Person: Calvo Padilla, María Luisa
Universidad Complutense de Madrid
Faculty / Institute
Now showing 1 - 10 of 44
PublicationIntroduction to gyrator transform(American Institute of Physics (AIP), 2007) Alieva, Tatiana Krasheninnikova; Rodrigo Martín-Romo, José Augusto; Calvo Padilla, María LuisaWe introduce the gyrator transform which produces a rotation of two-dimensional signal in phase space. Main properties of this transform are considered. The flexible optical set up for gyrator transform experimental implementation is discussed. The applications of the gyrator transform to image processing such as filtering, noise reduction, encryption are demonstrated. PublicationDiffraction on the structures generated by the multiplicative iterative procedures(SPIE--The International Society for Optical Engineering, 2003) Alieva, Tatiana Krasheninnikova; Calvo Padilla, María LuisaThe Fresnel and Fraunhofer diffraction on the regular structures generated by the multiplicative iterative procedures is considered. It is proved that the iterative procedure of field construction is preserved during Fresnel diffraction, meanwhile the initiator of the structure in the Fresnel region is the Fresnel transform of the original one. The theoretical results are proved experimentally. PublicationPhotopolymerizable sol-gel nanocomposites for holographic recording(IOP Publishing Ltd., 2009-02) Calvo Padilla, María Luisa; Cheben, PavelThe research into new photosensitive materials with advanced performance for holographic applications is an active branch in material science and photonics, still challenging the field. We proposed a new class of volume hologram recording materials, sol-gel nanocomposites, with important advantages for various holographic applications, including data storage. Here we review several aspects of different types of photosensitive sol-gel glasses that we have developed. Our photopolymerizable glasses exhibit high refractive index modulation, diffraction efficiencies close to the theoretical maxima, along with low scattering and negligible shrinkage. Beside these and other practical advantages discussed in this paper, our recently developed nanocomposite glass incorporating high refractive index species has enabled fundamental studies of new optical phenomena such as the Pendellosung effect, which was observed for the first time in the optical band. PublicationFresnel diffraction effects in Fourier-transform arrayed waveguide grating spectrometer(The Optical Society Of America, 2007-12-10) Rodrigo Martín-Romo, José Augusto; Cheben, Pavel; Alieva, Tatiana Krasheninnikova; Calvo Padilla, María Luisa; Scott, Alan; Solheim, Brian; Xu, Dan-Xia; Delâge, AndréWe present an analysis of Fourier-transform arrayed waveguide gratings in the Fresnel diffraction regime. We report a distinct spatial modulation of the interference pattern referred to as the Moire-Talbot effect. The effect and its influence in a FT AWG device is explained by deriving an original analytical expression for the modulated field, and is also confirmed by numerical simulations using the angular spectrum method to solve the Fresnel diffraction integral. We illustrate the retrieval of spectral information in a waveguide Fourier-transform spectrometer in the presence of the Moire-Talbot effect. The simulated device comprises two interleaved waveguide arrays each with 180 waveguides and the interference order of 40. It is designed with a Rayleigh spectral resolution of 0.1 nm and 8 nm bandwidth at wavelength λ~1.5 µm. We also demonstrate by numerical simulations that the spectrometer crosstalk is reduced from -20 dB to -40 dB by Gaussian apodization. PublicationStress sensor based on light scattering by an array of birefringent optical waveguides(SPIE--The International Society for Optical Engineering, 2003) Limeres, J.; Calvo Padilla, María Luisa; Lakshminarayanan, Vasudevan; Enoch, Jay M.We propose a new stress-sensing technique based upon measurement of light scattering produced by an array of birefringent waveguides. When external; stress is applied to the array of waveguides, their optical properties are modified via the photo-elastic effect. By monitorizing the scattered light amplitude this change can be detected and analysed in order to assess the strength and direction of the external force. PublicationFourier series analysis of fractal lenses: theory and experiments with a liquid-crystal display(The Optical Society Of America, 2006-02-20) Davis, Jeffrey A.; Sigarlaki, Sean Paul; Craven, Julia M.; Calvo Padilla, María LuisaWe report on a Fourier series approach that predicts the focal points and intensities produced by fractal zone plate lenses. This approach allows us to separate the effects of the fractal order from those of the lens aperture. We implement these fractal lenses onto a liquid-crystal display and show experimental verification of our theory. PublicationA novel wavelength dispersive device with a dispersive element based on staircase-like straight and parallel arrayed waveguides(Elsevier Science BV, 2007-02-01) Martínez Matos, Óscar; Calvo Padilla, María Luisa; Cheben, Pavel; Rodrigo Martín-Romo, José Augusto; Janz, Siegfried; Xu, Dan-Xia; Delâge, AndréWe propose a new type of arrayed waveguide grating (AWG) multiplexer/demultiplexer based on modified group refractive index. This device is composed by an array of straight and parallel waveguides of equal length and each waveguide consist of two sections with different width. The length of the two sections are changed from a waveguide to the adjacent one following a linear dependence resulting in a wavelength dispersive waveguide array. An example of the device design for silicon-on-insulator (Sol) platform is provided and numerical simulations have been carried out for various arrayed waveguide parameters. We demonstrate that the group index modification can be used for tailoring device dispersion properties, and that it can also result in new dispersion characteristics predicted numerically not observed in conventional AWGs. Additional advantages are that the demultiplexer does not necessarily require bending waveguide sections as in a conventional AWG (de)multiplexers, and thus yields highly compact devices with potentially very low insertion loss. Channel spacing of I nm have been predicted for sub-micron waveguides sizes. In this paper it is also proposed a novel wavefront converter based on waveguide array lens-like element with waveguides broadened sections. Numerical results for different input/output geometries are analized. PublicationNeutron fibres: a three-dimensional analysis of bending losses(IOP Publishing Ltd, 2000-07-21) Calvo Padilla, María LuisaThe confined propagation of slow neutrons along waveguides of a small cross section (fibres), discussed theoretically some time ago and demonstrated experimentally by other authors later, is analysed further. Motivated by those experiments, a three-dimensional quantum-mechanical treatment of the associated bending losses is presented. An approximate (two-parameter) formula is derived for the transmission coefficient Upsilon of the curved fibre, which displays its explicit dependence on the curvature radius Rcu, for 0 PublicationPower filtering of nth order in the fractional Fourier domain(IOP Publishing, 2002-09-13) Bastiaans, Martin J.; Alieva, Tatiana Krasheninnikova; Calvo Padilla, María LuisaThe main properties of the power filtering operation in the fractional Fourier domain and its relationship to the differentiation operation are considered. The application of linear power filtering for solving the phase retrieval problem from intensity distributions only is proposed. The optical configuration for the experimental realization of the method is discussed. PublicationFresnel diffraction by deterministic fractal gratings: An experimental study(Maik Nauka, Interperiodica, Springer-Verlag, 2003-07) Rodrigo Martín-Romo, José Augusto; Rodríguez Merlo, Daniel; Calvo Padilla, María Luisa; Alieva, Tatiana KrasheninnikovaExperimental results are presented for light diffraction under the Fresnel regime by two types of fractal gratings: triadic Cantor bars and Vicsek fractals. It is shown that the evolution of the diffraction patterns in the Fresnel regions reveals the hierarchical structure of deterministic fractal gratings.