L'oscillateur optoélectronique (OEO) a été introduit pour la première fois en 1996 par S. Yao et L. Maleki, en tant qu'oscillateur microondes à très faible bruit de phase et obtenu par synthèse directe. Les développements de l'OEO concernent les applications en photonique microondes, télécommunications optiques, radar et traitement du signal. Mais l'OEO devrait aussi pouvoir être utilisé dans le domaine des capteurs. Dans cette thèse nous étudiants plusieurs aspects de l'OEO pour son application à la mesure d'indice de réfraction d'un liquide. Compte tenu de sa structure l'OEO dépend fortement des conditions ambiantes d'utilisation. S'il n'est pas bien optimisé ni contrôlé, il ne peut pas fonctionner correctement sur une longue durée. Nous avons étudié les influences de la température sur le modulateur électrooptique (EOM) et sur le comportement global de l'OEO. Un contrôle de température réduit de façon significative le phénomène de dérive de l'EOM. Afin de la supprimer complètement, nous avons mis au point une instrumentation construite autour d'une carte DSP, permettant de détecter et compenser la dérive du point de fonctionnement optique de l'EOM tout en contrôlant simultanément sa température. Une première technique est basée sur un signal de test, basse fréquence, appliqué à l'électrode DC du modulateur. Une deuxième solution consiste à travailler sur la puissance optique en sortie du modulateur. En combinant les deux on peut profiter des avantages de ces deux méthodes. Utilisant ainsi l'OEO nous avons testé plusieurs configurations pour mesurer l'indice de réfraction de quatre solutions chimiques bien connues, nous avons obtenu une variance de 3 pour mille. Les résultats sont en assez bon accord avec les publications correspondantes. Enfin nous avons aussi introduit une nouvelle méthode pour améliorer les mesures d'indice de réfraction faites à long terme en suivant, grâce à un analyseur vectoriel de réseau, les évolutions au cours du temps du temps de propagation dans la fibre optique. En introduisant à partir de cette mesure une correction aux mesures de la fréquence d'oscillation il est possible de réduire les fluctuations de cette fréquence à seulement 606 Hz, sur une durée de 62 h, ce que l'on peut comparer aux 8 GHz de l'oscillateur. Ainsi le rapport signal à bruit, peut être grandement amélioré lors de la mesure d'indice de réfraction et il doit être possible de diminuer la limite de détection des variations de l'indice de réfraction au cours du temps. / The optoelectronic oscillator (OEO) was first introduced in 1996 by S. Yao and L. Maleki as a very low phase noise microwave oscillator working in direct synthesis. The OEO developments concern applications in microwave photonics, optical telecommunication, radar and high speed signal processing systems but it should also be used in the sensing domain. In this thesis, we study several aspects to apply the OEO to liquid refractive index measurement. Because of its structure the OEO is very dependent on the ambient conditions. If the OEO is not optimized and controlled, it cannot operate well for long duration. We have analyzed the influences of temperature on the electrooptic modulator (EOM) and the global OEO behavior. Temperature control can significantly reduce the drift phenomena of the EOM. In order to totally remove this drift, we have developed a complete digital system, based on a DSP kit, to detect and compensate automatically the EOM optical bias point drift and to control simultaneously its temperature. The first technique is based on a dither signal at low frequency, injected to DC electrode of the EOM. The second one is based on the average optical output power of the EOM. A combination of these two techniques can take advantages from both of them. Using like that the OEO, we have tested several configurations to measure the refractive index of four classical chemical solutions leading to a standard deviation of 3 per thousand. The results are in rather good agreement with previous publications. Finally, we have introduced a new method to improve the long-term refractive index measurement by monitoring, with a vector network analyzer, the variations of the optical delay in the fiber loop of the OEO. Introducing by this way a correction to the long-term frequency measurement it is possible to reduce the oscillation frequency fluctuations to only 606 Hz, compared to the 8 GHz of the oscillator, for a duration of 62 hours. Therefore the signal-to-noise ratio in the refractive index measurement can be enhanced and so the detection resolution of the refractive index variations during time.

