J. Mora

Photonic microwave tunable single-bandpass filter based on a Mach-Zehnder interferometer

The authors present the theoretical analysis and experimental demonstration of a novel single-bandpass tunable microwave filter. The filter is based on a broadband optical source and a fiber Mach-Zehnder interferometer and shows a high Q factor over a tuning range of 5-17 GHz. A generalized analysis considering that the optical signal propagates along optical delay lines with a dispersion slope different from zero is presented.

A magnetostrictive sensor interrogated by fiber gratings for DC-current and temperature discrimination

A magnetostrictive sensor head with temperature compensation has been developed for measurement of static magnetic fields. The device consists on two different alloys with similar thermal expansion coefficient one of which has a giant magnetostriction, the expansion of both materials produced by heat and magnetism is detected by two fiber gratings. One of the gratings measures the temperature of the sensor and the difference between the wavelengths reflected by the gratings is a measurement of the magnetically induced strain.

Demonstration of incoherent microwave photonic filters with all-optical complex coefficients

We propose and demonstrate for the first time to our knowledge an incoherent microwave photonic filter with complex coefficients implemented in the optical domain. The system is based on a tunable optically induced RF phase-shift that is obtained by means of a novel optical signal processing technique that makes combined use of optical single-sideband modulation and stimulated Brillouin scattering. A two-tap filter is built demonstrating full tunability of its frequency response by dynamically changing the phase shift of a complex coefficient

Tunable all-optical negative multitap microwave filters based on uniform fiber Bragg gratings.

We present a novel and simple technique for obtaining transversal filters with negative coefficients by using uniform fiber Bragg gratings. We demonstrate a wide tuning range, good performance, low cost, and easy implementation of multitap filters in an all-optical passive configuration in which negative taps are obtained by use of the transmission of a broadband source through uniform Bragg gratings.

High-efficiency Q-switched erbium fiber laser using a Bragg grating-based modulator

Abstract In this work we analyze the behavior of an erbium-doped fiber laser which is based on a simple scheme. Excitation of the active medium is performed in the 980 nm pump band with a CW semiconductor laser source. Two fiber Bragg gratings acting as mirrors of the Fabry–Perot laser cavity were used. One of these gratings was mounted over a piezoelectric (PZT) element. By applying voltage pulses to the piezoelectric, the laser cavity was temporally modulated and Q-switched laser pulses up to 530 mW peak powers at 3 kHz were obtained. Typical laser emission of 2–3 μs temporal widths and 0.1 nm of optical bandwidth have been achieved when the system was operated at 18.5 kHz repetition rates. Different behaviors were observed depending on the pumping level of the active medium and on the amplitude and frequency of the signal applied on the PZT. Q-switched laser output, in the erbium spectral gain region, with high laser efficiency of energy conversion was generated. Pumping at 76 mW and operating the laser at 18.5 kHz, an efficiency of 26% was obtained.

Automatic tunable and reconfigurable fiberoptic microwave filters based on a broadband optical source sliced by uniform fiber Bragg gratings.

We demonstrate an automatic tunable transversal notch filter based on uniform fiber Bragg gratings and a broadband optical source. High tunability can be performed by stretching the fiber with the gratings written in series. Also, high sidelobe supression can be achieved by introducing tunable attenuators in a parallel configuration of the gratings.

Equity in Spanish higher education

The most outstanding event in the recent evolution of higher education in developed countries has been the continuously increasing proportion of students entering higher education and, therefore, its extension to more and more inclusive groups. It seems reasonable to assume that the expansion of higher education must have facilitated access of less privileged social classes, but it is important to analyze to what extent this significant increase in higher education participation has reached all social, economic, and cultural groups. This analysis could be useful in designing a policy to help those students who have more difficulty accessing higher education. The goal in this paper is to analyze this subject thoroughly focusing especially on the level of participation of young adults in Spanish higher education controlling for economic level, parental education and occupation, and other environmental characteristics. We present a logistic model which jointly values the influence of different family and social characteristics of the individual on his/her decision to enroll in higher education. The main conclusions of the study are these: (a) There has been improvement in the equity of access to higher education. In spite of this overall improvement, about 30 per cent of the less privileged population is still underrepresented in higher education, (b) Family educational level is the most important factor in the decision to enter higher education. The weight of these educational characteristics exceeds by far the influence of family income level.

Single-Bandpass Microwave Photonic Filter With Tuning and Reconfiguration Capabilities

We demonstrate a very simple implementation of a single-bandpass microwave photonic finite-impulse response filter (MPF) with discrete tuning of the bandpass frequency and reconfigurability of the bandpass shape. We also discuss the notion of wavelength sampling in an MPF. A theoretical analysis has been developed to exploit the properties of the proposed MPF.

Simple fiber optic device to interrogate fiber optic Bragg gratings used as sensors

A simple and compact device for the monitoring and diagnostic of fiber optic Bragg gratings, employed in optical sensor applications, was developed. The deice consist of an optical fiber Bragg grating bound to a piezoelectric element. When a sinusoidal voltage is applied to the piezoelectric, the Bragg wavelength of the grating changes and the transmission spectrum swings in time. The device acts as a temporal window and can be used to interrogate a Bragg grating sensor, permitting to monitor the sensor state in real time and with very good resolution.

Wavelength-switchable fiber laser using acoustic waves

We report a wavelength-switchable fiber ring laser that includes a Bragg grating-based acoustooptic superlattice modulator. Wavelength switching of the laser emission is achieved by controlling the peak reflectivity of the different reflection bands that appear on both sides of the Bragg wavelength when a longitudinal acoustic wave propagates along the grating.