Person:
Alonso Fernández, José

First Name

José

Last Name

Alonso Fernández

URI

https://hdl.handle.net/20.500.14352/79966

Affiliation

Universidad Complutense de Madrid

Faculty / Institute

Óptica y Optometría

Department

Óptica

Area

Optica

Identifiers

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Search Results

Now showing 1 - 10 of 12

Incremental PCA algorithm for fringe pattern demodulation
(Optics express, 2022) Gómez Pedrero, José Antonio; Estrada, Julio César; Alonso Fernández, José; Quiroga Mellado, Juan Antonio; Vargas Balbuena, Javier
This work proposes a new algorithm for demodulating fringe patterns using principal component analysis (PCA). The algorithm is based on the incremental implantation of the singular value decomposition (SVD) technique for computing the principal values associated with a set of fringe patterns. Instead of processing an entire set of interferograms, the proposed algorithm proceeds in an incremental way, processing sequentially one (as minimum) interferogram at a given time. The advantages of this procedure are twofold. Firstly, it is not necessary to store the whole set of images in memory, and, secondly, by computing a phase quality parameter, it is possible to determine the minimum number of images necessary to accurately demodulate a given set of interferograms. The proposed algorithm has been tested for synthetic and experimental in ter ferograms showing a good performance. (C) 2022 Optica Publishing Group under the terms of the Optica Open Access Publishing Agreement
Optical method for the surface topographic characterization of Fresnel lenses
(Optical Fabrication, Testing and Metrology IV, 2011) Martínez Antón, Juan Carlos; Gómez Pedrero, José Antonio; Alonso Fernández, José; Quiroga Mellado, Juan Antonio
Fresnel lenses and other faceted or micro-optic devices are increasingly used in multiple applications like solar light concentrators and illumination devices. As applications are more exigent this characterization is of increasing importance. We present a technique to characterize the surface topography of optical surfaces. It is especially well adapted to Fresnel lenses where abrupt surface slopes are usually difficult to handle in conventional techniques. The method is based on a new photometric strategy able to codify the height information in terms of optical absorption in a liquid. A detailed topographic map is simple to acquire by capturing images of the surface. Some experimental results are presented. A single pixel height resolution of similar to 0.1 mu m is achieved for a height range of similar to 50 mu m. A surface slope analysis is also made achieving a resolution of similar to +/- 0.15 degrees.
Enhancement of Cryo-EM maps by a multiscale tubular filter
(Optics express, 2022) Vargas Balbuena, Javier; Gómez Pedrero, José Antonio; Quiroga Mellado, Juan Antonio; Alonso Fernández, José
We present an approach to enhance cryo-electron microscopy (cryo-EM) postprocessed maps based on a multiscale tubular filter. The method determines a tubularness measure locally by the analysis of the eigenvalues of the Hessian matrix. This information is used to enhance elongated local structures and to attenuate blob-like and plate-like structures. The approach, thus, introduces a priori information in the reconstructions to improve their interpretability and analysis at high-resolution. The proposed method has been tested with simulated and real cryo-EM maps including recent reconstructions of the SARS-CoV-2. Our results show that our methods can improve obtained reconstructions.
Colorimetric matching by minimum-square-error fitting
(Applied Optics, 1994) Quiroga Mellado, Juan Antonio; Alonso Fernández, José; Zoido Chamorro, Jesús Manuel; Bernabéu Martínez, Eusebio
Least-squares approximation can be used in image-based colorimetry once the set of sampling functions is selected. We discuss the accuracy obtained in earlier research, and we compare it with a better calculation method.
Deflectometric method for the measurement of user power for ophthalmic lenses
(Applied Optics, 2010) Quiroga Mellado, Juan Antonio; Gómez Pedrero, José Antonio; Alonso Fernández, José; Vargas Balbuena, Javier
This paper presents a deflectometric technique to measure the power of an ophthalmic lens as perceived by the user. It is based on a calibrated camera acting as a pinhole in order to measure ray deflection along the same path as the visual axis when the lens is held in front of the eye. We have analyzed numerically the accuracy of our technique, and it has been compared experimentally with a commercial "lens mapper" and with the real user power calculated from the measured topography of the lens surfaces to state the reliability and accuracy of the presented technique.
