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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Now showing 1 - 10 of 20

Generalized grating imaging using an extended monochromatic light source
(Journal of the Optical Society of America A-Optics Image Science And Vision, 2000) Crespo Vázquez, Daniel; Alonso Fernández, José; Bernabeu Martínez, Eusebio
It is a well-known fact that one grating can act as an imaging element for another grating when the first is illuminated with an extended monochromatic light source. The conditions for image formation in such a system are studied when the finite size and position of the broad light source are considered. From the presented analysis, expressions for the location and the depth of focus of such images can be derived.
Generation of optical reference signals robust to diffractive effects
(Ieee Photonics Technology Letters, 2007) Saez Landete, José; Salcedo Sanz, Sancho; Rosa Zurera, Manuel; Alonso Fernández, José; Bernabeu Martínez, Eusebio
In grating measurement systems, a reference signal is needed to achieve an absolute measurement of the position. The zero reference signals are normally obtained illuminating two identical superimposed zero reference codes (ZRCs) and registering the transmitted light by means of a photodiode. As one ZRC moves with respect to the other, the two codes overlap and the signal registered is the autocorrelation of the ZRC transmittance. In high resolution systems, the diffraction effects degrade the geometrical shadow of the first ZRC as it propagates to the second one. As a result, the autocorrelation is also degraded and the amplitude of the reference signal is greatly reduced. In this letter, we present a method for designing ZRCs with minimum diffractive effects. The method is based on the optimization of ZRCs by means of a genetic algorithm.
Zero reference signal for displacement measuring systems by use of speckle
(Applied Optics, 2003) Pérez Quintián, Fernando; Alonso Fernández, José; Atencia Carrizo, Jesús; Bernabeu Martínez, Eusebio
An optical method for generating a reference signal for an incremental displacement measurement system is proposed. We achieved this zero reference signal by comparing two speckle patterns arriving from two symmetric diffusers, which are used as natural random codes that are identical only when the reading head is located equidistantly between the diffusers. The comparison of the speckles is obtained either by interference, as in a Michelson interferometer, or by intensity correlations.
Quasicontinuous pseudoimages in sinusoidal grating imaging using an extended light source
(Optics Communications, 2004) Sánchez Brea, Luis Miguel; Alonso Fernández, José; Bernabeu Martínez, Eusebio
When a polychromatic light illuminates a grating, an achromatic and continuous self-imaging regime is produced, what means that Talbot planes are eliminated. In this work, we investigate the existence of this continuous regime for generalized grating imaging. We have found that amplitude gratings with sinusoidal profiles may form, under monochromatic and partially coherent illumination, pseudoimages whose contrast or modulation present a smooth dependence on the gap between the two gratings.
Invariant grating pseudoimaging using polychromatic light and a finite extension source
(Applied Optics, 2008) Sánchez Brea, Luis Miguel; Saez Landete, José; Alonso Fernández, José; Bernabeu Martínez, Eusebio
The Talbot effect is a well studied phenomenon by which grating pseudoimages appear at certain periodic distances when monochromatic light is used. Recently, numerical simulations have shown a new phenomenon; when a polychromatic light beam is used in a double grating system, the intensity of the pseudoimages presents a transverse-profile that remains unaffected over a wide range of propagation distances. This effect can be used to increase the tolerances of gratings based optical devices, such as displacement measurement systems, interferometers, and spectrometers. The pseudoimages formation with a polychromatic and finite extension light source is analytically and experimentally demonstrated. Relatively simple analytical expressions for the intensity and the contrast allow us to predict when pseudoimages present a constant contrast and when they disappear. Furthermore, we experimentally obtain the pseudoimages using the proposed configuration, corroborating the theoretical predictions.