Cette thèse de doctorat a pour but de fabriquer des systèmes électro-optiques compacts en utilisant les propriétés des cristaux photoniques (CP).). Le niobate de lithium (LiNbO3) est très attractif pour les applications optiques (télécommunications optiques, biomédical, astrophysique) car il a de faibles pertes en propagation (0.1 dB/cm ou moins), une faible dispersion en longueur d’onde, une large bande de transparence (350-5000 nm), et des forts coefficients Electro-optiques, non-linéaires et acousto-optiques. Cependant, les composants optiques utilisant ce matériau présentent classiquement un encombrement supérieur au centimètre, ce qui est dommageable pour leur intégration dans des circuits optiques compacts. Nous cherchons à démontrer plus précisément la faisabilité de modulateurs électro-optiques ultra-compacts tout en gardant les performances des modulateurs de type Mach-Zehnder, telles que de faibles pertes d'insertion, une faible tension de commande et un fort taux d'extinction. Nous proposons de remplir ces objectifs par l'usinage de cristaux photoniques à haut facteur de forme sur des guides LiNbO3, en associant découpe à la scie circulaire de précision et gravure par faisceau d'ion focalisé. La configuration s’appuie d’une part sur une tranche fine (ridge) de LiNbO3 qui confine la lumière transversalement, et d’autre part sur l'usinage du CP à haut facteur de forme pour favoriser une forte sensibilité à la présence de champs électriques externes sur des longueurs actives de l'ordre du micromètre. Les hauts facteurs de forme seront obtenus en usinant les ridges sur leur sommet et sur leurs flancs. Un premier enjeu, technologique, est destiné à optimiser les technologies développées à l’institut FEMTO-ST en vue d’applications à l’optique intégrée. Le deuxième enjeu, scientifique, s’agit de mettre en oeuvre une nouvelle configuration de contrôle de la lumière à l’aide d’un cristal photonique, présentant un double usinage sur les flancs et le sommet. C'est la première démonstration expérimentale de nanostructures LiNbO3 à haut facteur de forme. / The main goal of this PhD thesis is to fabricate compact electro-optical devices in exploiting the properties of photoniccrystal (PhC). Lithium niobate (LiNbO3) is a very attractive material for optical applications (such as opticaltelecommunication, biomedicine, astrophysics) thanks to its low propagation losses (0.1 dB/cm or less), its weakwavelength dispersion, its large optical bandwidth (350-5000 nm), and its strong electro-optical, non linear and acoustoopticalcoefficients. However, classical LiNbO3-based optical components possess active lengths of several centimers,which is not benefic for their good integration in compact optical circuits.We will focus this study more precisely on the feasibility of ultra-compact electro-optical modulators while keeping theperformances of commercialized LiNbO3 Mach-Zehnder type modulators, like their low insertion losses, their high extinctionratios, and their low power consumptions. To overcome this challenge, we will structure high aspect ratio photonic crystalson lithium niobate waveguides by combining optical grade dicing and focused ion beam milling. The main configuration isbased on the technology of LiNbO3 ridge waveguide in order to confine the light laterally and on the nano-structuration ofhigh aspect ratio photonic crystal on the ridge waveguide to enhance the sensibility to electric field stimuli on a fewmicrometers only. Structuring such high aspect ratio PhC will be possible thanks to focused ion beam milling from thetopside and the lateral side of the waveguide.The first issue is to optimize the technology developed in FEMTO-ST Institute for the fabrication of LiNbO3 integratedcomponents. The second issue is to create new configurations to control the propagation of light. This will be the firstexperimental demonstration of high aspect ratio LiNbO3 nanostructures.

