitividad (España)
We theoretically and experimentally investigate a metasurface supporting a silicon-slot quasi-bound state in the continuum (qBIC) mode resonating in the near-infrared spectrum. The metasurface is composed of circular slots etched in a silicon layer on a sapphire substrate. The symmetry of the metasurface unit cell is reduced in order to provide access to the symmetry-protected mode, whose properties are investigated by finite-element full-wave and eigenfrequency analysis. The measured transmittance spectra verify the excitation of the investigated qBIC mode with experimental quality factors exceeding 700. The near-field distribution of the resonant qBIC mode shows strong field confinement in the slots, leading to high sensitivity values for refractometry.
Experimental Validation of High Spatial Resolution of Two-Color Optical Fiber Pyrometer
(MDPI, 2023-05-01) Safarloo, Sahar; Tapetado Moraleda, Alberto; Vázquez García, María Carmen; Comunidad de Madrid; Agencia Estatal de Investigación (España); Ministerio de Ciencia e Innovación (España)
Taking non-contact temperature measurements in narrow areas or confined spaces of non-uniform surfaces requires high spatial resolution and independence of emissivity uncertainties that conventional cameras can hardly provide. Two-color optical fiber (OF) pyrometers based on standard single-mode (SMF) and multi-mode optical fibers (MMF) with a small core diameter and low numerical aperture in combination with associated commercially available components can provide a spatial resolution in the micrometer range, independent of the material’s emissivity. Our experiment involved using a patterned microheater to generate temperatures of approximately 340 °C on objects with a diameter of 0.25 mm. We measured these temperatures using two-color optical fiber pyrometers at a 1 kHz sampling rate, which were linearized in the range of 250 to 500 °C. We compared the results with those obtained using an industrial infrared camera. The tests show the potential of our technique for quickly measuring temperature gradients in small areas, independent of emissivity, such as in microthermography. We also report simulations and experiments, showing that the optical power gathered via each channel of the SMF and MMF pyrometers from hot objects of 250 µm is independent of distance until the OF light spot becomes larger than the diameter of the object at 0.9 mm and 0.4 mm, respectively.
Infiltrated Photonic Crystal Fibers for Sensing Applications
(MDPI, 2018-12-04) Algorri Genaro, José Francisco; Zografopoulos, Dimitrios; Tapetado Moraleda, Alberto; Poudereux, David; Sánchez-Pena, José Manuel; Ministerio de Educación, Cultura y Deporte (España); Comunidad de Madrid
Photonic crystal fibers (PCFs) are a special class of optical fibers with a periodic arrangement of microstructured holes located in the fiber's cladding. Light confinement is achieved by means of either index-guiding, or the photonic bandgap effect in a low-index core. Ever since PCFs were first demonstrated in 1995, their special characteristics, such as potentially high birefringence, very small or high nonlinearity, low propagation losses, and controllable dispersion parameters, have rendered them unique for many applications, such as sensors, high-power pulse transmission, and biomedical studies. When the holes of PCFs are filled with solids, liquids or gases, unprecedented opportunities for applications emerge. These include, but are not limited in, supercontinuum generation, propulsion of atoms through a hollow fiber core, fiber-loaded Bose-Einstein condensates, as well as enhanced sensing and measurement devices. For this reason, infiltrated PCF have been the focus of intensive research in recent years. In this review, the fundamentals and fabrication of PCF infiltrated with different materials are discussed. In addition, potential applications of infiltrated PCF sensors are reviewed, identifying the challenges and limitations to scale up and commercialize this novel technology.
Spectral Voltage Contour Plots of Optical Constants and Interface Parameters of the Active Layer of a Multilayer Structure Suspended Particle Device Smart Window from Clear on to Dark off States
(Center for Science and Technology, 2023-01-01) Barrios Puerto, David; Álvarez, Carlos
Smart windows based on suspended particle devices (SPDs) are able to switch optically from dark to clear visual appearance when applying an AC electrical signal. This effect is due to light absorbing nanoparticles that get aligned by the applied voltage. The sandwich structure of an SPD consists of several layers and includes two outer glass substrates, each one covered on its inwards-facing side with a transparent conducting thin layer surrounding the centrally positioned SPD active layer. A knowledge of the optical constants of each layer-i.e., the complex refractive index, including its real and imaginary (absorption) parts-is a key in the design of the visual appearance of the SPD window and is a useful tool to determine the optimum thickness of the active layer.
