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The luminescence properties of Pt(II) compounds can be modulated by controlling the assembly of their molecules both in the solution and in the solid state. This fact constitutes a powerful tool for developing materials with stimuli-responsive luminescence properties. Herein, we describe the self-assembly behaviour of several series of Pt(II) metallomesogens in two different media upon controlled conditions. On the one hand, we explore the ability of several metal cations to induce the formation of Pt⋯Pt aggregates in solution, with the main goal of enhancing the phosphorescent emission of these compounds. On the other hand, since these compounds exhibit liquid crystalline mesophases and the temperature can control the aggregation, we have fabricated Pt(II) compound-doped polymer films and silicone membranes that show stimuli-responsive luminescent properties. In both cases, the interactions between the Pt(II) compounds and the metal cations, or the polymer matrices, play a key role in the aggregation-induced emission enhancement (AIEE) behaviour of the dyes. The effects of the alkyl chain length, the molecular asymmetry, and the nature of the ligands in the establishment of these interactions are also evaluated., Ministerio de Economía y Competitividad, MINECO/FEDER (Spain), project CTQ2015-63858-P, PROTEOMASS Scientific Society (Portugal), Associate Laboratory for Green Chemistry-LAQV/REQUIMTE, FCT/MEC (Portugal), project UID/QUI/50006/2013, Universidad Complutense de Madrid-Santander Universidades (Spain), Fundación Alfonso Martín Escudero (Spain), Ministerio de Economía y Competitividad (Spain) and European Social Fund - BES-2014-070964, Depto. de Química Inorgánica, Fac. de Ciencias Químicas, TRUE, pub

Liquid Crystal-based mm-wave spatially fed antennas with electronic reconfiguration are a promising solution at the higher frequencies required in next generation networks. However, one of the main drawbacks of the technology in these bands stems from the high reconfigurability times they present. Through this work, a relevant step towards overcoming the temporal problem by using Dual Frequency Liquid Crystals (DFLC) is presented. This paper details, for the first time, both the electromagnetic and temporal characterization of four commercially available DFLC mixtures in W-band, enabling their use in designing faster devices. To evaluate the experimental characterization, a reflectarray surface (made of 50x50 cells) specifically designed to achieve fast switching times with a sufficient phase range has been manufactured and measured. For this cell, a preliminary addressing technique based on overdriving has been used, exhibiting reconfigurability (rise and decay) times of 20 ms, one order of magnitude faster than the current state of the art of LC-based mm-wave planar devices. The measured results match the simulations, and reveal that a precisely designed biasing technique using overdrive must be used for DFLC-cells to achieve time reduction. Additionally, the benefits of this technology compared with other LC acceleration strategies in mm-wave are discussed.

En este artículo se presenta una original configuración óptica transmisiva sintonizable para generar una gama de haces con vórtice perfecto (PVB) que transportan diferentes cargas topológicas (TC) sin utilizar partes móviles. Se denomina haz con vórtice perfecto a aquel que, al variar la carga topológica, no varía el tamaño del vórtice. La configuración se compone de un dispositivo transparente de fase en espiral (SPP) de cristal líquido (LC) reconfigurable fabricado ad hoc, un axicón refractivo y una lente refractiva convergente. Los electrodos del dispositivo SPP se fabrican mediante ablación de ITO (óxido de estaño e Indio) en sustratos de vidrio empleando escritura láser directa (DLW), lo que da como resultado un dispositivo con un factor de llenado muy elevado. La electrónica construida ad hoc excita los 72 electrodos del SPP, dando lugar a 72 configuraciones diferentes con momento angular orbital. En este trabajo se logra la generación de haces con vórtice perfecto con 36 cargas topológicas positivas o 36 negativas utilizando esta configuración óptica.

A transparent variable diffractive spiral axicon (DSA) based on a single LC cell is presented. The manufactured DSA can be switched between 24 different configurations, 12 convergent and 12 divergent, where the output angle is varied as a function of the applied topological charge. The active area of the device is created using a direct laser writing technique in indium-tin oxide coated glass substrates. Liquid crystal is used to modulate the phase of the incoming beam generating the different DSA configurations. The DSA consists in 24 individually driven transparent spiral shaped electrodes, each introducing a specific phase retardation. In this article, the manufacture and characterization of the tunable DSA is presented and the performance of the DSA is experimentally demonstrated and compared to the corresponding simulations.

