We present a spatial frequency domain imaging (SFDI) system based on single-pixel imaging (SPI) techniques with a single digital micromirror device (DMD) modulating simultaneously the sinusoidal pattern and the spatial sampling masks.
In this contribution, we present an optical imaging system with structured illumination and integrated detection based on the Kubelka-Munk light propagation model for the spatial characterization of scattering and absorption properties of turbid media. The proposed system is based on the application of single-pixel imaging techniques to achieve spatial resolution. Our strategy allows to retrieve images of the absorption and scattering properties of a turbid media slab by using integrating spheres with photodiodes as bucket detectors. We validate our idea by imaging the absorption and scattering coefficients of a spatially heterogeneous phantom and an organic sample.
We present a diffuse optical imaging system with structured illumination and integrated detection for spatial characterization of scattering and absorption properties of turbid media. It is based on the application of single- pixel imaging techniques with integrating spheres, which allows us to develop a spatial resolved version of the Kubelka-Munk method.
In the last years, many efforts have been devoted to use electrically addressed spatial light modulators (SLMs) in
Adaptative Optics. In this contribution we have optimized a low-cost SLM based on a liquid crystal (LC) device for the
compensation of eye aberrations. This kind of devices is seldom used in ophtalmic applications due to the relatively low
dynamic range of the phase retardation that can be introduced at each pixel. Here, we have optimized the phase
modulation response of a commercial twisted nematic liquid crystal display (TNLCD) by means of a polarimetric
arrangement that includes retarder plates and polarizers. Furthermore, we describe an efficient four-level phase encoding
scheme that allows us to use these conventional SLMs for the compensation of optical aberrations as those typically
found in human eyes. For obtaining experimental compensation results we have used artificial aberrated eyes simulated
with refractive phase plates. This proof-of-concept is the first step to develop a low-cost real-time system for the
correction of eye aberrations.
Off-the-shelf spatial light modulators (SLMs) like those commonly included in video projection devices have been seldom used for the compensation of eye aberrations, mainly due to the relatively low dynamic range of the phase retardation that can be introduced at each pixel. They present, however, some interesting features, such as high spatial resolution, easy handling, wide availability, and low cost. We describe an efficient four-level phase encoding scheme that allows us to use conventional SLMs for compensating optical aberrations as those typically found in human eyes. Experimental results are obtained with artificial eyes aberrated by refractive phase plates introducing either single Zernike terms or complex eye aberration patterns. This proof-of-concept is a step toward the use of low-cost, general purpose SLMs for the compensation of eye aberrations.
We present an achromatization procedure for multiple images obtained with the Talbot illuminator. It consists on joining in
one optical arrangement an achromatic Fresnel diffraction setup and the kinoform Talbot illuminator. In this way the multiple
images produced by the Talbot illuminator are obtained using totally incoherent light, both spatially as well as temporally.
We present the experimental results which confirm the correctness of the proposed approach.
We describe several methods to extend security techniques based on optical processing to work under broadband illumination. The key question of our procedures is the design of dispersion-compensated optical processors by combining a small number of diffractive and refractive lenses. Our optical configurations provide, in a first-order approximation, the Fraunhofer diffraction pattern of the input signal in a single plane and with the same scale for all the wavelengths of the incident light. In this way, our achromatic hybrid systems allow us to reconstruct color holograms with white light. These achromatic hybrid (diffractive-refractive) systems are applied, in a second stage, for implementing color processing operations with white light, such as color pattern recognition. In this direction, we design also a technique to encrypt color input objects into computer generated color holograms, which are decrypted optically with an achromatic joint transform correlator architecture under white-light illumination. Finally, we describe a totally-incoherent optical processor that is able to perform color processing operations under natural illumination (both spatially and temporally incoherent). This system is applied to perform color pattern recognition and optical encryption operations under natural light. Numerical and experimental results are shown.
When an axicon is illuminated under an angle different than the assumed one, its focal segment looses quality and broadens significantly. In order to compensate this aberration, harmful in scanning and metrological applications of axicons, a concept of an aberrationless axicon doublet working in the real time is proposed. The constant part of the doublet is an ordinary and conventional linear axicon, whereas the second, variable part, for which the application of spatial light modulator (SLM) device is proposed, introduces a phase shift completing the transmittance of the whole
doublet to that of the corresponding elliptical axicon forming in a given moment a properly inclined focal segment.