Reorientation of single-wall carbon nanotubes in negative anisotropy liquid crystals by an electric field
(Beilstein-Institut, 2016-06-08) García García, Amanda; Vergaz Benito, Ricardo; Algorri Genaro, José Francisco; Zito, Gianluigi; Cacace, Teresa; Marino, Antigone; Oton Sanchez, Jose Manuel; Geday, Morten A.; Comunidad de Madrid; Ministerio de Economía y Competitividad (España)
Single-wall carbon nanotubes (SWCNT) are anisotropic nanoparticles that can cause modifications in the electrical and electro-optical properties of liquid crystals. The control of the SWCNT concentration, distribution and reorientation in such self-organized fluids allows for the possibility of tuning the liquid crystal properties. The alignment and reorientation of CNTs are studied in a system where the liquid crystal orientation effect has been isolated. Complementary studies including Raman spectroscopy, microscopic inspection and impedance studies were carried out. The results reveal an ordered reorientation of the CNTs induced by an electric field, which does not alter the orientation of the liquid crystal molecules. Moreover, impedance spectroscopy suggests a nonnegligible anchoring force between the CNTs and the liquid crystal molecules.
Effect of different buffer layers on the quality of InGaN layers grown on Si
(2018-10-22) Gomez, V. J.; Grandal, J.; Nuñez Cascajero, Arantzazu; Naranjo, F. B.; Varela, M.; Sanchez Garcia, M. A.; Calleja, E.
Control of disability glare by means of electrochromic filtering glasses: A pilot study
(World Scientific Pub Co Pte Lt., 2017-01-01) Coco Martin, Rosa Maria; Cuadrado Asensio, Ruben; Vega Colado, César; Vergaz Benito, Ricardo; Sánchez Pena, José Manuel; Viñuales, Ana; Peris, Sergi; Artus, Pau; Coco Martin, M. Begoña; Comunidad de Madrid
Purpose: To evaluate the potential clinical usability of a new prototype of ophthalmic blue light filters developed by using electrochromic technology in pseudophakic patients complaining of glare.Methods: A prototype of electrochromic device was developed, with a specific frame that enclosed an electronic driver that allowed personalizing its function for each patient. A prospective, observational case series study was performed to test it. Five patients who had undergone cataract surgery with clear intraocular lenses and complaining of glare were included in the study. Main outcome measures were the results obtained in the satisfaction questionnaire that was delivered to patients. Then, visual acuity, contrast sensitivity, and reading ability data were evaluated with and without the prototype under different lighting conditions and different modes of the prototype after a complete month of use. Lens transmittance was also measured.Results: Visual acuity, contrast sensitivity and reading function did not change significantly with prototype use. The main activity for which the prototype was used was walking. Only one patient found that the dimming level was insufficient. No patients reported variable discomfort when passing tunnels, not sufficiently clear indoors, or put on and remove discomfort. The lenses slightly decreased their transmittance at the end of the study. Conclusion: Glasses based onelectrochromic technology may be acceptable for outdoor/indoor use and for distance-near vision. Future studies with larger samples must be conducted to confirm the clinical usability of these glasses.
Positive-negative tunable liquid crystal lenses based on a microstructured transmission line
(Springer Nature Limited, 2020-06-23) Algorri Genaro, José Francisco; Morawiak, P.; Bennis, N.; Zografopoulos, Dimitrios; Urruchi del Pozo, Virginia; Rodríguez Cobo, L.; Jaroszewicz, L. R.; Sánchez Pena, José Manuel; López-Higuera, J. M.; Comunidad de Madrid; Ministerio de Economía y Competitividad (España); Ministerio de Ciencia, Innovación y Universidades (España)
In this work, a novel technique to create positive-negative tunable liquid crystal lenses is proposed and experimentally demonstrated. This structure is based on two main elements, a transmission line acting as a voltage divider and concentric electrodes that distribute the voltage homogeneously across the active area. This proposal avoids all disadvantages of previous techniques, involving much simpler fabrication process (a single lithographic step) and voltage control (one or two sources). In addition, low voltage signals are required. Lenses with switchable positive and negative focal lengths and a simple, low voltage control are demonstrated. Moreover, by using this technique other optical devices could be engineered, e.g. axicons, Powell lenses, cylindrical lenses, Fresnel lenses, beam steerers, optical vortex generators, etc. For this reason, the proposed technique could open new venues of research in optical phase modulation based on liquid crystal materials.
