Person: Alonso Fernández, José
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First Name
José
Last Name
Alonso Fernández
Affiliation
Universidad Complutense de Madrid
Faculty / Institute
Óptica y Optometría
Department
Óptica
Area
Optica
Identifiers
20 results
Search Results
Now showing 1 - 10 of 20
Item Design of two-dimensional zero reference codes by means of a global optimization method(Optics Express, 2005) Saez Landete, José; Alonso Fernández, José; Bernabeu Martínez, EusebioA method to obtain the absolute measure of the position is by means of the autocorrelation of two zero reference marks. In one-axis measurement systems one dimensional mark are used and the design of these marks is relatively complex. When the movement is in two-axes, two dimensional reference marks are required and they are even harder to design. We report a method of global optimization to calculate the optimal two dimensional zero reference marks which generate the reference signal with the highest central peak. This method proves to be a powerful tool for solving this problem.Item Laser beam profiling with extended-image-range techniques(Optical Engineering, 2005) Quiroga Mellado, Juan Antonio; González Moreno, Ricardo; Alonso Fernández, José; Bernabeu Martínez, EusebioA 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.Item 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, EusebioCCD-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.Item Experimental measurements of generalized grating images(Applied Optics, 2002) Crespo Vázquez, Daniel; Alonso Fernández, José; Bernabeu Martínez, EusebioThe term generalized grating imaging is used to describe the process of image formation of a grating using only another grating as imaging system. The moiré and the Lau effects could be regarded as particular cases of such a process. Here we deal with the less-studied case of images formed at finite distances from the gratings, using an extended monochromatic light source. Some experimental results are shown for the images obtained in this last case, and they are compared with theoretical predictions.Item 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, EusebioIt 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.Item 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, EusebioAn 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.Item Laser beam deflectometry based on a subpixel resolution algorithm(Optical Engineering, 2001) Canabal Boutureira, Héctor Alfonso; Alonso Fernández, José; Bernabéu Martínez, EusebioA 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.Item 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, EusebioIn 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.Item Optical autofocus for high resolution laser photoplotting(Photonic Materials, Devices, and Applications, 2005) Alonso Fernández, José; Crespo Vázquez, Daniel; Jiménez Castillo, Isidoro; Bernabéu Martínez, Eusebio; Badenes, Goncal; Abbott, Derek; Serpenguzel, AliAn all optical autofocus has been designed and tested for tight line width control in a high NA laser photoplotter system. The laser system is based in a GaN semiconductor laser with power 30 mW and wavelength 405 nm. The advantage of using this laser, despite the relatively long wavenlength, is compactness and easy for high frequency modulation. The autofocus system is based in a secondary 635 nm GaAlAs laser without need for wavelength, neither power stabilization. The two beams are delivered coaxially through the focusing lens by means of a dichroic beamsplitter. Focusing lens need no correction for chromatic aberration, as this is compensed by appropriate autofocus beam divergence. After reflection in the sample, the autofocus beam is separated from the returning writing beam and then guided to a collimation sensor, in which defocus of about 1/20 of the Rayleigh range of the writing beam can be detected and compensated by an analogue PID electronic control. Stable linewidth within 5% is achieved with different numerical aperture focusing lenses.Item Colorimetric matching by minimum-square-error fitting(Applied Optics, 1994) Quiroga Mellado, Juan Antonio; Alonso Fernández, José; Zoido Chamorro, Jesús Manuel; Bernabéu Martínez, EusebioLeast-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.