0000000001234758
AUTHOR
A. Pons
Application Of Anamorphic Systems To Directional Pseudocolor Encoding
An optical nonsymmetrical imaging system composed of two anamorphic spectrum analyzers in cascade is implemented. This system can provide an undistorted final image in spite of the geometrical distortion effects in the intermediate Fourier plane. The introduction of chromatic sector filters in this plane provides a real-time technique to pseudocolor encode the spatial frequency information of a black-and-white transparency. In this way, greater discrimination is achieved in the angular orientation of object details that generate the same spatial frequencies. Experimental pseudocolored images, obtained with a symmetrical system and a nonsymmetrical system, of a black-and-white transparency a…
Non-Conventional Tunable Spatial Filtering
A virtual display of the Fraunhofer diffraction pattern of any object is formed in the transverse source plane by theyirtual diffracted rays extqn0ing in the region to the left of the screen containing the transparencyl),2). Except for a few cases '')"°), the concept of virtual Fourier transform appears not to have been made use of. The main idea of this paper is, bearing in mind the property referred to in the above paragraph, to describe a novel spatial filtering technique. In this way, one can obtain different filtered images, by simply moving the point source along the optical axis. The basic theory is described below.
Optical implementation of micro-zoom arrays for parallel focusing in integral imaging.
We report 3D integral imaging with an electronically tunable-focal-length lens for improved depth of field. The micro-zoom arrays are generated and implemented based on the concept of parallel apodization. To the best of our knowledge, this is the first report of parallel dynamic focusing in integral imaging based on the use of micro-zoom arrays.
The effect of fractal contact lenses on peripheral refraction in myopic model eyes.
Purpose: To test multizone contact lenses in model eyes: Fractal Contact Lenses (FCLs), designed to induce myopic peripheral refractive error (PRE). Methods: Zemax ray-tracing software was employed to simulate myopic and accommodation-dependent model eyes fitted with FCLs. PRE, defined in terms of mean sphere M and 90–180 astigmatism J180, was computed at different peripheral positions, ranging from 0 to 35 in steps of 5, and for different pupil diameters (PDs). Simulated visual performance and changes in the PRE were also analyzed for contact lens decentration and model eye accommodation. For comparison purposes, the same simulations were performed with another commercially available conta…
Facet braiding: a fundamental problem in integral imaging.
A rigorous explanation of a phenomenon that produces significant distortions in the three-dimensional images produced by integral imaging systems is provided. The phenomenon, which we refer to as the facet-braiding effect, has been recognized in some previous publications, but to our knowledge its nature has never been analyzed. We propose a technique for attenuating the facet-braiding effect. We have conducted experiments to illustrate the consequences of the facet-braiding effect on three-dimensional integral images, and we show the usefulness of the proposed technique in eliminating this effect.
Optically-corrected elemental images for undistorted Integral image display
Conventional macro objectives are generally used as relay systems in the capture stage in Integral Imaging. This choice leads to microimage overlap and shift, which produce undesirable effects on the reconstructed three-dimensional images, such as loss in resolution and image distortions. In this paper, we propose and demonstrate a new architecture for the capture stage. Our method uses a telecentric relay system to overcome the conventional drawbacks. Experiments conducted with our system show an important improvement in the quality of displayed images.
A virtual laboratory designed for teaching diffractive lenses
[EN] We present a virtual laboratory generated in Matlab GuiQc (Graphical User Interface) for its use in Optics courses as an informatic tool for teaching the focusing properties of a diffractive lens. This Gui allows the students to learn easily and rapidly about the influence on the focal volume of the lens construction parameters. As an example in this work we analyze fractal diffractive lenses because we found that fractal geometry is a highly motivating topic for students since it is related to a wide range of scientific and technological phenomena.
Axial resolution in two-color excitation fluorescence microscopy by phase-only binary apodization
We study the effect of a kind of binary phase-only filters, the Toraldo filters, in two-color excitation fluorescence microscopy. We show that by simple insertion of a properly designed Toraldo filter in one of the illumination arms the axial resolution of the system is significantly improved. Specifically, the main peak of the point spread function is narrowed by 22% along the axial direction.
Axial behavior of diffractive lenses under Gaussian illumination: complex-argument spectral analysis
We present a general procedure to analyze the axial-irradiance distribution generated by an unlimited diffractive lens under coherent, Gaussian illumination. The resulting on-axis diffraction pattern, which is evaluated in terms of the power complex spectrum of the Fresnel-zone transmittance, explicitly depends on the truncation parameter that we define, which evaluates the effective number of zones illuminated by the Gaussian beam. Depending on the value of this parameter, different kinds of axial behavior are observed. In particular, for moderate values a multiple-focal-shift phenomenon appears, and a simple formula for its evaluation is presented. Additionally, for low values of the trun…
Inverse focal shift: A new effect in truncated cylindrical waves
We report on a general analytical procedure to analyse the axial focusing properties of uniform cylindrical waves truncated by a rectangular window. The resulting on-axis diffraction pattern explicitly depends on the square of the window height-to-width ratio. Depending on the value of this parameter, different kinds of axial behaviour are observed. In particular, it is found that for low values of this parameter and low Fresnel number, instead of the expected focal-shift effect, an inverse focal-shift phenomenon can appear, i.e. the maximum of the axial-irradiance distribution is displaced further away from the window.