SI-POF supporting power-over-fiber in multi-Gbit/s transmission for in-home networks
(IEEE, 2021-01-01) Al Zubaidi, Fahad Mohammed Abdulhusse; Sánchez Montero, David Ricardo; Vázquez García, María Carmen; Comunidad de Madrid; European Commission; Ministerio de Ciencia e Innovación (España)
We propose the integration of power-over-fiber (PoF) in home networks with multi Gbit/s data transmission based on wavelength-division-multiplexing (WDM) in step-index plastic optical fibers (SI-POF). Different powering architectures are described. The efficiencies of different components are discussed to address the maximum remote energy that can be delivered. Experimental results show the ability of the system to deliver several mW of optical power with negligible data signal quality degradation and with BER of 1 × 10¿10. The potential of utilizing PoF in combination with low-loss WDM-POF to optically powering multiple devices for specific in-home applications and IoT ecosystems is discussed. A PoF scalability analysis is detailed.
Engineering aspheric liquid crystal lenses by using the transmission electrode technique
(MDPI, 2020-09) Algorri Genaro, José Francisco; Zografopoulos, Dimitrios; Rodriguez Cobo, Luis; Sánchez Pena, José Manuel; López Higuera, José Miguel; Comunidad de Madrid; Ministerio de Economía y Competitividad (España); Ministerio de Ciencia, Innovación y Universidades (España); Agencia Estatal de Investigación (España)
The transmission electrode technique has been recently proposed as a versatile method to obtain various types of liquid-crystal (LC) lenses. In this work, an equivalent electric circuit and new analytical expressions based on this technique are developed. In addition, novel electrode shapes are proposed in order to generate different phase profiles. The analytical expressions depend on manufacturing parameters that have been optimized by using the least squares method. Thanks to the proposed design equations and the associated optimization, the feasibility of engineering any kind of aspheric LC lenses is demonstrated, which is key to obtain aberration-free lenses. The results are compared to numerical simulations validating the proposed equations. This novel technique, in combination with the proposed design equations, opens a new path for the design and fabrication of LC lenses and even other types of adaptive-focus lenses based on voltage control.
Self-referenced optical networks for remote interrogation of quasi-distributed fiber-optic intensity sensors
(Elsevier, 2020-09) Sánchez Montero, David Ricardo; Vázquez García, María Carmen; Comunidad de Madrid; Ministerio de Ciencia, Innovación y Universidades (España)
Different multiplexing techniques for passively addressingfiber-optic sensors and compensation schemes forovercoming the undesirable optical signal losses to provide self-referenced quasi-distributed sensing from in-tensity-basedfiber-optic point sensors are revisited. Furthermore, a passive wavelength division multiplexing(WDM) network operating in reflective configuration with remote Radio-Frequency self-referencedfiber-opticintensity sensors with electro-optical configuration is proposed. Delay lines in the electrical domain providemore compact sensor-heads and easy-reconfigurable performance of the sensing points. The technique is ana-lyzed following the Z-transform formalism and measurements validating the theoretical model are reported.There are two measurement parameters providing self-referenced remote interrogation for the sensing heads.The paper shows their experimental validation in a 2-sensor network based on tapered SMF micro-displacementsensors, testing sensor self-referencing as well as sensor crosstalk. Those results provide the background toextrapolate them to a quasi-distributed passive CWDM-based 16-sensor network at around 65 km of remotedistance from the central office, with possible upgrade to a 25 km-long DWDM-based 48-sensor network.
Limitations of Standard Accessible Captioning of Sounds and Music for Deaf and Hard of Hearing People: An EEG Study
(Frontiers Media, 2020-02-18) Revuelta Sanz, Pablo; Ortiz, Tomas; Lucía Mulas, María José; Ruiz Mezcua, María Belén; Sánchez Pena, José Manuel
Captioning is the process of transcribing speech and acoustical information into text to help deaf and hard of hearing people accessing to the auditory track of audiovisual media. In addition to the verbal transcription, it includes information such as sound effects, speaker identification, or music tagging. However, it just takes into account a limited spectrum of the whole acoustic information available in the soundtrack, and hence, an important amount of emotional information is lost when attending just to the normative compliant captions. In this article, it is shown, by means of behavioral and EEG measurements, how emotional information related to sounds and music used by the creator in the audiovisual work is perceived differently by normal hearing group and hearing disabled group when applying standard captioning. Audio and captions activate similar processing areas, respectively, in each group, although not with the same intensity. Moreover, captions require higher activation of voluntary attentional circuits, as well as language-related areas. Captions transcribing musical information increase attentional activity, instead of emotional processing.
