We generate Hermite-Gauss and Ince-Gauss beams by using kinoform phase holograms encoded onto a liquid crystal display. The phase transmittance of this holograms coincide with the phases of such beams. Scale versions of the desired beams appear at the Fourier domain of the KPHs. When an appropriated pupil size is employed, the method synthesizes HG and IG beams with relatively high accuracy and high efficiency. It is noted that experimental and numerical results are agreement with the theory.
In recent years we have been working in the characterization of the objective average performance of a set of
uncorrected human eyes with a 20/20 visual acuity, described as the resultant average wavefront aberration function
(WA), point-spread function (PSF), modulation transfer function (MTF), and power refractive maps. This objective
performance has been used as our clinical reference to analyze the objective pre- and post-operated performance in laser
refractive surgery in different situations. We show some of our current results obtained from the application of our
clinical reference.
The design of diffractive optical elements (DOEs) to generate a desired light intensity distribution has been
studied in the realm of diffractive optics. Within the proposed algorithms to perform the design and optimization
of DOEs are the iterative Fourier transform algorithms (IFTAs). In this work we are interested in generating a
spot array using an IFTA. We propose a modified error-reduction IFTA which allows us to reach a target error
with high effciency.
The analysis and measurement of the wavefront aberration function are very important tools in the field of visual optics;
they are used to understand the performance of the human eye in terms of its optical aberrations. In recent years, we have
compared, through two different methods, the wavefront aberration function of a reference refractive surface of 5 mm in
diameter and we have demonstrated its equivalence1. Now, we want to extend these results to a set of hard contact
lenses. These hard contact lenses have been subjected to different laser ablation techniques which are typically used in
refractive surgery. Our goal is to characterize the resultant ablation profile. We show our results obtained for both, a nonablated
hard contact lens and the corresponding ablated samples.
We present a modification to the classic Michelson interferometer that allows the interference of multiple beams with equal amplitude. The proposed architecture presents the same advantages and simplicity as those of a classic Michelson interferometer. The basic unit of the device consists of a beamsplitter and two mirrors arranged as in a Michelson interferometer. To increase the number of interfering beams, the mirrors are replaced by a basic unit. In order to demonstrate the type of interference patterns that can be obtained, we present interferograms corresponding to three to eight interfering beams. The system can be used to optically induce photonic lattices.
Nonlinear phase contrast microscopy is an optical technique that uses an intensity-dependent refractive index material to
produce high-contrasted images of transparent specimens. Earlier proposal of liquid crystals as phase filters for phase
contrast applications used optically addressed spatial light modulators fabricated with photoconductive film. Here, we
propose the use of a simpler planar nematic liquid crystal cell doped with 1% wt methyl red. Owing to their polarization
dependent enhancement factor a tunable phase filter can be photoinduced efficiently. Thus, images of different degree of
contrast (and even contrast reversal) can be obtained either by rotating the polarization vector. All optical real-time
imaging of dynamic events can be performed and image processing such as edge enhancement is demonstrated.
Phase contrast microscopy, is a technique that can be used to produce high-contrast images of transparent objects. The
technique employs a phase mask, at the object Fourier transform plane, to create a synthetic reference wave that
interferes with the object wave at the image plane. However, the fabrication and alignment of these masks is an
expensive and delicate process. In this work, we present a nonlinear phase contrast microscope that can be implemented
with a conventional optical microscope using a low power CW coherent light source to illuminate the specimen. An
intensity dependent refractive index material is used to photoinduce the filter. Therefore, the aligning procedure is
greatly simplified. The nonlinear material is a thin cell of dye doped liquid crystal where it is possible to produce a
tunable phase delay depending on the incident light intensity, the light polarization, and the temperature. Due to these
characteristics the resulting setup is relatively inexpensive, easy to implement, and extremely robust.
We propose and describe an optoelectronic system that emulates a minimum digital system; which typically consists of
a microprocessor, a memory device, an input device and an output data device, with its corresponding data, control and
addressing busses. These devices work following a program which is stored in the memory device, as codified
instructions. In our proposal, the memory device is a reconfigurable single-lens holographic memory. The instructions
to be stored are coded and decoded as binary pages by software. The software interprets the data and carries out the
instructions as a microprocessor does in a minimum digital system. We present preliminary results of the performance
of our proposal.