The slow response time of planar Liquid Crystal (LC)-based phase-shift metasurface and Reconfigurable Intelligent Surfaces (RIS) cells is addressed in this paper by introducing a polymer network LC (PNLC) mixture suitable at mm-wave bands. Since the conventional effective isotropic model used in optical cells for describing the PNLC is not suitable in RF, an effective anisotropic and uniaxial model for such mixture is provided and experimentally validated at 100 GHz for the first time. In order to compare the temporal performance and tunability of the PNLC, transmissive and reflective cells, containing conventional LC and PNLC, have been manufactured and measured at optical and mm-wave frequencies. The temporal responses of PNLC are also compared for both RF and optical cells, obtaining relevant differences between their improvement factors, which are also discussed. Specifically, a 50 fold response time improvement is attained in cells designed to work at 100 GHz, although at the expense of a 3X tunability reduction. The model, which is robust to varying angle of incidence and cell dimensions, has been experimentally validated by designing and manufacturing a PNLC reflectarray cell of a different geometry. The cell shows reconfigurability times of 210ms, representing a significant improvement with respect to state-of-the-art response time in mm-wave cells, which are in the order of several seconds.

Las células de cristal líquido están normalmente formadas dos sustratos de cristal, recubiertos en su cara interna por electrodos de óxido de estaño e indio (ITO) u óxido de estaño fluorado (FTO). Sobre estos metales se deposita una capa de alineamiento, estando finalmente el cristal líquido contenido entre estos dos sustratos. Para el correcto funcionamiento de las células, es crítico verificar un correcto aislamiento entre electrodos antes de continuar con la fabricación. Para que, en caso de detectar errores, estos puedan ser corregidos durante la etapa inicial. Existen diferentes técnicas para la fabricación de estos electrodos siendo las más comunes la fotolitografía y la ablación láser. Una mala configuración de los parámetros de fabricación, como por ejemplo falta de potencia en el caso de la ablación laser, puede suponer que no se elimine correctamente el material obteniendo un aislamiento insuficiente entre electrodos. Para realizar estas comprobaciones es necesario medir la resistividad entre un gran número de electrodos. El objetivo de este proyecto es el desarrollo de un sistema automatizado capaz de medir la conductividad entre electrodos, permitiendo la detección de posibles errores de forma temprana. Con este fin, se ha realizado el diseño del circuito para la medición de la resistividad entre electrodos de una célula de cristal líquido. Posteriormente, se ha llevado a cabo un estudio sobre los componentes necesarios para implementar dicho circuito en una placa de circuito impreso (PCB). Finalmente, se ha diseñado la PCB mediante un programa de diseño electrónico, importando las huellas de los componentes necesarios y realizando el diseño de los esquemáticos. Por otro lado, se ha realizado la distribución de los componentes dentro de la placa y se ha llevado a cabo el enrutado. Con el fin de verificar el funcionamiento del circuito diseñado se ha realizado una prueba de concepto del mismo, detectando correctamente cortocircuitos y circuitos abiertos.

Optical beam steering (BS) has multiple applications in fields like target seeking and tracking, optical tweezers, billboard displays and many others. In this work, a two-dimensional beam deflector based on blaze gratings is presented. Phase-only 1D blaze gratings have been prepared using maskless Direct Laser Writing (DLW) resulting in high-resolution structures in indium-tin oxide (ITO) coated glass wafers. The device is composed of two identical 1D liquid crystal (LC) cells cascaded orthogonally back-to-back, with a resultant active area of 1.1 × 1.1 mm2. The 1D cells have been prepared with 144 pixels each with a 7.5 µm pitch. The total 288 pixels are driven by a custom made 12-bit Pulse Width Modulation (PWM) electronic driver, allowing for an arbitrarily high resolution. The system performance is documented, and the efficiency of the system has been tested. A maximum diagonal steering angle of ± 3.42° was achieved.