Structural characterization of Al0.37In0.63N/AlN/p-Si (111) heterojunctions grown by RF sputtering for solar cell applications
(MDPI, 2021-05-01) Núñez Cascajero, Arantzazu; Naranjo, Fernando B.; De la Mata, María; Molina, Sergio I.; Comunidad de Madrid; Ministerio de Ciencia e Innovación (España)
Compact Al0.37In0.63N layers were grown by radiofrequency sputtering on bare and 15 nm-thick AlN-buffered Si (111) substrates. The crystalline quality of the AlInN layers was studied by high-resolution X-ray diffraction measurements and transmission electron microscopy. Both techniques show an improvement of the structural properties when the AlInN layer is grown on a 15 nm-thick AlN buffer. The layer grown on bare silicon exhibits a thin amorphous interfacial layer between the substrate and the AlInN, which is not present in the layer grown on the AlN buffer layer. A reduction of the density of defects is also observed in the layer grown on the AlN buffer.
Fiber-optic pyrometer for very localized temperature measurements in a turning process
(IEEE, 2017-03) Tapetado Moraleda, Alberto; Díaz Álvarez, José; Miguélez Garrido, María Henar; Vázquez García, María Carmen; Comunidad de Madrid; Ministerio de Economía y Competitividad (España)
A fiber-optic two-color pyrometer based on glass multimode fibers with 62.5 μm diameter and 0.275 numerical aperture is used for localized temperature measurements in turning processes. Operation wavelengths improve temperature measurement accuracy. The system is capable of measuring temperature in the range from 300 to 650 °C in a surface area below 0.16 mm 2 . Numerical simulation of the calibration curves including manufacturer tolerances are reported, showing good agreement with the experimental results. Temperature evolution is performed in a lathe at different feed rates and cutting speeds at an Inconel 718 turning process, using a glass fiber-optic sensor embedded into a modified tool member. The results are used to in-process prevent premature failure of the components related to the fatigue and validate feed rates recommended by the tool manufacturer.
Aspherical liquid crystal lenses based on a variable transmission electrode
(Optica, 2022-04-11) Bennis, N.; Jankowski, T.; Morawiak, P.; Spadlo, A.; Zografopoulos, Dimitrios; Sánchez Pena, José Manuel; López-Higuera, M.; Algorri, F.; Comunidad de Madrid; Ministerio de Ciencia e Innovación (España)
In this work, a technique to generate aspherical liquid crystal lenses with positive and negative optical power is experimentally demonstrated. The main enabling element is a micro-metric electrode with variable spatial size. This produces a decreasing resistance towards the lens centre that generates the desired voltage/phase profiles. Then, the voltage is homogeneously distributed across the active area of the lens by micro-metric concentric electrodes. As it is demonstrated, the phase shift can be controlled with voltages from 0 to 4.5 VRMS. As a result, parabolic profiles are obtained both for negative and positive optical powers. Furthermore, this approach avoids some disadvantages of previous techniques; parabolic profiles can be obtained with only one lithographic step and one or two voltage sources. Other complex aspherical profiles could be fabricated using the same technique, such as elliptical or hyperbolic ones.
Emotion elicitation through vibrotactile stimulation as an alternative for deaf and hard of hearing people: An EEG study
(MDPI, 2022-07-02) García López, Álvaro; Cerdán, Víctor; Ortiz, Tomás; Sánchez Pena, José Manuel; Vergaz Benito, Ricardo; Comunidad de Madrid
Despite technological and accessibility advances, the performing arts and their cultural offerings remain inaccessible to many people. By using vibrotactile stimulation as an alternative channel, we explored a different way to enhance emotional processes produced while watching audiovisual media and, thus, elicit a greater emotional reaction in hearing-impaired people. We recorded the brain activity of 35 participants with normal hearing and 8 participants with severe and total hearing loss. The results showed activation in the same areas both in participants with normal hearing while watching a video, and in hearing-impaired participants while watching the same video with synchronized soft vibrotactile stimulation in both hands, based on a proprietary stimulation glove. These brain areas (bilateral middle frontal orbitofrontal, bilateral superior frontal gyrus, and left cingulum) have been reported as emotional and attentional areas. We conclude that vibrotactile stimulation can elicit the appropriate cortex activation while watching audiovisual media.
