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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. This work was supported by 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). Also, the Ministry of National Defense of Poland (GBMON/13-995/2018/WAT).

Introduction SARS-CoV-2 has affected the whole world as a global health pandemic in 2020. A nationwide home confinement was declared in our country by beginning of March. Cardiac rehabilitation programs (CRP) had to adapt to new health requirements and the impact of these changes is unknown. Purpose To analyse the impact of COVID-19 pandemic in improvement of cardiopulmonary exercise test (CPET) with maximal oxygen consumption uptake (VO2max) and control of cardiovascular risk factors in patients with cardiovascular established disease (coronary heart disease, heart failure or cardiac surgery) included in the phase II of our centre CRP. Methods 510 consecutive patients were evaluated. A maximal CPET was performed for each patient from the beginning and at the end of phase II of CRP. Enrolled patients were divided in two groups: from March 2019 to March 2020 (before Covid pandemic) and second one, from the beginning of the pandemic in March 2020 until February 2021. Results 296 patients were studied in preCovid group and 214 patients were studied in Covid group. There were no statistically significant differences between these two groups in reference to cardiovascular risk factors and medical treatment (Figure 1). 82.7% of patients completed a hospital-based program in preCovid group vs 36% in Covid (p=0.001). Comparing the percentage of patients that accomplished the risk factors control targets between pre- and Covid group, statistically significant differences have been seen referring to systolic BP Conclusions SARS-CoV-2 changed our practice from an in-hospital based phase II CRP to a home-based phase II CRP. COVID-19 pandemic had no negative impact in the control of risk factors in our phase II patients. In our experience, despite preCovid phase II patients have a better functional capacity in terms of VO2max, the improvement in VO2max after phase II CRP persists in the SARS-CoV-2 era. This might show that an accurate structure of home-based program could also have great results. Funding Acknowledgement Type of funding sources: None.

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.

A novel liquid crystal microlens array with tunable multifocal capability, high optical power and fill-factor is proposed and experimentally demonstrated. A specific hole pattern design produces a multifocal array with only one voltage control. Three operations modes are possible, "Off", "Tunable Multifocal" and "Unifocal". The design is patterned in both substrates. Then, the substrates are arranged in symmetrical configuration. The result is a high optical power in comparison with typical hole patterned structures. Besides, it is proposed a hexagonal pattern that produces a high fill factor, specially indicated for some applications as Integral Imaging. The array has several useful characteristics for this type of application: tunability for the loss of resolution; multifocal for extended DOF; high fill factor for increase the number of views; and low power consumption for integration in portable devices. Moreover, the optical characteristics of the proposed device could bring new applications in other fields. 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, N. Bennis, P. Morawiak and L. R. Jaroszewicz, thank the Polish Ministry of Science and Higher Education (Statutory Activity PBS-654 of Military University of Technology).

In this work, a novel wavelength selective switch is proposed and demonstrated. This new configuration avoid the use of grating and lenses, as a result, a very compact and lightweight ultra-selective wavelength switch can be obtained. For this, a novel tunable ultra-selective mirror is used. The tunability is achieved by using LC, the ultra-high Q-factor is obtained by means of dielectric metasurfaces based on hollow core nanocuboids. The metasurfaces are placed in the optical path with a specific angle. Each mirror can select any specific wavelength by applying an AC voltage. For 10°, a 44 nm of tunable range is possible. Absorption is negligible for low applied voltages. The bandwidth of the reflection resonance at 10° ranges from 0.02 nm to 0.035 nm, corresponding to a 2.5 GHz and 4.5 GHz resolution, respectively. This is far beyond the required bandwidth for future Ultra-DWDM systems.

In recent years, research on autostereoscopic vision has grown rapidly. One of the most promising technologies in order to capture and reproduce three-dimensional images is integral imaging (InI). Until now, most of the proposed technologies use microlens arrays in order to reproduce and capture this type of images. One disadvantage is the fixed parameters of these devices. In this letter, an InI capture system with a tunable field of view (FOV) is demonstrated. For this, a microlens array based on liquid crystal technology is used in order to have tunability of some important characteristics of the rendered images such as angular vision. The focal length of each microlens ranges from 2 to 0.5 mm when the applied voltage changes from 1.2 to 2.6 $\text{V}_{\mathrm {rms}}$ , respectively. This mutual dependence, between voltage and focal length, also produces a tunable FOV of an InI capture system ranging from 3° to 12°. A numerical reconstruction algorithm is used in order to synthesize several new views of a scene from different viewpoints and demonstrate this effect.

Wireless communication is growing quickly and now allows technologies like the Internet of Things (IoT). It is included in many smart sensors helping to reduce the installation and system costs. These sensors increase flexibility, simplify deployment and address a new set of applications that was previously impossible with a wired approach. In this work, a wireless temperature sensor based on a nematic liquid crystal as variable capacitance is proposed as a proof of concept for potential wearable applications. Performance analysis of the wireless temperature sensor has been carried out and a simple equivalent circuit has been proposed. Sensor prototype has been successfully fabricated and demonstrated as the beginning of new biomedical sensors. This research was funded by Agencia Estatal de Investigación and FEDER grant number TEC2016-77242-C3-1-R AEI/FEDER,UE and Comunidad deMadrid (SINFOTON-CM) grant number P2013/MIT-2790.

