Jose Luis Feliu Pesquera to James Meredith (2 October 1962)

https://egrove.olemiss.edu/mercorr_pro/1544/thumbnail.jp

Photonic generation of microwave signals using a single-mode VCSEL subject to dual-beam orthogonal optical injection

We experimentally and theoretically investigate the photonic generation of microwave signals using a long-wavelength single-transverse-mode vertical-cavity surface-emitting laser (VCSEL) subject to two-frequency orthogonal optical injection. We study if a significant reduction of the linewidth is achieved in the double injection locking regime. In this regime, the VCSEL is subject to optical injection by two master lasers in such a way that stable locking is also observed if only light from one of the master lasers is injected. Our model includes the effect of the injected light reflected at the VCSEL's mirror generalizing previous modeling of reflection-mode optical injection-locked VCSELs. Our model also describes the high coherence associated to stable injection locking states and takes into account phase fluctuations in both master lasers. We observe no significant reduction of the linewidth in the double injection locking regime because the linewidth is mainly determined by the phase fluctuations of the two master lasers.This work was supported in part by the Ministerio de Economía y Competitividad, Spain, under Project TEC2012-38864-C03-02 and Project TEC2012-38864-C03-03 and in part by FEDER funds

Thermal tolerance across latitudinal and altitudinal gradients in tadpoles

Del mismo modo que la temperatura y los efectos del cambo climático varían con en el espacio y en el tiempo, esta tesis doctoral se centra en conocer la variación en los límites térmicos fisiológicos a diferentes escalas espacio-temporales así como caracterizar el ambiente térmico al que actualmente se encuentran expuestos las poblaciones y especies de anfibios analizadas. Ello nos permitirá, en primer lugar, aportar información básica para tratar de predecir las consecuencias del calentamiento global, y en segundo lugar, poner a prueba algunas hipótesis macrofisiológicas recientes. Así, los capítulos 1, 2 y 3 se centran en la variabilidad espacial de los límites de tolerancia térmicos en anfibios (a lo largo de gradientes altitudinales y latitudinales). Dado que existe cierta controversia acerca del grado de variación encontrada entre poblaciones de la misma especie y entre especies distintas, los capítulos 1 y 3 adoptan un enfoque interespecífico mientras que el capítulo 2 se ocupa de analizar la variabilidad intraspecífica encontrada para una serie de poblaciones de Rana temporaria a lo largo de un gradiente climático altitudinal. Los capítulos 4, 5 y 6 se centran en analizar el cambio en los límites de tolerancia en el tiempo ya sea a través de procesos de aclimatación (capítulos 4 y 5) o el cambio en las tolerancias térmicas en diferentes estadios de desarrollo (capítulo 6). En el capítulo 1: “Testing the climate variability hypothesis in thermal tolerance limits of tropical and temperate tadpoles”, analizamos la variación latitudinal en los CTmax/CTmin de 47 sp. de anfibios, durante su etapa larvaria, comparando dos comunidades procedentes de Brasil (Bahía) y la Península Ibérica y el Norte de África. En este trabajo ponemos a prueba la hipótesis de variabilidad climática en renacuajos, analizando además la relevancia de la información térmica a escalas micro y macroclimáticas como predictores de estos parámetros fundamentales de las curvas de performance de los ectotermos. En el capítulo 2: “Can breeding phenology and plasticity prevent local adaptation in thermal tolerance?”, estudiamos la variación altitudinal de los límites de tolerancia térmica en once poblaciones de Rana temporaria, al tiempo que caracterizamos su ambiente térmico teniendo en cuenta la fenología de la especie, y discutimos acerca de los aspectos que pueden estar afectando al grado de diferenciación en las tolerancias térmicas mostrado entre las poblaciones, así como si esta diferenciación puede responder a procesos de adaptación local. En el capítulo 3: “Altitudinal variation of the critical thermal limits in 20 species of tadpoles in the tropical Andes”, realizamos una comparación altitudinal interespecífica en los límites térmicos de 20 especies de anuros andinos , durente su etapa larvaria, y una valoración preliminar del riesgo de extinción de estas especies, basándonos en las estimas de su tolerancia al calentamiento. Del mismo modo que en el capítulo 1, comprobaremos además como la hipótesis de variabilidad climática puede explicar los resultados obtenidos. La segunda parte de la tesis trata de los efectos sobre las tolerancias térmicas de la variación temporal, mediante cambios en las temperaturas de aclimatación y el estadio de desarrollo ontogénico: En el capítulo 4: “Acclimation of critical thermal limits in temperate and tropical tadpoles”, analizamos las supuestas diferencias en el potencial de aclimatación de anfibios tropicales y templados, sometidos a temperaturas constantes en el laboratorio (hipótesis de Brattstrom, Brattstrom (1968)). En el capítulo 5: “The effect of constant vs fluctuating acclimation on critical thermal limits in three temperate tadpoles”, comparamos los efectos que la aclimatación puede tener sobre las tolerancia térmica de tres especies de anfibios de la Península Ibérica cuando se usan a) unas temperaturas de aclimatación constantes, o b) simulando unas condiciones similares a las que pueden ocurrir en la naturaleza, mediante el empleo de aclimataciones con temperaturas diarias fluctuantes. En el capítulo 6: “Ontogenetic shifts in thermal tolerances in temperate anurans. Does metamorphosis impose a thermal constraint that may affect vulnerability to global warming?”, analizamos los cambios que tienen lugar a lo largo del desarrollo ontogenético (larvas, metamórficos y juveniles) en la tolerancia térmica de los individuos de seis especies de anuros procedentes de Marruecos y la Península Ibérica

