Temporal self-imaging effect for periodically modulated trains of pulses.

In this paper, the mathematical description of the temporal self-imaging effect is studied, focusing on the situation in which the train of pulses to be dispersed has been previously periodically modulated in phase and amplitude. It is demonstrated that, for each input pulse and for some specific values of the chromatic dispersion, a subtrain of optical pulses is generated whose envelope is determined by the Discrete Fourier Transform of the modulating coefficients. The mathematical results are confirmed by simulations of various examples and some limits on the realization of the theory are commented.

[Treatment of wet age-related macular degeneration with ranibizumab in clinical practice: results and prognostic factors]. / Tratamiento de la degeneración macular asociada a la edad exudativa con ranibizumab en la práctica clínica. Resultados y factores pronósticos.

OBJECTIVES: To evaluate the efficacy of ranibizumab in wet age-related macular degeneration (ARMD), and to identify prognostic factors. METHODS: A retrospective longitudinal study of 79 eyes treated with intravitreal Ranibizumab in our hospital due to wet ARMD, with an initial regimen of three consecutive monthly injections, followed by injections on demand based on the exploratory findings. We conducted a descriptive study of the baseline examination (n=79), and 3 (n=79), 6 (n=67) and 12 months (n=49) after starting treatment. The characteristics of the baseline examination and annual examination results were compared using univariate and multivariate analysis. RESULTS: After the three initial injections, the 93.67% of patients lost fewer than 15 letters, and 19% gained 15 points or more. This result remained similar at 1 year (83.67% and 20.40%, respectively). After 1 year of treatment 40.82% had a VA ≥ 0.3 and 22'45% had a VA ≤ 0.1. We used a median of 5 injections per year. The increased AV at the beginning and the persistence of large intraretinal cysts at 3 months (P=.0013), as well as the development of fibrosis during evolution (P=.0005), are associated with visual deterioration. CONCLUSIONS: The guidelines used here stabilised or improved visual acuity in most patients. The most favourable cases are those with initially lower VA or large intraretinal cysts resolved after the loading phase. The appearance of fibrosis implies a poor long-term visual prognosis.

Tratamiento de la degeneración macular asociada a la edad exudativa con ranibizumab en la práctica clínica. Resultados y factores pronósticos / Treatment of wet age-related macular degeneration with ranibizumab in clinical practice: results and prognostic factors

Objetivos: Evaluar la eficacia del tratamiento con ranibizumab en la degeneración macularasociada a la edad (DMAE) exudativa e identificar los factores pronósticos.Método: Estudio longitudinal retrospectivo de 79 ojos, tratados con ranibizumab intravítreoen nuestro centro por DMAE exudativa, con una pauta inicial de 3 inyecciones consecutivasmensuales, seguidas de inyecciones a demanda en función de los hallazgos exploratorios.Se realizó un estudio descriptivo de la exploración basal (n = 79), y a los 3 (n=79), 6 (n=67)y 12 meses (n = 49) del inicio del tratamiento. Mediante análisis univariante y multivariantese correlacionaron las características de la exploración basal y anual con los resultadosvisuales.Resultados: Después de las 3 inyecciones iniciales, el 93,67% de los casos pierde menos de15 letras, y un 19% gana 15 letras o más. Este resultado es similar al año (83,67 y 20,40%,respectivamente). Tras un año de tratamiento mantiene una agudeza visual (AV) ≥ 0,3 el40,82%, y un 22,45% tiene una AV ≤ 0,1. Se ha utilizado una mediana de 5 inyecciones/año.La AV elevada al inicio y la persistencia de quistes intrarretinianos grandes a los 3 meses(p = 0,0013), así como la aparición de fibrosis durante la evolución (p = 0,0005) se asocian conun empeoramiento visual.Conclusiones: La pauta utilizada permite una estabilización o mejoría de la AV en la mayorparte de los pacientes. Los casos más favorables inicialmente son aquellos que presentanuna AV más baja o quistes intrarretinianos grandes resueltos tras la fase de carga. Laaparición de fibrosis implica un mal pronóstico visual a largo plazo(AU)

Objectives: To evaluate the efficacy of ranibizumab in wet age-related macular degeneration(ARMD), and to identify prognostic factors.Methods: A retrospective longitudinal study of 79 eyes treated with intravitreal Ranibizumabin our hospital due towet ARMD, with an initial regimen of three consecutive monthly injections,followed by injections on demand based on the exploratory findings.We conducted adescriptive study of the baseline examination (n = 79), and 3 (n= 79), 6 (n= 67) and 12 months(n = 49) after starting treatment. The characteristics of the baseline examination and annualexamination results were compared using univariate and multivariate analysis.Results: After the three initial injections, the 93.67% of patients lost fewer than 15 letters,and 19% gained 15 points or more. This result remained similar at 1 year (83.67% and 20.40%,respectively). After 1 year of treatment 40.82% had a VA ≥ 0.3 and 22‘45% had a VA ≤ 0.1.We used a median of 5 injections per year. The increased AV at the beginning and thepersistence of large intraretinal cysts at 3 months (P = .0013), as well as the development offibrosis during evolution (P = .0005), are associated with visual deterioration.Conclusions: The guidelines used here stabilised or improved visual acuity in most patients.The most favourable cases are those with initially lower VA or large intraretinal cysts resolvedafter the loading phase. The appearance of fibrosis implies a poor long-term visualprognosis(AU)

WDM compatible and electrically tunable SPE-OCDMA system based on the temporal self-imaging effect.

