Several SBN-x crystals of different composition have been investigated using the following methods: Optical absorption in the band gap spectral region, optical absorption of the OH-stretch-mode in the near infrared, Raman scattering, pyroelectric and dielectric measurements.The band edge position depends on the crystal composition in a non-linear manner, thus showing band bowing, typical for mixed systems. A new method has been developed to increase the hydrogen content in the bulk. This doping depends on the composition in an almost linear manner. The observed OH stretch mode spectra have been deconvoluted into three sub bands which can be attributed to different sites in the lattice. The composition dependent spectra have been modelled with a few parameters, using different line shapes and both linear and quadratic dependences of the band position.Raman spectra of several crystals of different composition were recorded for four different scattering configurations. Changes for wave numbers below 500 have been found, but could not attributed to particular modes. A prominent feature at about 600 wave numbers was not disturbed by other modes allowing a decomposition and an assigned of this mode to a certain vibration. It was found that the behaviour of this mode is governed by the [Sr]/[Ba] ratio in the pentagonal channel of SBN-x.The ferroelectric relaxor phase-transition of SBN-x has been studied with pyroelectric measurements. From the nonlinear susceptibility as a function of temperature the phase-transition temperature was deduced using the inflection point. The non fully-linear dependence of the phase-transition temperature as a function of the [Sr]/[Ba] ratio can be explained by a system of three different sublattices for the Strontium and Barium atoms.First results obtained with a setup for measuring the dielectric constant confirmed already reported data of other groups.

No description available.

Lithium niobate (LiNbO3) is a human-made crystalline which is widely used in modern photonics due to its useful properties. In recent years, there has been significant progress in the development of lithium niobate on insulator (LNOI) technology, realizing a fully functional photonic integrated circuits, thanks to its capabilities in both electro-optics and second-order optical nonlinearity. To integrate laser source and amplifier onto the photonic integrated chips, rare-earth-ion doping has been considered while traditional laser source is difficult to integrate on chip. Among the rare-earth ions, erbium ions can provide laser source at 1550nm, which can meet the requirements of high-speed telecommunication band. In this thesis, we investigated a recent-made erbium-implanted LNOI sample through setting up a homebuilt microscope system. By exciting the erbium-implanted area with 980nm continuous wave laser, the emission light around 1550nm was collected and measured. Developing the setup with an automatic scanning code, the photoluminescence response of the implanted area on the sample was mapped. Conclusively, the investigation of the implanted samples demonstrated that the erbium-ion emitters could emit measurable photoluminescence signal around 1550 nm wavelength in spite of background noise and notably at room temperature. These results demonstrated the capability of the designed microscope while still need to be improved in terms of detectors sensitivity and signal to noise ratio. It also revealed the promising implantation of active Er ions into LNOI chips conveying the fabrication of Er photon sources on thin film lithium niobate in next step. / Lithiumniobat (LiNbO_3) är en konstgjord kristall som är allmänt använd inom modern fotonik på grund av dess användbara egenskaper. Under de senaste åren har det skett betydande framsteg inom utvecklingen av teknologin för litiumniobat på isolator (LNOI), vilket har resulterat i fullt fungerande fotoniska integrerade kretsar, tack vare dess förmågor inom både elektrooptik och optisk icke-linjäritet av andra ordningen. För att integrera laserskälla och förstärkare på de fotoniska integrerade kretsarna har överväganden gjorts om tillsats av sällsynta jordartsmetaller, eftersom det är svårt att integrera traditionella laserskällor på kretsar. Bland de sällsynta jordartsmetalljonerna kan erbiumjoner fungera som laserskälla vid 1550 nm, vilket uppfyller kraven för höghastighetstelekommunikationsbandet. I denna avhandling undersökte vi nyligen tillverkat ett LNOI-prov som hade implanterats med erbiumjoner genom att bygga upp ett hemgjort mikroskopsystem. Genom att excitera det erbium-implanterade området med en 980 nm kontinuerlig våglaser samlades och mättes utstrålningen vid 1550 nm. Genom att utveckla installationen med en automatisk skanningskod kartlades fotoluminescensresponsen hos det implanterade området på provet. Sammantaget visade undersökningen av de implanterade proverna att erbiumjonemitterare kunde avge mätbara fotoluminescenssignaler vid en våglängd omkring 1550 nm trots bakgrundsbuller och framför allt vid rumstemperatur. Dessa resultat bekräftade mikroskopets kapacitet, även om förbättringar behövs vad gäller detektorns känslighet och signal-till-brusförhållandet. De avslöjade också den lovande implanteringen av aktiva Er-joner i LNOI-kretsar och möjligheten att tillverka Er-fotonkällor på tunna filmer av litiumniobat i nästa steg.

