Thèses : « NONLINEAR CRYSTAL »

1

Griffiths, J. « Crystal engineering for nonlinear optics ». Thesis, University of Cambridge, 2003. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.599722.

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Chapter Two details the design, synthesis and characterisation of some compounds of general formula p-DC₆F₄A-p’. Donor and acceptor groups are discussed both in the context of maximising the molecular NLO response, and in the context of the promotion of polar chain formation through supramolecular synthons. Of the ten compounds presented in this chapter, nine are noncentrosymmetric. Preliminary NLO measurements show that these nine compounds exhibit an appreciable SHG response. Semi-empirical calculations were performed on these and related systems to determine molecular hyperpolarisabilities. Similar calculations were also used to draw Molecular Electrostatic potential maps for these compounds in an attempt to rationalise the observed packing. Chapter Three discusses some compounds of general formula DC₆F₄C₆F₄A. The synthetic difficulties associated with the preparation of these perfluorinated biphenyl derivatives are highlighted, and semi-empirical calculations are used to identify some idealised systems. The syntheses and crystal structures of some methoxy substituted derivatives are reported. Chapters Four and Five discuss some compounds in which donor-acceptor substituted rings are linked by delocalised spacer groups. The synthesis and characterisation of some donor-acceptor substituted aromatic Schiff base compounds is presented in Chapter Four, along with some initial calculations and NLO measurements. Chapter Five describes the design, synthesis and characterisation of some thiazyl chain compounds. UV measurements and preliminary calculations on some of these systems are also presented.

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CLEMENTI, MARCO. « Nonlinear Optics in Photonic Crystal Cavities ». Doctoral thesis, Università degli studi di Pavia, 2020. http://hdl.handle.net/11571/1317094.

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Harnessing the properties of light for technological applications is perhaps the ultimate objective of photonics, whereas the generation, manipulation and detection of light in chip-based structures has an important impact both on industry and on fundamental research1. The integration to semiconductor-based nanostructures makes possible the application of the photonics paradigm to compact devices which on one hand enable the processing of information at high speed, and on the other hand allow to include, onto a single chip, complex experimental apparatuses, opening the way towards novel technological and physical applications. In this perspective, an effective light-matter interaction is primarily important, as this feature greatly enhances capability of integrated optical and opto-electronic devices, in terms of switching time, energy consumption and spectrum of applications. For these reasons, the development of structures capable to enhance the interaction of light and matter covers great interest in the field of integrated optics. In this thesis work, we investigate on the linear and nonlinear properties of photonic crystal (PhC) microresonators2, a specific type of integrated optical cavity which capabilities to confine the electromagnetic field both in time and space are particularly suited for enhanced photonic devices. In particular, this type of nanostructure benefits from an enhanced nonlinear response with respect to bulk or non-resonant nonlinear devices, and they are characterized by a minimal footprint, a crucial feature in view of integration, thanks to a Bragg-type physical confinement mechanism. Throughout the work, we focus on three specific topics. The first one consists in the design, fabrication and characterization of PhC cavities realized in silicon suspended membranes, designed for the demonstration of integrated optical frequency combs. These rely on a specific cavity design, engineered to provide equally spaced resonances in energy, as a consequence of the effective confinement potential3. We discuss experimental results showing comb-like resonant spectra and we investigate the possibility to use the structures for the implementation of triply-resonant nonlinear processes, such as four-wave mixing (FWM), with unprecedented conversion efficiency. In a second part, we investigate on the suitability of a novel material, silicon-rich silicon nitride (SRSN)4, for the fabrication of PhC cavities and their operation as nonlinear devices. We show how SRSN deposited films can be successfully used to fabricate high-quality factor PhC cavities and we experimentally study the generation of second- and third-harmonic under resonant pumping regime. Finally, we investigate the suitability of otherwise parasitic nonlinear effects, related to two-photon absorption in silicon microcavities, for the implementation of nonlinear properties based on the dynamical thermo-optic response of the material. We show that the PhC platform provides a way to achieve narrow spectral holes and gain windows, associated to a pronounced dispersion. This feature, associated to a dramatic decrease in group velocity, can be exploited to achieve slow-light on a chip exclusively via thermo-optic effect, in a completely novel approach. 1. Thomson, D. et al. Roadmap on silicon photonics. J. Opt. 18, 073003 (2016). 2. Notomi, M. Manipulating light with strongly modulated photonic crystals. Reports Prog. Phys. 73, 096501 (2010). 3. Alpeggiani, F., Andreani, L. C. & Gerace, D. Effective bichromatic potential for ultra-high Q-factor photonic crystal slab cavities. Appl. Phys. Lett. 107, 261110 (2015). 4. Clementi, M. et al. Cavity-enhanced harmonic generation in silicon rich nitride photonic crystal microresonators. Appl. Phys. Lett. 114, 131103 (2019).

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Merlin, Jessica M. « SURFACE MEDIATED NONLINEAR OPTIC EFFECTS IN LIQUID CRYSTALS ». Case Western Reserve University School of Graduate Studies / OhioLINK, 2007. http://rave.ohiolink.edu/etdc/view?acc_num=case1169755107.

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Erbschloe, D. R. « Nonlinear effects in photorefractive crystals ». Thesis, University of Oxford, 1988. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.233532.

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McCutcheon, Murray William. « Nonlinear optics of multi-mode planar photonic crystal microcavities ». Thesis, University of British Columbia, 2007. http://hdl.handle.net/2429/31426.