The luminescence properties of Pt(II) compounds can be modulated by controlling the assembly of their molecules both in the solution and in the solid state. This fact constitutes a powerful tool for developing materials with stimuli-responsive luminescence properties. Herein, we describe the self-assembly behaviour of several series of Pt(II) metallomesogens in two different media upon controlled conditions. On the one hand, we explore the ability of several metal cations to induce the formation of Pt⋯Pt aggregates in solution, with the main goal of enhancing the phosphorescent emission of these compounds. On the other hand, since these compounds exhibit liquid crystalline mesophases and the temperature can control the aggregation, we have fabricated Pt(II) compound-doped polymer films and silicone membranes that show stimuli-responsive luminescent properties. In both cases, the interactions between the Pt(II) compounds and the metal cations, or the polymer matrices, play a key role in the aggregation-induced emission enhancement (AIEE) behaviour of the dyes. The effects of the alkyl chain length, the molecular asymmetry, and the nature of the ligands in the establishment of these interactions are also evaluated.

A new concept of thin, flat, transparent variable lenses with unprecedented performance in terms of active diameter and focal distance range is presented. The diffractive lens consists of two cascaded variable liquid crystal-based spiral diffractive lenses. Changing concertedly the topological charge changes the focal length with no mechanical motion. The implemented lens has a focal range from –2 to +2 diopters, an active diameter of 25 mm, a low operating voltage (<10 V), and a fill factor of 98%. These characteristics are unique in planar tunable lenses, opening for applications ranging from human vision correction to space applications.

The construction of a low-cost spectrophotometer as part of project-based teaching for postgraduate students in the field of Photonics Engineeringis depicted. The criteria followed in designing this project include considerations about budget, portability and multidisciplinary skills. The proposal has been carriedout in the context of a 3 credit Experimental Projects I course, part of the Master in Photonics Engineering taught by the Polytechnic University of Madrid, University Carlos III of Madrid and University of Alcala. During its performance, students have been supplied with all the necessary mechanical and optomechanical hardware, as well as passive and active optical elements and driving circuitry. Their tasks include the manufacture of a diffraction grating by a brand-new nanoimprint technique, the optimization of the optical alignment for improving the optical transfer function and the signal-to-noise ratio at the detection stage, and the programming of the control system and data acquisition in a LabView environment. The outcome is a fully functional spectrophotometer.Although it has been designed and tested with students of photonics, its multidisciplinary and modular character makes it useful also for undergraduate students from different disciplines, such as Industrial, Electronics or Automation Engineering. The open availability of the mechanical and electronic designs further allows its use by secondary teachers as a demonstrator of the different concepts used in their implementation (photonics, mechanics, electronicsand software).

Optical waveguides in photonic integrated circuits are traditionally passive elements merely carrying optical signals from one point to another. These elements could contribute to the integrated circuit functionality if they were modulated either by variations of the core optical properties, or by using tunable claddings. In this work, the use of liquid crystals as electro-optically active claddings for driving integrated waveguides has been explored. Tunable waveguides have been modeled and fabricated using polymers. Optical functions such as variable coupling and optical switching have been demonstrated.

In this work, the performance of a Mach–Zehnder interferometer manufactured in silicon nitride with a liquid crystal cladding is studied. The device consists of two multi-mode interference couplers linked by two rectangular waveguides, the cladding of one of which is a liquid crystal. The structure demonstrates the potential of using liquid crystals as tunable cladding material in simple waveguides as well as in more complex coupling or modulating structures. Liquid crystal cladding permits a local fine-tuning of the effective refractive index of the waveguide, avoiding coarse global temperature control. The study is realized in the visible region (632.8 nm), for its intrinsic interest region in (bio-)sensing or metrology.

Lyotropic liquid crystals play an important role in many biological environments, such as micelles, liposomes, and phospholipid bilayers of cell membranes. In this work, we explore the performance of lyotropic liquid crystals as biosensors for macromolecules, proteins and whole microorganisms in hydrophilic media, i.e., the natural media where these specimens exist. The aim is to detect specific targets employing simple, unpowered sensors that can be used in the field, with minimum additional equipment. A number of different structures have been explored. The novelty in this work is the inclusion of a new optical effect, flow enhanced amplification, that allows for the semiquantitative detection of microscopic targets in lyotropic liquid crystal cells using the naked eye only.