Axial apodization in 4Pi-confocal microscopy by annular binary filters
We present a novel technique for considerably decreasing the sidelobe height of the axial point-spread function of one-photon 4Pi-confocal microscopes. By means of a numerical example, in which the ratio between the excitation and the fluorescence wavelengths was set to epsilon = lambdaexc/lambdadet = 0.8, we show that simply inserting a pair of properly designed two-ring binary masks in the illumination set allows the height of the axial sidelobes to be reduced from 20% to 5% of the height of the central peak. This allows one to receive the full benefit of the strong narrowness of the central lobe provided by the 4Pi-confocal technique.
Scale-tunable optical correlation with natural light
We describe two different scale-tunable optical correlators working under totally incoherent light. They behave as spatially incoherent wavelength-independent imaging systems with an achromatic point-spread function (PSF). In both cases it is possible to adapt the scale of the achromatic PSF, i.e., to modify the scaling factor of the PSF and preserve the chromatic compensation, by one's shifting the input along the optical axis. The remarkable properties of these systems allow us to carry out a scale-tunable color pattern-recognition experiment with natural light.
Undergraduate experiment with fractal diffraction gratings
We present a simple diffraction experiment with fractal gratings based on the triadic Cantor set. Diffraction by fractals is proposed as a motivating strategy for students of optics in the potential applications of optical processing. Fraunhofer diffraction patterns are obtained using standard equipment present in most undergraduate physics laboratories and compared with those obtained with conventional periodic gratings. It is shown that fractal gratings produce self-similar diffraction patterns which can be evaluated analytically. Good agreement is obtained between experimental and numerical results. © 2011 IOP Publishing Ltd.
Difract: Un nuevo laboratorio virtual para la modelización matemática de las propiedades de difracción de redes fractales
[EN] This work presents a new virtual laboratory, Difract, developed with Easy Java Simulations, for using in Optics courses as a computer tool for the mathematical modelling of the diffraction properties of 1D and 2D fractal gratings. This virtual laboratory enables students to quickly and easily analyze the influence on the Fraunhofer diffraction pattern of the different construction parameters of the fractal grating. As an application example, the Cantor fractal set has been considered.
Sidelobe decline in single-photon 4Pi microscopy by Toraldo rings.
We demonstrate theoretically the feasibility of single-photon 4Pi-confocal microscopy. By inserting a pair of properly designed multi-ring phase-only pupil filters in the illumination path of a 4Pi microscope the height of the sidelobes of the point spread function substantially reduced, so that there is no ambiguity in the 3D image. Then, an axial resolution up to four times higher than that of single-photon confocal microscope can be effectively achieved.
Enhanced field-of-view integral imaging display using multi-Köhler illumination.
A common drawback in 3D integral imaging displays is the appearance of pseudoimages beyond the viewing angle. These pseudoimages appear when the light rays coming from each elemental image are not passing through the corresponding microlens, and a set of barriers must be used to avoid this flipping effect. We present a pure optical arrangement based on Köhler illumination to generate these barriers thus avoiding the pseudoimages. The proposed system does not use additional lenses to project the elemental images, so no optical aberrations are introduced. As an added benefit, Köhler illumination provides a higher contrast 3D display. This work was supported in part by the Plan Nacional I + D …
An experiment to study the structure of the focal volume in apertured focusing systems
We present a simple experiment, specifically designed for students of undergraduate optics courses, where the influence of an aperture stop position on the three-dimensional structure of the focal volume of focusing systems is studied. The experiment, which involves only simple optical elements, permits an undergraduate student to generate different focal structures by simply axially displacing the aperture stop.
Three-dimensional behavior of apodized nontelecentric focusing systems.
The scalar field in the focal volume of nontelecentric apodized focusing systems cannot be accurately described by the Debye integral representation. By use of the Fresnel–Kirchhoff diffraction formula it is found that, if the aperture stop is axially displaced, the focal-volume structure is tuned. We analyze the influence of the apodizing function and find that, whereas axially superresolving pupil filters are highly sensitive to the focal-volume reshaping effect, axially apodizing filters are more inclined to the focal-shift effect.
Fractal photon sieve
A novel focusing structure with fractal properties is presented. It is a photon sieve in which the pinholes are appropriately distributed over the zones of a fractal zone plate. The focusing properties of the fractal photon sieve are analyzed. The good performance of our proposal is demonstrated experimentally with a series of images obtained under white light illumination. It is shown that compared with a conventional photon sieve, the fractal photon sieve exhibits an extended depth of field and a reduced chromatic aberration.