<p>This thesis is the result of several experiments designed to probe the low temperature physics underlying the 1D-Ising-like behaviour of chains of spins in the structure of Cobalt Niobate, CoNb2O6. A collection of prior work has been done by several groups prior to this, focusing on mapping the phase diagram above 0.5K. Interest in this material was renewed recently based upon theoretical work and experimental confirmation of the unique structure of the spins in the system. The bulk of this work was done at temperatures below the previously investigated range to probe the unique properties of this system.</p> <p>The material was grown at McMaster University using the optical floating zone technique from oxide powders. The crystal was examined and oriented using single crystal and Laue diffraction and was cut for use in further experiments. Squid magnetometry was used to confirm the material properties and phase transition temperatures, and was compared to literature values.</p> <p>Heat capacity measurements were performed locally down to 2K, and by collaborators at Waterloo in the range from 330mK to 1K. The heat capacity measurement confirmed the 2.9K transition and explored the relaxation time of the material. Cobalt niobate was found to have an exceptionally long relaxation time at low temperatures indicating strong spin-spin interactions. A sharp transition with zero applied field was found to become a broad, smooth feature at 2.9K when a small field was applied.</p> <p>We performed muSR measurements in zero, longitudinal and transverse field. The muSR results confirmed the long relaxation time found by the heat capacity measurements, which may reflect the coupling of the spin system to the lattice. Additionally, the material was never seen to statically order in zero or longitudinal field down to 700mK and up to 1T. The material was found to behave dynamically throughout all the field ranges.</p> / Master of Science (MSc)

This thesis contains the results of the extensive study into the synthesis of nickel niobate (NiNb2O6) including the formation of what was a previously unreported polymorph of the material, as well as the magnetic properties of both cobalt niobate (CoNb2O6) and nickel niobate using techniques including SQUID magnetometry, powder and single crystal x-ray scattering, powder and single crystal neutron scattering and muon spin rotation/relaxation. In cobalt niobate we found extremely long relaxation times in the heat capacity which showed up strongly in muon spin rotation experiments but not in neutron measurements. Additionally, with field applied to the system we see the emergence of spin-wave like structures in the neutron scattering data. Within cobalt niobate the strongest interaction is ferromagnetic and along the chain. The chains themselves are laid out on a triangular fashion and interact, although far more weakly, in an antiferromagnetic manner. This triangular patterning as well as an antiferromagnetic interaction results in interchain frustration, which protects the quasi-1D nature of the system due to the difficulty generated in creating 3D order. In nickel niobate we found that growth conditions caused highly variable changes, and we were able to create two different polymorphs. One polymorph was in the same space group as cobalt niobate, which gave us an opportunity to explore the magnetic difference between a spin-½ and spin-1 magnetic system and in nickel niobate in the new space group we performed an ab initio characterization solving the unit cell structure, the magnetic structure with neutron scattering as well as a magnetic characterization with SQUID magnetometry and muon spin rotation, allowing us to contrast the significant crystallographic differences. For the new polymorph we were able to determine its magnetic structure, characterized by Ising-like spins arranged in frustrated tetrahedra with three of the four points lying in the same plane as the spin, and for both materials we were able to use zero-field μSR data to estimate behaviour near the critical point and determine a critical exponent near the magnetic transitions. In both polymorphs there is evidence of constrained magnetism or reduced dimensionality, although the evidence for low dimensionality is much stronger in the columbite polymorph. / Thesis / Doctor of Philosophy (PhD) / This thesis examines two different niobium-based compounds: cobalt niobate (CoNb2O6) and nickel niobate (NiNb2O6). In these systems the cobalt and nickel atoms provide interesting magnetic properties. Within a magnetic material, the magnetic atoms tend to have their spins align in certain ways. The atoms themselves are fixed to particular sites by the way the material is assembled; an atomic framework. In the case of cobalt niobate, the magnetic atoms are arranged in well-separated chains so that a magnetic atom interacts strongly with its magnetic neighbours within a chain, and weakly with ones that are further away. This is an example of a material that is called `low dimensional'. The chains themselves form triangular patterns, and the interactions between chains are both weaker and antialigned, which creates a frustrated competition between the chains, protecting the low dimensional state by creating conditions where it is hard for all the spins in the material to order. For nickel niobate, the magnetic moments all want to anti-align, or be pointing in the opposite direction as its nearest neighbour. The magnetism is `frustrated' because each magnetic atom is tetrahedrally connected to three other atoms, so it cannot meet that condition. This can be visualized by drawing a triangle and trying to make each corner have an arrow pointing up or down. The third corner of the triangle cannot satisfy this requirement for its neighbours (one up and one down arrow). Both decreased dimensionality and frustration can lead to the emergence of novel quantum states of matter at low temperature. This thesis explores these materials with that in mind.

