Suchergebnisse

Hydrogenated amorphous silicon (a-Si:H) solar cells have some performance limitations related to the mobility and lifetime of their carriers. For this reason, it is interesting to explore thin-film solutions, achieving a tradeoff between photons optical absorption and the electrical path of the carriers to get the optimum thickness. In this work, we propose the insertion of a metasurface based on a cross-patterned ITO contact film, where the crosses are filled with nanospheres. We numerically demonstrate that this configuration improves the photogenerated current up to a 40% by means of the resonant effects produced by the metasurface, being independent on the impinging light polarization. Light handling mechanisms guide light into the active and auxiliary layers, increasing the effective absorption and mitigating the Staebler-Wronski effect. The selection of optimum materials and parameters results in nanospheres of ZnO with a 220 nm radius. ; This work was supported by the Ministerio de Economía y Competitividad of Spain (TEC2016-77242-C3-1-R Grant, AEI/FEDER, European Union funds). López-Fraguas thanks funding support from Ministerio de Educación y Formación Profesional of Spain for his doctoral grant (FPU research fellowship Ref. FPU17/00612). The authors acknowledge Prof. Joshua M. Pearce for providing them with experimental n and k values of the optical constants of the aSi-H.

We theoretically investigate the possibility to load microwave waveguides with dielectric particle arrays that emulate the properties of infinite, two-dimensional, all-dielectric metasurfaces. First, we study the scattering properties and the electric and magnetic multipole modes of dielectric cuboids and identify the conditions for the excitation of the so-called anapole state. Based on the obtained results, we design metasurfaces composed of a square lattice of dielectric cuboids, which exhibit strong toroidal resonances. Then, three standard microwave waveguide types, namely parallel-plate waveguides, rectangular waveguides, and microstrip lines, loaded with dielectric cuboids are designed, in such a way that they exhibit the same resonant features as the equivalent dielectric metasurface. The analysis shows that parallel-plate and rectangular waveguides can almost perfectly reproduce the metasurface properties at the resonant frequency. The main attributes of such resonances are also observed in the case of a standard impedance-matched microstrip line, which is loaded with only a small number of dielectric particles. The results demonstrate the potential for a novel paradigm in the design of "metasurface-loaded" microwave waveguides, either as functional elements in microwave circuitry, or as a platform for the experimental study of the properties of dielectric metasurfaces. ; This work was supported by the European Union COST Action CA16620 "European Network for High Performance Integrated Microwave Photonics", by the Research and Development Program through the Comunidad de Madrid and FEDER Program under grants 2013/MIT-2790 and S2018/NMT-4326, the Ministerio de Economía y Competitividad of Spain (TEC2013-7342-C2-2-R), and the mobility programs of Carlos III University and "José Castillejo" of the Ministerio de Educación, Cultura y Deporte of Spain.

In this work, we present a novel kind of LC mixture (5005) for photonic applications, with emphasis on a LC microlens array. This mixture is a nematic composition of three different families of rod like liquid crystals. The key is that frequency dependence of parallel component of electric permittivity is different for each component, resulting in a strongly dependent on frequency dielectric anisotropy. The unique properties of this LC mixture are demonstrated to work in a frequency modulated LC microlens array. A hole patterned structure is used. Thanks to the special characteristics of this mixture, the microlenses are reconfigurable by low voltage signals with variable frequency. This is a first demonstration of a LC lens with tunable focal length by frequency in an analog way. The result of this type of control are microlenses with low aberrations and fast switching (the frequency switching is around 10 times faster than amplitude modulation). The tunability with frequency and the fast switching, makes this liquid crystal of special interest not only for microlenses but for all kind of optical phase modulators. ; This work was supported by the Research and Development Program through the Comunidad de Madrid (SINFOTON S2013/MIT-2790), the Ministerio de Economía y Competitividad of Spain (TEC2013-47342-C2-2-R) and the funding from Agencia Estatal de Investigación (AEI) and Fondo Europeo de Desarrollo Regional (FEDER) for the Project TEC2016-77242-C3-1-R AEI/FEDER,UE. N Bennis and P Kula acknowledge the Polish Ministry of Science and Higher Education the Statutory Activity PBS-654 and PBS-651 of Military University of Technology respectively.