KEYWORDS: Colorimetry, Diffraction gratings, Lenses, Diffraction, Near field diffraction, Objectives, Light sources, Local area networks, Chemical elements, Wave propagation
A novel optical set-up that allows a totally incoherent Lau effect is demonstrated. It is based on dispersion-compensated techniques that employ strong dispersive elements. In this way, three commercially available diffractive lenses and a refractive objective are used for achromatic Lau fringes production with spatial and temporally incoherent illumination.
We report on a hybrid (diffractive-refractive) wavelength-independent imaging setup with an intermediate achromatic filtering plane in the Fresnel domain. Therefore, the system acts as a chromatically-compensated Fresnel processor able to perform space-variant color pattern recognition operations in a single step.
Diffraction efficiency of blazed diffractive elements turns out to be more resistant to changes of the illuminating wavelength if the blaze angle of their periods varies randomly within a certain range.
KEYWORDS: Geometrical optics, Diffraction, Lenses, Transformers, Colorimetry, Point spread functions, Transparency, Near field diffraction, Chromatic aberrations, Optical signal processing
The scope of this work is the compensation of the chromatic dispersion inherent to free-space light propagation, both in the Fraunhofer and in the Fresnel diffraction region. The cornerstone of our procedure lies in achieving, in a first- order approximation, the incoherent superposition of the monochromatic versions of the selected diffraction pattern in a single plane and with the same scale for all the wavelengths of the incident light. Our novel optical configurations with achromatic properties for the field diffracted by a screen are formed by a proper combination of a small number of conventional diffractive and refractive lenses, providing an achromatic real image of the diffraction pattern of interest. The residual chromatic aberrations in every case are low even when the spectrum of the incident light spreads over the whole visible region. The resulting achromatic hybrid (diffractive- refractive) systems are applied, in a second stage, for implementing several achromatic diffraction-based applications with white light, like wavelength-independent spatial- frequency filtering, achromatic pattern recognition, white- light array generation, and to designing a totally-incoherent optical processor that is able to perform color processing operations under natural illumination (both spatially and temporally incoherent).
We report herein an hybrid (diffractive-refractive) lens triplet showing quasi-wavelength-independent optical Fourier transform capabilities. The wavelength compensation carried out by our novel optical design is exact for the axial position of the Fourier transform of the input. Nevertheless, a very low residual transversal chromatic aberration remains. Results of laboratory experiments will be shown.
Different optical architectures designed for compensating the chromatic dispersion inherent to free-space broadband light diffraction are presented. These devices are formed by a small number of conventional refractive objectives and diffractive lenses. In a second stage, several achromatic diffraction-based information processing techniques working with spatially-coherent or spatially-incoherent white-light illumination are also discussed.
The scope of this work is the compensation of the chromatic dispersion inherent to free-space light propagation, both in the Fraunhofer and in the Fresnel diffraction region. The cornerstone of our procedure lies in achieving, in a first-order approximation, the incoherent superposition of the monochromatic versions of the selected diffraction pattern in a single plane and with the same scale for all the wavelengths of the incident light. Our novel optical configurations with achromatic properties for the field diffracted by a screen are formed by a proper combination of a small number of conventional diffractive and refractive lenses, providing an achromatic real image of the diffraction pattern of interest. The residual chromatic aberrations in every case are low even when the spectrum of the incident light spreads over the whole visible region. The resulting achromatic hybrid (diffractive- refractive) systems are applied, in a second stage, for implementing several achromatic diffraction-based applications with white light, like wavelength-independent spatial-frequency filtering, achromatic pattern recognition, white-light array generation, and to designing a totally-incoherent optical processor that is able to perform color processing operations under natural illumination (both spatially and temporally incoherent).
We report a new achromatic Fourier processor constituted basically by a quasi wavelength- independent imaging forming system whose first half performs an achromatic Fourier transform of a color input object. Consequently, this optical architecture, formed by a small number of diffractive and refractive lenses, provides an intermediate achromatic real Fraunhofer plane and a final color image with a high signal-to-noise ratio. In this way, our optical processor can perform simultaneously the same spatial filtering operation for all the spectral components of the broadband illumination.
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