Analysis of holographic data storage using a PA-LCoS device

Holographic data storage systems (HDSS) have been a promising and very appealing technology since the first laser developments in the sixties. Impact of ongoing advances in the various components needs to be explored in its specific application to HDSS. In this sense, continuous progress is being produced in spatial light modulator (SLM) technology where parallel-addressed liquid crystal on silicon (PA-LCoS) microdisplays have replaced previous liquid-crystal displays (LCD) in most of optics and photonics applications. PA-LCoS microdisplays are well adapted to display phaseonly elements without coupled amplitude. In this paper, we analyse how PA-LCoS devices can also be used to display the widely applied binary intensity modulated (BIM) data pages. We also investigate hybrid-ternary modulated (HTM) data pages, which are very much demanding on the phase and amplitude modulation properties of an SLM. HTM data pages combine the ease of detection of BIM data pages, together with a large reduction of the DC term of the Fourier Transform of the data page. This reduction is necessary to avoid saturation of the recording material dynamic range. Simulated results show the magnitude of the expected DC term in the Fourier plane. We have verified the good performance of PA-LCoS to display BIM data pages. We have also obtained that pure HTM data pages cannot be produced with PA-LCoS devices, however, a rather close performance is obtained when implementing the pseudo-HTM data pages. In this work a more complete study of pseudo-HTM modulation is offered.This work was supported by the “Ministerio de Economía y Competitividad” (projects FIS2014-56100-C2-1-P and FIS2015-66570-P) and by the “Generalitat Valenciana” of Spain (projects PROMETEOII/2015/015 and ISIC/2012/013)

Efficient split eld FDTD analysis of third-order nonlinear materials in two-dimensionally periodic media

In this work the split-field finite-difference time-domain method (SF-FDTD) has been extended for the analysis of two-dimensionally periodic structures with third-order nonlinear media. The accuracy of the method is verified by comparisons with the nonlinear Fourier Modal Method (FMM). Once the formalism has been validated, examples of one- and two-dimensional nonlinear gratings are analysed. Regarding the 2D case, the shifting in resonant waveguides is corroborated. Here, not only the scalar Kerr effect is considered, the tensorial nature of the third-order nonlinear susceptibility is also included. The consideration of nonlinear materials in this kind of devices permits to design tunable devices such as variable band filters. However, the third-order nonlinear susceptibility is usually small and high intensities are needed in order to trigger the nonlinear effect. Here, a one-dimensional CBG is analysed in both linear and nonlinear regime and the shifting of the resonance peaks in both TE and TM are achieved numerically. The application of a numerical method based on the finite- difference time-domain method permits to analyse this issue from the time domain, thus bistability curves are also computed by means of the numerical method. These curves show how the nonlinear effect modifies the properties of the structure as a function of variable input pump field. When taking the nonlinear behaviour into account, the estimation of the electric field components becomes more challenging. In this paper, we present a set of acceleration strategies based on parallel software and hardware solutions.This work was supported by the Ministerio de Economa y Competitividad of Spain under project FIS2014-56100- C2-1-P and by the Generalitat Valenciana of Spain under projects PROMETEOII/2015/015, ISIC/2012/013 and GV/2014/076

Holographic Characteristics of Photopolymers Containing Different Mixtures of Nematic Liquid Crystals

A holographic polymer dispersed liquid crystal (HPDLC) is used to record holographic diffraction gratings. Several mixtures of nematic liquid crystals (LC) are used as components of the HPDLC to evaluate their influence in static and dynamic basic properties. The diffraction efficiency obtained in the reconstruction of the holograms is evaluated to compare the influence of the different LC. Additionally, the samples are exposed to a variable electric field and the diffracted light intensity as a function of the applied voltage is measured to evaluate the influence of the LC. The results obtained show significant differences depending on the LC incorporated to the photopolymer.This work was supported by ‘Ministerio de Ciencia, Innovación y Universidades’ (before ‘Ministerio de Economía, Industria y Competitividad’), Spain, under projects FIS2017-82919-R (MINECO/AEI/FEDER, UE) and FIS2015-66570-P (MINECO/FEDER), and by Generalitat Valenciana, Spain, under project PROMETEO II/2015/015

Dimensional changes in slanted diffraction gratings recorded in photopolymers

Photopolymers are appealing materials for many optical applications. For most of them, shrinkage plays an important role in the final properties of the display, especially in holographic data storage applications. In this paper, we demonstrate that to quantify correctly the shrinkage, it is mandatory to measure the angle of propagation for both diffracted orders ± 1, so that an accurate value of the grating vector can be calculated. Experimental evidence from three different photopolymers supports this affirmation. Firstly, polyvinyl alcohol acrylamide based photopolymer, which has been studied by many research groups; secondly, one environmentally compatible photopolymer developed by our group; and thirdly, a photopolymer with dispersed liquid crystal molecules. We studied the deviation from the sinusoidal profile analyzing the higher diffracted orders.This work was supported by the “Ministerio de Economía y Competitividad” (projects FIS2015-66570-P and FIS2014-56100-C2-1-P) and by the “Generalitat Valenciana” of Spain (projects PROMETEOII/2015/015 and ISIC/2012/013)

