No description available.

No description available.

No description available.

No description available.

Proefschrift Universiteit van Amsterdam. / Met samenvatting in het Nederlands.

In this work, the opto-piezo actuation and piezoelectric actuation in gallium arsenide (GaAs) is experimentally and theoretically verified. Experimentally the response of the respective actuations are measured using the current generated from the inverse piezoelectric effect. The mechanical structure used to generate this current is a micron size torsional resonator fabricated from a GaAs photodiode heterostructure. The photodiode heterostructure is optically and electrically designed as a photovoltaic (PV) cell while mechanically the structure resembles a bimorph. The bimorph design is a result of the PV cell consisting of a pn junction and a heterojunction where the depletion regions have the additional property of being piezoelectric. The opto-piezo actuation results from using the photogenerated voltage to piezoelectrically drive a mechanical structure. Using light modulated at the resonance frequency of the torsional resonator the measured current is shown to linearly increase with intensity. For the electrical actuation case, the torsional resonator is driven using the non- linear response of the pn junction to an applied voltage. The non-linear response results in generation of voltage at the harmonic frequencies of the applied voltage. The voltage generated at twice the applied frequency is given the label 2f and is used to piezoelectrically drive the mechanical structure. The above results for the two methods of actuation are theoretically validated by deriving a model for the expected current. The model predicts the current as a function of the voltage. For the opto-piezo case this voltage is the photovoltage. The photovoltage is determined using the AC PV model. This model is derived using the DC PV model and predicts the AC operation of a photodiode in the 3rd and 4th quadrants to resistive and reactive loads. Using the opto-mechanical coupling coefficient the efficiency of the opto-piezo actuation is compared to opto-thermal actuation and radiation pressure actuation. It is shown that the opto-piezo effect, in general, is several orders of magnitude better than the other two in converting optical energy into mechanical energy. This is an important result because in situations where low optical powers are only available and power, in general, cannot be spared, for e.g. on a satellite, devices that make use of the opto-piezo effect could be used for either actuation or sensing. Generally however, using the opto-piezo effect can lead to either integration of existing photonic devices with mechanical resonators or new photonic devices all together. For e.g. using the opto-piezo effect an adaptable optical correlator can be made which could be used to make artificial intelligent machines. / Thesis / Doctor of Philosophy (PhD)

Ce travail s'inscrit dans le cadre d'un projet commun soutenu par la DGA (procédure RAPID), le projet Récepteur Optique Hyperfréquences LArge Bande ou ROHYLAB, dont VectraWave fait parti. Ce travail de thèse s'inscrit dans le domaine de la radio-sur-fibre en particulier au niveau de la réception. Nous nous inscrivons dans le contexte des photorécepteurs faible bruit, le but étant d'optimiser l'interface optique-électrique de ceux-ci tout en garantissant une grande dynamique. Après avoir présenté les avantages de la radio-sur-fibre à savoir : hauts débits, robustesse et encombrements, nous présentons les photorécepteurs et les différents paramètres qui les caractérisent. Cette étape nous permet de les comparer entre eux en les regroupant en fonction des techniques de conception utilisées dans la littérature. Cette étape nous permet d'identifier la technique de conception à utiliser. Nous choisissons de concevoir photorécepteur bande étroite dont on viendra élargir la bande. Nous définissons ensuite les paramètres nécessaires à la comparaison des technologies entre elles afin de justifier le choix de la technologie de transistor à utiliser. Nous étudions le photorécepteur en tant que système afin de mettre en évidence l'importance des paramètres présentés précédemment sur les performances de celui-ci. De cette analyse nous proposons une méthode de conception bande étroite liant l'ensemble des grandeurs. Nous montrons aussi comment estimer les performances limites en fonction de la technologie utilisée pour la photodiode et celle de l'amplificateur. Aussi nous montrons l'expression de cercles à densité équivalente de courant de bruit constants et de cercles à transimpédance constants. A partir de la modélisation théorique du photorécepteur et l'expression théorique des grandeurs caractéristiques, nous proposons la mise en œuvre et l'utilisation des outils présentés au chapitre précédent avec un logiciel de conception assisté par ordinateur. Nous montrons la modélisation de composants opto-microondes dans un environnement de simulation électrique. A l'aide de ces outils nous concevons trois photorécepteurs faible bruit et à grande dynamique dans la bande 2,9 GHz - 3,4 GHz. Les objectifs fixés sont : 300 de transimpédance, 5 pA/pHz. Ces circuits ont été simulés sous l'environnement électrique ADS mais aussi sous l'environnement électromagnétique MOMEMTUM. Les trois circuits présentent des performances records en bruit à de 3 GHz vis à vis de l'état de l'art. La réalisation du deuxième circuit conçu permet la caractérisation des photorécepteurs dans la bande 2,9 GHz - 3,4 GHz. Nous validons ainsi la démarche et proposons un circuit compétitif vis-à-vis de l'état de l'art. Dans une dernière section de cette thèse, nous illustrons le fait que cette méthode peut être exploitée sur d'autres technologies. Nous mettons en avant aussi le fait que l'on peut envisager la conception de photorécepteurs autour de 20 GHz. Nous envisageons aussi l'utilisation d'une inductance active pour réaliser des photorécepteurs accordables en fréquence pour des fréquences basses / This work is based on a common project support by the DGA, the project ROHYLAB for “wide band opto-microwave receiver” with Vectrawave . This work aim to optimized the optic-electric interface of a receiver in the radio-over-fiber field to design a low noise and high dynamic receiver. After an overview of radio-over-fiber's avantages such as: high data rates, security and security, we presented different photoreceiver and the figure of merit used to caracterized them. This step allow a comparison of the photoreceiver classified by the design topologies used in order to choose which design methodology we will used in this work. In an other hand, the same analysis is done for the transistor technologies. We presented a study of photoreceiver as a system in order to highlight the impact of main caracteritics on its performances. From this analysis allow to show a narrow band design method which link the caracteristics of the photodiode to the transistor's caracteristics. We also present some design tools such as circles of constant equivalent noise current density and circles of constant transimpedance. From the photoreceiver's theoritical model and the expressions of the main caracteristics, we implement the deisgn tools presented in ADS. In this section we also present the opto-microwave components models. Using this tools, we design three photoreceiver with low noise and high dynamics. This photoreceiver's aims to reach 300 Ohms of transimpedance and 5pA/Hz of noise. This circuits are implemented in ADS's eletrical fields and also in MOMENTUM's fields. All of this circuits appears as a competitive one in terms of noise at 3GHz .From the photoreceiver's design, we realized some cicuirts which permit photoreceiver's caracterization in 2.9 GHz - 3.4 GHz bandwidth. This measurements validate our approach and confirm a competitive circuit in term of noise compare to litterature. In a final sectin of this work, we illustrate an extension of this approach on other technologies. We also highlight a design of a photoreceiver at 20 GHz. In the end, we suggest the using of an active inductor to realize switchable frequency photoreceiver in low frequency