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The nonlinear properties of multi-mode InP and Si planar photonic crystal microcavities are investigated in experiments relevant to integrated schemes for classical and quantum optical information processing. Normally incident, short laser pulses are used to coherently initialize the relative phase and amplitudes of two modes of a single-missing-hole InP microcavity. The two modes are orthogonally polarized, and separated by less than the bandwidth of the ~130 fs excitation pulses. The relative amplitudes of the two modes can be controlled by adjusting the polarization and the centre frequency of the excitation beam. Cross-polarized detection of the resonantly scattered light reveals a well-defined relative phase between the modes that is characteristic of their coherence. When the short-pulse excitation is used to coherently excite two modes in a three-hole line-defect (L3) InP microcavity, second-order harmonic radiation is observed due to the interactions of the resonant fields with the second-order nonlinear susceptibility (χ⁽²⁾) of the host InP slab. Second-harmonic and sum-frequency generated signals are observed due to the intra- and inter-mode nonlinear mixing of the microcavity fields. When a separate non-resonant pulse is focussed onto an InP microcavity, sum-frequency light is generated conditional to the resonant mode population of the microcavity. The conditionally generated signals can be tuned by tuning the frequency of the non-resonant pulse. All of the results can be explained with reference to the bulk χ⁽²⁾ properties of the InP slab. While the transient, multi-mode response of the microcavities is harnessed with the short-pulse technique, a continuous wave excitation laser exploits the local-field enhancement intrinsic to these wavelength-scale microcavities. A single-mode InP L3-microcavity with Q = 3,800 is pumped on resonance with a CW laser, and the 2D pattern of far-field second-harmonic radiation is directly imaged. The second-harmonic light is enhanced by 1000 times compared to non-resonant excitation, demonstrating integrated low-power frequency generation. The spatial pattern of the radiation is consistent with simulations based on the bulk χ⁽²⁾ tensor, and reveals the importance of scattering and material absorption of the harmonic light. Ultrafast, all-optical switching is demonstrated in a Si microcavity with a single Q = 35, 000 resonant mode. The mode is resonantly excited with a weak probe pulse, and a non-resonant 200 pJ pump pulse with a precisely controlled time delay is used to inject free-carriers above the silicon bandgap. The free-carrier dispersion shifts the mode frequency by 9 line-widths, and broadens its width by a factor of 4. When the excited mode is perturbed while it is ringing down, coherent oscillations in the spectra are observed which can be explained in terms of a model of an instantaneously perturbed harmonic oscillator, The implications for frequency conversion and for the generation of squeezed optical states are considered.
Science, Faculty of
Physics and Astronomy, Department of
Graduate

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Lombardini, Alberto. « Nonlinear optical endoscopy with micro-structured photonic crystal fibers ». Thesis, Aix-Marseille, 2016. http://www.theses.fr/2016AIXM4377.

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Dans cette thèse, nous proposons l'utilisation d'un nouveau type de fibre à cristal photonique, la fibre Kagomé à coeur creux, pour la livraison d'impulsions ultra-courtes en endoscopie non linéaire. Ces fibres permettent la livraison d'impulsions sans distorsion sur une large bande spectrale, avec un faible bruit de fond, grâce à la propagation dans le cœur creux. Nous avons résolu le problème de la résolution spatiale, à l'aide d'une microbille en silice, insérée dans le cœur de la fibre Kagomé. Nous avons développé un système d'imagerie compacte, qui utilise un tube piézo-électrique pour le balayage du faisceau, un système achromatiques de microlentilles et une fibre Kagomé double gaine, spécialement conçue pour l'endoscopie. Avec ce système, nous avons réussi à imager des tissus biologiques, à l'extrémité distale de la fibre (endoscopie), en utilisant des différentes techniques tels que TPEF, SHG et CARS, un résultat qui ne trouve pas d'égal dans la littérature actuelle. L'intégration dans une sonde portable (4,2 mm de diamètre) montre le potentiel de ce système pour de futures applications en endoscopie multimodale in-vivo
In this thesis, we propose the use of a novel type of photonic crystal fiber, the Kagomé lattice hollow core fiber, for the delivery of ultra-short pulses in nonlinear endoscopy. These fibers allow undistorted pulse delivery, over a broad transmission window, with minimum background signal generated in the fiber, thanks to the propagation in a hollow-core. We solved the problem of spatial resolution, by means of a silica micro-bead inserted in the Kagomé fiber large core. We have developed a miniature imaging system, based on a piezo-electric tube scanner, an achromatic micro-lenses assembly and a specifically designed Kagomé double-clad fiber. With this system we were able to image biological tissues, in endoscope modality, activating different contrasts such as TPEF, SHG and CARS, at the distal end of the fiber, a result which finds no equal in current literature. The integration in a portable probe (4.2 mm in diameter) shows the potential of this system for future in-vivo multimodal endoscopy

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Williams, Ceili. « Structure/property relationships in a polymorphic nonlinear optical crystal ». Thesis, University of Oxford, 1992. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.314895.

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Hui, Pui Chuen. « Optomechanics and nonlinear mechanics of suspended photonic crystal membranes ». Thesis, Harvard University, 2014. http://nrs.harvard.edu/urn-3:HUL.InstRepos:13068536.

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The recent demonstration of strong interactions between optical force and mechanical motion of an optomechanical structure has led to the triumphant result of mechanical ground-state cooling, where the quantum nature of a macroscopic object is revealed. Another intriguing demonstration of quantum physics on a macroscopic level is the measurement of the Casimir force which is a manifestation of the zero- point energy. An interesting aspect of the Casimir effect is that the anharmonicity of the Casimir potential becomes significant when the separation of microscale objects is in the sub-100nm regime. This regime is readily accessible by many of the realized gradient-force-based optomechanical structures. Hence, a new avenue of probing the Casimir effect on-chip all-optically has become available. We propose an integrated optomechanical platform, consisting of a suspended photonic crystal membrane evanescently coupled with a silicon-on-insulator substrate, for (i) measuring the Casimir force gradient and (ii) counteracting the attractive force by exerting a resonantly enhanced repulsive optical gradient force. This thesis first presents the full characterization of the optomechanical properties of the system in vacuo. The interplay of the optical gradient force (optomechanical coupling strength \(g_{om}/2\pi=- 66GHz/nm\)) and the photothermal force manifested in the optical spring effect and dynamic backaction is elucidated. Static displacement by the repulsive force of 1nm/mW is also demonstrated. In the second part of the thesis, the nonlinear mechanical signatures upon a strong coherent drive are reported. By resonantly driving the photonic crystal membrane with a piezo-actuator and an optical gradient force, we observed mechanical frequency mixing, mechanical bistability and non-trivial interactions of the Brownian peak with the driving signal. Finally we present our recent progress in establishing electro- static control of individual photonic crystal membranes to reduce and calibrate the electrostatic artifact which plagues Casimir measurements. The results discussed in this thesis point towards an auspicious future of a complete realization of a Casimir optomechanical structure and novel applications with nonlinearity afforded by the Casimir force and the optical gradient force.
Engineering and Applied Sciences

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Ortigosa, Blanch Arturo. « Highly birefringent photonic crystal fibres : linear and nonlinear effects ». Thesis, University of Bath, 2002. https://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.760818.

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Wall-Clarke, Alex D. « Nonlinear effects in the Josephson-vortex terahertz photonic crystal ». Thesis, Loughborough University, 2013. https://dspace.lboro.ac.uk/2134/13222.

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Analysis has been made of the amplitudes of the second and third harmonics when pumping a discrete frequency to the Josephson-vortex photonic crystal within the THz range of the electromagnetic spectrum. The results of numerical simulations show that there are certain resonance frequencies for these harmonics where the amplitudes are strongly enhanced. The frequencies at which these resonances occur can be tuned by an applied magnetic field and tilting the material with respect to the incident radiation. For the second harmonic it has been possible to describe these resonances analytically with a resonance approximation which displays good agreement with numerical simulations at and near the resonances. A similar perturbative method has been used to simulate the nonlinear mixing of two discrete THz frequencies in the JV photonic crystal, producing resonances for harmonics at the sum and the difference of these two input frequencies. This method can allow a high degree of control over the harmonic frequencies produced.

