[Show abstract][Hide abstract] ABSTRACT: We present in this work a study of the diffraction of a focused Gaussian beam by a microrefractive cylinder, and the dependence of the far field diffracted pattern with the location of the beam focal plane, relative to the center of the cylinder. A numerical study of the problem is carried out and validated with experimental verification. We center our attention on two parameters: the divergence and the number of peaks of the diffracted field. Both present a minimum for a particular position of the focal plane inside the refractive cylinder. This analysis can be used as a novel control technique for ablation of optical fibers and it can also be used as a criterion for the proper location of a focused laser beam inside an optical fiber with high accuracy. This criterion, based on the distribution of the far-field diffracted pattern, can be automated or used as a visual clue for a human operator.
Optics and Lasers in Engineering 04/2014; 55:53–58. DOI:10.1016/j.optlaseng.2013.10.020 · 2.24 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: work is aimed to design and evaluate different achromatic Fresnel lens solutions capable of operating as concentrators aimed at photovoltaic cells systems. Throughout this study, the theoretical parametric design of the achromatic lens will be shown together with a series of simulations to verify the performance of each lens topology. The results will be compared with a standard Fresnel lens to ascertain the validity and effectiveness of the obtained design. Finally, a novel kind of hybrid lens is proposed, which combines the advantages of each type of lens (standard and Fresnel) according to the optimal operating region of each design. Efficiency and concentration ratios of each particular lens are shown, regarding lens dimension, light's incidence angle, or wavelength. Through this innovative achromatic design concentration ratios above 1000 suns, which hardly reach standard Fresnel lenses. Furthermore chromatic dispersion is minimized and the efficiency rate is over 85% of efficiency for a wide spectral range (from 350 nm to 1100 nm).
International Journal of Photoenergy 03/2014; 2014(787392). DOI:10.1155/2014/787392 · 1.56 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: Two plates of different birefringence material can be combined to obtain an achromatic wave retarder. In this work, we achieve a correction for the overall retardation of the system that extends the relation to any azimuth. Current techniques for the design of achromatic wave retarders do not present a parameter that characterizes its achromatism on a range of wavelengths. Thus, an achromatic degree has been introduced, in order to determine the optimal achromatic design composed with retarder plates for a spectrum of incident light. In particular, we have optimized a quarter retarder using two wave plates for the visible spectrum. Our technique has been compared to previous results, showing significant improvement.
[Show abstract][Hide abstract] ABSTRACT: We analyze the effect of the fill factor of binary diffraction gratings
on the near field propagation. We show that the location of the
best-visibility planes changes with the configuration parameters of the
grating, that is, the amplitude and phase modulation and the fill
factor. Moreover, different intensity patterns and contrast shapes can
be obtained when different configurations are used. Analytical
expressions describing the contrast of the diffracted field are
obtained, that agree with numerical simulations.
Journal of the European Optical Society Rapid Publications 12/2011; 6:11055. DOI:10.2971/jeos.2011.11055 · 1.23 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: Recent advances in LED technology have relegated the use of optical fibre for general lighting, but there are several applications where it can be used as scanners lighting systems, daylight, cultural heritage lighting, sensors, explosion risky spaces, etc. Nowadays the use of high intensity LED to inject light in optical fibre increases the possibility of conjugate fibre + LED for lighting applications. New optical fibres of plastic materials, high core diameter up to 12.6 mm transmit light with little attenuation in the visible spectrum but there is no an efficient and controlled way to extract the light during the fibre path. Side extracting fibres extracts all the light on 2pi angle so is not well suited for controlled lighting. In this paper we present an extraction system for mono-filament optical fibre which provides efficient and controlled light distribution. These lighting parameters can be controlled with an algorithm that set the position, depth and shape of the optical extraction system. The extraction system works by total internal reflection in the core of the fibre with high efficiency and low cost. A 10 m length prototype is made with 45° sectional cuts in the fibre core as extraction system. The system is tested with a 1W white LED illuminator in one side.