Laser beam profiling with extended-image-range techniques
(Optical Engineering, 2005) Quiroga Mellado, Juan Antonio; González Moreno, Ricardo; Alonso Fernández, José; Bernabeu Martínez, Eusebio
A method to enlarge the dynamic range of a CCD-based laser beam profiler is presented. The method is based on extended-image-range techniques. The algorithm that generates the extended-irradiance-range image is described in detail. An equivalent dynamic range and number of bits are defined and computed for the new profiling system. To test the method, experimental measurements of the principal widths of the output beam from a single-mode optical fiber have been made, as well as the Fraunhofer diffraction pattern of a 200-μm m pinhole back-illuminated by a HeNe laser.
Improvements in laser beam characterization with a CCD-based setup
(Photonics in Measurement, 2004) Quiroga Mellado, Juan Antonio; González Moreno, Ricardo; Alonso Fernández, José; Bernabeu Martínez, Eusebio
CCD-based setups are widely extended in commercial beam profilers. In many beam-profiling applications the high sensitivity of CCD-camera makes necessary the attenuation of the beam. It can affect the beam profile and cause lost of information in regions of low irradiance. In this work we analyze the combined influence of noise and masking in the beam characterization, particularly in the measurement of second order moments. We also apply an extended intensity range imaging technique to improve the quality of the information obtained by a generic instrument. It is achieved merging several images with different sensitivities which are obtained with different integration times.
Robust fitting of Zernike polynomials to noisy point clouds defined over connected domains of arbitrary shape
(Optics Express, 2016) Rodríguez Ibáñez, Diego; Gómez Pedrero, José Antonio; Alonso Fernández, José; Quiroga Mellado, Juan Antonio
A new method for fitting a series of Zernike polynomials to point clouds defined over connected domains of arbitrary shape defined within the unit circle is presented in this work. The method is based on the application of machine learning fitting techniques by constructing an extended training set in order to ensure the smooth variation of local curvature over the whole domain. Therefore this technique is best suited for fitting points corresponding to ophthalmic lenses surfaces, particularly progressive power ones, in non-regular domains. We have tested our method by fitting numerical and real surfaces reaching an accuracy of 1 micron in elevation and 0.1 D in local curvature in agreement with the customary tolerances in the ophthalmic manufacturing industry.
Reversible photoalignment of liquid crystals: a path toward the creation of rewritable lenses
(Scientific reports, 2020) Quiroga Mellado, Juan Antonio; Canga, Ignacio; Alonso Fernández, José; Crespo Vázquez, Daniel
In this work, we describe a new reversible photoalignment effect for the director in nematic liquid crystals that provides an approach for the creation of lenses whose optical power can be recorded and erased. The possibility of creating a rewritable lens has very important practical implications, for example, in the ophthalmic lens industry. A rewritable ophthalmic lens could be a convenient solution for patients whose compensation needs change over time due to age-related physiological changes, such as the onset and progression of presbyopia. Using rewritable lenses, small lens power corrections could be implemented through a rewriting procedure on the mounted lens without resurfacing or manufacturing and mounting a new lens. More generally, this new effect multiple potential applications in the creation of rewritable optical systems, such as reconfigurable optical networks, index-tunable antireflective coatings and optically rewritable phase gratings.
Squareness error calibration of a CMM for quality control of ophthalmic lenses
(International Journal of Advanced Manufacturing Technology, 2013) Quiroga Mellado, Juan Antonio; Rodríguez Ibáñez, Diego; Alonso Fernández, José
This paper proposes a calibration procedure for the squareness error of small-sized coordinate measuring machines like those used for ophthalmic lenses quality control. The proposed procedure only requires a spherical lens as a reference surface and it only needs to be measured once making this calibration method faster and cheaper than the existing ones.