The new generation of non-linear optical devices, based on periodically-poled lithium niobate thin film platforms, aims at achieving record-high conversion efficiencies and a formerly unknown capability for integration into modern quantum optical systems. It thus not only suits the demands of high-end telecommunication applications, but also provides striking potential for further performance enhancement. However, most of these record-setting new developments lack in in-depth analysis of their domain grid structures to determine whether the key requirements for efficient non-linear optical conversion are ideally fulfilled. Established analysis techniques for the exploration of bulk lithium niobate, like Raman spectroscopy, have not been adapted for these thin film structures, because the low interaction volumes require long acquisition times. In this work, the importance of Raman spectroscopy analysis for thin film lithium niobate device optimization is demonstrated in cross-correlated co-imaging with second-harmonic imaging and piezoresponse force microscopy. Key performance indicators of quasi-phase matching are identified and specifically investigated. The experiments show that Raman spectroscopy is capable of detecting all these indicators and is unique in its ability to identify performance-inhibiting mechanical and electrical stress fields. In an attempt to establish high-speed Raman imaging on lithium niobate structures, the coherent four-wave mixing method of broadband coherent anti-Stokes Raman scattering (B-CARS) is, for the first time, systematically introduced for fundamental solid state analysis by theoretically and experimentally addressing all special implications of crystalline material systems via the model material lithium niobate, e.g. phase matching conditions, phase retrieval, and complex selection rules. It is shown that the resonant B-CARS signal can be retrieved in post-processing and allows a direct comparison with spontaneous Raman spectroscopy. The predicted CARS selection rules are experimentally confirmed, and phonons are assigned to their respective B-CARS peaks. Furthermore, B-CARS signals are shown to be predominantly generated by scattering in forward direction. The insights of these fundamental investigations are applied for lithium niobate domain wall imaging via B-CARS. Hyperspectral spontaneous Raman spectroscopy and B-CARS images are compared with regard to imaging speed, signal-to-noise ratio, domain wall contrast mechanism, and signature width. The experiments prove that B-CARS allows at least a 20-fold speed increase with an improved signal-to-noise ratio as compared to spontaneous Raman spectroscopy. The domain wall signature is of similar nature for both techniques, and is not changed via phase retrieval, thus allowing high-speed B-CARS domain wall imaging in lithium niobate without post-processing. The massive B-CARS domain wall signal is attributed to a Čerenkov-like effect analogous to second-harmonic imaging. This is the first time that such an effect has been shown by a Raman scattering technique. These findings show the importance of Raman scattering investigations for the optimization of modern non-linear optical devices, and outline a way to massively increase the speed of Raman crystal analysis via B-CARS. Thus, with further studies that quantify the effects detailed qualitatively in this work and take B-CARS analyses to a broader range of crystalline samples, this work can form the basis towards establishing the high-speed and in-depth analysis of modern non-linear optical platforms via coherent Raman imaging.:1. Motivation .......... 1 2. Fundamentals .......... 4 2.1 Lithium Niobate .......... 4 2.1.1 Ferroelectric Structures .......... 4 2.1.2 Domain Engineering .......... 6 2.1.3 Thin Film Lithium Niobate (TFLN) .......... 8 2.2 Spontaneous Raman Spectroscopy .......... 10 2.2.1 Raman Spectroscopy of Lithium Niobate Crystals .......... 14 2.2.2 Domain Imaging with Spontaneous Raman Spectroscopy .......... 18 2.3 Coherent anti-Stokes Raman Scattering (CARS) .......... 20 2.3.1 Signal Generation .......... 21 2.3.2 Broadband Coherent anti-Stokes Raman Scattering (B-CARS) .......... 24 2.3.3 The Non-Resonant Background .......... 25 2.3.4 Selection Rules .......... 27 2.3.5 Phase Matching .......... 30 3. Experimental Methods .......... 32 3.1 Spontaneous Raman Spectroscopy (SR) Setup .......... 32 3.2 B-CARS Setup .......... 34 3.3 Raman Data Analysis .......... 35 3.4 B-CARS Phase Retrieval .......... 36 3.5 Second-Harmonic Generation Microscopy .......... 38 3.6 Piezoresponse Force Microscopy .......... 40 4. Thin Film Lithium Niobate Co-Imaging .......... 42 4.1 TFLN Sample and Co-Imaging Approach .......... 45 4.2 Piezoresponse Force Microscopy Imaging .......... 47 4.3 Second-Harmonic Generation Imaging .......... 49 4.4 Hyperspectral Raman Imaging .......... 53 4.5 Conclusions on Cross-Correlated Co-Imaging .......... 58 5. Fundamental Aspects of B-CARS on Lithium Niobate .......... 61 5.1 Phase Matching .......... 62 5.2 Phase Retrieval .......... 65 5.3 Selection Rules and Phonon Assignment .......... 67 5.4 Conclusions .......... 71 6. B-CARS Domain Wall Analysis in Lithium Niobate .......... 73 6.1 Preliminary Considerations .......... 73 6.2 Sample Preparation .......... 74 6.3 Spectral Analysis .......... 75 6.4 Determination of Acquisition Times .......... 78 6.5 Domain Wall Signatures .......... 79 6.6 Domain Imaging .......... 82 6.7 Conclusions .......... 83 7. Summary and Outlook .......... 85 Appendix .......... I References .......... XIII Own Publications .......... XXIV Acknowledgements .......... XXV