Equilibrium between radiation and matter for classical relativistic multiperiodic systems. Derivation of Maxwell-Boltzmann distribution from Rayleigh-Jeans spectrum

The motion of a charged pointlike relativistic particle under the action of a given force field plus a random electromagnetic radiation is studied. It is assumed that the given force field alone should produce a multiply periodic motion, which is perturbed by the action of both the random radiation and the reaction damping. The random radiation is represented by a stochastic process and an equation is obtained for the equilibrium probability density of the particle in phase space. In the particular case of a random radiation with Rayleigh-Jeans spectrum, it is shown that the stationary solution, corresponding to radiation-matter equilibrium, is given by the Maxwell-Boltzmann distribution

Effect of temperature on polarization switching in long-wavelength VCSELs

Trabajo presentado al Vertical-Cavity Surface-Emitting Lasers XIX, celebrado en San Francisco, California (US) del 11 al 12 de febrero de 2015.We have measured the effect of the temperature on the polarization-resolved characteristics of a 1550-nm singletransverse mode vertical-cavity surface-emitting laser (VCSEL). Two double polarization switchings (PS) are observed. For low temperatures a PS from longer to shorter wavelengths (Type II PS) followed by the opposite PS (Type I) is observed. For higher temperatures Type I followed by Type II PS are measured. A simple expression relating the spin flip rateto the dichroism, differential gain, threshold current and PS current is derived. With this expression the dependence of the spin-flip rate on the temperature is obtained.This work has been funded by the Ministerio de Economía y Competitividad, Spain under project TEC2012-38864-C03-03 and cofinanced by FEDER funds. A. Quirce acknowledges FWO for her Post Doc fellowship and H. Thienpont and K. Panajotov are grateful to the Methusalem foundation for financial support.Peer reviewe

Polarization-resolved nonlinear dynamics in long-wavelength single-mode VCSELs subject to orthogonal optical injection

In this work we perform an experimental study of the polarization-resolved nonlinear dynamics of a 1550 nm single-mode linearly polarized VCSEL when subject to orthogonal optical injection. We have measured the stability maps that identify the boundaries between regions of different nonlinear dynamics by using the RF-spectrum of the total power. These maps are measured in the plane of the frequency detuning between the injected light and the orthogonal linear polarization of the VCSEL versus injected power. Stability maps are obtained for two different values of the bias current. Analysis of the dynamics is given in terms of the time traces of the total power and of both linearly polarized output signals. The corresponding RF and optical spectra are also measured. Different dynamical regimes including periodic, period doubling, and irregular dynamics are observed for both polarizations. When the frequency detuning is positive polarization switching can be observed in a periodic dynamical regime, including both period one and period two behaviours. For positive frequency detuning, the only polarization that contributes to the dynamics of the total power is the orthogonal polarization. For negative frequency detuning values both linear polarizations contribute to the dynamics of the total power.The authors acknowledge support from the Ministerio de Ciencia e Innovación under project TEC2009-14581-C02-02. The authors also acknowledge Prof. Krassimir Panajotov from Vrije Universiteit Brussels, Dr. Antonio Hurtado and Prof. Mike Adams from the Univ. of Essex (UK) for fruitful discussions

Is energy intensity a driver of structural change? Empirical evidence from the global economy

