Estudio teórico de la dinámica no lineal en diodos láser acoplados lateralmente

En los últimos años la dinámica no lineal en láseres de semiconductor ha sido objeto de numerosos estudios. Aunque el diodo láser de por sí no puede mostrar un comportamiento caótico ya que su dinámica viene determinada por dos variables independientes, al añadir un tercer grado de libertad se posibilita la aparición de no linealidades. Esto puede ocurrir por diferentes mecanismos, como la modulación directa de la corriente, la inyección externa de luz o el acoplo lateral de los láseres de un array. En este proyecto se estudia esta última configuración, la cual ha sido propuesta con éxito para alcanzar velocidades de transmisión por encima del límite tradicional del ancho de banda de los láseres de semiconductor: la frecuencia de relajación de oscilación. Se han observado experimentalmente en estos dispositivos comportamientos no lineales y caóticos que no han sido clarificados a nivel teórico. A nivel experimental se verifica que la dinámica no lineal tiene su origen en la interacción entre la frecuencia de batido de los modos laterales del array y la frecuencia de relajación del diodo láser. Analizamos en detalle un modelo habitual basado en ecuaciones de tasa en las que un factor de acoplo complejo representa la interacción entre las colas evanescentes de los modos laterales de los emisores. Sin embargo, este modelo no consigue explicar la dinámica no lineal observada, por lo que, para una mejor comprensión de las no linealidades, se elabora un sencillo modelo fenomenológico con el objeto de simular los efectos no lineales que pueden llevar al régimen caótico, los cuales se estudian mediante una serie de diagramas de bifurcación construidos sobre distintos parámetros. ---------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------In recent years nonlinear dynamics in semiconductor lasers has been the subject of numerous studies. Although the diode laser can exhibit no chaotic behavior on his own because its dynamics are fully determined by two independent variables, the addition of a third degree of freedom enables the rising of nonlinearities. This can happen by means of different mechanisms, like direct current modulation, external optical injection or lateral coupling in a lasers array. In this thesis the latter configuration is studied, having been proposed successfully for reaching transmission speeds above the traditional bandwidth limitation in semiconductor lasers imposed by the relaxation oscillation frequency. Non linear and chaotic behaviors have been observed experimentally in these kind of devices, but have not been fully explained by theoretical studies. Experiments show that these non linear dynamics are related to the interaction between the lateral modes beating frequency of the array and the relaxation frequency of the diode laser. We analize in detail one usual model based on rate equations in which a complex coupling factor represents the interaction between the evanescent fields of the emitters lateral modes. However, this model fails to explain the observed nonlinear dynamics. Thus, to achieve a better understanding of these nonlinearities, a simpler phenomenological model is implemented, with the scope of simulating the nonlinear effects which can lead to chaotic regime. These are studied through a series of bifurcation diagrams where different parameters are varied.Ingeniería de Telecomunicació

Viscerotropic disease: case definition and guidelines for collection, analysis, and presentation of immunization safety data

Viscerotropic disease (VTD) is defined as acute multiple organ system dysfunction that occurs following vaccination. The severity of VTD ranges from relatively mild multisystem disease to severe multiple organ system failure and death. The term VTD was first used shortly after the initial published reports in 2001 of febrile multiple organ system failure following yellow fever (YF) vaccination. To date, VTD has been reported only in association with YF vaccine and has been thus referred to as YF vaccine-associated viscerotropic disease (YEL-AVD)

Influence of fenoldopam and quinpirole in the guinea-pig stomach

1 The influence of the selective DA1-agonist fenoldopam and the selective DA2-agonist quinpirole was investigated in the guinea-pig intact stomach model and in guinea-pig gastric corpus muscle strips. 2 In the intact stomach model, quinpirole induced a relaxation from 10(-6) M on. The relaxation by quinpirole (3 x 10(-5) M) was significantly inhibited by rauwolscine (10(-7) M), yohimbine (10(-7) M) and domperidone (10(-6) M). In the presence of tetrodotoxin, quinpirole (3 x 10(-5) M) induced a contraction. 3 In the same model, fenoldopam induced a relaxation but only at 3 x 10(-5) M. The relaxation by fenoldopam (3 x 10(-5) M) was not inhibited by SCH 23390 (10(-6) M). The relaxant effect of dopamine (3 x 10(-6) M) was significantly inhibited by rauwolscine (10(-7) M), yohimbine (3 x 10(-7) M), haloperidol (10(-6) M) and domperidone (10(-6) M). 4 In circular muscle strips of the gastric corpus, the electrically induced cholinergic contractions were inhibited by dopamine but not consistently influenced by quinpirole or fenoldopam. 5 Dopamine, fenoldopam and quinpirole induced an increase in basal tone of the strips. The contraction by dopamine (10(-5) M) was significantly antagonized by prazosin and methysergide. 6 No evidence was thus found for the presence of DA1-receptors in both guinea-pig stomach models. Equally, no evidence for the presence of DA2-receptors was found when studying quinpirole in the strips. Although the relaxant effect of quinpirole in the intact stomach seems predominantly mediated via alpha-2-adrenoceptors, an involvement of DA2-receptors cannot be excluded