Person: Calvo Padilla, María Luisa
Universidad Complutense de Madrid
Faculty / Institute
Now showing 1 - 10 of 33
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. 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. 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. PublicationWavefield imaging via iterative retrieval based on phase modulation diversity(The Optical Society Of America, 2011-09-12) Rodrigo Martín-Romo, José Augusto; Alieva, Tatiana Krasheninnikova; Cristóbal Pérez, Gabriel; Calvo Padilla, María LuisaWe present a fast and robust non-interferomentric wavefield retrieval approach suitable for imaging of both amplitude and phase distributions of scalar coherent beams. It is based on the diversity of the intensity measurements obtained under controlled astigmatism and it can be easily implemented in standard imaging systems. Its application for imaging in microscopy is experimentally studied. Relevant examples illustrate the approach capabilities for image super-resolution, numerical refocusing, quantitative imaging and phase mapping. 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. PublicationArrayed waveguide grating based on group-index modification(IEEE - Inst. Electrical Electronics Engineers Inc., 2006-03) Martínez Matos, Óscar; Calvo Padilla, María Luisa; Cheben, Pavel; Janz, Siegfried; Rodrigo Martín-Romo, José Augusto; Xu, Dan-Xia; Delâge, AndréThe authors propose a new wavelength-dispersive principle based on waveguide group-index modification and apply this principle in a new type of arrayed waveguide dispersive element based on modified group index. The element is composed by an array of waveguides consisting of two sections with different group indexes. We deduce the applicable dispersion formula and demonstrate that the group-index modification can be used for controlling or enhancing device wavelength dispersion. Two device examples are provided. First, dispersive properties of a waveguide array with silicon on insulator (SOI) straight waveguides with group index modified by waveguide widening are calculated. Then, the authors show that by placing the element with modified group index in a phased array of a conventional arrayed waveguide grating (AWG) device, the dispersive properties of the AWG are markedly enhanced. Dispersion-enhancement factor of up to 60 is calculated for a compact demultiplexer designed for SOI platform with group index modified by photonic-bandgap effect. PublicationExperimental creation of chainlike beams and investigation of their structure(Maik Nauka, Interperiodica, Springer-Verlag, 2008-05) Kundikova, Nataliya D.; Ryzhkova, A. V.; Alieva, Tatiana Krasheninnikova; Calvo Padilla, María Luisa; Rodrigo Martín-Romo, José AugustoThe effect of the Gaussian beam width on the focusing properties of the chainlike Gaussian beam formed upon diffraction of laser radiation on a binary amplitude mask is studied. It is found that a decrease in the Gaussian beam width increases the sizes of focal spots and the focus depth, decreases the intensity in the focuses, and does not affect the focus position. PublicationOptical systems and algorithms for phase-space tomography of one- and two-dimensional beams(Society of Photo-Optical Instrumentation Engineers (SPIE), 2011) Cámara, Alejandro; Alieva, Tatiana Krasheninnikova; Rodrigo Martín-Romo, José Augusto; Calvo Padilla, María LuisaThe application of partially coherent optical beams for imaging, free space communication, random medium analysis requires controlling its mutual intensity. This task can be done using the phase-space tomography method consisting on the reconstruction of the Wingner distribution (WD), and therefore the mutual intensity, from its projections associated with the fractional power spectra. We propose two schemes that apply spatial light modulators (SLMs) for the measurements of the required WD projections in the case of one- and two-dimensional optical signals. The use of the SLMs allows rapid data acquisitions and operative change of the projection number. Moreover, the measured intensity distributions do not require further rescaling, which accelerates the WD reconstruction algorithm and improves its efficiency. The developed numerical methods provide different ways for data analysis such as the reconstuction of the WD using the inverse Radon transform and its visualization for the case of one-dimensional signal; the determination of the mutual intensity for two fixed points without previous reconstruction of the entire WD for two-dimensional signal, ets. The validity of the proposed approaches has been verified experimentally for the test signals and results are in a good agreement with the numerical simulation. PublicationGyrator transform: properties and applications(The Optical Society Of America, 2007-03-05) Rodrigo Martín-Romo, José Augusto; Alieva, Tatiana Krasheninnikova; Calvo Padilla, María LuisaIn this work we formulate the main properties of the gyrator operation which produces a rotation in the twisting (position-spatial frequency) phase planes. This transform can be easily performed in paraxial optics that underlines its possible application for image processing, holography, beam characterization, mode conversion and quantum information. As an example, it is demonstrated the application of gyrator transform for the generation of a variety of stable modes. PublicationAdvanced concepts in waveguide spectrometers(IEEE, 2006) Martínez Matos, Óscar; Cheben, Pavel; Schmid, Jens H.; Bogdanov, Alexei L.; Calvo Padilla, María Luisa; Delâge, André; Densmore, Adam; Janz, Siegfried; Lamontagne, Boris; Lapointe, Jean; Post, Edith; Powell, Ian; Rodrigo Martín-Romo, José Augusto; Waldron, Phillip; Xu, Dan-XiaWe present several new concepts to extend the capabilities of arrayed waveguide grating spectrometers. Strong lateral mode confinement wavegaide structure in the focal plane is used to increase resolution, a Michelson-type AWG spectrometer can improve optical throughput or etendue, and we show that AWG dispersion can be magnified many times by modifying the waveguide group index.