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Travers, John Colins. « Controlling nonlinear optics with dispersion in photonic crystal fibres ». Thesis, Imperial College London, 2008. http://hdl.handle.net/10044/1/1362.

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Nonlinear optics enables the manipulation of the spectral and temporal features of light. We used the tailorable guidance properties of photonic crystal fibres to control and enhance nonlinear processeswith the aim of improving nonlinearity based optical sources. We utilised modern, high power, Ytterbium fibre lasers to pump either single photonic crystal fibres or a cascade of fibres with differing properties. Further extension of our control was realised with specifically tapered photonic crystal fibres which allowed for a continuous change in the fibre characteristics along their length. The majority of our work was concerned with supercontinuum generation. For continuous wave pumping we developed a statistical model of the distribution of soliton energies arising from modulational instability and used it to understand the optimum dispersion for efficient continuum expansion. A two-fold increase in spectral width was demonstrated, along with studies of the noise properties and pump bandwidth dependence of the continuum. For picosecond pumping we found that the supercontinuum bandwidth was limited by the four wave mixing phase-matching available in a single fibre. A technique to overcome this by using a cascade of fibres with different dispersion profiles was developed. Further improvement was achieved by using novel tapered PCFs to continuously extend the phase-matching. Analysis of this case showed that a key role was played by soliton trapping of dispersive waves and that our tapers strongly enhanced this effect. We demonstrated supercontinua spanning 0.34-2.4 ¹mwith an unprecedented spectral power; up to 5 mW/nm. The use of long, dispersion decreasing photonic crystal fibres enabled us to demonstrate adiabatic soliton compression at 1.06 ¹m. From a survey of fibre structures we found that working around the second zero dispersion wavelength was optimal as this allows for decreasing dispersion without decreasing the nonlinearity. We achieved compression ratios of over 15.

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VALERA, ROBLES JESUS DANIEL. « NONLINEAR GUIDED WAVES AND NONLINEAR PRISM COUPLING IN THIN FILM WAVEGUIDES WITH LIQUID-CRYSTAL CLADDING ». Diss., The University of Arizona, 1986. http://hdl.handle.net/10150/183891.

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The rigorous descriptions of linear and nonlinear guided wave theory are given together with a geometrical description that helps in the understanding of the physical phenomena taking place. The nonlinear waveguide discussed in this dissertation is composed of a linear thin film and substrate with a cladding material whose refractive index varies with the intensity of the light. Experimentally, this was accomplished, by placing an oriented liquid crystal (highly nonlinear but extremely slow) on top of a thin film glass waveguide. When the liquid crystal used was K15, light-induced mode cutoff was observed. The TE(,0) mode became leaky as the guided wave power was increased. This was a consequence of the light-induced increase in refractive index due to thermal effects. This behaviour was studied as a function of temperature. Light by light modulation was also accomplished with this setup. The theory of the linear and nonlinear prism coupler and the first experimental investigations on the nonlinear prism coupler are given. The nonlinear prism coupler used was obtained by depositing a small amount of MBBA liquid crystal in the gap beween the input coupling prism and the thin film. The basic properties of the nonlinear prism coupler were demonstrated experimentally and the results obtained were verified to have their origin in the temperature component of the nonlinear index of refraction. Good qualitative agreement between the theory developed and experiments were obtained. Bistability and switching in a thin film waveguide with a K18 liquid crystal cladding has been demonstrated for the first time. These experiments made use of the interesting phenomena associated with the nematic to isotropic phase transition. Such behaviour was satisfactorily explained by the intense light scattering associated with the critical opalescence that accompanies such a phase transition in a liquid crystal. Both the TE(,0) and the TM(,0) modes were found to exhibit such behaviour.

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Zheng, Juanjuan. « Design and fabrication of photonic crystal fibers for nonlinear microscopy / ». View abstract or full-text, 2008. http://library.ust.hk/cgi/db/thesis.pl?ECED%202008%20ZHENG.

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Brunstein, Maia. « Nonlinear Dynamics in III-V Semiconductor Photonic Crystal Nano-cavities ». Phd thesis, Université Paris Sud - Paris XI, 2011. http://tel.archives-ouvertes.fr/tel-00606315.

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L'optique non linéaire traite les modifications des propriétés optiques d'un matériau induites par la propagation de la lumière. Depuis ses débuts, il y a cinquante ans, des nombreuses applications ont été démontrées dans presque tous les domaines de la science. Dans le domaine de la micro et nano-photonique, les phénomènes non linéaires sont à la fois au cœur d'une physique fondamentale fascinante et des applications intéressantes: ils permettent d'adapter et de contrôler le flux de lumière à une échelle spatiale inferieure à la longueur d'onde. En effet, les effets non linéaires peuvent être amplifiés dans des systèmes qui confinent la lumière dans des espaces restreints et avec de faibles pertes optiques. Des bons candidats pour ce confinement sont les nanocavités à cristaux photoniques (CPs), qui ont été largement étudiées ces dernières années. Parmi la grande diversité des processus non linéaires en optique, les phénomènes dynamiques tels que la bistabilité et l'excitabilité font l'objet de nombreuses études. La bistabilité est bien connue pour ces applications potentielles pour les mémoires et les commutateurs optiques et pour les portes logiques. Une réponse excitable typique est celle subjacente dans le déclanchement du potentiel d'action dans les neurones. En optique, l'excitabilité a été observée il y a une quinzaine d'années. Dans ce travail, nous avons étudié les régimes bistables, auto-oscillants et excitables dans des nanocavités semiconductrices III-V à CP. Afin de coupler efficacement la lumière dans les nanocavités, nous avons développé une technique de couplage par onde évanescente en utilisant une microfibre optique étirée. Grâce à cette technique, nous avons démontré pour la première fois l'excitabilité dans une nanocavité à CP. En parallèle, nous avons accompli la première étape vers la dynamique non linéaire dans un réseau de cavités couplées en démontrant le couplage optique linéaire entre nanocavitités adjacentes. Ceci a été réalisé en utilisant de mesures de photoluminescence en champ lointain. Un ensemble de résonateurs non linéaires couplés ouvre la voie à une famille de phénomènes dynamiques non linéaires très riches, basés sur la rupture spontanée de symétrie. Nous avons démontré théoriquement ce phénomène dans deux cavités couplées par onde évanescente. Les premières études expérimentales de ce régime ont été menées, établissant ainsi les bases pour une future démonstration de la rupture spontanée de symétrie dans un réseau de nanocavités non linéaires couplées.