Le développement de nouveaux matériaux est essentiel dans la réalisation de capteurs de petites dimensions et pour les composants micro-nano-optoélectroniques. Les matériaux à base d'oxydes en sont de bons candidats. Ce travail de thèse a concerné la synthèse de matériaux ferroélectriques tels le BaTiO3 (BTO) et le Ba1-xSrxTiO3 (BST), associés à des électrodes inférieures et supérieures en oxyde d'indium-d'étain (ITO), tous déposés par pulvérisation cathodique RF (radio fréquence). Nous nous sommes concentrés sur la relation existante entre les propriétés optiques et électro-optiques de guide d'ondes et l'orientation cristalline, la couche d'interface ainsi que la nature du substrat. Après la caractérisation des propriétés structurales, nous avons évalué les propriétés optiques de ces matériaux par la technique du couplage par prisme pour une gamme de longueurs d'ondes de l'UV au proche IR. Les résultats ont montré un bon confinement de la lumière dans le film, avec des pertes planaires de propagation optique de l'ordre de 3 dB/cm aux longueurs d'onde télécoms, résultats à l'état de l'art pour ces matériaux.Cette méthode de couplage optique a permis de mettre en évidence les propriétés électro-optiques du BTO et du BST dans cette même gamme de longueurs d'onde et pour les deux polarisations optiques, à partir de la variation des spectres de réflectivité. Si le BTO a montré un coefficient r33 de 23 pm/V aux longueurs d'onde télécoms, nous avons mesuré autour de 19 pm/V pour le BST(70/30). / The development of new material is essential for the realization of small sized sensors and for micro-nanooptoelectronics. Functional oxides are candidates of a major interest for the realization of new devices. This work concerns the growth of heterostructures formed by BaTiO3 (BTO) or Ba1-xSrxTiO3 (BST) ferroelectric multilayers associated to (ITO: Indium Tin Oxide) conductive oxides bottom and top electrodes. We focused on the relation between waveguide and electro-optic (EO) properties and the crystalline orientation, the interface layer and the nature of the substrate.RF (Radio Frequency) magnetron sputtering is a selected deposition technique for these applications. While the characterization of properties has become an integral part of research for the understanding of the material behavior, we evaluate the optical properties by prism coupling at wavelengths ranging from 450 nm to 1539 nm.The guided mode spectrum indicates that a good confinement of light is achieved in the film witch is necessary for optical waveguide devices. Ordinary and extraordinary refractive indices for BST/BTO are respectively 2,111/2,224 and 2,052/2,219 at 1539 nm. Optical propagation loss in a planar waveguide configuration in TE at 1539 nm wavelength was determined to be 3 dB/cm. The electro-optic effects were investigated in this study through the variation of the resonant coupling angle, refractive index variation ( n) in the prism coupling measurements. Finally, the EO coefficient of our BTO is 23 pm/V and 19 pm/V for BST(70/30) at 1539 nm.

<p>Ova disertacija sadrži analizu mogućnosti merenja brzih impulsnih<br />napona i izražavanja odgovarajuće merne nesigurnosti. Dokazano je da<br />je moguće izvršiti numeričku simulaciju odziva mernog sistema na<br />impuls brzine porasta reda veličine pikosekunde. Izražena je merna<br />nesigurnost kapacitivnog razdelnika napona Monte Karlo metodom.<br />Prikazan je način konstruisanja kapacitivnog razdelnika napona sa<br />talasovodnim prilagodnim otporom. Konstruisano je više tipova<br />kapacitivnih razdelnika napona izuzetno dobrih karakteristika. Na<br />osnovu dobijenih rezultata je odabran kapacitivni razdelnik napona<br />najboljih karakteristika i izražena je njegova merna nesigurnost</p> / <p>This thesis contains an analysis of the possibilities for measurement of very<br />fast pulse voltages and proper expression of measurement uncertainty. It has<br />been proven that it is possible to perform numerical simulation to the<br />response of the very fast pulse voltage with rise time at the order of<br />picoseconds of the measuring system. Measurement uncertainty of<br />capacitive voltage dividers is expressed by Monte Carlo method. The way of<br />constructing capacitive voltage dividers with a waveguide resistance is<br />shown in this thesis. The design of four types of capacitive voltage dividers<br />with extremely good features are shown. Based on these results, capacitive<br />voltage divider with best characteristics is selected and its measurement<br />uncertainty is expressed.</p>

Study of electric field in radiation detectors by Pockels effect (Master Thesis) by Michael Hakl Abstract Cadmium Telluride (CdTe) is a convenient candidate for room tem- perature detection of X-ray and gama radiation due to 1.5 eV band- gap energy and high atomic mass. Since CdTe has the highest linear electro-optical coefficient among II-VI compounds, the detector rep- resents a Pockels cell. Transmittance of the crystal is modulated by the internal electric field. Processing of infrared camera photographs results in an electric field profile between biasing electrodes. The elec- tric field in semi-insulting CdTe is influenced with deep level traps causing charge polarization under the electrodes. Occupation of traps is dependent on metal-semiconductor interface. Relation of charge accumulation and band bending for gold and indium contacts was studied. Repolarization/depolarization induced by additional illumi- nation with sub/above bandgap excitation laser was observed and ex- ploited for determination of the deep level energy. Results obtained by the Pockels-effect method were supported with luminescence measure- ments. Correlation between the occurrence of deep levels and surface point defects was discovered. Keywords: Pockels electro-optical effect, Cadmium Telluride ra- diation detector, Electric field, Schottky...