A novel liquid crystal spherical microlens array with high optical power and almost 100% of fill-factor is proposed and experimentally demonstrated. The combination of a specific structure and electrical waveforms applied to the electrodes generates an array of spherical microlenses with square aperture. The manufacturing process is simple (patterned electrodes) and the microlenses are reconfigurable by low voltage signals (the electrodes are in contact with the LC layer). This device could be a key for the next generation of autostereoscopic devices based on Integral Imaging technique. ; This work was supported by the Research and Development Program through the Comunidad de Madrid (SINFOTON S2013/MIT-2790), the Ministerio de Economía y Competitividad of Spain (TEC2013-47342-C2-2-R) and the funding from Agencia Estatal de Investigación (AEI) and Fondo Europeo de Desarrollo Regional (FEDER) for the Project TEC2016-77242-C3-1-R AEI/FEDER,UE. Finally, we thank the Polish Ministry of Science and Higher Education (Statutory Activity PBS-654 of Military University of Technology).

Visible light communications (VLC) have been proposed for several applications beyond the traditional indoor scenarios, from vehicular to underwater communications. The common element in all these applications is the use of light-emitting diodes (LEDs) in which the forward current that flows through each LED plays a major role. Therefore, knowing the electrical equivalent of the LEDs is a useful tool for the proper design of the VLC systems. Currently, some measurement instruments exist, such as the LCR (inductance, capacitance, and resistance) meters or impedance analyzers to characterize the main parameters of the LEDs. However, these instruments and measurement procedures are subject to satisfying some requirements, such as a minimum value of the input impedance or the maximum forward current. In this work, the LED LXHL-BW02 is used to obtain its equivalent circuit, using different measurement methods and traditional methods of measurement with our proposed method. The equivalent model is implemented on the simulation tool LTSPICE. Our alternative method can be used for determining the electrical equivalent circuit of LEDs subject to high current variations at very high frequencies, in the MHz range, i.e., in an operating range for VLC applications. ; This research was co-financed by Comunidad de Madrid and the FSE/FEDER Program under grant SINFOTON2-CM (S2018/NMT-4326), the Madrid Government (Comunidad de Madrid) under the Multiannual Agreement with UC3M in the line of "Fostering Young Doctors Research" (GEOVEOLUZ-CM-UC3M), and in the context of the V PRICIT (Regional Programme of Research and Technological Innovation, and the Ministerio de Ciencia e Innovación and Agencia Estatal de Investigación (PID2019-109072RB-C31) and under the CDTI (Centre for the Development of Industrial Technology, Ministerio de Ciencia e Innovación) throughthe European Regional Development Fund (ERDF) EXP 00119337/IDI-2019029.

ABSTRACT: 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. ; Funding: European Social Fund (NAWA PROM projekt nr POWR.03.03.00-00-PN13/18); Comunidad de Madrid and FEDER Program (S2018/NMT-4326); MCIN/ AEI/10.13039/501100011033 and European Union "Next generation EU"/PTR (PDC2021-121172-C21); MCIN/ AEI/10.13039/501100011033 and FEDER "A way to make Europe" (PID2019-107270RB-C21, PID2019-109072RB-C31, RTC-2017-6321-1).