Ce mémoire traite de l’ étude et de la réalisation de composants à ondes élastiques de surface (SAW) pour des applications de filtrage dans les gammes VHF et UHF. Nous y étudions différentes structures de ces filtres, à commencer par des filtres à couplage acoustique longitudinal centrés aux alentoursdu gigahertz, de bande passante relative inférieure à 0,1 % réalisés sur quartz. Leur fabrication et leur caractérisation ont révélé des pertes d’insertion inférieures à 5 dB et des niveaux de rejet supérieurs à 20 dB, conformément aux prévisions de notre modèle de matrice mixte. Un tel filtre a été inséré dans un oscillateur pour valider la fonction réalisée. Pour une maîtrise accrue de la conception de ces filtres, nous avons développé un modèle tenant compte de la contribution des modes transverses sur leur fonction de transfert. Des comparaisons entre théorie et expérience ont permis de démontrer la précision de ce modèle. Nous nous sommes également intéressés à des structures de filtres à éléments d’impédance et à transducteurs en éventails (fan-shaped) pour la réalisation de bandes passantes relatives comprises entre 1 et 15 % dans la bande 100 − 300 MHz. Pour chacune de ces structures, nous avons développé un modèle permettant d’en étudier le comportement. Une configuration de filtre en treillis de bande passante relative proche de 2 %a été fabriquée et caractérisée, ainsi que plusieurs filtres à transducteurs en éventails de bandes passantes relatives supérieures à 10 %. Enfin, nous avons étudié deux approches qui nous ont permis de réaliser des dispositifs fonctionnant à des fréquences voisines de 3 GHz. La première, consiste à exploiter les vitesses de phase supérieures à 5 km.s−1 d’un guide d’ondes à base de carbone-diamant. La seconde exploite la résolution d’un procédé de lithographie par nano-impression pour réduire la période des réseaux d’ électrodes. / This thesis deals with the development of surface acoustic wave devices (SAW) for filtering applications in the VHF and UHF bands. Several filter structures are studied. The first ones are longitudinally coupled resonator filters (LCRF) manufactured on Quartz with a relative pass-band narrower than 0,1 % centered at about 1 GHz. These filters have been fabricated and characterized, yielding less than 5 dB insertion loss with rejection levels in excess of 20 dB as predicted by our P-matrix model. One of these filters has been mounted in an oscillator to validate its characteristics.To improve the design of such filters, we have developed a model accounting for transverse mode contributions on their spectral function. Comparisons between theory and experiment emphasizes the accuracy of the developed model. We also have investigated impedance element and slanted transducers (fan-shaped) filter structures to produce filters with relative pass-band ranging from 1 to 15 % in the 100 − 300 MHz frequency range. For each type of filters, we have developed a model to predict their electrical response. A balanced-bridge filter configuration with a 2 % relative pass-band and four fan-shaped filters with pass-band larger than 10 % have been fabricated and characterized. Finally, we have studied two approaches for the development of SAW devices operating at frequencies in the vicinity of 3 GHz. The first approach exploits Diamond-based substrates, providing phase velocity higher than 5 km.s−1. The second one uses a nano-imprint lithography process to reduce the pitch of electrode gratings.

