Person: Calvo Padilla, María Luisa
Universidad Complutense de Madrid
Faculty / Institute
Now showing 1 - 10 of 35
PublicationMultiple scattering of classical electromagnetic waves by volume gratings: completion of Fujiwara's solution(Taylor and Francis Ltd., 1999-02-15) Calvo Padilla, María Luisa; Cheben, PavelWe present a general formulation for multiple scattering of classical electromagnetic waves by volume gratings. Fujiwara's electron multiple scattering theory is modified and extended to the case of both, the transmission and the reflection geometries. The analytical solution for the amplitude Φ_n corresponding to the nth scattering order is given. The convergence of the solution is proved for the transmission by a sinusoidal symmetric phase grating. By employing a structural Green's function and a vectorial formulation for diffraction of a classical electromagnetic wave by a thin periodical slab, as previously given by Alvarez-Estrada and Calvo, the solution for the back scattered field amplitude is derived and shown to coincide with that obtained within the framework of the multiple scattering theory. 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. PublicationWave-front conversion between a Gaussian beam with a cylindrical phase function and a plane wave in a monomode on-axis transmission holographic coupler(Optical Society of America, 1993-12) Cheben, Pavel; Calvo Padilla, María LuisaWe present a coupled-wave-analysis-based treatment for a wave-front conversion problem between a Gaussian beam with a cylindrical phase and a plane wave for a two-dimensional on-axis geometry. A coupled-wave approach to the multiple-scattering process in an inhomogeneous dielectric medium offers a clear physically interpretable description of the diffraction phenomena in volume media as well as the possibility of an intelligible mathematical treatment. An analytical integral solution for the amplitudes of the two modes of diffraction is submitted. High diffraction efficiency (≈1) and the deterioration of reconstruction fidelity are predicted. It is of interest to apply the model to the analysis and design of a monomode holographic fiber-to-fiber coupler, wave-front correctors, and holographic interconnection devices. 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. PublicationTeorías de la difracción de ondas electromagnéticas por redes de volumen: Una revisión(Sociedad Mexicana de Física, 1998-08) Cheben, Pavel; Calvo Padilla, María LuisaSe presenta una revisión de las teorías de la difracción de ondas electromagnéticas por redes de volumen. En el enfoque de este trabajo se encuentran las teorías de los siguiente grupos: teorías de ondas acopladaseorías modales, teorías de dispersión múltiple y teorías electromagnéticas, siempre y cuando sean apropiadas para el análisis de redes de volumen. Se incluye también una revisión de teorías y métodos con menor impacto en el campo estudiado, tales como teorías de medio efectivo, método de difracción por el entorno, método de elementos finitos o algoritmos microgenéticos. Se recogen un tofal de 225 publicaciones seleccionadas que abarcan un período de aproximadamente cien años: 1891-1997. 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. PublicationSubwavelength grating Fourier-transform interferometer array in silicon-on-insulator(Wiley-V C H Verlag GMBH, 2013-11) Bock, Przemek J.; Cheben, Pavel; Villafranca Velasco, Aitor; Schmid, Jens H.; Delâge, André; Florjańczyk, Mirosław; Lapointe, Jean; Xu, Dan-Xia; Vachon, Martin; Janz, Siegfried; Calvo Padilla, María LuisaA planar waveguide Fourier-transform spectrometer with densely arrayed Mach-Zehnder interferometers is demonstrated. Subwavelength gratings are used to produce an optical path difference without waveguide bends. The fabricated device comprises of an array of 32 Mach-Zehnder interferometers, which produce a spatial interferogram without any moving parts, yielding a spectral resolution of 50 pm and a free-spectral range of 0.78 nm. As a result of similar propagation losses in subwavelength grating waveguides and conventional strip waveguides, loss imbalance is minimized and high interferometic extinction ratio of -25 to -30 dB is obtained. Furthermore, phase and amplitude errors arising from normal fabrication variation are compensated by the spectral retrieval process using calibration measurements. 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. PublicationHigh-resolution Fourier-transform spectrometer chip with microphotonic silicon spiral waveguides(The Optical Society Of America, 2013-03-01) Villafranca Velasco, Aitor; Cheben, Pavel; Bock, Przemek J.; Schmid, Jens H.; Delâge, André; Lapointe, Jean; Janz, Siegfried; Calvo Padilla, María Luisa; Xu, Dan-Xia; Florjańczyk, Mirosław; Vachon, MartinWe report a stationary Fourier-transform spectrometer chip implemented in silicon microphotonic waveguides. The device comprises an array of 32 Mach-Zehnder interferometers (MZIs) with linearly increasing optical path delays between the MZI arms across the array. The optical delays are achieved by using Si-wire waveguides arranged in tightly coiled spirals with a compact device footprint of 12 mm(2). Spectral retrieval is demonstrated in a single measurement of the stationary spatial interferogram formed at the output waveguides of the array, with a wavelength resolution of 40 pm within a free spectral range of 0.75 nm. The phase and amplitude errors arising from fabrication imperfections are compensated using a transformation matrix spectral retrieval algorithm. PublicationUltracompact polarization converter with a dual subwavelength trench built in a silicon-on-insulator waveguide(The Optical Society Of America, 2012-02-01) Villafranca Velasco, Aitor; Calvo Padilla, María Luisa; Cheben, Pavel; Ortega Moñux, Alejandro; Alonso Ramos, Carlos Alberto; Molina fernández, Íñigo; Lapointe, Jean; Vachon, Martin; Janz, Siegfried; Xu, Dan-XiaThe design and fabrication of an ultracompact silicon-on-insulator polarization converter is reported. The polarization conversion with an extinction ratio of 16 dB is achieved for a conversion length of only 10 mu m. Polarization rotation is achieved by inducing a vertical asymmetry by forming in the waveguide core two subwavelength trenches of different depths. By taking advantage of the calibrated reactive ion etch lag, the two depths are implemented using a single mask and etching process. The measured converter loss is -0.7 dB and the 3 dB bandwidth is 26 nm.