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Khan, Md Kaisar. « NUMERICAL MODELING OF WAVE PROPAGATION IN NONLINEAR PHOTONIC CRYSTAL FIBER ». Doctoral diss., University of Central Florida, 2008. http://digital.library.ucf.edu/cdm/ref/collection/ETD/id/4096.

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In this dissertation, we propose numerical techniques to explain physical phenomenon of nonlinear photonic crystal fiber (PCF). We explain novel physical effects occurred in PCF subjected to very short duration pulses including soliton. To overcome the limitations in the analytical formulation for PCF, an accurate and efficient numerical analysis is required to explain both linear and nonlinear physical characteristics. A vector finite element based model was developed to precisely synthesize the guided modes in order to evaluate coupling coefficients, nonlinear coefficient and higher order dispersions of PCFs. This finite element model (FEM) is capable of evaluating coupling length of directional coupler implemented in dual core PCF, which was supported by existing experimental results. We used the parameters extracted from FEM in higher order coupled nonlinear Schrödinger equation (HCNLSE) to model short duration pulses including soliton propagation through the PCF. Split-step Fourier Method (SSFM) was used to solve HCNLSE. Recently, reported experimental work reveals that the dual core PCF behaves like a nonlinear switch and also it initiates continuum generation which could be used as a broadband source for wavelength division multiplexing (WDM). These physical effects could not be explained by the existing analytical formulae such as the one used for the regular fiber. In PCF the electromagnetic wave encounters periodic changes of material that demand a numerical solution in both linear and nonlinear domain for better accuracy. Our numerical approach is capable of explaining switching and some of the spectral features found in the experiment with much higher degree of design freedom. Numerical results can also be used to further guide experiments and theoretical modeling.
Ph.D.
School of Electrical Engineering and Computer Science
Engineering and Computer Science
Electrical Engineering PhD

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Stone, James. « Photonic crystal fibres and their applications in the nonlinear regime ». Thesis, University of Bath, 2009. https://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.503388.

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This thesis presents several advances in the technology and applications of photonic crystal fibres achieved over the last three years. Chapters 1 and 2 give the background material important to understand the results presented in chapters 3, 4 and 5. In chapter 1, linear properties of optical fibres are described. This chapter focuses particularly on how the engineering of the cladding structure of solid core photonic crystal fibres can be used to vary the fibre properties, most importantly the group index and dispersion. Propagation in all-solid photonic bandgap fibres is also discussed in terms of the anti-resonant reflecting optical waveguide model. Chapter 2 introduces the nonlinear optical effects that are important to understand the work presented in chapters 4 and 5. In chapter 3, a method to reduce bend losses in all-solid photonic bandgap fibres is outlined. The reduction of these losses is achieved by redesigning the high-index inclusions in the cladding structure to suppress cladding modes that strongly couple to the fundamental core-guided mode when the fibre is bent. In chapter 4, a method of tapering photonic crystal fibres in order to decrease the dispersion along their length is described. The tapers are used to compress solitons via adiabatic soliton compression and a combination of adiabatic soliton compression and soliton effect compression, achieving a factor of 15 compression of a transform-limited pulse to below 50 fs. Chapter 5 describes how engineering the cladding structure of photonic crystal fibres can be used to generate shorter frequencies in supercontinuum generation. The method by which this achieved is experimentally verified and then exploited to generate a continuum incorporating the entire visible spectrum using low cost, low maintenance pump sources.

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Jiang, Rui. « Parametric band translation using highly-nonlinear and photonic crystal fibers ». Diss., Connect to a 24 p. preview or request complete full text in PDF format. Access restricted to UC campuses, 2008. http://wwwlib.umi.com/cr/ucsd/fullcit?p3330316.

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Thesis (Ph. D.)--University of California, San Diego, 2008.
Title from first page of PDF file (viewed November 17, 2008). Available via ProQuest Digital Dissertations. Vita. Includes bibliographical references (p. 234-247).

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Ghafari, Banaee Mohamadreza. « Classical and quantum nonlinear optics in confined photonic structures ». Thesis, University of British Columbia, 2007. http://hdl.handle.net/2429/406.

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Nonlinear optical phenomena associated with high-order soliton breakup in photonic crystal fibres and squeezed state generation in three dimensional photonic crystal microcavities are investigated. In both cases, the properties of periodically patterned, high-index contrast dielectric structures are engineered to control the dispersion and local field enhancements of the electromagnetic field. Ultra-short pulse propagation in a polarization-maintaining microstructured fibre (with 1 um core diameter and 1.1 m length) is investigated experimentally and theoretically. For an 80 MHz train of 130 fs pulses with average propagating powers in the fibre up to 13.8 mW, the output spectra consist of multiple discrete solitons that shift continuously to lower energies as they propagate in the lowest transverse mode of the fibre. The number of solitons and the amount that they shift both increase with the launched power. All of the data is quantitatively consistent with solutions of the nonlinear Schrodinger equation, but only when the Raman nonlinearity is treated without approximation, and self-steepening is included. The feasibility of using a parametric down-conversion process to generate squeezed electromagnetic states in 3D photonic crystal microcavity structures is investigated for the first time. The spectrum of the squeezed light is theoretically calculated by using an open cavity quantum mechanical formalism. The cavity communicates with two main channels, which model vertical radiation losses and coupling into a single-mode waveguide respectively. The amount of squeezing is determined by the correlation functions relating the field quadratures of light coupled into the waveguide. All of the relevant model parameters are realistically estimated using 3D finite-difference time-domain (FDTD) simulations. Squeezing up to ~20% below the shot noise level is predicted for reasonable optical excitation levels. To preserve the squeezed nature of the light generated in the microcavity, a unidirectional coupling geometry from the microcavity to a ridge waveguide in a slab photonic crystal structure is studied. The structure was successfully fabricated in a silicon membrane, and experimental measurements of the efficiency for the signal coupled out of the structure are in good agreement with the result of FDTD simulations. The coupling efficiency of the cavity mode to the output channel is ~60%.

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Грідякіна, Олександра Валеріївна, et Аркадій Петрович Поліщук. « Nonlinear-optical recording in ionic liquid crystalline medium ». Thesis, Physikzentrum in Bad Honnef, 2017. http://er.nau.edu.ua/handle/NAU/32390.

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Spurny, Marcel. « Photonic crystal waveguides in chalcogenide glasses ». Thesis, University of St Andrews, 2011. http://hdl.handle.net/10023/2111.

