Accurate control of a liquid-crystal display to produce a homogenized Fourier transform for holographic memories

We show an accurate procedure to obtain a Fourier transform (FT) with no dc term using a commercial twisted-nematic liquid-crystal display. We focus on the application to holographic storage of binary data pages, where a drastic decrease of the dc term in the FT is highly desirable. Two different codification schemes are considered: binary π radians phase modulation and hybrid ternary modulation. Any deviation in the values of the amplitude and phase shift generates the appearance of a strong dc term. Experimental results confirm that the calculated configurations provide a FT with no dc term, thus showing the effectiveness of the proposal.This work was supported by the “Ministerio de Educación y Ciencia (Spain)” under projects FIS2005-05881-C02-01 and FIS2005-05881-C02-02, and by the “Generalitat Valenciana” under Project GV06/007

Validation of Fresnel–Kirchhoff Integral Method for the Study of Volume Dielectric Bodies

In this work, we test a nondestructive optical method based on the Fresnel–Kirchhoff integral, which could be applied to different fields of engineering, such as detection of small cracks in structures, determination of dimensions for small components, analysis of composition of materials, etc. The basic idea is to apply the Fresnel–Kirchhoff integral method to the study of the properties of small-volume dielectric objects. In this work, we study the validity of this method. To do this, the results obtained by using this technique were compared to those obtained by rigorously solving the Helmholtz equation for a dielectric cylinder of circular cross-section. As an example of the precision of the method, the Fresnel–Kirchhoff integral method was applied to obtain the refractive index of a hair by fitting the theoretical curve to the experimental results of the diffraction pattern of the hair measured with a CCD camera. In a same manner, the method also was applied to obtain the dimensions of a crack artificially created in a piece of plastic.This work was supported by the “Ministerio de Ciencia e Innovación” (Spain) under project FIS2017-82919-R (MINECO/AEI/FEDER, UE)

Measurement of the refractive index profile of an optical fiber by Fresnel diffraction

In this work we present a non-destructive technique based on Fresnel diffraction to obtain the refractive index profile of a fiber grating. The system has been firstly calibrated by using the experimental data of the diffraction pattern of rectangular slits at different distances.This work was supported by the Ministerio de Economía y Competitividad (Spain) (FIS2015-66570-P and FIS2017-82919-R) and by Generalitat Valenciana (Spain) (PROMETEOII/2015/015)

Analytical evaluation of normalization criteria for the diffraction efficiency of blazed gratings on LCoS devices

Through analytical expressions, three experimental-based normalizations are evaluated for the diffraction efficiency of blazed gratings on LCoS devices. We find that non-inclusion of the fill factor, usually the case, leads to wrong conclusions.Ministerio de Ciencia e Innovación, Spain (FIS2017-82919-R (MINECO/AEI/FEDER, UE)); Generalitat Valenciana, Spain (IDIFEDER/2021/014, potential FEDER funding); Universidad de Alicante, Spain (UATALENTO18-10)

Incorporación de la Web 2.0 en la docencia de Proyectos e Infraestructuras de Telecomunicación II: Curso de adaptación al grado

Comunicación y póster presentados en las IX Jornadas de Redes de Investigación en Docencia Universitaria, Alicante, 16-17 junio 2011.La llegada de las nuevas titulaciones de Grado en la UA ha favorecido la implantación de un Curso de adaptación al Grado en Ingeniería en Sonido e Imagen, orientado a los ya titulados en Ingeniería Técnica de Telecomunicación, especialidad en Sonido e Imagen. La mayoría de este alumnado está interesado en compaginar su horario laboral y el calendario lectivo. Aunque en muchos casos es una tarea complicada. Por ello, en la asignatura de Proyectos e Infraestructuras en Telecomunicación II se han recurrido a diversas herramientas Web colaborativas: Google Apps y Moodle. Estas herramientas y su aplicación han servido para facilitar la comunicación entre el profesorado y el estudiante, a través del trabajo colaborativo y la realimentación entre ambas partes ya que permiten entre otras actividades compartir documentos, entrega de trabajos online, realización y autocorrección de test, chat entre los miembros de la plataforma y una temporización a priori bastante precisa. También se ha recurrido a ciertas aplicaciones libres basadas en navegador para facilitar el trabajo a distancia, permitiendo a los estudiantes trabajar desde cualquier PC con acceso a Internet. La aplicación de estas herramientas ha favorecido el proceso de enseñanza aprendizaje significativamente a aquellos estudiantes con incompatibilidades horarias.Este trabajo ha sido financiado por el Vicerrectorado de Tecnología e Innovación Educativa de la Universidad de Alicante (proyecto GITE-09006-UA y proyecto GITE-09014-UA)