5 págs.; 3 figs., © 1989-2012 IEEE. The resonant modes observed in semiconductor nanoparticles and the coherent interaction between them, producing directional light scattering, may be very interesting for CMOS integrated all-optical devices. In these systems, the control over the light scattering should be crucial, as well as the strength of this control. Fabrication parameters such as the size and shape of the nanoparticles and the optical properties of the environment can strongly affect to the emergence of these phenomena. In this letter, we numerically explore the size dependence of the directional scattering conditions of semiconductor nanoparticles. Several semiconductor materials and a large size range have been considered as a reference for further works. An interesting and unexpected linear behavior has been observed., This work has been supported by Ministerio de Economía y Competitividad of Spain (grants no. TEC2013-47342-C2-2-R and no.TEC2013-50138-EXP) and the R&D Program SINFOTON S2013/MIT-2790 of the Comunidad de Madrid.

In this paper, a novel liquid crystal (LC) temperature sensor is proposed and theoretically analyzed. A detailed analytical model has been presented. The sensor is designed and optimized to produce maximum sensitivities. This sensor is composed of only three electrodes. The electrodes are very simple and can be easily designed for different sizes. The structure uses the temperature dependence of the LC permittivity as sensing magnitude. Several LC have been investigated. The response improves the characteristics of previous LC sensors and even some commercial sensors in terms of sensitivity or linearity. The sensor has a high sensitivity, low-voltage control, low power consumption, and high linearity. The main advantage is the possible integration of this sensor in other LC devices.

The typical sidewalls produced in the fabrication of protrusion electrodes are proposed to create a low voltage (4.5 Vrms) and high transmittance (93%) blue-phase liquid crystal display (BP-LCD). The tilted electrodes produce a strong horizontal electrical field that reduces the operating voltage considerably. The common problem of the ‘dead zones’ is solved by reflecting the light onto the electrodes. In order to estimate the phase retardation of the reflected light, a ray tracing simulation program for anisotropic mediums has been developed. The proposed device is more competitive than vertical field switching based BP-LCD and also, has the advantages of protruded in-plane-switching structures. These facts make this technology a potential candidate for the next generation of BP-LCDs.

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.

The shape of the vaults in masonry bridges has evolved during the history, so that we can find bibliography where, besides recommending one way of build instead of others depending on the period, is also prescribed the way to carry out the backfill of the extrados. All of this emerged initially as a result of the experiences acquired during the construction and the observation of bridges. Hence, during the 18th century new formulations started to arise, but they led to one result in some cases and to the opposite in others. This article tries to make a comparison between some of these formulations, as well as carrying out an analysis of the influence of both, the lowering rise/span ratio of the vaults and the presence of a resistant backfill in its extrados, on the variation of the breaking load., La forma de las bóvedas de los puentes de piedra ha ido evolucionando con el tiempo, existiendo bibliografía en la que además de recomendarse una tipología frente a otra, según la época, se prescribía la manera de ejecutar el relleno del trasdós. Todo ello surgía en un principio como fruto de las experiencias adquiridas durante la construcción y observación de los puentes. Así fueron emergiendo, a partir del siglo xviii, formulaciones que en unos casos aportaban un resultado y en otros el contrario. Este artículo pretende realizar una comparación entre varias de estas formulaciones, así como efectuar un análisis de la influencia en la variación de la carga de rotura, tanto del rebajamiento de la bóveda como de la participación del relleno rígido en el trasdós del mismo.

A subwavelength resonant grating based on plasmonic silver nanowires is proposed and theoretically analyzed. The structure is composed of several Ag nanowires distributed in a parallel configuration with subwavelength grating constant. Despite the use of TM mode, we have discovered that for certain subwavelength distances, the combination with the plasmonic resonances of the nanowires produces a strong reflection at the resonant peaks. This structure could be used to measure deformation variation down to the nanometer range and use it as a micrometric all optical gauge. The effects of the size of the cylindrical metal nanowires on the performance of the sensing have been studied in detail. Two operation modes are observed depending on the structural parameters. Either a phase or amplitude modulation in the visible range could be obtained. In the first case, a sensitivity of 7.5 pm/mu epsilon has been obtained. In the second case, an amplitude modulation of -256.10(-6) dB/mu epsilon has been obtained. This kind of sensor would be cheap and easy to measure by means of a fiber optic link. The structure is simple and easily scalable. This work was supported in part by the Ministerio de Economía y Competitividad of Spain under Grant TEC2013-47342-C2-2-R and Grant TEC2013-50138-EXP and the R&D Program SINFOTON S2013/MIT-2790 of the Comunidad de Madrid. Publicado

In recent years, many experimental and theoretical research groups worldwide have actively worked on demonstrating the use of liquid crystals (LCs) as adaptive lenses for image generation, waveform shaping, and non-mechanical focusing applications. In particular, important achievements have concerned the development of alternative solutions for 3D vision. This work focuses on the design and evaluation of the electro-optic response of a LC-based 2D/3D autostereoscopic display prototype. A strategy for achieving 2D/3D vision has been implemented with a cylindrical LC lens array placed in front of a display; this array acts as a lenticular sheet with a tunable focal length by electrically controlling the birefringence. The performance of the 2D/3D device was evaluated in terms of the angular luminance, image deflection, crosstalk, and 3D contrast within a simulated environment. These measurements were performed with characterization equipment for autostereoscopic 3D displays (angular resolution of 0.03 $^{\circ}$ ).