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The growing speed and bandwidth requirements of telecommunication systems demand all-optical on-chip solutions. Microphotonic devices can deliver low power nonlinear signal processing solutions. This thesis looks at the slow light photonic crystals in chalcogenide glasses to enhance low power nonlinear operation. I demonstrate the development of new fabrication techniques for this delicate class of materials. Both, reactive ion etching and chemically assisted ion beam etching are investigated for high quality photonic crystal fabrication. A new resist-removal technique was developed for the chemical, mechanical and light sensitive thin films. I have developed a membraning method based on vapor phase etching in combination with the development of a save and economical etching tool that can be used for a variety of vapour phase processes. Dispersion engineered slow light photonic crystals in Ge₃₃As₁₂Se₅₅ are designed and fabricated. The demonstration of low losses down to 21±8dB/cm is a prerequisite for the successful demonstration of dispersion engineered slow light waveguides up to a group index of around n[subscript(g)] ≈ 40. The slow light waveguides are used to demonstrate highly efficient third harmonic generation and the first advantages of a pure chalcogenide system over the commonly used silicon. Ge₁₁.₅As₂₄24Se₆₄.₅ is used for the fabrication of photonic crystal cavities. Quality factors of up to 13000 are demonstrated. The low nonlinear losses have enabled the demonstration of second and third harmonic generation in those cavities with powers up to twice as high as possible in silicon. A computationally efficient model for designing coupled resonator bandpass filters is used to design bandpass filters. Single ring resonators are fabricated using a novel method to define the circular shape of the rings to improve the fabrication quality. The spectral responses of the ring resonators are used to determine the coupling coefficient needed for the design and fabrication of the bandpass filters. A flat top bandpass filter is fabricated and characterized as demonstration of this method. A passive all-optical regenerator is proposed, by integrating a slow-light photonic crystal waveguide with a band-pass filter based on coupled ring resonators. A route of designing the regenerator is proposed by first using the dispersion engineering results for nonlinear pulse propagation and then using the filter responses to calculate the nonlinear transfer function.

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Lazo-Martinez, Israel Esteban. « Liquid Crystal Enabled Electrokinetic Phenomena ». Kent State University / OhioLINK, 2014. http://rave.ohiolink.edu/etdc/view?acc_num=kent1397725003.

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Zhang, Yuji. « Coherence properties of supercontinuum generated in highly nonlinear photonic crystal fibers ». Thesis, Tufts University, 2015. http://pqdtopen.proquest.com/#viewpdf?dispub=3684584.

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In this dissertation, experimentally measured spectral and coherence evolution of supercontinuum (SC) is presented. Highly nonlinear soft-glass photonic crystal fibers (PCF) were used for SC generation, including lead-silicate (Schott SF6) PCFs of a few different lengths: 10.5 cm, 4.7 mm, and 3.9 mm, and a tellurite PCF of 2.7 cm. The pump is an optical parametric oscillator (OPO) at 1550 nm with pulse energy in the order of nanojoule (nJ) and pulse duration of 105 femtosecond (fs). The coherence of SC was measured using the delayed-pulse method, where the interferometric signal was sent into an optical spectrum analyzer (OSA) and spectral fringes were recorded. By tuning the pump power, power-dependent evolution of spectrum and coherence was obtained. Numerical simulations based on the generalized nonlinear Schrodinger equation (GNLSE) were performed. To match the measured data, the simulated spectral evolution was optimized by iteratively tuning parameters and comparing features. To further match the simulated coherence evolution with the measurement, shot noise and pulse-to-pulse power fluctuation were added in the pump, and the standard deviation of the fluctuation was tuned. Good agreement was obtained between the simulated and the measured spectral evolution, in spite of the unavailability of some physical parameters for simulation. It is demonstrated in principle that, given a measured spectral evolution, the fiber length, and the average power of SC, all other parameters can be determined unambiguously, and the spectral evolution can be reproduced in the simulations. Most importantly, the soliton fission length can be simulated accurately. The spectral evolution using the 4.7- and the 3.9-mm SF6 PCFs shows a pattern dominated by self phase modulation (SPM). This indicates that, these fiber lengths are close to the soliton fission length at the maximum power. The spectral evolution using the 10.5-cm SF6 PCF and the 2.7-cm tellurite PCF shows a soliton-fission-dominated pattern, indicating these lengths are much longer than the soliton fission length at the maximum power. For the coherence evolution using the SF6 PCFs, the simulations and the measurements show qualitative agreement, confirming the association between coherence degradation and soliton fission. For the case of the tellurite PCF, nearly quantitative agreement is shown, and it is shown that the solitonic coherence degrades slower than the overall coherence. Fluctuation of coherence occurs at the regime where the coherence starts to degrade, in the measurement and the simulations of the SF6-PCF case. It is shown that the cause is the pulse-to-pulse power fluctuation in the pump. The pulse-to-pulse stability of spectral intensity is another characterization of SC stability, other than the coherence. It is shown by simulations that these two exhibit different dynamics, and have low correlation.

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Fu, Ling, et n/a. « Fibre-optic nonlinear optical microscopy and endoscopy ». Swinburne University of Technology, 2007. http://adt.lib.swin.edu.au./public/adt-VSWT20070521.155004.