A coding/decoding setup for a spectral phase encoding optical code-division multiple access (SPE-OCDMA) system has been developed. The proposal is based on the temporal self-imaging effect and the use of an easily tunable electro-optic phase modulator to achieve line-by-line coding of the transmitted signal, thus assuring compatibility with WDM techniques. Modulation of the code is performed at the same rate as the data, avoiding the use of high-bandwidth electro-optic modulators. As proof of concept of the technique, experimental results are presented for a back-to-back coder/decoder setup transmitting a 10 GHz unmodulated optical pulse train within an 80 GHz optical window and using 8-chip Hadamard codes.

Apodized coupled resonator waveguides.

In this paper we propose analyse the apodisation or windowing of the coupling coefficients in the unit cells of coupled resonator waveguide devices (CROWs) as a means to reduce the level of secondary sidelobes in the bandpass characteristic of their transfer functions. This technique is regularly employed in the design of digital filters and has been applied as well in the design of other photonic devices such as corrugated waveguide filters and fiber Bragg gratings. The apodisation of both Type-I and Type-II structures is discussed for several windowing functions.

Simultaneous multiwavelength real-time optical spectrum analysis.

We propose a technique for performing a real-time Fourier transformation simultaneously over all the channels of a multiwavelength signal traveling in a single optical fiber. The technique requires only the reflection of the original signal in an appropriately designed structure of superimposed chirped fiber gratings. The potential and the limitations of superimposed fiber-grating structures for implementing known applications of fiber gratings over various multiwavelength channels (including the application proposed herein) are analytically and numerically studied. To demonstrate our proposal we design a real-time optical spectrum analyzer operating on three different wavelength channels. Numerical calculations show that the design works properly, and we use joint time-frequency signal representations to get a better understanding of the physical processes that determine the behavior of the system.

[Identification of yeast and sensitivity in vitro against different antifungal agents]. / Identificación de levaduras y sensibilidad in vitro a diversos antifúngicos.

INTRODUCTION: The increasing incidence of Candida yeasts infections and its hospital and community repercussion (vaginal thrush), as well as the will to acquire the knowledge of the new antifungal that were launched to the therapeutic store, have motivated us to identify that type of yeasts from different sources, as well as to study their behaviour against the antifungal, using commercial procedures with easy clinical application. MATERIALS AND METHODS: An amount of 317 Candida yeasts were identified through commercial procedures (CHROMagar Candida and Auxacolor): 108 vaginals, 138 from ICU newborn children and 71 from ICU adults, while the antifungal drug susceptibilities was done to 199 of the isolated ones using another commercial procedure (Fungitest). RESULTS AND CONCLUSIONS: Candida albicans is identified as the most frequent in both hospital and community samples (78.7 and 45.93%, respectively), followed by Candida glabrata (19.44 and 28.23%, respectively). The sensitivity to amphotericin B and to 5-flucytosine was very high in every studied group, while sensitivity to imidazole derivatives depends on the samples source (lower sensitivity in the ICU newborn isolated ones) and the species (C. glabrata is less sensitive than C. albicans).

Identificación de levaduras y sensibilidad in vitro a diversos antifúngicos / Identification of yeasts and sensitivity in vitro against different antifungal

Introducción: El aumento en la incidencia de infecciones por hongos levaduriformes del género Candida y su repercusión en el ámbito hospitalario y comunitario (vaginitis recidivante), así como el conocimiento de los nuevos antifúngicos en el arsenal terapéutico, nos han motivado a identificar levaduras de este género de diverso origen y a estudiar su comportamiento frente a los antifúngicos utilizando métodos comerciales de fácil aplicación en el uso clínico. Material y métodos: Se han identificado por métodos comerciales (CHROMagar Candida® y Auxacolor®), un total de 317 levaduras del género Candida: 108 vaginales, 138 de unidades de cuidados intensivos de neonatos y 71 de unidades de cuidados intensivos de adultos, realizándose el antifungigrama a 199 de los aislados utilizando un método comercial (Fungitest®). Resultados y conclusiones: Candida albicans se identifica como el microorganismo más frecuente en ambos tipos de muestras, comunitarias y hospitalarias (el 78,7 y el 45,93 por ciento, respectivamente) seguida de Candida glabrata (el 19,44 y el 28,23 por ciento, respectivamente). La sensibilidad a anfotericina B y 5-fluorocitosina ha sido muy elevada en todos los grupos estudiados, mientras que la sensibilidad a derivados imidazólicos depende de la procedencia de las muestras (menor sensibilidad en los aislados de unidades de cuidados intensivos de neonatos), así como de la especie (C. glabrata es menos sensible que C. albicans) (AU)

Reconstruction of fiber grating period profiles by use of Wigner-Ville distributions and spectrograms.