Liquid crystal (LC) lenses have been the subject of research due to their advantage of focal length tunability that brings added value to applications typically based on conventional gradient index lenses. A novel approach for modeling the unwrapped phase defects in modal LC microlenses is presented. For solving the gradual voltage across the lenses, the proposed analytical method uses only circuit theory exploiting partial differential equations and conformal mapping techniques. The LC molecular ordering has been modeled on the basis of the continuum theory and optical response has been deduced through inspection of phase retardations. The model validity has been checked for predicting some defects of the modal microlenses in the phase of the lens design, comparing experimental characterization with simulation. This work was supported in part by the Ministerio de Ciencia e Innovación of Spain under Grant TEC2009-13991-C02-01 and in part by the Comunidad de Madrid under Grant FACTOTEM2 S2009/ESP-1781. Publicado

A novel cylindrical liquid crystal microlens array with rotary power and tunable capability is proposed and experimentally demonstrated. This structure is capable of generating tunable cylindrical microlenses in two different axis by low voltage control. For this, complex electrical signals are required (electrical phase shift of 180°). A control over the maximum phase shift from $4\pi $ to $34\pi $ radians has been demonstrated. This effect modifies the effective focal length (from 0.2 to 1.2 mm). Moreover, an OFF-state is also possible (behaving like a transparent medium). The structure is simple and does not require a complex fabrication process. The proposed device has several advantages over the existing microlens arrays and is simple and low cost. The device could contribute to developing new applications and to reducing the fabrication costs of current devices. For example, this device can be used in the next generation of mobile displays with autostereoscopic capability.

Three-dimensional vision has acquired great importance in the audiovisual industry in the past ten years. Despite this, the first generation of autostereoscopic displays failed to generate enough consumer excitement. Some reasons are little 3D content and performance issues. For this reason, an exponential increase in three-dimensional vision research has occurred in the last few years. In this review, a study of the historical impact of the most important technologies has been performed. This study is carried out in terms of research manuscripts per year. The results reveal that research on spatial multiplexing technique is increasing considerably and today is the most studied. For this reason, the state of the art of this technique is presented. The use of microlenses seems to be the most successful method to obtain autostereoscopic vision. When they are fabricated with liquid crystal materials, extended capabilities are produced. Among the numerous techniques for manufacturing liquid crystal microlenses, this review covers the most viable designs for its use in autostereoscopic displays. For this reason, some of the most important topologies and their relation with autostereoscopic displays are presented. Finally, the challenges in some recent applications, such as portable devices, and the future of three-dimensional displays based on liquid crystal microlenses are outlined. This work was supported in part by Ministerio de Economía y Competitividad of Spain (grant No. TEC2013-47342-C2-2-R) and the R&D Program SINFOTON S2013/MIT-2790 of the Comunidad de Madrid.

Objetivo: La purificacion del preparado comercial de triamcinolona acetonido disponible es importante para evitar el efecto potencialmente toxico del disolvente alcohol bencilico. Presentamos una nueva tecnica de preparacion de triamcinolona en polvo, a partir de su forma pura, sin disolventes y diluida con agua destilada esteril. Dada su escasa solubilidad en agua se describe como preparar y controlar dicha suspension. Material y metodo: El acetonido de triamcinolona es preparado por el Servicio de Farmacia del Hospital, en condiciones de maxima esterilidad, bajo campana de flujo laminar. La suspension de triamcinolona es envasada en un vial primario, capsulado y posteriormente esterilizado en autoclave a 121 .C. Del vial primario se obtienen dosis individualizadas de 4 mg/0,1 ml. Resultados: Se obtiene la dosis real administrada (3,77 mg/0,1 ml) mediante cuantificacion de triamcinolona por cromatografia liquida de alta resolucion (HPLC). La estabilidad fisica, quimica y microbiologica conservando el vial entre 2-8. se mantiene a los 6 meses. Concusion: Se presenta un metodo de preparacion de triamcinolona en estado puro, obteniendo una concentracion muy proxima a la dosis optima, evitando el uso de disolventes y con maxima garantia de esterilidad

In this work, V-shaped liquid crystals are proposed for phase modulation optical devices. The aim is to measure the relationship between phase shift and the applied voltage by an experimental set-up based on an interferometer. The optical retardation of the liquid crystal medium could then be determined simply by measuring the phase difference of the waves of the two arms. By supplying a voltage, the liquid crystal molecules are reoriented and the effective refractive index of the liquid crystal changes. Preliminary results show that the devices may be used such as phase modulators, but the phase modulation is polarization sensitive.

Diamond-Like Carbon (DLC) films are promising materials for micro and nano electronic industries, by their particular physical-chemical properties. For these applications, DLC films are usually etched by using plasma reactors that operate at low gas pressure thus requiring sophisticated vacuum and gas admission systems. In this work a much simple and inexpensive plasma etching system was used which is based on a dielectric barrier discharge (DBD), operating with oxygen at near atmospheric pressure. The DBD was integrated to a working chamber where a substrate holder was placed to intercept the plasma flow at a distance from the discharge outlet. The performance of the etch process in this system was evaluated by etching DLC films under various operating conditions: pressures in the range (55.0 75.0) kPa, time of process varying from 1min to 20min and electrode-substrate distance (5 and 10 mm). The main characterization techniques to analy ze the etched films were atomic force microscopy (AFM), Raman spectroscopy and profilometry. The results show that etching rates up to 7nm/min can be attained with power as low as 2.3W for a 2.0cm2 exposed area. Overall the etching process in this high pressure oxygen plasma medium differs substantially from the case of low pressure etching. It causes low damage to the substrate and promotes more homogeneous etching.

