Papers by Kevin Contreras
High capacity Lippmann storage in a page-oriented architecture
Institut d'Optique Graduate School.
Characterization of new thermo-responsive hydrogels for optical sensing applications
We report the use of new hydrogels based on poly-N-isopropylacrilamide and MeOXA in order to meas... more We report the use of new hydrogels based on poly-N-isopropylacrilamide and MeOXA in order to measure temperature using optical transmittance. We have obtained thermo-responsive hydrogels based on the radical copolymerization of N-isopropylacrylamide (NIPAAm) and bis-macromonomers of 2-methyl-2-oxazoline (MeOXA). The hydrogels show conformational transitions at defined temperatures, which are a function of the molar ratio NIPAAm/MeOXA inside of the hydrogel.
Angular selectivity behavior of a grating imaging in thick photorefractive media
Abstract It is well known that a thin phase grating holographically produced exhibits Raman-Nath ... more Abstract It is well known that a thin phase grating holographically produced exhibits Raman-Nath behavior and a thick phase grating shows Bragg behavior in the diffraction process. In the Raman-Nath regime several diffracted waves are produced. Usually, in a photorefractive material such as a sillenite BSO crystal, volume phase holograms are stored by means of the interference of two coherent beams intersecting inside the crystal.
Enregistrement de pages de données de forte résolution dans une mémoire optique de type LIppmann
Les mémoires holographiques sont connues pour leurs très fortes capacités. Nous présentons ici un... more Les mémoires holographiques sont connues pour leurs très fortes capacités. Nous présentons ici une architecture de mémoire optique inspirée de la photographie interférentielle de Lippmann, architecture très voisine de l'holographie, mais néanmoins plus simple à mettre en œuvre.
Lippmann Holographic Storage with Homodyne Detection and Single Side Access
Lippmann interference photography is an elegant process to record colour photographs. From this p... more Lippmann interference photography is an elegant process to record colour photographs. From this principle, wavelength multiplexed data storage systems were developed. Hereafter, we propose to further simplify and enhanced the performances of these Lippmann architectures. Therefore, we describe the implementation of an homodyne detection for enhancing the readout signal combined with an architecture in which the access to a single side of the recording medium is required for both recording and readout.
Real-time measurement of micrometer-order amplitude transverse vibrations using the photo-emf effect in photoconductive materials
We report the use of the photo-emf effect in BTO photorefractive crystals to measure sub-micromet... more We report the use of the photo-emf effect in BTO photorefractive crystals to measure sub-micrometer-order amplitude transverse vibrations. The method is based on the illumination of the surface under analysis by a direct laser beam of wavelength λ= 532 nm and the collection of the back-scattered speckled patterns of light onto the photoconductor.
Homodyne Detections for Lippmann Data Storage
Interferential colour photography was efficiently demonstrated by Gabriel Lippmann in the late 18... more Interferential colour photography was efficiently demonstrated by Gabriel Lippmann in the late 1800 [1, 2]. In this technique, the image is recorded in the depth of the photographic plate by interfering the incident beam with itself after a reflection on a mirror set just beneath and in direct contact with the photosensitive layer. The mirror is then removed and the recording plate is chemically processed. The image is thus reproduced under the form of Bragg gratings in the thickness of the material.
Observation of new modal patterns in experiments with Hermite-Gaussian and Laguerre-Gaussian laser modes
We present several experiments that allow us to show the intensity and phase structure of transve... more We present several experiments that allow us to show the intensity and phase structure of transverse modal patterns, Hermite-Gaussian and Laguerre-Gaussian laser modes and dynamical transverse patterns. These new spatial configurations of the light depend on the dynamics of laser resonator, and on the boundary conditions. The Laguerre-Gaussian modes are obtained either by the direct conversion of Hermite-Gaussian modes using a modal converter or with a computer-generated hologram.
Very cheap plastic optical fiber sensors for measurement of displacement without contact
ABSTRACT We present an alternative development of very cheap sensors utilizing plastic optical fi... more ABSTRACT We present an alternative development of very cheap sensors utilizing plastic optical fibers and diode lasers extracted from laser pointers. We have applied these sensors to perform measurements of displacement and distance without physical contact. The development of these sensors started with the characterization and control of these semiconductor lasers. We have achieved to control various diode lasers by means of a current controller, specially designed for this application.