Producción CientíficaInput–output tables (IOTs) provide a relevant picture of economic structure as they represent the composition and interindustry relationships of an economy. The technical coefficients matrix (A matrix) is considered to capture the technological status of an economy; so, it is of special relevance for the evaluation of long-term, structural transformations, such as sustainability transitions in integrated assessment models (IAMs). The A matrix has typically been considered either static or exogenous. Endogenous structural change has rarely been applied to models. The objective of this paper is to analyze energy intensity, a widely used variable in IAMs, and its role as a driver of structural change. We therefore identify the most relevant technical coefficients in the IOTs time series and estimate an econometric model based on the energy intensity of five different final end-use energy sources. The results of this analysis show that energy intensity has a significant influence on the evolution of the A matrix and should therefore be taken into consideration when analyzing endogenous structural change in models.Ministerio de Asuntos Económicos y Transformación Digital, project MODESLOW (grant ECO2017-85110-R)European Union’s Horizon 2020 research and innovation program. Project “Low Carbon society: An enhanced modelling tool for the transition to sustainability (LOCOMOTION) grant award H2020-LC-CLA-01-2018, n. 82110

Transverse mode selection and injection locking in 1550-nm multimode VCSELs induced by optical injection

An experimental investigation of the modal selection induced by optical injection in 1550 nm multitransverse-mode VCSELs is performed. The free-running VCSEL emits in two transverse modes that are linearly polarized in a direction referred as parallel. We consider the situation in which parallel polarized laser light is injected in the VCSEL in order to select its fundamental transverse mode. We analyze the dependence of the modal selection process on the wavelength detuning between the externally injected signal and the fundamental mode. The injected power needed to select the fundamental mode as a function of the wavelength detuning is measured for several values of the bias current. This injected power exhibits a minimum at a positive wavelength detuning. The curves obtained for different bias currents are very close for positive and large wavelength detuning, while they are very separated for smaller detuning. The selection of the fundamental mode can be obtained with a value of the injected power that changes only slightly with the bias current when the wavelength detuning is large and positive. These results indicate that operation at large and positive wavelength detuning is of interest in the long-distance single-mode fiber transmission of multimode injection-locked VCSELs because the selection of the fundamental mode is obtained with an injected power that is almost independent on the VCSEL bias current. Both, the minimum injected power and the wavelength detuning at which it appears increase with the VCSEL bias current. We describe the relation between transverse mode selection and injection locking by comparing the dependence of both phenomena on the wavelength detuning. Modal selection is accompanied by injection locking only for large and positive values of the wavelength detuning. For small detuning values, with the VCSEL biased with a low (high) current, the injected power required for modal selection is lower (higher) than that needed for injection locking.The authors would like to thank Matías Salvide and Marita Torre from the Instituto de Física “Arroyo Seco”, U.N.C.P.B.A. for fruitful discussions. The authors acknowledge support from the Ministerio de Ciencia e Innovación under project TEC2009-14581-C02-02 and from the Marie Curie Intra-European Fellowships for Career Development (IEF), European Commission

Polarization switching and injection locking in vertical-cavity surface-emitting lasers subject to parallel optical injection

Polarization switching in a long-wavelength vertical-cavity surface-emitting laser (VCSEL) under parallel optical injection is analyzed in a theoretical and experimental way. For the first time, to our knowledge, we report experimentally a state in which injection locking of the parallel polarization and excitation of the free-running orthogonal polarization of the VCSEL are simultaneously obtained. We obtain very simple analytical expressions that describe both linear polarizations. We show that the power of both linear polarizations depend linearly on the injected power in such a way that the total power emitted by the VCSEL is constant. We perform a linear stability analysis of this solution to characterize the region of parameters in which it can be observed. Our measurements qualitatively confirm the previous theoretical predictions.Ministerio de Economía y Competitividad (MINECO/FEDER) (TEC2015-65212-C3-1-P); Fonds Wetenschappelijk Onderzoek (FWO); Methusalem Foundation.Peer Reviewe

Numerical and Experimental Analysis of Optical Frequency Comb Generation in Gain-Switched Semiconductor Lasers

We have performed a systematic experimental and simulation analysis of the optical frequency combs generated by gain-switching single mode laser diodes, either free-running or subjected to optical injection. The simulations have been produced with a dynamical model consisting of three rate equations that include stochastic noise terms. The model parameters have been extracted from experiments. An exhaustive comparison between the simulated and the experimental temporal profiles and optical spectra generated under a wide range of switching and optical injection conditions has been performed. The excellent quantitative agreement found in the entire range of the explored operating conditions supports the validity of the model for the analysis of the comb generation mechanisms. The detailed maps generated provide guidelines for selecting suitable operating conditions for specific comb characteristics.This work was funded by the Ministerio de Economia y Competitividad of Spain (COMBINA, TEC201565212-C3-1-P and TEC201565212-C3-2-P)