7 págs.; 7 figs., © 2015 American Chemical Society. 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., This work has been supported by Ministerio de Economia y Competitividad of Spain (Grant Nos. TEC2013−47342-C2−2-R, TEC2012−38901-C02−01, and TEC2013−50138-EXP) and the R&D Program SINFOTON S2013/MIT-2790 of the Comunidad de Madrid.

A tunable aberration compensation device for rectangular micro-optical systems is proposed and demonstrated. This device, which is based in nematic liquid crystal and a micro-electrode structure, forms gradients in the index of refraction as a function of voltage. We have developed a fringe skeletonizing application in order to extract the 3D wavefront from an interference pattern. This software tool obtains the optical aberrations using Chebyshev polynomials. By using phase shifted electrical signals the aberrations can be controlled independently. A complete independent control over the spherical and coma aberration has been demonstrated. Also, an independent control over the astigmatism aberration has been demonstrated in a broad range. This device has promising applications where aberration compensation is required. The independent compensation achieved for some coefficients, such as astigmatism for example, is more than 2.4 waves.

The main characteristic of liquid crystals is that their properties, both electrical and optical, can be modified through a convenient applied signal, for instance a certain voltage. This tunable behavior of liquid crystals is directly related to the orientation of their nanometric components with respect to a director direction. However, the initial alignment is a fabrication-dependent parameter and may be either planar or homeotropic. In addition, the strong dependence of the properties of liquid crystals with the temperature is well known and widely used for several temperature sensors. This dependence is produced by the influence of the temperature on the ordering of the molecules. In this work, we have studied the temperature dependence of the electric properties of a liquid crystal cell, in particular the dielectric permittivity, with the temperature as a function of the initial alignment set during the fabrication process. Starting from experimental measurements, an equivalent circuit model including the temperature dependence has been proposed. We have observed that a good linearity in a wide temperature range is provided at a suitable exciting frequency. Finally, a proper conditioner circuit is proposed as a powerful tool for linear and high sensibility temperature measurement. This work was supported by the Ministerio de Economía y Competitividad of Spain (grant No. TEC2013-47342-C2-2-R) and Comunidad de Madrid (SINFOTON-CM, reference P2013/MIT-2790).

Over the last twenty years, there has been a growing interest in the design of tunable devices at microwave frequencies by us- ing liquid crystals technology. In particular, the use of liquid crystals with high dielectric anisotropy allows manufacturing voltage-controlled devices to operate in a wide frequency range. In this work the frequency response of a liquid crystal band-pass filter with dual-mode microstrip structure has been studied in depth by using a simulation software tool. A reshap- ing of a conventional dual-mode square patch resonator bandpass filter with a square notch, studied in the literature, has been proposed with the goal of improving the filter performance. The main features achieved are a significant increase in the return loss of the filter and a narrowing of a 3-dB bandwidth. Specifically, a reduction in the filter bandwidth from 800 MHz to 600 MHz, which leads to a return loss increase from 6 dB to 12.5 dB, has been achieved. The filter centre frequency can be tuned from 4.54 GHz to 5.19 GHz.

Surface stabilisation of ferroelectric liquid crystals (SSFLC) shows interesting properties: in plane switching, high viewing angle and fast response. Liquid crystal on silicon (LCOS) devices have an active matrix fabricated onto a silicon buffer, which requires metallization of the inner surface to achieve reflectivity. In this work, the influence of the cell thickness on the device colour upon switching has been studied. Little variations of the cell thickness without damaging surface stabilisation change phase delays, selecting the reflected wavelength if the birefringence is unchanged. Light path is double than that in a transmissive cell, thus similar thickness variations cause higher colour deviations.

Addressing waveforms for reflective LCOS devices filled with V-shape chiral smectic liquid crystals, have been tested and optimised. Analogue greyscale generation has been tested on passive devices mimicking the behaviour in active matrix based devices. A comparative study of a number of experimental chiral smectic mixtures showing V-shape response has been carried out. Specific driving waveforms have been designed and optimised in order to improve the material's electro-optic response. This procedure is lengthy since every voltage level of the waveform ought to be separately optimised, and interdependences between the different waveform fragments lead to an iterative optimisation process. The effect of a short blanking pulse named well pulse has been particularly remarkable, thus forcing a thorough tune-up as a function of working temperature and video rate.

Antiferroelectric Liquid crystal cells having a SiOx on one side and a conventional alignment layer on the other side have been prepared. This manufacturing process allows the antiferroelectric cell to be driven as a ferroelectric cell. This behavior opens the possibility of driving the cell with simple bipolar pulses, allowing some interesting effects such as video-rate multiplexed analogue gray scale.

A new manufacturing procedure producing asymmetric hysteresis curves in surface-stabilized antiferroelectric liquid crystal cells has been developed. It is based on the use of dissimilar surface conditionings on either side of the cell. The central relaxed AFLC state is not located at zero volts. The AF→F transitions on either side, consequently, are not produced at the same switching voltage. This behavior opens the possibility of driving the cell with several new modes, allowing some interesting effects such as video-rate multiplexed analogue grayscale with simple bipolar pulses, and longterm multistability.

The ethylene-propylene diene monomer (EPDM) rubber is an important material for rocket engine technology due to its thermal and mechanical characteristics. The improvement of the adhesion character...