Self-imaging properties of a periodic microlens array: versatile array illuminator realization
Abstract The general features of the wavefield diffracted by a microlens array are described. The transversal periodicity of both a refractive and a diffractive periodic microlens array allows to obtain a set of replicas of the focal intensity distribution along the optical axis of the system, with different multiplicity. The result is applied for implementing a versatile optical array illuminator, with a variable density of bright spots at the output plane. Some experimental results of the procedure are shown.
Geometrical Transformations In The Fraunhofer Plane
A virtual display of the Fraunhofer diffraction pattern is generated solely by illuminating the object with a point source. If this pattern is imaged with an anamorphic system, several linear geometrical transformations can be achieved. Furthermore, a nonsymmetrical Fourier transformer with a variable degree of anamorphic magnification on the Fraunhofer pattern can be implemented.
All-diffractive achromatic Fourier-transform setup
An achromatic Fourier transformation under broadband converging spherical-wave illumination is optically achieved by use of only two on-axis blazed zone plates. The novel optical configuration provides the achromatic Fraunhofer diffraction pattern of an arbitrary input signal with adjustable magnification. Further analysis of the system permits us to obtain a simple analytical expression to evaluate both the longitudinal and the transversal residual chromatic aberration, resulting in a compact achromatic Fourier transformer with low chromatic errors, even for a wide spectral content of the point source.
Wavefront sensing using a graphical user interface
Contract grant sponsor: Ministerio de Economia y Competividad; Contract grant number: FIS2011-23175; Contract grant sponsor: Generalitat Valenciana; Contract grant number: PROMETEOII/2014/072; Contract grant sponsor: Universitat de Valencia; Contract grant number: UV-SFPIE_DINV14-222801
Simple demonstration of the impact of spherical aberration on optical imaging
We present an experiment, well adapted for students of introductory optics courses, for the visualization of the impact of spherical aberration in the point spread function of imaging systems. The demonstrations are based on the analogy between the point-spread function of spherically aberrated systems, and the defocused patterns of 1D slit-like screens.
Strehl ratio versus defocus for noncentrally obscured pupils.
We discuss from the viewpoint of the Strehl ratio versus defocus, or the normalized axial-irradiance distribution, the influence of decentering the dark mask of an annular pupil. Our treatment, which is valid for pupil apertures with any Fresnel number, permits us to infer that the axial behavior of a noncentrally obscured pupil is equivalent to that of an apodizer with continuous amplitude variations. Hence the Strehl ratio versus defocus of an optical system can be shaped by use of noncentered dark masks that act as continuous gray apodizers. Several numerically evaluated examples are presented.
Detection of wave aberrations in the human eye using a retinoscopy-like technique
The influence of optical aberrations on the retinoscopic reflex is theoretically analyzed from a geometrical point of view. The relationship between the wave aberrations to the ray aberrations is applied to explain the appearance of the retinoscopic patterns for different types of ocular aberrations. Several schematic models of the human eye are tested numerically, showing that a careful retinoscopic examination can detect the usual eye aberrations.
Telepsychology: public speaking fear treatment on the internet
El objetivo es presentar un sistema de telepsicología para el tratamiento del miedo a hablar en público. El sistema utiliza procedimientos de auto-ayuda y está compuesto por: a) Un protocolo de evaluación que rastrea información clínicamente relevante; b) Un protocolo de tratamiento basado en procedimientos cognitivo-comportamentales que cuenta con una serie de vídeos de audiencias reales que permiten a la persona afrontar las situaciones temidas. Está organizado en bloques separados a los que se accede a medida que se supera cada fase previa. c) Un protocolo de control que rastrea el progreso durante todo el proceso y controla que la persona no se salta partes del tratamiento (algo común e…
Progresses in 3D integral imaging with optical processing
Integral imaging is a promising technique for the acquisition and auto-stereoscopic display of 3D scenes with full parallax and without the need of any additional devices like special glasses. First suggested by Lippmann in the beginning of the 20th century, integral imaging is based in the intersection of ray cones emitted by a collection of 2D elemental images which store the 3D information of the scene. This paper is devoted to the study, from the ray optics point of view, of the optical effects and interaction with the observer of integral imaging systems.
Lightfield recording and reconstruction by integral imaging
Integral imaging is a rising 3D imaging technique that can be considered the incoherent version of holography. In integral imaging the multiperspective information of 3D scenes is stored in a 2D picture. Such picture is nothing but a sampling version of the lightfield emitted by the 3D scene. The recorded lightfield can be used for many purposes. One is the display of 3D color scenes to audiences or much more than one person. Other is the 3D display, with full parallax, in personal monitors, like the screen of a Smartphone, a tablet, or the monitor used by a surgeon in an endoscopic operation. Other important types of applications are connected with the topographic reconstruction, slice by …