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Cancer is a major health problem in the world today. Almost all cancers have a significantly better chance for therapy and recovery if detected at their early stage. The capability to perform disease diagnosis at an early stage requires high-resolution imaging that can visualise the physiological and morphological changes at a cellular level. However, resolving powers of current medical imaging systems are limited to sub-millimeter sizes. Furthermore, the majority of cancers are associated with morphological and functional alterations of cells in epithelial tissue, currently assessed by invasive and time-consuming biopsy. Optical imaging enables visualisations of tissue microstructures at the level of histology in non-invasive means. Optical imaging is suitable for detecting neoplastic changes with sub-cellular resolution in vivo without the need for biopsy. Nonlinear optical microscopy based on multi-photon absorption and higher harmonic generation has provided spectacular sights into visualisation of cellular events within live tissue due to advantages of an inherent sectioning ability, the relatively deep optical penetration, and the direct visualisation of intrinsic indicators. Two-photon excited uorescence (TPEF) from intrinsic cell components and second harmonic from asymmetric supermolecular structures can provide complementary information regarding functionalities and morphologies in tissue environments, thus enabling premalignant diagnosis by detecting the very earliest changes in cellular structures. During the past sixteen years, nonlinear optical microscopy has evolved from a photonic novelty to a well-established laboratory tool. At present, in vivo imaging and long-term bedside studies by use of nonlinear optical microscopy have been limited due to the fact that the lack of the compact nonlinear optical instrument/imaging technique forces the performance of nonlinear optical microscopy with bulk optics on the bench top. Rapid developments of fibre-optics components in terms of growing functionalities and decreasing sizes provide enormous opportunities for innovation in nonlinear optical microscopy. Fibre-based nonlinear optical endoscopy will be the soul instrumentation to permit the cellular imaging within hollow tissue tracts or solid organs that are inaccessible with a conventional optical microscope. Lots of efforts have been made for development of miniaturised nonlinear optical microscopy. However, there are major challenges remaining to create a nonlinear optical endoscope applicable within internal cavities of a body. First, an excitation laser beam with an ultrashort pulse width should be delivered eciently to a remote place where ecient collection of faint nonlinear optical signals from biological samples is required. Second, laser-scanning mechanisms adopted in such a miniaturised instrumentation should permit size reduction to a millimeter scale and enable fast scanning rates for monitoring biological processes. Finally, the design of a nonlinear optical endoscope based on micro-optics must maintain great exibility and compact size to be incorporated into endoscopes to image internal organs. Although there are obvious diculties, development of fibre-optic nonlinear optical microscopy/endoscopy would be indispensible to innovate conventional nonlinear optical microscopy, and therefore make a significant impact on medical diagnosis. The work conducted in this thesis demonstrates the new capability of nonlinear optical endoscopy based on a single-mode fibre (SMF) coupler or a double-clad photonic crystal fibre (PCF), a microelectromechanical system (MEMS) mirror, and a gradientindex (GRIN) lens. The feasibility of all-fibre nonlinear optical endoscopy is also demonstrated by the further integration of a double-clad PCF coupler. The thesis concentrates on the following key areas in order to exploit and understand the new imaging modality. It has been known from the previous studies that an SMF coupler is suitable for twoii photon excitation by transmitting near infrared illumination and collecting uorescence at visible wavelength as well. Although second harmonic generation (SHG) wavelength is farther away from the designed wavelength of the fibre coupler than that of normal TPEF, it is demonstrated in this thesis that both SHG and TPEF signals can be collected simultaneously and eciently through an SMF coupler with axial resolution of 1.8 um and 2.1 um, respectively. The fibre coupler shows a unique feature of linear polarisation preservation along the birefringent axis over the near infrared and the visible wavelength regions. Therefore, SHG polarisation anisotropy can be potentially extracted for probing the orientation of structural proteins in tissue. Furthermore, this thesis shows the characterisation of nonlinear optical microscopy based on the separation distance of an SMF coupler and a GRIN lens. Consequently, the collection of nonlinear signals has been optimised after the investigation of the intrinsic trade-off between signal level and axial resolution. These phenomena have been theoretically explored in this thesis through formalisation and numerical analysis of the three-dimensional (3D) coherent transfer function for a SHG microscope based on an SMF coupler. It has been discovered that a fibreoptic SHG microscope exhibits the same spatial frequency passband as that of a fibreoptic reection-mode non-uorescence microscope. When the numerical aperture of the fibre is much larger than the convergent angle of the illumination on the fibre aperture, the performance of fibre-optic SHG microscopy behaves as confocal SHG microscopy. Furthermore, it has been shown in both analysis and experiments that axial resolution in fibre-optic SHG microscopy is dependent on the normalised fibre spot size parameters. For a given illumination wavelength, axial resolution has an improvement of approximately 7% compared with TPEF microscopy using an SMF coupler. Although an SMF enables the delivery of a high quality laser beam and an enhanced sectioning capability, the low numerical aperture and the finite core size of an SMF give rise to a restricted sensitivity of a nonlinear optical microscope system. The key innovation demonstrated in this thesis is a significant signal enhancement of a nonlinear optical endoscope by use of a double-clad PCF. This thesis has characterised properties of our custom-designed double-clad PCF in order to construct a 3D nonlinear optical microscope. It has been shown that both the TPEF and SHG signal levels in a PCF-based system that has an optical sectioning property for 3D imaging can be significantly improved by two orders of magnitude in comparison with those in an SMF-based microscope. Furthermore, in contrast with the system using an SMF, simultaneous optimisations of axial resolution and signal level can be obtained by use of double-clad PCFs. More importantly, using a MEMS mirror as the scanning unit and a GRIN lens to produce a fast scanning focal spot, the concept of nonlinear optical endoscopy based on a double-clad PCF, a MEMS mirror and a GRIN lens has been experimentally demonstrated. The ability of the nonlinear optical endoscope to perform high-resolution 3D imaging in deep tissue has also been shown. A novel three-port double-clad PCF coupler has been developed in this thesis to achieve self-alignment and further replace bulk optics for an all-fibre endoscopic system. The double-clad PCF coupler exhibits the property of splitting the laser power as well as the separation of a near infrared single-mode beam from a visible multimode beam, showing advantages for compact nonlinear optical microscopy that cannot be achieved from an SMF coupler. A compact nonlinear optical microscope based on the doubleclad PCF coupler has been constructed in conjunction with a GRIN lens, demonstrating high-resolution 3D TPEF and SHG images with the axial resolution of approximately 10 m. Such a PCF coupler can be useful not only for a fibre-optic nonlinear optical probe but also for double-clad fibre lasers and amplifiers. The work presented in this thesis has led to the possibility of a new imaging device to complement current non-invasive imaging techniques and optical biopsy for cancer detection if an ultrashort-pulsed fibre laser is integrated and the commercialisation of the system is achieved. This technology will enable in vivo visualisations of functional and morphological changes of tissue at the microscopic level rather than direct observations with a traditional instrument at the macroscopic level. One can anticipate the progress in bre-optic nonlinear optical imaging that will propel imaging applications that require both miniaturisation and great functionality.

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Husakou, Anton. « Nonlinear phenomena of ultrabroadband radiation in photonic crystal fibers and hollow waveguides ». [S.l. : s.n.], 2002. http://www.diss.fu-berlin.de/2002/246/index.html.

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Chowdhury, Avishek. « Mechanical nonlinear dynamics of a suspended photonic crystal membrane with integrated actuation ». Thesis, Université Paris-Saclay (ComUE), 2016. http://www.theses.fr/2016SACLS284/document.