Surface-stabilized antiferroelectric liquid crystals (AFLCs) and V-shape smectics share the spontaneous generation of intermediate transmission states, i.e. analogue grayscale. On the other hand, liquid crystal on silicon (LCOS) appears to be a promising alternative to thin-film transistors (TFTs) in the preparation of reflective microdisplays and spatial light modulators (SLMs). The feasibility of preparing LCOS SLMs using AFLC and V-shaped LCs has been analyzed. A comparative study of a number of AFLC and V-shape materials as candidates for LCOS SLMs has been carried out. Test cells below 1 µm have been prepared using an ITO-coated transparent glass plate and an aluminized silicon back plate mimicking the actual LCOS device. AFLC waveforms compatible to low-voltage operation of the silicon backplane have been demonstrated. V-shape waveforms have been designed and demonstrated as well. The results show that both LC families may be employed in this specific application. Dynamic behavior, with frame rates ...

Nematic liquid crystal (LC)-based beam steering has 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. In this work, novel beam steering based on polymer stabilized blue phase liquid crystal (PS-BPLC) has been designed and theoretically analyzed. This special mesophase of the chiral doped nematic LC has several advantageous characteristics, for example no need for alignment layers, microsecond response time and an isotropic voltage-off state. The results reveal control over phase retardation. The direction of the steered beam can be tuned by voltage. Depending on voltage configuration, either diffractive beam steering (0.5deg deviation for 1st order) or a tunable continuous phase (tunable deviation of 0.002deg) can be obtained. In the first case, the deflection angle could be tuned by stacks of samples. The second option has the same phase shift for the TE and TM modes so unpolarized light could be used. Full Text: PDF References F. Feng, I. White, T. Wilkinson, "Free Space Communications With Beam Steering a Two-Electrode Tapered Laser Diode Using Liquid-Crystal SLM", J. Lightwave Technol. 31, 2001 (2013). CrossRef E. Oton, J. Perez-Fernandez, D. Lopez-Molina, X. Quintana, J.M. Oton, M.A. Geday, "Reliability of Liquid Crystals in Space Photonics", IEEE Photonics Journal 7, 1 (2015). CrossRef J. Stockley, S. Serati, "Multi-access laser terminal using liquid crystal beam steering", IEEE in Aerospace Conference, 1972 (2005). CrossRef D. Zografopoulos and E. Kriezis, "Switchable beam steering with zenithal bistable liquid-crystal blazed gratings", Opt. Lett. 39, 5842 (2014). CrossRef Benedikt Scherger, et al., "Discrete Terahertz Beam Steering with an Electrically Controlled Liquid Crystal Device", J. Infrared. Millim. Terahertz Waves 33, 1117 (2012). CrossRef M.A. Geday, X. Quintana, E. Oton, B. Cerrolaza, D. Lopez, F. Garcia de Quiro, I. Manolis, A. Short, Proc. ICSO, Rhodes, Greece, pp. 1-4 (2010). CrossRef Y. Chen, S.-T. Wu, "The outlook for blue-phase LCDs", Proc. SPIE 9005, Advances in Display Technologies IV, 900508 (2014). CrossRef G.D. Love, A.F. Naumov, "Modal liquid crystal lenses", Liq. Cryst. Today 10, 1 (2000). CrossRef V. Urruchi, J.F. Algorri, J.M. Sanchez-Pena, M.A. Geday, X. Quintana, N. Bennis, "Lenticular Arrays Based on Liquid Crystals", Opto-Electron. Rev. 20, 38 (2012). CrossRef J.F. Algorri, G. Love, and V. Urruchi, "Modal liquid crystal array of optical elements", Opt. Express 21, 24809 (2013). CrossRef J.F. Algorri, V. Urruchi, N. Bennis, J. Sanchez-Pena, "Modal liquid crystal microaxicon array", Opt. Lett. 39, 3476 (2014). CrossRef J.F. Algorri, V. Urruchi, B. Garcia-Camara, J.M. Sanchez-Pena, "Generation of Optical Vortices by an Ideal Liquid Crystal Spiral Phase Plate", IEEE Elect. Dev. Lett. 35, 856 (2014). CrossRef D. Xu, Y. Chen, Y. Liu, S. Wu, "Refraction effect in an in-plane-switching blue phase liquid crystal cell", Opt. Express 21, 24721 (2013). CrossRef Z. Ge, S. Gauza, M. Jiao, H. Xianyu, S.T. Wu, "Electro-optics of polymer-stabilized blue phase liquid crystal displays", Appl. Phys. Lett. 94 101104 (2009). CrossRef J. Yan et al., "Extended Kerr effect of polymer-stabilized blue-phase liquid crystals", Appl. Phys. Lett. 96, 071105 (2010). CrossRef X. Wang, D. Wilson, R. Muller, P. Maker, D. Psaltis, "Liquid-crystal blazed-grating beam deflector, Appl. Opt. 39, 6545 (2000). CrossRef

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).

An ideal spiral phase plate based on liquid crystals and two high resistivity layers is proposed and theoretically analyzed. The proposed structure generates a spiral-like voltage with simple voltage control. The liquid crystal layer produces an optical phase shift that depends on the voltage distribution. These two effects cause light passing through the device to be twisted like a corkscrew around its travel axis. Because of the continuous phase shift, the proposed device is expected to exhibit a conversion efficiency of similar to 100%. In addition, this device is more efficient and simpler than previously reported optical vortex generators. Moreover, the device is completely reconfigurable, i.e., the operating wavelengths and topological charges are tunable. The device can be used to reduce the fabrication costs of current devices and generate different orbital angular momentum modes with improved light efficiency, simplicity, and possibility of reconfiguration. This work was supported by the Comunidad de Madrid under Grant FACTOTEM2 S2009/ESP-1781. Publicado

A localized surface plasmon resonance based fiber optic sensor for temperature sensing has been analyzed theoretically. The effects of the size of the spherical metal nanoparticle on the performance of the sensor have been studied in detail. The high sensitivity of localized surface plasmon resonances to refraction index changes, in collaboration with the high thermo-optic coefficients of Liquid Crystal materials, has result in a fiber optical sensor with high temperature sensitivity. This sensitivity has been demonstrated to be dependent on nanoparticle size. Maximum sensitivities of 4nm/°C can be obtained for some specific temperature ranges. The proposed sensor will be low cost, and will have all the typical advantages of fiber optic sensors.