Flow visualization refers to a method used for qualitatively obtain information in the field of fluid mechanics. In this work, we show a simple single lens system using laser light illumination to observe flow dynamics using a setup similar to the schileren setup. As we will detail, it is based on a phase contrast technique in which the filter is made of a nonlinear optical material, therefore it is self-aligned and depends mainly on the illuminating intensity. Due to these characteristics, the resulting setup is extremely robust and builds up within a few milliseconds.
Flow visualization refers to a method used for qualitatively obtain information in the field of fluid mechanics. In this work, we show a simple single lens system using laser light illumination to observe flow dynamics using a setup similar to the schileren setup. As we will detail, it is based on a phase contrast technique in which the filter is made of a nonlinear optical material, therefore it is self-aligned and depends mainly on the illuminating intensity. Due to these characteristics, the resulting setup is extremely robust and builds up within a few milliseconds.
Eduardo Tepichin, Roberto Cantu, Marco Rosales, David Sanchez de la Llave, Jorge Ibarra Galitzia, Gustavo Ramirez Zavaleta, Andree Curioca, Victor Montes, Julio Bonilla
We started our study with a group of Mexican Males with an Uncorrected Visual Acuity (UCVA) of 20/20, 20/30, and 20/40. The data was obtained using a Nidek OPD Scan ARK 10000 with the Version 1.11b of the working software. With the resulting Zernike coefficients, we calculated the average of the total Wavefront map, the Point Spread Function (PSF), the Optical Transfer Function, (OTF) and the corresponding Modulation Transfer Function (MTF). The purpose of these calculations was to obtain a pattern to be used as a reference to compare with the performance of human eyes after a laser surgery procedure and virgin eyes. In our case, the surgery was performed with an excimer laser Nidek EC-5000 Ver.1.26 W. When the OPD Scan software was upgraded, we realized that the Zernike coefficients for a given eye were different, for each version. Therefore, the aim of this work is to compare our reference pattern of the Zernike coefficients obtained with two different version of the working software.
KEYWORDS: Point spread functions, Eye, Drug discovery, Visualization, Wavefront aberrations, Modulation transfer functions, Optical transfer functions, Imaging systems, Visual analytics, Surgery
In the area of ophthalmic refractive surgery research, the Zernike expansion of the Wavefront aberrations has been the key factor in the measurement, representation and evaluation of the human eye aberrations in many different clinical situations. The Wavefront Aberrations described by the Zernike expansion can be translated as the polynomial expansion of the exit pupil of an optical system that represents the total Wavefront aberrations (corneal + internal elements) of the eye. In this direction, we can use this exit pupil to calculate both the incoherent Point Spread Function (PSF) and the Optical Transfer Function (OTF) of this system. With either of these two functions (PSF or OTF), we can easily calculate the output image of a certain object. This information can be used to evaluate the visual performance of the eyes with a set of pre-determined objects and their corresponding images. We apply these results to characterize the behavior of the aberrations of human eyes that in principle do not need any type of refractive compensation or correction, in order to have a reference which may be ethnical-dependent. We are interested in describing the set of aberration characterizing the Normal Mexican Eye (NME). To achieve our goal, we start our study with a group of Mexican Males with an Uncorrected Visual Acuity (UCVA) of 20/20, 20/30, and 20/40. We present the preliminary results of our characterization.
The nonlinear common path interferometer is a simple and robust single lens optical processor using an intensity dependent medium placed on its geometrical focal plane to observe deformed wavefronts. It is described either as a nonlinear inteferometer or as an image processor. We demonstrate that this system requires excess surrounding illumination beyond the geometrical boundaries of the disturbance to operate. We discuss recent progress on this setup. In particular, the effect of large phase changes in the filter and the dynamics of the filter formation.
In this work, we show a simple single lens system using laser light illumination to observe flow dynamics. It is based on a phase contrast technique in which the filter is made of a nonlinear optical material, therefore it is self-aligned and depends mainly on the illuminating intensity. Due to these characteristics, the resulting setup is extremely robust and builds up within a few milliseconds.
In this paper we show numerically and experimentally the generation of ring dark spatial solitons using a phase disk and an opaque ring. In the first case one dark ring is generated and in the second a pair. The propagation and stability of this solitons is analyzed.
An analysis of the image fill factor effect on Zernike-type phase contrast filtering is presented. We define image fill factor as the ratio of the object support area over the illuminating area. Numerical simulations are presented for binary phase objects where the contrast of the output image is evaluated as a function of the image fill factor and image phase variations. The results obtained show that the image fill factor can significantly modify the contrast of the output image.