Analysis of surfaces and small dimensions mechanical objects with projections of fringes illuminated with optical fibers
This paper describe the surface analysis based on the fringe projection technique. The grating of... more This paper describe the surface analysis based on the fringe projection technique. The grating of fringes is illuminated with plastic optical fiber multimode on a surface under test of the order of the This technique can be used to analyze the deformations of surfaces or errors of manufacture of objects when the projected fringes are compared with the original patterns generated by a computer program.
Alarm system of optical fibre using the thermal-optical sensibility of the PNIPAAm polymer
abstract An alarm system as extrinsic sensor on optical fibers for detecting and controlling infl... more abstract An alarm system as extrinsic sensor on optical fibers for detecting and controlling inflammable liquids based on thermosensitive proprieties of the PNIPAAm hydrogel is presented. The changes on the optical proprieties of the PNIPAAm with the temperature (being its LCST 32 C), induce abrupt changes on the light intensity and they act as an alarm signal, which is transmitted by optical fibers and after they will be processed by an optoelectronic circuit, responsible to active an alarm.
Monte Carlo evaluation of the maximum data capacity of holographic memories
Institut d'Optique Graduate School.
Homodyne detection for Lippmann data storage [6620-19]
Non-contact torsion transducer based on the measurement of Moire patterns using plastic optical fibres [6616-110]
An angular and displacement sensor that uses a polymer optical fiber and Moire patterns is demons... more An angular and displacement sensor that uses a polymer optical fiber and Moire patterns is demonstrated. Moire fringes are generated using two transparent superimposed planar gratings placed in front of an optical mirror. Moire patterns with periods ranging from 0.4 to 2 mm have been obtained in this way with 1mm-diameter plastic optical fibers for torsion angles ranging from 10 to 20 have been compared with theoretical calculations and a good agreement has been confirmed.
Coherence and modal structure of optical cavity under conditions of thermic instability in a He-Ne gas laser [4419-105]
We performed a study of temporal coherence of a commercial He-Ne laser in conditions of thermic i... more We performed a study of temporal coherence of a commercial He-Ne laser in conditions of thermic instability through calculations based on interference pattern digital images helping by direct measurements of its output power and by temperature and polarization monitoring. This study is based on the variation of the complex degree of coherence with the optical path difference between two laser beams, obtained with the help of an experimental setup based on a Michelson interferometer with collimated light.
High density “Lippmann” data storage in thick holographic materials
Lippmann interference photography is a, more than one century old, colour photographic process [1... more Lippmann interference photography is a, more than one century old, colour photographic process [1]. In spite of this oldness, we decided to revisit this photographic process and to evaluate its ability to use it for mass data storage. Lippmann photography indeed shares many features with Denisyuk volume holography used for high density data storage [2]. In this photographic process, a lens images the scene onto a mirror set in contact with a thick photographic plate.
Optical data storage based on the Lippmann photography
Institut d'Optique Graduate School.
Francisco. Observación de nuevos patrones modales en experimentos con modos láser Hermite-gaussianos y Laguerre-gaussianos
Resumen Presentamos algunos experimentos que nos permiten mostrar la estructura de intensidad y f... more Resumen Presentamos algunos experimentos que nos permiten mostrar la estructura de intensidad y fase de los patrones modales transversales, los modos Hermite-gaussianos (HG) y Laguerre-gaussianos (LG) y patrones transversales dinámicos. Estas nuevas configuraciones espaciales de la luz dependen de la geometría del resonador y de sus condiciones de frontera.
Summary We investigate the storage capacity of an optical data storage setup based on Lippmann in... more Summary We investigate the storage capacity of an optical data storage setup based on Lippmann interference photography. We have used computational simulations to demonstrate the possibility to achieve data capacities as large as those achievable with common holographic techniques.
Abstract It is well recognized that holographic data storage may represent the next generation of... more Abstract It is well recognized that holographic data storage may represent the next generation of optical data storage. Unlike DVDs and other optical discs in which information is stored in a plane, holographic storage technologies have a volumetric memory. Among several configurations, the page-oriented architectures present great advantages, such as the high data rate that stems from their inherent parallelism.
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Papers by Kevin Contreras