In this work, a silicon metasurface designed to support electromagnetically induced transparency (EIT) based on quasi-bound states in the continuum (qBIC) is proposed and theoretically demonstrated in the near-infrared spectrum. The metasurface consists of a periodic array of square slot rings etched in a silicon layer. The interruption of the slot rings by a silicon bridge breaks the symmetry of the structure producing qBIC stemming from symmetry-protected states, as rigorously demonstrated by a group theory analysis. One of the qBIC is found to behave as a resonance-trapped mode in the perturbed metasurface, which obtains very high quality factor values at certain dimensions of the silicon bridge. Thanks to the interaction of the sharp qBIC resonances with a broadband bright background mode, sharp high-transmittance peaks are observed within a low-transmittance spectral window, thus producing a photonic analogue of EIT. Moreover, the resonator possesses a simple bulk geometry with channels that facilitate the use in biosensing. The sensitivity of the resonant qBIC on the refractive index of the surrounding material is calculated in the context of refractometric sensing. The sharp EIT-effect of the proposed metasurface, along with the associated strong energy confinement may find direct use in emerging applications based on strong light-matter interactions, such as non-linear devices, lasing, biological sensors, optical trapping, and optical communications. ; This work is part of the project PID2019-107270RB-C21 and PID2019-109072RB-C31 funded by MCIN/ AEI/10.13039/501100011033 and FEDER "A way to make Europe", PDC2021-121172-C21 funded by MCIN/ AEI/10.13039/501100011033 and European Union "Next generation EU"/PTR, TeDFeS Project (RTC-2017-6321-1 funded by MCIN/AEI /10.13039/501100011033 and FEDER "A way to make Europe") and project S2018/NMT-4326 funded by the Comunidad de Madrid and FEDER Program. J.F.A. acknowledges the financial support from Ministerio de Ciencia, Innovación y Universidades of Spain under Juan de la Cierva-Incorporación grant and P.R-V. the financial support from Ministerio de Educación, Cultura y Deporte of Spain under PhD grant FPU2018/02797. V. D. thanks the Brazilian Agency National Council of Technological and Scientific Development (CNPq) for financial support.

There is an increasing need to control light phase with tailored precision via simple means in both fundamental science and industry. One of the best candidates to achieve this goal are electro-optical materials. In this work, a novel technique to modulate the spatial phase profle of a propagating light beam by means of liquid crystals (LC), electro-optically addressed by indium-tin oxide (ITO) grating microstructures, is proposed and experimentally demonstrated. A planar LC cell is assembled between two perpendicularly placed ITO gratings based on microstructured electrodes. By properly selecting only four voltage sources, we modulate the LC-induced phase profle such that non-difractive Bessel beams, laser stretching, beam steering, and 2D tunable difraction gratings are generated. In such a way, the proposed LC-tunable component performs as an all-in-one device with unprecedented characteristics and multiple functionalities. The operation voltages are very low and the aperture is large. Moreover, the device operates with a very simple voltage control scheme and it is lightweight and compact. Apart from the demonstrated functionalities, the proposed technique could open further venues of research in optical phase spatial modulation formats based on electro-optical materials. ; This work was supported by the Comunidad de Madrid and FEDER Program (S2018/NMT-4326), the Ministerio de Economía y Competitividad of Spain (TEC2013-47342-C2-2-R and TEC2016-76021-C2-2-R), the FEDER/Ministerio de Ciencia, Innovación y Universidades and Agencia Estatal de Investigación (RTC2017-6321-1, PID2019-109072RB-C31 and PID2019-107270RB-C21). The authors also acknowledge the support by the Ministry of National Defense of Poland (GBMON/13-995/2018/WAT), Military University of Technology (Grant no. 23-895).

Correction to: Scientific Reports https://doi.org/10.1038/s41598-020-70783-8, published online 14 August 2020 This Article contains a typographical error in the Acknowledgements section. "the Ministerio de Economía y Competitividad of Spain (TEC2013-47342-C2-2-R)" should read: "the Ministerio de Economía y Competitividad of Spain (TEC2016-77242-C3-1-R)" ; This work was supported by the Comunidad de Madrid and FEDER Program (S2018/NMT-4326), the Ministerio de Economía y Competitividad of Spain (TEC2013-47342-C2-2-R and TEC2016-76021-C2-2-R), the FEDER/Ministerio de Ciencia, Innovación y Universidades and Agencia Estatal de Investigación (RTC2017-6321-1, PID2019-109072RB-C31 and PID2019-107270RB-C21). The authors also acknowledge the support by the Ministry of National Defense of Poland (GBMON/13-995/2018/WAT), Military University of Technology (Grant no. 23-895).