A novel temperature sensor based on nematic liquid crystal permittivity as a sensing magnitude, is presented. This sensor consists of a specific micrometric structure that gives considerable advantages from other previous related liquid crystal (LC) sensors. The analytical study reveals that permittivity change with temperature is introduced in a hyperbolic cosine function, increasing the sensitivity term considerably. The experimental data has been obtained for ranges from -6 degrees C to 100 degrees C. Despite this, following the LC datasheet, theoretical ranges from -40 degrees C to 109 degrees C could be achieved. These results have revealed maximum sensitivities of 33 mV(rms)/degrees C for certain temperature ranges; three times more than of most silicon temperature sensors. As it was predicted by the analytical study, the micrometric size of the proposed structure produces a high output voltage. Moreover the voltage's sensitivity to temperature response can be controlled by the applied voltage. This response allows temperature measurements to be carried out without any amplification or conditioning circuitry, with very low power consumption. This work was supported in part by the Ministerio de Ciencia e Innovación of Spain (grant No.TEC2009-13991-C02-01) and Comunidad de Madrid (grant No. FACTOTEM2 S2009/ESP-1781).

Light scattering by semiconductor nanoparticles has been shown to be more complex than was believed until now. Both electric and magnetic responses emerge in the visible range. In addition, directional effects on light scattering of these nanoparticles were recently obtained. In particular, zero backward and minimum-forward scattering are observed. These phenomena are very interesting for several applications such as, for instance, optical switches or modulators. The strong dependence of these phenomena on the properties of both the particle and the surrounding medium can be used to tune them. The electrical control on the optical properties of liquid crystals could be used to control the directional effects of embedded semiconductor nanoparticles. In this work, we theoretically analyze the effects on the directional distribution of light scattering by these particles when the refractive index of a surrounded liquid crystal changes from the ordinary to the extraordinary configuration. Several semiconductor materials and liquid crystals are studied in order to optimize the contrast between the two states. This work has been supported by the Spanish Ministry of Science and Innovation (Grant No. TEC2009-13991-C02-01) and Comunidad de Madrid (Grant No. FACTOTEM2 S2009/ESP-1781). B.G.-C. thanks Carlos III University of Madrid for his postdoctoral grant.

Until now, several attempts have been made to obtain axicons by using liquid crystals. Previous results had always a considerable deviation from the linear response and the resulting aperture is square. In addition, classical fabrications methods are expensive and only produce fixed phase profiles. In this study, a novel structure to obtain tunable axicons with a perfect conical shape and a circular aperture is proposed and theoretically studied. The proposed optical device is based on nematic liquid crystal and phase shifted electrical signals. A simulation program consisted of Finite Elements Method to solve the voltage distribution combined with the Frank-Oseen equation to solve the molecular position of the nematic liquid crystal is employed. This device is totally reconfigurable by using low voltage signals. The focus depth and the position of this one can be controlled electrically. This work was supported in part by the Ministerio de Ciencia e Innovación of Spain (grant No. TEC2009-13991-C02-01) and the Comunidad de Madrid (grant No. FACTOTEM2 S2009/ESP-1781).

In this paper, the design and experimental characterization of a tunable microstrip bandpass filter based on liquid crystal technology are presented. A reshaped microstrip dual-mode filter structure has been used in order to improve the device performance. Specifically, the aim is to increase the pass-band return loss of the filter by narrowing the filter bandwidth. Simulations confirm the improvement of using this new structure, achieving a pass-band return loss increase of 1.5 dB at least. Because of the anisotropic properties of LC molecules, a filter central frequency shift from 4.688 GHz to 5.045 GHz, which means a relative tuning range of 7.3%, is measured when an external AC voltage from 0 Vrms to 15 Vrms is applied to the device. © 2014 by the authors. Authors acknowledge Grupo de Fotónica Aplicada (Universidad Politécnica de Madrid, Spain) for the use of their facilities for the manufacture of the device. Authors thank funding support from the Spanish Ministerio de Economía y Competitividad (grant No. TEC2009-13991-C02-01) and Comunidad de Madrid (grant No. FACTOTEM2 S2009/ESP/1781).

This letter presents a novel temperature sensor, which consists of an interdigitated comb electrode structure with a micrometric-scale size, nanometric metallic layer, and nematic liquid crystal (NLC) film. This sensor exploits the permittivity dependence of the NLC with temperature and principle of electrical conductivity above the percolation threshold in thin film metallic layers. The latter has been demonstrated to increase the temperature sensitivity considerably. The high impedance input reduces the power dissipation, and the high enough voltage output makes it easy to measure the output signal with high precision. The operation principle and fabrication process as well as the characterization of the temperature sensor are presented. Experimental results show that the device offers a sensitivity of 9 ${\rm mV}/^{\circ}{\rm C}$ and is dependent on the applied voltage. This is six times greater than the same structure without the use of a nanometric layer.

