Sincronización óptica de osciladores de microondas diseñados utilizando transistores PHEMTs

Optical synchronization of microwaves oscillators designed with PHEMTs transistors

Lis Tamayo Rivera (2004)

La presente tesis está relacionada con el control óptico de osciladores de microondas. El oscilador fue diseñado utilizando como dispositivo activo un transistor pseudomórfico comercial. La frecuencia del oscilador es sincronizada a la frecuencia de modulación de un láser de λ = 850nm que iluminó directamente al transistor. En este trabajo se mencionan y describen los efectos causantes de la fotorrespuesta positiva y negativa en el transistor (el efecto fotoconductivo y el efecto fotovoltaico). Se reportan los resultados de la caracterización electro-óptica del transistor, en donde, el efecto de la iluminación se manifiesta con una variación en los elementos intrínsecos del circuito eléctrico equivalente que a su vez, influyen en el desplazamiento de la frecuencia de oscilación en el oscilador iluminado. Se reportan los cambios de frecuencia y potencia del oscilador iluminado obtenidos de forma experimental y mediante simulación, y se comparan entre ellos. Se reporta además la banda de sincronía obtenida experimentalmente (40 kHz y 25 kHz) de dos osciladores de microondas con diferente factor de calidad. En base a estos resultados se comprueba, con la ecuación de Adler, que la banda de sincronía es función inversa del factor de calidad del circuito y que además varía en relación cuadrática con la potencia inyectada. Por último se muestra gráficamente la variación de la banda de sincronía en función de la polarización del transistor.

This dissertation is related with the optical control of microwaves oscillators. The oscillator was designed using a commercial pseudomorfic transistor. The frequency of the oscillator is synchronized at the modulation frequency of an 850 nm laser that illuminates directly the transistor. In this work, the effects that give rise the positive and negative photorresponse in the transistor (the photoconductive effect and the photovoltaic effect) are mentioned and discussed. The results of the electro-optical transistor characterization shows that the illumination produce variations of the intrinsic elements (CGS and CGD). Moreover these effects produce a shift in the oscillation frequency. The oscillation frequency and power of the oscillator in dark and under illumination is obtained by simulation and measured, are reported and compared among them. In addition, the experimental injection locking band (40 kHz y 25 kHz) measured in the two different Q factor microwaves oscillators is reported. With these results it was demonstrated that the locking band is an inverse function of the Q factor of the oscillator, as predicted by the Adler equation. Finally the changes of the locking band are graphically presented as function of the bias points of the transistor.

Master thesis

Oscilador, Transistor Pseudomórfico, Sincronización por inyección Oscillator, Pseudomorfic transistor, Injection-locked . CIENCIAS FÍSICO MATEMÁTICAS Y CIENCIAS DE LA TIERRA FÍSICA ELECTRÓNICA TRANSISTORES TRANSISTORES

Quo Vadis Nonlinear Optics? An Alternative and Simple Approach to Third Rank Tensors in Semiconductors

Adalberto Alejo Molina (2022)

It is well understood that nonlinear optical (NLO) phenomena are deeply related to the material’s symmetry. Mathematically, the material symmetry can be described in terms of the nonzero parameters in the nonlinear susceptibility tensors. Generally, more complex structures involve more nonzero parameters in the tensor. The number of parameters increases rapidly if higher NLO orders are considered, complicating the physical analysis. Conventionally, these parameters are obtained via abstract symmetry analysis, e.g., group theory (GT). This work presents a novel theoretical analysis to approach the nonlinear tensor using the simplified bond hyperpolarizability model (SBHM) and compare it with GT. Our analysis is based on a light–matter interaction classical phenomenological physical framework. Rather than just looking at the symmetry of the crystal, the model applies physical considerations requiring fewer independent parameters in the tensor than GT. Such a simplification significantly improves the determination of the surface–bulk SHG contribution factors, which cannot be extracted from the experiment alone. We also show for the case of perovskite that the SHG contribution can be addressed solely from their surface dipoles with only one independent component in the tensor. Therefore, this work may open the path for a similar analysis in other complicated semiconductor surfaces and structures in the future, with potential applications to nanoscale surface characterization and real-time surface deposition monitoring.

Article

INGENIERÍA Y TECNOLOGÍA CIENCIAS TECNOLÓGICAS nonlinear tensor, bond model, group theory, second-harmonic generation