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Les nonlinéarités dans les systèmes nanomécaniques peuvent provenir d’effets dispersif ou dissipatif et ce dans divers systèmes (résistifs, inductifs et capacitifs). Au-delà de l’intérêt fondamental pour tester la réponse dynamique d’un système non-linéaire à plusieurs dégrées de libertés, les nonlinéarités de tels systèmes ouvre la voie vers des capteurs nanomécanique et le traitement du signal. Le résonateur nanomécanique dont la réponse nonlinéaire est étudié, est une membrane suspendue à cristal photonique bidimensionnel utilisée comme miroir déformable. Sa faible masse et sa haute réflectivité en font un candidat idéal pour l’électro-opto-mécanique. L’actuation d’une telle membrane dans le domaine fréquentiel du MHz est rendu possible par des électrodes inter-digitées en dessous de la membrane assurant ainsi l’uniformité de la force d’actuation sur cette dernière. La fabrication de telles structures est basée sur l’intégration hétérogène 3D.La force électrostatique qui s’applique sur la membrane induit des non-linéarités mécaniques avec notamment un effet bistable, des résonances superharmoniques et des résonances stochastiques.La membrane est mise en mouvement par un potentiel électrique V(t) = Vdc + Vac cos(w.t), où Vdc est l’amplitude du courant continu, Vac l’amplitude du courant alternatif à la fréquence d’excitation w;. Le système se comporte alors comme une capacité de sorte que la force qui s’applique sur la membrane varie de manière quadratique avec la tension appliquée. Selon la tension DC ou AC, le comportement de la structure est différent. L’augmentation de la tension DC induit une augmentation de la tension de polarisation sur le matériau qui par conséquent modifie la fréquence propre de la membrane. Tandis que l’augmentation de la tension AC cause l’augmentation de l’amplitude des oscillations de la membrane pouvant aller jusqu’à atteindre le régime non-linéaire.Dans une première série de mesure, la membrane est excitée à la résonance avec une fréquence w; égale à la fréquence du mode mécanique fondamental wm. A partir de la réponse fréquentielle du système, il est possible d’identifier différents modes mécaniques de la membrane sondé optiquement. Pour une excitation plus importante, il est possible d’observer des effets de bistabilité mécanique. Ces non-linéarités sont dues à l’élongation au niveau des points d’ancrage de la membrane.La méthode la plus commune pour agir sur la membrane est l’excitation proche de la résonance fondamentale. Cependant la technique de la résonance superharmonique peut également être utilisée. Cela consiste à appliquer la fréquence d’excitation w; à une fréquence égale à wm/n où n est un entier. La possibilité d’utiliser cette technique est fortement dépendante des nonlinéarités présentes dans le système. Ainsi, l’existence d’une résonance super harmonique à wm/n résulte de la présence d’une nonlinéarité d’ordre n. Dans une seconde série de mesure, un balayage des résonances superharmoniques en fonction de la fréquence et de la puissance a été réalisé en modulant la tension à la fréquence wm/n et en enregistrant la réponse de la membrane autour de wm. Il a été ainsi possible d’observer des résonances superharmoniques allant de n=2 jusqu’à 8. Il a également été possible d’obtenir l’évolution de la phase le long des résonances et ce pour toutes celles observées.Dans une dernière série de mesure, nous utilisons la nonlinéarité présente pour observer des effets de résonance stochastique. L’idée est d’amplifier un signal de faible amplitude (basse fréquence) en injectant du bruit (haute fréquence) dans le système nonlinéaire. Dans le cas de notre système, nous avons été capables d’observer des résonances stochastiques à la fois en amplitude et en phase. Une étude comparative de ces deux régimes est détaillée. Le fait de pouvoir observer la résonance stochastique en phase peut permettre d’envisager la réalisation de communications codées en phase
Nonlinearities in nanomechanical systems can arise from various sources such as spring and damping mechanisms and resistive, inductive, and capacitive circuit elements. Beyond fundamental interests for testing the dynamical response of discrete nonlinear systems with many degrees of freedom, non-linearities in nanomechanical devices, open new routes for nanomechanical sensing, and signal processing.The nonlinear response of a nanomechanical resonator consisting in a suspended photonic crystal membrane acting as a deformable mirror has been investigated. The low-mass and high reflectivity of suspended membranes pierced by a two-dimensional photonic crystal, makes them good candidates as electro-optomechanical resonator. Actuation of the membrane motion in the MHz frequency range is achieved via interdigitated electrodes placed underneath the membrane. The choice of these electrodes is due to the fact they are able to uniformly actuate these membranes. The processing of such platforms relies on 3D-heterogenous integration process.The applied electrostatic force induces mechanical non-linearities, in particular bistability, superharmonic resonances and stochastic resonance.The membrane is actuated by an electric load V(t) = Vdc + Vac cos(w.t), where Vdc is the DC polarization voltage, Vac the amplitude of the applied AC voltage, and w; the excitation frequency. The system acts as a capacitive system and thus the force applied on the membrane varies as a quadratic function of the applied voltage. Application of either DC or AC voltages can have different implications. Increasing the DC voltage increases the polarizing voltage on the material which in turn causes modulation of the eigenfrequency of the membranes. While an increase in the periodic AC voltage causes the membrane to oscillate more, pushing the system towards non-linear regime.In a first series of experiments, the membrane is actuated resonantly, with an excitation frequency w; equal to the fundamental mechanical modes frequency wm. From the frequency response spectra of the system it was possible to identify different mechanical modes of these membranes via optical measurements. For increased actuation voltages, bistability effects are observed with two different behaviors (spring hardening or softening). The mechanical nonlinearities due to stretching at the clamping point dominate the resonator dynamics.The most commonly used method to act upon the membrane is the primary-resonance excitation, in which the frequency of the excitation is tuned closed to the fundamental natural frequency of the nanostructure. Superharmonic resonance can also be implemented. It consists in applying an excitation frequency w; equal to wm/n, with n being integer. Existence of these superharmonic resonances is highly dependent on the non-linearity of the system. For example existence of n-th order non-linearity results in presence wm/n superharmonic resonance. In a second series of experiments, frequency-power sweep for superharmonic resonance has been performed, by modulating the electric load at a frequency wm/n and recording the response of the membrane at the fundamental frequency wm. High-order superharmonic resonances are observed with n=2 up to 8. Under superharmonic excitation, the control of the phase across the resonance has been shown for every observed resonance.In the next set of experiments, we used the nonlinearity existing in the system to perform stochastic resonance. The idea of stochastic resonance is amplification of a weak signal (with low frequency) by means of noise injected (higher frequency) in a nonlinear system. For our system we were able to achieve stochastic resonance with both amplitude and phase noise. A comparative study between these two schemes was also done in details. The idea of observing stochastic resonance in phase is very interesting as it opens doors to realize phase encoded communications

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Pevnyi, Mykhailo Y. « Induced shape changes in liquid crystal elastomers ». Kent State University / OhioLINK, 2015. http://rave.ohiolink.edu/etdc/view?acc_num=kent1437989598.

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MacNeil, John Michael Larratt. « Solitary waves in focussing and defocussing nonlinear, nonlocal optical media ». Thesis, University of Edinburgh, 2016. http://hdl.handle.net/1842/20951.