Proceeding of: 2014 IEEE SENSORS proceedings: Valencia, Spain, November 2-5, 2014 In this work, a novel liquid crystal (LC) temperature sensor, based on a Silver (Ag) wire grating, is proposed and theoretically analyzed. The structure is composed of several Ag nanowires distributed in a parallel configuration (see Fig. 1). These wires can be deposited onto a silica glass or plastic substrate. Another substrate positioned on it is separated by spacers of 1.2 mum. The resulting cavity is filled with an E7 LC. The high thermo-optic coefficient of the LC is used to modify the plasmonic resonance of the wire grating. The structure is simple and easily scalable. The application of a 420 nm laser allows an output power ratio sensitivity of 16.7.10 -2 dB/degC with a high linearity. This is ten times more than other related temperature sensors based on light intensity variation. This work was supported in part by the Ministerio de Ciencia e Innovación of Spain (grant no.TEC2009-13991-C02-01) and the Comunidad de Madrid (grant no. FACTOTEM2 S2009/ESP-1781).

We have developed new analytical expressions for designing liquid crystal (LC) microlenses. These equations are based on a novel equivalent electric circuit and can be used to create an optimum design for the LC lenses in which the lens diameter ranges from a few micrometers to several millimeters. Thus far, only experimental studies have been conducted on the LC lenses. The analytical expressions developed in this letter depend on various manufacturing parameters and can be used to design lenses with specific focal lengths and a parabolic phase profile. The required driving scheme (modal or hole-patterned) can be predicted. The LC microlenses were manufactured and electrooptically characterized: the measurements were compared using an analytical approach.

In this article, the design, fabrication, and characterization of a tunable microwave notch filter based on liquid crystal (LC) using inverted-microstrip technology is presented. A spiral spurline structure is used because of its good performance as a single-resonator notch filter. Based on the LC dielectric anisotropy, a voltage-controlled rejection frequency of the filter is achieved, ranging from 3.40 to 3.75 GHz, which means that the tuning range relative to the central rejection frequency is about 10%. At the same time, this device exhibits negative group delay around the rejection frequency and the measured values throughout the tuning frequency range are presented. J. A. and M.M.S.L. acknowledge funding support from the Spanish Ministerio de Economia y Competitividad through project FIS2012-39158-C02-02. J. T., C. M., V. U. and J. M. S. P. thank funding support from the Spanish Ministerio de Economia y Competitividad (grant no. TEC2009–13991-C02-01) and Comunidad de Madrid (grant no. FACTOTEM S2009/ESP/1781). Publicado

Copyright 2013 American Institute of Physics. This article may be downloaded for personal use only. Any other use requires prior permission of the author and the American Institute of Physics. The following article appeared in Review of Scientific Instruments (2013), 84 (2). and may be found at http://dx.doi.org/10.1063/1.4790555 In this work, a compact design of an electrically tunable notch filter, based on liquid crystal (LC) technology, has been designed, manufactured, and characterized. The proposal has been achieved through particular configuration schemes with low cost inverted-microstrip structures and conventional spurlines structures due to its ease of integration. Central frequency tunability has been induced by applying low ac voltages, thus involving low power consumption. For these devices, filter responses have been approached specifically at microwave C-band frequency allocated for many satellite communications applications. Also, it has taken advantage of new highly anisotropic nematic LC mixtures at those frequency ranges. Financial support of the Spanish Ministry of Science and Innovation, Grant No. TEC2009-13991-C02-01, and Comunidad de Madrid, Project No. FACTOTEM2 S2009/ESP-1781. Publicado

Copyright 2013 American Institute of Physics. This article may be downloaded for personal use only. Any other use requires prior permission of the author and the American Institute of Physics. The following article appeared in Review of Scientific Instruments (2013), 84 (11). and may be found at http://dx.doi.org/10.1063/1.4832419 In this work, a novel equivalent electric circuit for modeling liquid crystal microlenses is proposed. This model is focused on explaining a lens behavior at the micrometric scale, using its manufacturing parameters. It suggests an approach to predict the solution of the voltage gradient distribution across a microlens. An interesting feature of the model is that it provides an analytical solution for microlenses with modal and hole-patterned electrode schemes, by a simple software tool. The model flexibility allows lens designers to apply complex waveform signals with different harmonics. The voltage distribution has been tested. The simulated and measured voltage profiles are fairly in agreement. Spanish Ministerio de Economia y Competitividad (Grant No. TEC2009-13991-C02-01) and Comunidad de Madrid (Grant No. FACTOTEM S2009/ESP/1781). Publicado