There is an increasing need to control light phase with tailored precision via simple means in both fundamental science and industry. One of the best candidates to achieve this goal are electro-optical materials. In this work, a novel technique to modulate the spatial phase profile of a propagating light beam by means of liquid crystals (LC), electro-optically addressed by indium-tin oxide (ITO) grating microstructures, is proposed and experimentally demonstrated. A planar LC cell is assembled between two perpendicularly placed ITO gratings based on microstructured electrodes. By properly selecting only four voltage sources, we modulate the LC-induced phase profile such that non-diffractive Bessel beams, laser stretching, beam steering, and 2D tunable diffraction gratings are generated. In such a way, the proposed LC-tunable component performs as an all-in-one device with unprecedented characteristics and multiple functionalities. The operation voltages are very low and the aperture is large. Moreover, the device operates with a very simple voltage control scheme and it is lightweight and compact. Apart from the demonstrated functionalities, the proposed technique could open further venues of research in optical phase spatial modulation formats based on electro-optical materials. ; This work was supported by the Comunidad de Madrid and FEDER Program (S2018/NMT-4326), the Ministerio de Economía y Competitividad of Spain (TEC2016-77242-C3-1-R and TEC2016-76021-C2-2-R), the FEDER/Ministerio de Ciencia, Innovación y Universidades and Agencia Estatal de Investigación (RTC2017-6321-1, PID2019-109072RB-C31 and PID2019-107270RB-C21). The authors also acknowledge the support by the Ministry of National Defense of Poland (GBMON/13-995/2018/WAT), Military University of Technology (Grant no. 23-895).

We demonstrate a technique to engineer cylindrical and Powell liquid crystal lenses with positive or negative optical power. The device is based on two indium-tin-oxide electrode combs and a microstructured voltage transmission electrode. The technique features the advantages of a multielectrode lens, albeit using a single lithographic step and only two voltage sources. Extensive control of the phase profile across the device active area is demonstrated, achieving both positive and negative optical power. The lens aperture is not constrained by the geometrical parameters and can be scaled to larger values. ; This work was supported in part by the Comunidad de Madrid and FEDER Program under Grant S2018/NMT-4326, in part by the Ministerio de Economía y Competitividad of Spain under Grant TEC2013-47342-C2-2-R and Grant TEC2016-76021-C2-2-R, in part by the FEDER/Ministerio de Ciencia, Innovación y Universidades and Agencia Estatal de Investigación under Grant RTC2017-6321-1, Grant PID2019-109072RB-C31, and Grant PID2019-107270RB-C21, in part by the Ministry of National Defense of Poland under Grant GBMON/13-995/2018/WAT, and in part by the Military University of Technology under Grant 23-895.

A single-layer, all-dielectric metasurface exhibiting a strong toroidal resonance in the low-atmospheric loss radio window of the subterahertz W-band is theoretically proposed and experimentally demonstrated. The metasurface is fabricated on a high-resistivity floating-zone silicon wafer by means of a single-process, wet anisotropic etching technique. The properties of the toroidal mode of both the constituent dielectric elements and the metasurface are rigorously investigated by means of the multipole decomposition technique and full-wave simulations. The experimental demonstration of such a compact, all-silicon metasurface opens new venues of research in the investigation of toroidal modes and the engineering of functional millimeter-wave components, which can be scaled to terahertz and higher frequencies of the electromagnetic spectrum. ; This work was supported by the European Union COST Action CA16220 "European Network for High Performance Integrated Microwave Photonics", by the Comunidad de Madrid and FEDER Program under grant 2018/NMT-4326, the Ministerio de Economía y Competitividad of Spain (TEC2013-47342-C2-2-R), and the mobility programs of Carlos III University and & "José Castillejo" of the Ministerio de Educación, Cultura y Deporte of Spain

The peculiar optical response of polydimethylsiloxane (PDMS) doped with metallic nanoparticles can be employed to develop optical sensing materials. These nanocomposites may work in an ample range of temperatures, showing good linearity and high sensitivity. Plasmon resonances of the metallic nanoparticles produce interesting effects on the optical response by affecting the effective refractive index of PDMS. The high resonant response leads to a number of different configurations of optical filters and phase devices whose resonant frequency depends on the chosen nanoparticle. Moreover, the wavelength can be tuned up by external manufacturing conditions such as nanoparticle size or fill factor, and by working parameters such as temperature. This work develops the theoretical background required for the design of these structures, and evaluates the adequate dimensional and doping ranges for device optimization. ; This work was supported by Spanish Government RETOS Program grant no. TEC2013-47342-C2-R and no. TEC2013-50138-EXP, the R&D Program SINFOTON S2013/MIT-2790 of the Comunidad de Madrid, and the European COST Action IC1208.