L'augmentation exponentielle de la quantité d'information à transmettre afin d'assurer les télécommunications futures amène à rechercher de nouvelles voies pour faire face à ces nouveaux besoins. L'optique peut, pour suppléer aux systèmes électroniques essoufflés, répondre à ces défis naissant en autorisant le multiplexage en longueur d'onde (WDM). Celui ci permet non seulement d'accroître fortement le débit en ligne (ici une fibre optique), mais autorise l'existence de réseaux dont les fonctions sont assurées par voie optique. L'implantation de ces nouvelles architectures repose sur des composants clefs comme le filtre spectral accordable. Cette thèse a concerné l'étude théorique, la conception, la réalisation pratique et les perspectives d'application et d'amélioration d'un filtre accordable étroit intégré sur niobate de lithium et fonctionnant à une longueur d'onde proche de 1.55 μm. Nous avons tout d'abord comparé différents principes de filtre accordable intégré et avons retenu un dispositif fonctionnant entièrement par effet électrooptique qui présentait une vitesse de commutation élevée. Son fonctionnement est similaire à celui du filtre biréfringent de Šolc qui est constitué d'un convertisseur de polarisation sélectif en longueur d'onde placé entre polariseurs croisés. En approfondissant l'étude de la propagation de la lumière dans le filtre nous montrons que les irrégularités que présente la transmittance en intensité du dispositif sont dues à l'existence de variations anormales de la différence d'indice de phase dans le guide d'onde diffusé. Ces variations peuvent être reliées à des défauts dans le procédé de fabrication. Cette constatation nous amène à faire une étude théorique complète des effets de différents types de défauts dont on retrouve expérimentalement la trace sur le filtrage. Poussés par ces simulations, nous étudions en détail les différentes étapes du procédé technologique d'intégration sur niobate de lithium et en proposons des améliorations afin d'atteindre expérimentalement les caractéristiques théoriques du filtre. Finalement nous présentons des applications du filtre (laser à fibre accordable et modulable) et discutons de ses perspectives de développement (insensibilité à la polarisation).

No description available.

A slab-coupled optical fiber sensor (SCOS) falls into a narrow class of all-dielectric optical fiber electric field sensors, which makes it a perfect candidate for measurements of high electric fields in environments where presence of conductors is highly perturbing to the system under test. Its nonlinear response to high fields requires a new nonlinear calibration technique. A nonlinear calibration method is explained and demonstrated to successfully measure high electric fields, as well as high voltages with dynamic range up to 50 dB. Furthermore, a SCOS can be fitted into narrow spaces and make highly localized measurements due to its small size. This allows a SCOS to be integrated inside a standard high voltage coaxial cable, such as RG-218. Effects of partial discharge and arcing is minimized by development of a fabrication method to avoid introduction of impurities, especially air-bubbles, into the cable during SCOS insertion. Low perturbation of the measured voltage is shown by simulating the introduced voltage reflections to be on the order of –50 dB. It is also shown that a SCOS can be inserted into other cables without significant perturbation to the voltage. A complete high voltage and high electric field measurement system is built based on the high-voltage modifications of the SCOS technology. The coaxial SCOS is enhanced for robustness. Enhancements include packaging a SCOS into stronger ceramic trough, strengthening the fiber with kevlar reinforced furcation tubing and protecting the sensor with metal braces and protective shells. The interrogator is protected from electromagnetic interference with an RF-shielded box. Reduction in power losses introduced by the new PANDA-SCOS technology allows interrogator bandwidths to be increased up to 1.2 GHz. The whole measurement process is streamlined with dedicated software, developed specifically for high voltage and electric field measurements with support for the nonlinear calibration.