VIII Reunión Española de Optoelectrónica (OPTOEL 2013), Alcalá de Henares, Madrid, 10-12 de julio de 2013. In this study, a novel algorithm to solve the position of a nematic liquid crystal molecular director inside a device has been proposed. The formulation for minimizing the Gibbs free energy, composed by the free energy deformation (Frank-Oseen equations) minus the electrical energy, has been established using a vectorial representation of the director. The three liquid crystal elastic constants have been considered. The differential equations involved have been solved by applying numerical methods, using an algorithm developed by the authors. It has been compared with other techniques and the main advantages are that the new algorithm is faster and more accurate than other previous methods such as finite difference method (FDT) or a boundary value problem solver of MATLAB (bvp4c). Simulation program is also a powerful tool for analyzing other liquid crystal properties such as refractive index and permittivity as a function of voltage. To validate the simulation results, they have been compared with some measurements of a nematic liquid crystal device manufactured for that purpose. The comparison of birefringences simulated and measured show results that are fairly in agreement. This work also aims to provide a software simulation tool easy to reprogram for more complex devices. En este trabajo se propone un nuevo algoritmo para resolver la posición molecular del cristal liquido nemático (CLN) en un dispositivo afectado por un campo eléctrico. La formulación característica del CLN bajo la influencia de un campo eléctrico se compone de la energía libre de deformación de Frank-Oseen menos la energía eléctrica. Este resultado, considerado como energía libre de Gibbs, tiene un mínimo cuando el director molecular se encuentra en equilibrio. La minimización de esta energía ha sido establecida usando una representación esférica del director molecular. Se han considerado las constantes elásticas del CLN y se ha resuelto mediante métodos numéricos. Para ello se emplea un algoritmo desarrollado por los autores, que ha sido comparado con otros métodos propuestos en la literatura como el método de las diferencias finitas (FDT) o un método de resolución propietario de MATLAB conocido como bvp4c. Las comparativas realizadas muestran un comportamiento superior del algoritmo propuesto, siendo más rápido y preciso que los métodos anteriores. Una vez que se conoce la posición de las moléculas en el dispositivo, otros parámetros como índice de refracción y permitividad en función del voltaje, pueden ser determinados. Para dar una validez a los resultados de simulación, se ha fabricado y caracterizado un dispositivo monopixel de CLN. Las medidas experimentales de birrefringencia y permitividad para diferentes tensiones de alimentación muestran una gran concordancia con los resultados de simulación. Este trabajo pretende proporcionar una herramienta de simulación que puede emplearse en otros dispositivos de CLN más complejos en los cuales se conoce la distribución de tensión. Acknowledgements: This work was supported in part by the Ministerio de Ciencia e Innovación of Spain (grant no. TEC2009-13991-C02-01) and Comunidad de Madrid (grant no. S2009/ESP-1781).

Copyright 2012 American Institute of Physics. This article may be downloaded for personal use only. Any other use requires prior permission of the author and the American Institute of Physics. The following article appeared in Review of Scientific Instruments (2012), 83 (8). and may be found at http://dx.doi.org/10.1063/1.4738645 In this work, tunable series and parallel resonators based on a nematic liquid crystal cell as variable capacitance are proposed and characterized. Tunable resonance frequencies in the range of kHz have been obtained for the combination of the inductance and the liquid crystal cell (capacitance) used in the proposed circuits. Tuning range in frequency obtained is around an octave. This work was supported in part by the Spanish Ministry of Science and Technology (TEC2009- 13991-C02-01) and the Comunidad de Madrid (FACTOTEM2-CM, REF.S2009/ESP- 1781). Publicado

Copyright 2011 American Institute of Physics. This article may be downloaded for personal use only. Any other use requires prior permission of the author and the American Institute of Physics. The following article appeared in Review of Scientific Instruments (2011), 82 (12). and may be found at http://dx.doi.org/10.1063/1.3666865 A phase-locked loop is demonstrated using a twisted-nematic liquid crystal cell as a capacitance that can be varied as a function of applied voltage. The system is formed by a phase detector, a low-pass filter, as well as a voltage controlled oscillator including such variable capacitance. A theoretical study is proposed and experimentally validated. Capture and locked ranges of hundreds of kHz have been obtained for the configuration used in this circuit. An application as frequency demodulator using a practical implementation of this circuit has been demonstrated. This work was supported in part by the Spanish Ministry of Science and Technology (TEC2009-13991-C02-01) and the Comunidad de Madrid (FACTOTEM2-CM, REF.S2009/ESP-1781). Publicado

Lenticular array products have experienced a growing interest in the last decade due to the very wide range of applications they can cover. Indeed, this kind of lenses can create different effects on a viewing image such as 3D, flips, zoom, etc. In this sense, lenticular based on liquid crystals (LC) technology is being developed with the aim of tuning the lens profiles simply by controlling the birefringence electrically. In this work, a LC lenticular lens array has been proposed to mimic a GRIN lenticular lens array but adding the capability of tuning their lens profiles. Comb control electrodes have been designed as pattern masks for the ITO on the upper substrate. Suitable high resistivity layers have been chosen to be deposited on the control electrode generating an electric field gradient between teeth of the same electrode. Test measurements have allowed us to demonstrate that values of phase retardations and focal lengths, for an optimal driving waveform, are fairly in agreement. In addition, results of focusing power of tuneable lenses were compared to those of conventional lenses. The behaviour of both kinds of lenses has revealed to be mutually similar for focusing collimated light and for refracting images. This work was supported partially by the Ministerio de Ciencia e Innovación of Spain (grant no.TEC2009−13991−C02−01) and Comunidad de Madrid (grant no. FACTOTEM2 S2009/ESP−1781).

Special Issue: The 11th European Conference on Liquid Crystals (ECLC 2011). Maribor, Slovenia, February 6-11 , 2011 In this work, one-dimensional arrays of cylindrical adaptive liquid crystal lenses were manufactured and characterized; and test devices were filled with nematic liquid crystal. Comb interdigitated electrodes were designed as a mask pattern for the control electrode on the top glass substrates. A radial graded refractive index along each microsized lens was achieved by fabricating a layer of high resistance sheet deposited as a control electrode. These tunable lenses were switched by applying amplitude and frequency optimized waveforms on the control electrode. Phase profiles generated by the radial electric field distribution on each lens were measured by a convectional interferometric technique. This work was supported in part by the Ministerio de Ciencia e Innovación of Spain (grant no.TEC2009-13991-C02-01) and Comunidad de Madrid (grant no. S2009/ESP-1781). Publicado