An all-dielectric metasurface exhibiting a strong toroidal resonance is theoretically designed and experimentally demonstrated as an angular-dependent resonant polarization beam-splitter in the microwave K-band. The metasurface is fabricated by embedding a square periodic array of high-permittivity ceramic cuboid resonators in a 3D-printed substrate of polylactic acid. It is demonstrated that by properly selecting the resonator geometry and by tuning the angle of incidence through mechanical rotation, the metasurface can switch between a polarization beam splitting and bandpass or bandstop operation. Such performance is achieved by exploiting the highly asymmetric Fano spectral profile of the toroidal resonance and the very low (high) dispersion of the associated p-(s-) polarized mode resulting from the resonant toroidal dipole mode's field profile, as evidenced by both full-wave and band structure simulations. Theoretically infinite extinction ratios are achievable for polarization beam splitting operation with very low insertion losses and adjustable bandwidth. The experimental demonstration of such a compact, all-dielectric metasurface expands the research portfolio of resonant metasurfaces toward not only the investigation of the intriguing physics of toroidal modes but also to the engineering of functional millimeter-wave components for polarization control, for instance, in the context of 5G wireless communication networks. ; This research was co-financed by the European Union and Greek national funds through the Operational Program Competitiveness, Entrepreneurship and Innovation, under the call RESEARCH CREATE INNOVATE (Project code: No. T1EDK-02784) and by the Comunidad de Madrid and FEDER Program (S2018/NMT-4326), the Ministerio de Economía y Competitividad of Spain (TEC2016-77242-C3-1-R and TEC2016-76021-C2-2-R), and the FEDER/Ministerio de Ciencia, Innovación y Universidades and Agencia Estatal de Investigación (RTC2017-6321-1, PID2019-107270RB-C21 and PID2019-109072RB-C31).

An all-dielectric metasurface exhibiting a strong toroidal resonance is theoretically designed and experimentally demonstrated as an angular-dependent resonant polarization beam-splitter in the microwave K-band. The metasurface is fabricated by embedding a square periodic array of high-permittivity ceramic cuboid resonators in a 3D-printed substrate of polylactic acid. It is demonstrated that by properly selecting the resonator geometry and by tuning the angle of incidence through mechanical rotation, the metasurface can switch between a polarization beam splitting and bandpass or bandstop operation. Such performance is achieved by exploiting the highly asymmetric Fano spectral profile of the toroidal resonance and the very low (high) dispersion of the associated p-(s-) polarized mode resulting from the resonant toroidal dipole mode's field profile, as evidenced by both full-wave and band structure simulations. Theoretically infinite extinction ratios are achievable for polarization beam splitting operation with very low insertion losses and adjustable bandwidth. The experimental demonstration of such a compact, all-dielectric metasurface expands the research portfolio of resonant metasurfaces toward not only the investigation of the intriguing physics of toroidal modes but also to the engineering of functional millimeter-wave components for polarization control, for instance, in the context of 5G wireless communication networks. ; This research was co-financed by the European Union and Greek national funds through the Operational Program Competitiveness, Entrepreneurship and Innovation, under the call RESEARCH CREATE INNOVATE (Project code: No. T1EDK-02784) and by the Comunidad de Madrid and FEDER Program (S2018/NMT-4326), the Ministerio de Economía y Competitividad of Spain (TEC2016-77242-C3-1-R and TEC2016-76021-C2-2-R), and the FEDER/Ministerio de Ciencia, Innovación y Universidades and Agencia Estatal de Investigación (RTC2017-6321-1, PID2019-107270RB-C21 and PID2019-109072RB-C31).