Title: Point defects in materials for detection of X-ray and gamma radiation Author: Martin Rejhon Department: Institute of Physics of Charles University Supervisor: prof. Ing. Jan Franc, DrSc., Institute of Physics of Charles Uni- versity Abstract: Cadmium telluride and its compounds are suitable materials for pro- duction of X-ray and gamma-ray detectors working at room temperature. How- ever, the detector quality is affected by material imperfections, such as crystal defects and impurities. It results into forming of deep levels which act as re- combination and trapping centers. Then, the accumulated space charge at these deep levels influences electric and spectroscopic properties of the detector. In the end it may result in the polarization effect, when the electric field is localized in vicinity of one contact and detection properties are decreased. This thesis reports a complex study of a detector band structure by various meth- ods with focus on differences between CdTe, CdZnTe, CdTeSe and CdZnTeSe. The electro-optic Pockels effect is used to investigate the influence of the illumi- nation in range 900 − 1800 nm on the inner electric field. The temperature and time evolutions of the electric field after application of bias or switching of the additional light at 940 nm were measured to determine deep levels...

A major limitation of acousto-optic (AO) leaky-mode modulator based holographic displays is their inability to present full-parallax. We propose that full-parallax capabilities can be bestowed on these displays by integrating an electro-optic (EO) phased array into the architecture. We validated this concept by rendering computational models and by fabricating and testing a basic two-axis AO/EO deflector prototype in lithium niobate. This was, to our knowledge, the first instantiation of an integrated, hybrid AO/EO deflector. The prototype had a 6° deflection range along the AO-axis, and a 3° deflection range along the EO-axis. A series of models provide us with a clear path forward for optimizing this deflector. They suggest that an AO/EO modulator with an EO deflection range of 24.5° and that requires less than 7.5 V can be fabricated within the limitations of standard photolithography.

Title: Point defects in materials for detection of X-ray and gamma radiation Author: Martin Rejhon Department: Institute of Physics of Charles University Supervisor: prof. Ing. Jan Franc, DrSc., Institute of Physics of Charles Uni- versity Abstract: Cadmium telluride and its compounds are suitable materials for pro- duction of X-ray and gamma-ray detectors working at room temperature. How- ever, the detector quality is affected by material imperfections, such as crystal defects and impurities. It results into forming of deep levels which act as re- combination and trapping centers. Then, the accumulated space charge at these deep levels influences electric and spectroscopic properties of the detector. In the end it may result in the polarization effect, when the electric field is localized in vicinity of one contact and detection properties are decreased. This thesis reports a complex study of a detector band structure by various meth- ods with focus on differences between CdTe, CdZnTe, CdTeSe and CdZnTeSe. The electro-optic Pockels effect is used to investigate the influence of the illumi- nation in range 900 − 1800 nm on the inner electric field. The temperature and time evolutions of the electric field after application of bias or switching of the additional light at 940 nm were measured to determine deep levels...