Study of the imaging characteristics of holographic waveguides

In this work we study and characterize and holographic waveguide system composed of two volume diffraction gratings, which act as optical couplers and a glass substrate that acts as a waveguide. The features such us high diffraction efficiencies and Bragg angle selectivity exhibited by volume diffraction gratings allow the appropriated adjustment of the incident light to be diffracted in the direction of total reflection condition inside the glass substrate with high efficiency. In this work the holographic waveguide is recorded on different photopolymer materials, which optimization is controlled to obtain high spatial frequencies and stable fringes. The effect of the shrinkage of the holograms after recording in the quality of the image obtained from the optical waveguide is also studied. To perform the experiments two kind of photopolymers were studied: a nanoparticle-(thiol-ene) polymer composite, NPC, and a penta/hexa-acrylate based polymer with dispersed nematic liquid crystal molecules, PDLC. The holographic characteristics such as diffraction efficiency or wavelength selectivity obtained with the waveguides recorded on the different photopolymers were also studied and compared.This work was supported by the “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) (PROMETEOII/2015/015)

Optimization of Photopolymer Materials for the Fabrication of a Holographic Waveguide

In this work, we present a method of manufacturing an optical see-through display based on a holographic waveguide with transmission holograms that couple the incident light between air and the glass substrate, accomplishing total internal reflection. The holograms (slanted transmission gratings with a spatial frequency of 1700 lines/mm) were recorded on a polyvinyl alcohol acrylamide (PVA/AA) photopolymer. We will also show that the addition of N,N′-methylene-bis-acrylamide (BMA) to the composition of the photopolymer allows the achievement of the index modulations necessary to obtain high diffraction efficiencies in non-slanted diffraction gratings of 1000 and 2200 lines/mm, and also in slanted gratings of 1700 lines/mm (which are the base of the optical system proposed).Work supported by the “Ministerio de Economía, Industria y Competitividad” of Spain (projects FIS2014-56100-C2-1-P and FIS2015-66570-P) and by the “Generalitat Valenciana” of Spain (projects PROMETEO II/2015/015)

Seguimiento del Máster en Ingeniería de Telecomunicación: medidas para conseguir la calidad y la excelencia

El Máster Universitario en Ingeniería de Telecomunicación en la Universidad de Alicante es el título que se imparte desde la Escuela Politécnica Superior y que habilita para el ejercicio de la profesión regulada de Ingeniero de Telecomunicación. Consta de 90 ECTS y se imparte a lo largo de 2 cursos académicos. El máster está implantado desde el curso 2011-2012 por lo que durante el actual curso 2012-2013 tendremos egresados de la primera promoción. Una vez implantado en su totalidad, es posible realizar un seguimiento del máster con la intención de obtener la excelencia académica mediante todas aquellas medidas y procesos de evaluación internos que sean necesarios. Además también es conveniente evaluar el impacto social, universitario y empresarial del máster evaluando las carencias, lagunas y oportunidades de formación que se detecten y tomando las oportunas medidas correctoras. Será necesario tener en cuenta la relación del título con el mundo empresarial y con la sociedad en general que tiene el sector de las telecomunicaciones en la evaluación de la calidad docente en el aula

Real-time interferometric characterization of a polyvinyl alcohol based photopolymer at the zero spatial frequency limit

We characterize the optical modulation properties of a polyvinyl alcohol/acrylamide (PVA/AA) photopolymer at the lowest end of recorded spatial frequencies. To achieve this goal we have constructed a double beam interferometer in combination with the setup to expose the recording material. This is a novel approach since usually holographic recording materials are only characterized at high spatial frequencies. Some benefits are provided by the approach we propose: a direct calculation of the properties of the material is possible, and on the other hand additional information can be obtained since the results are not influenced by diffusion processes. Furthermore, this characterization is needed to optimize the PVA/AA photopolymers for another range of applications, such as recording of diffractive optical elements, where very low spatial frequencies are recorded. Different PVA/AA compositions and layer thicknesses have been analyzed. We have found that, depending on the layer characteristics, we can achieve high values of the phase-shift modulation depth and enhance the sensitivity of the material.This work was supported by the “Ministerio de Educación y Ciencia” (Spain) under projects FIS2005-05881-C02-01 and FIS2005-05881-C02-02, and by Generalitat Valenciana under project GV06-007