Proceedings of SPIE - The International Society for Optical Engineering 09/2011; DOI:10.1117/12.896777 · 0.20 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: We report on optical sources for high bit rate Quantum Key Distribution (QKD) over free-space links. Semiconductor optical amplifiers have been used for the first time to our knowledge and allowing 100Mb/s with improved security.
[Show abstract][Hide abstract] ABSTRACT: We have developed optical sources for high bit rate Quantum Key Distribution (QKD) using active elements as well as passive schemes. These sources allow achieving 100Mb/s free space QKD with improved security and use components space qualifiable, the latter being an essential aspect for their deployment in space missions.
Lasers and Electro-Optics Europe (CLEO EUROPE/EQEC), 2011 Conference on and 12th European Quantum Electronics Conference; 05/2011
[Show abstract][Hide abstract] ABSTRACT: Micro-optical devices embedded in transparent materials are usually manufactured focusing a pulsed laser in bulk fused silica. Under this condition, pulsewidth becomes the most important parameter that rules the size of the inscriptions. Ultrafast pulses (pico- and femtosecond pulses) avoid thermal effects and the results present a high efficiency. Nevertheless, nanosecond lasers are more available due the reduced costs. Therefore, a study of the optical behavior of embedded elements micromachined by nanosecond pulses is required. In this study, we show that this regime of pulses can still be used for engraving diffractive optical elements in transparent materials, regardless of the thermal damage. A Fresnel zone plate and a far-field beam shaper have been manufactured as an example of the functionality of these devices.
[Show abstract][Hide abstract] ABSTRACT: A simple depolarization criterion for light is proposed. This criterion is based on the depolarization part derived from the degree of polarization formulation. Some reported Mueller matrices are employed to test its reliability and usefulness. Results prove that the criterion proposed can be employed as the first step to test the physical consistency of Mueller matrices.
Optik - International Journal for Light and Electron Optics 03/2011; 122(5):407-410. DOI:10.1016/j.ijleo.2009.11.033 · 0.68 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: A novel integrated optical source capable of emitting faint pulses with different polarization states and with different intensity levels at 100 MHz has been developed. The source relies on a single laser diode followed by four semiconductor optical amplifiers and thin film polarizers, connected through a fiber network. The use of a single laser ensures high level of indistinguishability in time and spectrum of the pulses for the four different polarizations and three different levels of intensity. The applicability of the source is demonstrated in the lab through a free space quantum key distribution experiment which makes use of the decoy state BB84 protocol. We achieved a lower bound secure key rate of the order of 3.64 Mbps and a quantum bit error ratio as low as 1.14×10⁻² while the lower bound secure key rate became 187 bps for an equivalent attenuation of 35 dB. To our knowledge, this is the fastest polarization encoded QKD system which has been reported so far. The performance, reduced size, low power consumption and the fact that the components used can be space qualified make the source particularly suitable for secure satellite communication.
[Show abstract][Hide abstract] ABSTRACT: This paper shows how corneal topographic data can be used to determine the value of the longitudinal spherical aberration. We have obtained the corneal profiles and the values of the longitudinal spherical aberration for the rays propagating within the steepest and flattest meridional planes, by using a real raytracing algorithm. These corneal profiles have been also fitted to conicoids and the asphericity parameter has been calculated. We have found that the longitudinal spherical aberration follows a parabolic dependence for a circular region of 5 mm in diameter. This parabolic dependence has been fitted with a polynomial function. The data provided by commercial topographic systems can be used to obtain the longitudinal spherical aberration along the selected meridians. (C) 2010 Elsevier GmbH. All rights reserved.