This dissertation presents the fabrication and analysis of in-fiber devices based on elliptical core D-shaped optical fiber. Devices created inside optical fibers are attractive for a variety of reasons including low loss, high efficiency, self-alignment, light weight, multiplexibility, and resistance to electromagnetic interference. This work details how D-fiber can be used as a platform for a variety of devices and describes the creation and performance of two of these devices: an in-fiber polymer waveguide and a surface relief fiber Bragg grating. In D-fiber the core is very close to the flat side of the ‘D’ shape. This proximity allows access to the fields in the fiber core by removal of the cladding above the core. The D-fiber we use also has an elliptical core, allowing for the creation of polarimetric devices. This work describes two different etch processes using hydrofluoric acid (HF) to remove the fiber cladding and core. For the creation of devices in the fiber core, the core is partially removed and replaced with another material possessing the required optical properties. For devices which interact with the evanescent field, cladding removal is terminated before acid breaches the core. Etching fibers prepares them for use in the creation of in-fiber devices. Materials are placed into the groove left when the core of a fiber is partially removed to form a hybrid waveguide in which light is guided by both the leftover core and the inserted material. These in-fiber polymer waveguides have insertion loss less than 2 dB and can potentially be the basis for a number of electro-optic devices or sensors. A polarimetric temperature sensor demonstrates the feasibility of the core replacement method. This work also describes the creation of a surface relief fiber Bragg gratings (SR-FBGs) in the cladding above the core of the fiber. Because it is etched into the surface topography of the fiber, a SR-FBG can operate at much higher temperatures than a standard FBG, up to at least 1100 degrees Celsius. The performance of a SR-FBG is demonstrated in temperature sensing at high temperatures, and as a strain sensor.

This thesis addresses basic scientific research in the field of transmitter front-end circuits for electro-optical data communication. First, the theoretical fundamentals are presented and analyzed. Based on the theoretical considerations, conceptual circuit designs are studied. Finally, in order to prove the described concepts, the circuits were experimentally characterized and subsequently compared to other works in the literature. The analysis covers key theoretical aspects regarding transmitter front-end circuits. It starts from the basic physical effects inside a transistor and ends with the design of high-swing modulator drivers. Furthermore, it comprises the fundamentals of optical modulators as well as the integration of the electrical driver with the modulator. First, the concept of a basic monolithically integrated transmitter consisting of a Mach-Zehnder modulator (MZM) and an electrical driver is presented. The circuit reaches a bit-error-free data rate of 37 Gb/s, which is a record among other monolithically integrated transmitters reported in the literature. It was shown that by employing a high-swing driver, high extinction ratios (ER) can be achieved (namely 8.4 dB at 25 Gb/s and 7.6 dB at 35 Gb/s) while using short-length phase shifters (2 mm of length). It was therefore proved that one of the main drawbacks of the MZM-based transmitters, namely their large chip area, can be mitigated by using high-swing drivers, however without sacrificing the ER. Next, an improved modulator driver design is investigated, the focus of the study being the linearity. In addition to a high peak-to-peak differential output voltage swing of 7.2 Vpp,d, the driver achieves record-low total harmonic distortion (THD) values of 1% (at 1 GHz, for the output swing of 6.5 Vpp,d) and 1.7% (at 1 GHz, for the output swing of 7 Vpp,d). Moreover, the driver reaches a bandwidth of 61.2 GHz and shows a high power efficiency when relating its DC power consumption to its output voltage swing. The achievement of a high linearity and bandwidth without an increased power consumption is due to the fact that the bias currents of the emitter-follower (EF) stages are provided by means of resistors instead of the conventional current sources. The two approaches were first analyzed mathematically and subsequently compared by means of circuit simulations. It was shown that the proposed approach for the realization of the EFs – i.e. by means of resistors – allows a reduction of the DC power consumption by 19% compared to the current-source approach for an equivalent performance in terms of linearity and bandwidth. Finally, a modulator driver concept suitable for higher-order modulation formats is studied, namely the 8-level pulse amplitude modulation (PAM-8). The circuit was realized as a 3-bit digital-to-analog converter (DAC), thus being able to yield 8-level output signals. Moreover, the circuit is able to function as a PAM-4 driver as well, thanks to the tunable tail currents of the DAC core. It achieves a symbol rate of 50 Gbaud, which corresponds to a bit rate of 150 Gb/s for the PAM-8 modulation and 100 Gb/s for PAM-4. The study showed that a modulator driver can be realized that is able to switch between different modulation formats (namely PAM-8 and PAM-4), without requiring extra power or additional circuit parts. Moreover, the use of on-chip single-to-differential converters (SDCs) targets the relaxation of the requirements on the stages that precede the driver. Finally, relating its DC power consumption (590 mW, including the SDCs) to its output voltage swing (4 Vpp,d), the driver shows one of the highest power efficiencies among PAM modulator drivers in the literature.