We modify the double-phase holographic code to implement arbitrary complex modulation with a transmission type twisted-nematic liquid crystal display. This device is employed in the mostly phase configuration, for which the phase modulation is coupled with a non-constant amplitude modulation. The modified double-phase code implements arbitrary complex modulation employing the constrained complex modulation of the display.
In this work we propose a generalization of the convolution kernel capable of realizing image processing operations as edge enhancement, phase visualization, image restoration, by using a joint transform correlator. The proposal convolution kernel is designed according to the operation to be performed. We present numerical simulations for each convolution kernel which performs the corresponding operation. On the other hand, experimental results are presented from the optical implementation of the convolution kernel by using a joint transform correlator which has the advantage of avoiding alignment difficulties presented by classical Fourier processors.
We show numerically and experimentally that ring dark spatial solitons can be generated using a phase disk mask or an opaque ring. In the first case one ring is produced and in the second a pair. Rings generated by phase disk are very stable when they are perturbed with one-dimensional dark solitons. The stability of rings generated by opaque rings depends on the size of the perturbation and symmetry of the initial condition. The propagation and stability of these solitons is analyzed numerically and experimentally.
In this paper we report the observation of nonlinear behavior of Kerr type of developed and bleached photographic film using cw laser sources. The nonlinear characterization is made using the Z-scan technique with Argon and He-Nel lasers beams. The results show that depending on the intensity, wavelength and exposition time the refractive index changes can be reversed or permanent giving new application to this material.
In this paper we demonstrate a novel phase contrast system that employs a BR film. Since the filter is optically induced by the Fourier transform of the phase object, no alignment is necessary at the filter plane making it extremely robust. Due to the optical properties of BR films the phase filter can be induced with low light intensity levels. The material response allows operation at video frame rates, processing of high spatial resolution objects, and the use of relatively inexpensive laser sources. Such characteristics and the fact that BR films can be produced at a low cost makes the system simple to implement, relatively inexpensive and extremely robust. The effects of varying the illuminating area beyond the phase object area and filter saturation are also analyzed.
Based on the Lau Effect we propose a system suitable for eliminating non-periodic noise on bi-dimensional periodic structures in which a liquid crystal display (LCD) is used as a dynamic grating source. Experimental results obtained with our proposal are shown.
In this work we propose a convolution kernel capable of realizing phase visualization when operated with a phase function. The proposed convolution kernel is a binary complex function. We present numerical simulations of its performance on one and two-dimensional binary phase functions. We also briefly discuss its implementation in a joint transform architecture and the requirements imposed by the detector at the system's Fourier plane. Finally, we analyze the effect of quantizing the Fourier data on the contrasted output images.
We discuss the performance of the double-phase holographic encoding of complex modulation, implemented with a phase-only spatial light modulator (SLM). A macro-pixel formed with two phase-modulated pixels of the SLM is required to encode each sampled value of the desired complex modulation. This complex modulation is obtained in the zero order term of the Fourier series associated to the macro-pixel structure. We discuss the performance of this holographic method with explicit consideration to the pixelated structure of the SLM. We show that an exact copy of the desired complex function, only attenuated by the SLM fill factor, is generated by the holographic code (with some additional high order off-axis terms). We derive a formula for the signal field reconstruction efficiency. This formula shows that the efficiency is dependent on the absorption (or modulus) of the encoded complex modulation. As an application, we show that the holographic code can be adapted (with slight modifications) to implement a highly isotropic edge enhancement filter.
We investigate the encoding of a phase-only filter together with a Fourier transforming lens using a single SLM. We consider the implementation of this composed filter with both phase-only and real-only SLMs. The restrictions on the optical setup parameters in terms of the SLM characteristics are discussed. We corroborate our proposals by presenting numerical simulations.
In this work we present three spatial filters that perform isotropic edge enhancement or recognition. Their design is based on first determining a convolution kernel that performs the desired operation and then, by Fourier transforming, obtaining the filter function. To the authors' best knowledge, these filters have not been proposed in the past. We present numerical simulations that corroborate our proposal. For the optical implementation of one of the proposed filters, a holographic technique capable of representing complex transmittances is required. In this case, the filter is simulated using a double-phase holographic code.
We present computer simulations of the 2D Fractional Hilbert Transform, of index P for both amplitude and phase objects. We also present, computer simulations of the isotropic version of the classical Hilbert Transform.
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