Optik - International Journal for Light and Electron Optics 12/2010; 121(24-24):2269-2272. DOI:10.1016/j.ijleo.2009.09.011 · 0.68 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: We analyze the near field behavior of binary amplitude gratings which present a curved profile. This configuration has an important application in rotary optical encoders. This kind of encoders is used to measure the angular displacement between two different parts of the devices. To our knowledge, its behavior in the near field has not been analyzed yet. We have found that Talbot effect is produced but the period of the self-images and Talbot distances change as we separate from the grating. We have fabricated a curved grating and have performed the experiment to corroborate the behavior theoretically found. This fact could be useful in systems that use Talbot effect to measure displacements, since the mechanical tolerances grow. (C) 2010 Elsevier B.V. All rights reserved.
[Show abstract][Hide abstract] ABSTRACT: A number of depolarization metrics is applied to a series of reported Mueller matrices. It is shown the depolarization scalar metric Q(M) provides consistent results with the reported scalar metrics like the depolarization index and the degree of polarization. It is shown Q(M) provides additional information about the internal nature of the Mueller matrices, specifically when the upper limit, 3, is reached. It is also shown the depolarization index and the Q(M) metric are only necessary but not sufficient conditions for the physical realizability of Mueller matrices. Finally, Q(M) is proven to be consistent in all cases studied here.
Optik - International Journal for Light and Electron Optics 06/2010; 121(12):1058-1068. DOI:10.1016/j.ijleo.2008.12.030 · 0.68 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: We present a family of three-dimensional concentrators constructed from the photic field generated by a Lambertian emitter. The profile of these concentrators is obtained from the field lines for a two-dimensional truncated wedge and is based on the union between a hyperbola and a tilted parabola. By revolution of this profile, we obtain hyperparabolic concentrators (HPCs). In the limiting case when the focal length of the hyperbola becomes the radius of the exit aperture, the HPC becomes the well-known compound parabolic concentrator. On the other hand, when the focal length of the hyperbola becomes infinite, the HPC achieves the thermodynamic limit of concentration.
[Show abstract][Hide abstract] ABSTRACT: Diffraction gratings are one of the most used elements in optics and even in other fields of science. They are used also like part of measurement devices in scientific and industrial applications. As it is well known, self-imaging effect appears when a diffraction grating is illuminated with a coherent beam, such as a plane wave. This effect has been analyzed in depth and its behavior is well known under ideal grating and illumination conditions. Usually, the illumination beam is not perfectly collimated but presents a certain degree of aberration. The motivation of this work is to try to explain the behavior of the self-images of an ideal amplitude grating when it is illuminated by a non-perfect beam, that is, an aberrated beam. The known of this effect can help to understand how much the aberration of the light beam affects to the diffraction pattern, and more in depth, to the self-imaging phenomenon. The results presented in this work can be very useful in metrology applications, since sometimes the contrast obtained experimentally does not correspond to the theoretical predictions, usually due to aberrations in the light beam. For this, we have used a formalism based in the Rayleigh-Sommerfeld approach. We have modeled the aberrations by using the Zernike polynomials. On the other hand, we have considered all kinds of aberrations, spherical, coma, tilt, astigmatism, etc. As it is expected the contrast of the self-images decrease when the order of them increases and also when the aberration degree increase. In some cases, contrast inversion is also produced for high aberrations.
Proceedings of SPIE - The International Society for Optical Engineering 01/2009; DOI:10.1117/12.827539 · 0.20 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: Steel tape gratings are used in different metrology applications. As the period of these gratings was large (around 100 mu m), its analytical study has been performed, up to date, using a geometrical approach. Nowadays, steel tape gratings can be manufactured with lower periods, around 20-40 mu m, and diffractive effects must be taken into account. Also, due to the roughness of the surface, statistical techniques need to be considered to analyze their behavior. In this work, an analysis of the pseudo-imaging formation in a double grating system including one steel tape grating is performed. In particular Moire and Lau configurations are analyzed. We have found that roughness significantly affects to Moire configuration. However, its effect is negligible in Lau configuration. Generalized grating imaging configuration is also studied in depth. It is shown that roughness does not affect to the contrast of pseudoimages, but it modifies their depth of focus. (C) 2008 Elsevier B.V. All rights reserved.