A high birefringence liquid crystal for lenses with large aperture
(Nature Research, 2022-08-26) Bennis, N.; Jankowski, T.; Strzezysz, O.; Pakula, A; Zografopoulos, Dimitrios; Perkowski, P.; Sánchez Pena, José Manuel; López Higuera, J.M.; Algorri Genaro, José Francisco; Comunidad de Madrid; Ministerio de Ciencia e Innovación (España)
This work presents the application of an experimental nematic liquid crystal (LC) mixture (1929) in a large aperture lens. The LC material is composed of terphenyl and biphenyl derivatives compounds with an isothiocyanate terminal group and fluorinated lateral substituents. The substitution with a strongly polar isothiocyanate group and an aromatic rigid core provides pi-electron coupling, providing high birefringence (Deltan=0.3375 at 636 nm and 23 °C) and low viscosity (eta = 17.03 mPa s). In addition, it also shows high values of birefringence at near infrared (0.318 at 1550 nm). The synthesis process is simple when comparing materials with high melting temperatures. The excellent properties of this LC mixture are demonstrated in a large aperture LC-tunable lens based on a transmission electrode structure. Thanks to the particular characteristics of this mixture, the optical power is high. The high birefringence makes this LC of specific interest for lenses and optical phase modulators and devices, both in the visible and infrared regions.
All-optical nanosensor for displacement detection in mechanical applications
(MDPI, 2022-11-02) Escandell Varela, Lorena; Rodríguez Álvarez, Carlos; Barreda, Ángela; Zaera, Ramón; García Cámara, Braulio; Comunidad de Madrid; Ministerio de Ciencia e Innovación (España); Universidad Carlos III de Madrid
In this paper, we propose the design of an optical system based on two parallel suspended silicon nanowires that support a range of optical resonances that efficiently confine and scatter light in the infrared range as the base of an all-optical displacement sensor. The effects of the variation of the distance between the nanowires are analyzed. The simulation models are designed by COMSOL Multiphysics software, which is based on the finite element method. The diameter of the nanocylinders (d = 140 nm) was previously optimized to achieve resonances at the operating wavelengths (lambda = 1064 nm and 1310 nm). The results pointed out that a detectable change in their resonant behavior and optical interaction was achieved. The proposed design aims to use a simple light source using a commercial diode laser and simplify the readout systems with a high sensitivity of 1.1 × 106 V/m2 and 1.14 × 106 V/m2 at 1064 nm and 1310 nm, respectively. The results may provide an opportunity to investigate alternative designs of displacement sensors from an all-optical approach and explore their potential use.
Simulation of the thickness dependence of the optical properties of suspended particle devices
(Elsevier, 2015-12-01) Barrios Puerto, David; Vergaz Benito, Ricardo; Sánchez Pena, José Manuel; García Cámara, Braulio; Granqvist, Claes G.; Niklasson, Gunnar A.; Comunidad de Madrid; European Commission; Ministerio de Economía y Competitividad (España)
Suspended particle devices (SPDs) are able to rapidly switch from a dark bluish-black state to a clear greyish appearance when an AC electric field is applied. Two-flux and four-flux models were used to derive refractive indices and extinction coefficients, as well as scattering and absorption coefficients, of the particle-containing active layer. These entities were used in model calculations to predict direct, total and diffuse components of transmittance and reflectance, along with color appearance and haze, as a function of the thickness of the active layer. An optimum thickness for optical contrast of the SPD was determined in this way and was found to be in the range of 200–300 nm. The devices exhibit significant haze particularly in reflection.
All-Optical Nanometric Switch Based on the Directional Scattering of Semiconductor Nanoparticles
(American Chemical Society, 2015-08-20) García Cámara, Braulio; Algorri Genaro, José Francisco; Cuadrado Conde, Alexander; Urruchi del Pozo, Virginia; Sánchez Pena, José Manuel; Serna, Rosalía; Vergaz Benito, Ricardo; Comunidad de Madrid; Ministerio de Economía y Competitividad (España)
A structure based on a dimer of silicon nanoparticles, presenting directional scattering in the visible range, was studied as a new design of an all-optical switch. The combination of spherical nanoparticles satisfying, at the same incident wavelength, the zero-backward and the minimum-forward scattering conditions can produce either a maximum or a minimum of the scattered field in the area between the nanoparticles. The modulation of the incident wavelength can be used as a switching parameter due to the sensitivity of these conditions to it. An optimization of the dimer setup, both in the distance between the nanoparticles and the incident wavelength, was numerically performed to obtain a maximum contrast. Also, near-field and far-field distributions of the electric field have been considered.

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