Correlation technique for the compensation of diffraction widening of optical reference signals
(Journal of The Optical Society Of America A-Optics Image Science and Vision, 2009) Saez Landete, José; Alonso Fernández, José; Sánchez Brea, Luis Miguel; Morlanes Calvo, Tomás; Bernabeu Martínez, Eusebio
Two-grating measurement systems are routinely employed for high-resolution measurements of angular and linear displacement. Usually, these systems incorporate zero reference codes (ZRCs) to obtain a zero reference signal (ZRS), which is used as a stage-homing signal. This signal provides absolute information of the position to the otherwise relative information provided by the two-grating incremental subsystems. A zero reference signal is commonly obtained illuminating the superposition of two identical pseudorandom codes and registering the transmitted light by means of a photodiode. To increase the resolution of the system, a reduction of the grating period and the ZRC widths is required. Due to this reduction, the diffractive effects produce a widening of the ZRS and, in turn, a loss of the measuring accuracy. In this work, we propose a method to narrow the distorted signal obtained with a Lau-based encoder, reinstating the accuracy of the ZRS. The method consists of the inclusion of a correlation mask on the detector. A theoretical model to design the mask has been developed, and experimental results have been obtained that validate the proposed technique.
Calculation of optical imbalances in ophthalmic lenses using a new algorithm based on the local dioptric power matrix formalism
(Journal of the Optical Society of America A-Optics Image Science And Vision, 2001) Gómez Pedrero, José Antonio; Alonso Fernández, José; Bernabeu Martínez, Eusebio
We present a new algorithm to calculate the optical imbalances and differential prismatic effects that appear when two eyes look at an object through correcting eyeglasses. These are important magnitudes in ophthalmic optics because large amounts of them will disturb the binocular vision of the spectacle wearer. As a practical application of our algorithm, the distribution of optical imbalances and differential prismatic powers for a pair of progressive addition lenses has been calculated, and we obtain information about the effects of this kind of lens on the binocular vision of the wearer.
Reflection optical encoders as three-grating moiré systems
(Applied Optics, 2000) Crespo Vázquez, Daniel; Alonso Fernández, José; Bernabeu Martínez, Eusebio
Reflection optical encoders are studied as three-grating moiré systems. An analysis is made of the differences that may appear between it and the standard case in which an optical encoder is regarded as a two-grating system.
Optoelectronic device for the measurement of the absolute linear position in the micrometric displacement range
(Materials, Devices, and Applications, 2005) Morlanes Calvo, Tomás; Peña, José Luis de la; Sánchez Brea, Luis Miguel; Alonso Fernández, José; Crespo Vázquez, Daniel; Saez Landete, José; Bernabeu Martínez, Eusebio; Badenes, Goncal; Abbott, Derek; Serpenguzel, Ali
In this work, an optoelectronic device that provides the absolute position of a measurement element with respect to a pattern scale upon switch-on is presented. That means that there is not a need to perform any kind of transversal displacement after the startup of the system. The optoelectronic device is based on the process of light propagation passing through a slit. A light source with a definite size guarantees the relation of distances between the different elements that constitute our system and allows getting a particular optical intensity profile that can be measured by an electronic post-processing device providing the absolute location of the system with a resolution of 1 micron. The accuracy of this measuring device is restricted to the same limitations of any incremental position optical encoder.
Laser beam deflectometry based on a subpixel resolution algorithm
(Optical Engineering, 2001) Canabal Boutureira, Héctor Alfonso; Alonso Fernández, José; Bernabéu Martínez, Eusebio
A deflectometric method for the characterization of optical systems is presented. It is based on the use of a CCD camera and a subpixel resolution algorithm for the measurement of the deflection of a laser beam that propagates through the system. To obtain accurate results, three different algorithms for measuring the position of the deflected beam are tested and compared. Based on this comparison, an algorithm based on the calculation of the phase of the fast Fourier transform (FFT) is selected, and an accuracy of 0.024 pixels is obtained on the determination of the beam position in our setup. Using an XY scanning stage, the proposed method is completely automated and applied for the characterization of ophthalmic lenses. In this application, the gradients of the wavefront refracted by the lens are measured directly, and from them, the thickness and the local power of the lens are computed.