Influence of the spatial frequency on the diffractive optical elements fabrication in PDLCs

Photopolymers are classical holographic recording materials. Recently their chemical composition and the fabrication techniques have been optimized for many new applications such as interconnectors, solar concentrations, 2-D photonic structures, or wave-guides. Their potential usefulness has been drastically increased by the introduction of dispersed liquid crystal molecules; these components can be concentrated in the non-exposed zones of the material by a photopolymerization induced phase separation process (PIPS). Therefore, by combining polymer and dispersed liquid crystal (PDLC) has emerged as a new composite material for switchable diffractive optical elements (DOEs). Parallel to the material advances some techniques have been proposed to record very low spatial frequencies DOE’s. Different researchers have reported proposes to record DOE like fork gratings, photonics structures, lenses, sinusoidal, blazed or fork gratings. In this work we have studied the behavior of a PDLC material to record DOE’s with different spatial periods: from 1 μm, using holographic technique, to more than 200 μm, Liquid Cristal on Silicon (LCoS) display working in mostly amplitude mode as a master. Due to the improvement in the spatial light modulation technology and the pixel miniaturization, this technique permits us store gratings with spatial frequencies until few microns. Additionally, this technology permits us an accurate and dynamic control of the phase and the amplitude of the recording beam. In particular, for our case, to generate the blazed gratings, we use an LCoS-Pluto provided by Holoeye with a resolution of 1920x1080 (HDTV) pixels and a pixel size of 7.7x7.7 m2.Work supported by the Ministerio de Economía y Competitividad of Spain under project FIS2014-56100-C2-1-P and FIS2015-66570-P and by the Generalitat Valenciana of Spain (projects PROMETEOII/2015/015 and ISIC/2012/013

Additives Type Schiff’s Base as Modifiers of the Optical Response in Holographic Polymer-Dispersed Liquid Crystals

Schiff’s bases with specific π-electron system have been synthesized and used as additives in holographic polymer-dispersed liquid crystals. It was observed that these substances modify different parameters such as current intensity, voltage, and diffracted light intensity. In addition, the maximum diffraction efficiency obtained in the reconstruction of the holograms is related to the additive molecule. We propose a relationship between this behavior and the molecular structure of these substances.This work was supported by “Ministerio de Economía, Industria y Competitividad”, Spain, projects: FIS2015-66570-P, FIS2014-56100-C2-1-P, “Generalitat Valenciana”, Spain, project: PROMETEOII/2015/015 and “Agencia de Ciencia y Tecnología de la Región de Murcia”, Spain, projects: 19278/PI/14, CTQ2015-67927-R

Parámetros que modifican la intensidad de corriente eléctrica en materiales compuestos H-PDLC

Este trabajo ha sido financiado por el Ministerio de Economía y Competitividad (proyectos FIS2014-56100-C2-1-P y FIS2015-66570-P) y por la Conselleria d' Educació, Investigació, Cultura i Esport de la Generalitat Valenciana (proyecto PROMETEOII/2015/015

Effective modeling of PA-LCoS devices and application in data storage in photopolymers

Parallel aligned liquid crystal on silicon (PA-LCoS) devices are widely used in many optics and photonics applications to control the amplitude, phase and/or state of polarization (SOP) of light beams. We present a novel model enabling to calculate the voltage dependent retardance provided by PA-LCoS devices for a very wide range of incidence angles and any wavelength in the visible. To our knowledge it represents the most simplified approach still showing predictive capability. We are particularly interested in the application of PA-LCoS microdisplays as the data pager in holographic data storage systems (HDSS). In this work we show both theoretical and experimental results addressing hybrid-ternary modulated (HTM) data pages and using our in-house produced PVA/AA photopolymer as the storage material. We demonstrate that PA-LCoS devices cannot implement pure HTM but a rather close approximation. Experimental results with PVA/AA show bit-error rates (BER) in the range of the threshold for potential application in HDSS (about 10−3).Work supported by the Ministerio de Trabajo y Competitividad of Spain (projects FIS2014-56100-C2-1-P and FIS2015-66570-P) and by the Generalitat Valenciana of Spain (projects PROMETEOII/2015/015 and ISIC/2012/013) and by the University of Alicante (GRE12-14)

Application of PA-LCoS Modulators in Multilevel Phase Elements and in Holographic Data Storage

This work was supported by the "Ministerio de Economía y Competitividad" (projects FIS2014-56100-C2-1-P y FIS2015-66570-P), by the "Generalitat Valenciana" (projects PROMETEOII/2015/015 and ISIC/2012/013) and by the "Universidad de Alicante" (project GRE12-14)

Application of PA-LCoS Modulators in Multilevel Phase Elements and in Holographic Data Storage

This work was supported by the "Ministerio de Economía y Competitividad" (projects FIS2014-56100-C2-1-P y FIS2015-66570-P), by the "Generalitat Valenciana" (projects PROMETEOII/2015/015 and ISIC/2012/013) and by the "Universidad de Alicante" (project GRE12-14)