Mounting of lenses in opto-mechanical assemblies can create surface figure errors and refractive index changes through thermal and pre-load stresses. As lenses and barrels change in size under temperature changes, the optical performance degrades due to stress and surface deformations. Currently there is no way of determining the effect of these mechanical perturbations on the system wavefront without performing tedious finite element analysis. Most in-depth opto-mechanical analyses involve case-by-case studies with specific designs while previous general studies fail to take into account the complex geometries. The assumptions made by previous general studies ignore the effects of lens shape. These omissions can have a large effect on the stiffness, stress and surface figure error. A parametric model can combine the best of both an in-depth and general study. By parametrizing the model, a simple analysis can be executed for approximating the environmental-mechanical effects on optical performance. This eliminates the time it takes for an opto-mechanical design to be iterated for an optical or mechanical engineer. This tool could be used for early opto-mechanical design or for finite element analysis verification. The parametric model allows the exploration of the broader design study without confining it to a local design space.

No description available.

The potential of terahertz time domain spectroscopy has until recently been neglected in the field of the ultrafast magnetism. At the same time this technique can serve as a useful complementary tool with respect with conventional methods to investigate ultrafast magnetization dynamics. This thesis aims to implement time domain terahertz spectroscopy to observe high frequency spin waves excited optically in different magnetic systems. This work covers several distinct phenomena related to the study of spin waves (magnonics) at terahertz frequencies. The generation of transient broadband nonlinear magnetization via inverse Faraday effect in terbium gallium garnet is described in chapter 4. We demonstrate a remarkable discrepancy of at least two orders of magnitude between the strengths of the direct and inverse Faraday effects, thereby challenging the commonly accepted understanding of their relationship. Additionally, a striking nonlocality of the optical response is found. In chapter 5 the results of THz absorption spectroscopy of the terbium gallium garnet are reported. The garnet exhibits an intricate paramagnetic state with several magnetic sub-lattices at cryogenic temperatures under the application of strong magnetic fields. Some precessional modes of these sub-lattices were measured. The components of the g-tensor of terbium ions were extracted from the data. In chapter 6 the ultrafast magnetization dynamics of thulium orthoferrite, studied my means of terahertz spectroscopy, is described. It is demonstrated that terahertz response of the orthoferrite provides crucial additional information with respect to the optical pump-probe signal. A novel exchange driven mechanism of optical manipulation of the magnetic state is demonstrated. Finally, chapter 7 is a theoretical discussion of so called planar magnonic metamaterials. It is shown that the arrays of ferromagnetic films may exhibit negative refraction index at sub-terahertz frequencies, provided the mechanism of spin wave quantization is introduced. The thesis ends with a brief conclusions chapter where a short summary of the results is given. Some possible future extensions of the conducted research are drawn as well.