The grating-period profile and length of an arbitrary fiber Bragg grating structure can be reconstructed from the structure's reflection response by use of a time-frequency signal representation based on the well-known Wigner-Ville distribution and spectrogram. We present a detailed description of this synthesis technique. By means of numerical simulations, the technique is tested with several fiber grating structures. In general, our results show good agreement between exact and reconstructed functions. The technique's advantages and limitations are discussed. We propose and demonstrate the application of the proposed synthesis technique to distributed mechanical strain or temperature sensing.

Reconstructing arbitrary strain distributions within fiber gratings by time-frequency signal analysis.

We apply time-frequency signal-analysis techniques to recover arbitrary distributions of axial strain along a fiber grating from its reflection spectral response. The proposed method permits accurate strain reconstruction with no restrictions on the applied strain profile or on the grating length. We demonstrate the validity and accuracy of the technique by reconstructing the strain field in a fiber grating with a nonmonotonic strain profile, which includes all the following: a constant strain section, high gradient variations, and strain discontinuities.

Real-time Fourier transformer based on fiber gratings.

We use the well-known duality between paraxial diffraction in space and dispersion in time to propose a time-domain analog to spatial Fraunhofer diffraction. This analog permits the design of real-time optical Fourier-transformer systems. These systems are shown to be realizable by use of linearly chirped fiber gratings as dispersive media.

Technique for multiplying the repetition rates of periodic trains of pulses by means of a temporal self-imaging effect in chirped fiber gratings.

We show that a temporal effect that is equivalent to the spatial self-imaging (Talbot) effect applies to the reflection of periodic signals from linearly chirped fiber gratings. The effect can be used for multiplying the repetition frequency of a given periodic pulse train without distorting the individual pulse characteristics. The practical limit on the frequency-multiplication factor depends only on the temporal width of the individual pulse. Thus we demonstrate that a suitable combination of well-known techniques for short-pulse generation, such as pulse mode locking, and the technique proposed here allows us to obtain short-pulse trains with ultrahigh repetition rates (in the terahertz regime). Results from simulations show good agreement with those predicted by theory.

Temporal Talbot effect in fiber gratings and its applications.

We show that a temporal effect equivalent to the spatial Talbot effect (self-imaging) applies to the reflection of periodic pulse trains from linearly chirped fiber gratings (LCFG's). For specific input repetition periods the reflected signal is an exact replica of the input signal. Input repetition period values that give rise to this effect depend on the dispersion coefficient of the grating. We propose to use this effect as an alternative for dispersion measurement in LCFG's. Furthermore, by using the properties of the temporal Talbot effect, we can design linear passive devices (LCFG's) for use as frequency multipliers, able to multiply the repetition rate of a given pulse train.

Fiber grating synthesis by use of time-frequency representations.

We propose a method to reconstruct the grating period in fiber grating structures from the field reflection coefficient or the related impulse response. The method is based on the joint time-frequency signal analysis and uses the Wigner-Ville and the spectrogram distributions. Results show good agreement between exact and reconstructed functions.

Fiber Bragg grating as an optical filter tuned by a magnetic field.

We describe a novel tunable optical filter for use in optical-frequency-domain multiplexed communication systems. The shift in the Bragg condition of a fiber Bragg grating as a result of magnetically induced circular birefringence is calculated with coupled-mode theory on the basis of circular states of polarization, and the values obtained for silica and terbium-doped optical fibers are compared.

Phase reconstruction from reflectivity in uniform fiber Bragg gratings.

We propose a method for phase, time-delay, and impulse-response reconstruction from spectral power reflectance or reflectivity and apply it to uniform fiber Bragg gratings. This method is based on causality conditions and uses Hilbert and Wiener-Lee transforms. Results show a good agreement between exact and reconstructed functions.

Model of an openable Faraday-effect hybrid-current optical transducer based on a square-shaped structure with internal mirror.

A new type of clamp-on magneto-optical current transducer based on the Faraday effect is presented. It is openable, hybrid, and square-shaped, and it has an internal mirror that allows the current sensitivity to improve and the effects of the optical activity and temperature-dependent linear birefringence to be rejected. The design and the simulated behavior of the proposed device are described and compared with the conventional (no mirror) transducer.

Analysis of double-parallel amplified recirculating optical-delay lines.

A novel method of analysis of double-parallel amplified recirculating optical-delay lines (DPAROD) is presented. The location of the maxima and the minima of the transfer function for this configuration is calculated and experimentally demonstrated. The influence of different parameters, such as the coupling coefficients, gains, lengths of the fiber loops and fractional losses of the directional couplers, on the shape of the transfer function are analyzed. Different measurements have been taken to verify this model. The potential application of these interconnected delay loops as filters is a reason for developing this method.

Transmission bistability in a double-coupler fiber ring resonator.

The transmission bistability of a two-coupler nonlinear ring resonator is demonstrated and described by using a geometrical method that provides a qualitative understanding of the operation characteristics of the device. Results showing the influence of the coupling constants and the linear phase are presented.