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Nonlinear, nonlocal optical media has emerged as an ideal setting for experimentally observing and studying spatial optical solitary waves which otherwise cannot occur in Kerr media. Of particular interest is the eventual application to all-optical circuits. However, there is considerable work left to do on the theoretical end before this is a possibility. In this thesis we consider three problems. The first is how to solve the governing equations for optical beam propagation in the particular medium of the nematic liquid crystal (NLC), which is used as a prototypical example, exactly and approximately. In this respect we provide the first known, explicit solutions to the model as well as a comprehensive assessment on how to use variational, or modulation theory, in this context. This leads to the discovery of a novel form of bistability in the system, which shows there are two stable solitary wave solutions for a fixed power or L2 norm. We then consider how to approximate solutions for optical solitary waves propagating in a more general class of nonlocal nonlinear media using asymptotic methods. This is a long open problem and is resolved in the form of a simple to implement method with excellent accuracy and general applicability to previously intractable models. We conclude with the discovery and characterization of an instability mechanism in a coupled, defocussing nonlinear Schrodinger system. We show there is no stable, coupled, localized solution. This result is compared with the more well-studied bright solitary wave system and physical and mathematical explanations are offered.

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Бордюг, Ганна Борисівна, et Аркадій Петрович Поліщук. « Fast photoconversion in viologen-doped lyotropic ionic liquid crystals ». Thesis, Physikzentrum in Bad Honnef, 2017. http://er.nau.edu.ua/handle/NAU/32391.

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Грідякіна, Олександра Валеріївна, et Ганна Борисівна Бордюг. « Nonlinear helical winding in highly viscous chiral thin films ». Thesis, NANO-2017, 2017. http://er.nau.edu.ua/handle/NAU/32389.

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Parreu, i. Alberich Isabel. « Crystal Growth and Characterization of ytterbium or neodymium doped type III-KGd(PO3)4. A new bifunctional nonlinear and laser crystal ». Doctoral thesis, Universitat Rovira i Virgili, 2006. http://hdl.handle.net/10803/9081.

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S'anomenen cristalls bifuncionals aquells que posseeixen simultàniament propietats d'òptica no lineal i propietats làser. Aquest tipus de materials són molt interessants ja que, combinant aquestes dues propietats, poden auto-generar radiació làser en la regió electromagnètica del blau (≈ 450 nm) o del verd (≈ 550 nm). Els materials làser d'estat sòlid que generen radiació làser en el rang electromagnètic visible (≈ 400-800 nm) tenen actualment un paper molt important en el desenvolupament tecnològic de dispositius làser i òptics en general ja que són interessants per un gran nombre d'aplicacions com són: l'emmagatzematge òptic d'informació d'alta densitat (HDVD, per exemple), reprografia, pantalles de color, medicina, biotecnologia, comunicacions submarines, comunicacions atmosfèriques transparents, etc.
Aquest tipus de fonts làser compactes emetent en el visible poden ésser desenvolupades utilitzant un cristall bifuncional. Aquests làsers auto-dobladors de freqüència tenen associades menys pèrdues (absorció, reflexió i dispersió) que làsers dobladors de freqüència intracavitat, que significa que el disseny del ressonador és més simple i compacte. Actualment, la recerca en aquest camp està centrada en el desenvolupament de nous materials no-centrosimètrics que presentin propietats d'òptica no-lineal i que puguin allotjar ions làser actius, majoritàriament ions lantànid. Els materials d'òptica no-lineal tenen la capacitat de generar el segon harmònic de la radiació, és a dir, de doblar la seva freqüència. Si un material d'òptica no-lineal conté un ió lantànid que generi radiació làser en la regió infraroja d'aproximadament =1000 nm, podrà auto-doblar-ne la freqüència, és a dir, reduir-ne a la meitat la longitud d'ona, =500 nm, que correspon a la regió electromagnètica del blau o el verd.
El fosfat doble de potassi i gadolini de tipus III, KGd(PO3)4 (KGP), que és objecte d'aquesta tesi doctoral, és un cristall d'estructura no-centrosimètrica i per tant amb el requisit estructural necessari per a posseir propietats d'òptica no-lineal. Es va plantejar l'objectiu de sintetitzar i caracteritzar aquest cristall i a més de substituir parcial o totalment l'ió gadolini per un ió lantànid actiu en la zona de 1000 nm, com són l'iterbi i el neodimi, per tal d'aconseguir desenvolupar un nou cristall auto-doblador de freqüència.
Així doncs, l'objectiu de la present tesi doctoral va ésser l'estudi del creixement cristal.lí del KGP i del KGP dopat amb iterbi o neodimi i la seva posterior caracterització. Com que el fosfats doble de potassi i lantànid fonen incongruentment, és a dir, que es descomponen abans de fondre, és necessari utilitzar un mètode de creixement cristal.lí a partir de solució a alta temperatura per créixer cristalls. Aquest mètodes permeten créixer a una temperatura per sota la temperatura de fusió del material, i per tant evitar-ne la seva descomposició. El mètode que nosaltres em utilitzat per créixer monocristalls de KGP pur i dopat és l'anomenat top seeded solution growth-slow cooling (TSSG-SC), que permet créixer els cristalls lliures en la solució disminuint lentament la seva temperatura a partir de la temperatura se cristal.lització. Això permet obtenir cristalls volúmics amb formes cristal.logràfiques desenvolupades lliurament i determinades a partir de l'estructura cristal.lina. Després d'optimitzar el procés de creixement, hem aconseguitr sintetitzar cristalls lliures de macrodefectes i d'una mida suficient pel seu estudi i possible posterior aplicació. Posteriorment, els cristalls han estat caracteritzats estructuralment, físicament, òpticament i espectroscòpicament.
Finalment, s'han realitzat experiències de laserat amb Yb:KGP, obtenint uns resultats força encoratjadors, ja que s'ha aconseguit generar radiació làser per primer cop en aquest cristall dopat amb iterbi amb un nivell de dopatge força baix.
Com a conclusió i després dels resultats de l'estudi, podem dir que els cristalls de Yb:KGP i Nd:KGP poden ésser considerats com a candidats prometedors per a ser aplicats com a cristalls auto-dobladors de freqüència ja que s'ha provat la seva capacitat tant de generar segon harmònic com de generar radiació làser.
Bifunctional crystals are those in which the nonlinear optical process and the laser effect occur simultaneously. This kind of materials is very promising for compact solid-state laser designs operating in the visible because solid-state lasers operate mainly in the infrared. So, the nonlinear and laser properties can combine to generate blue (≈ 450 nm) or green (≈550 nm) laser radiation by self-frequency doubling. Solid-state laser sources operating in the visible spectral region (≈400-800 nm) play an important role in laser technology they are potentially interesting for numerous applications such as high-density optical data storage, reprographics, colour displays, medicine, biotechnology, submarine communications, transparent atmosphere communications, etc.
Such compact laser sources can be managed from frequency conversion by nonlinear optical processes such as frequency doubling and sum-frequency mixing by using a bifunctional crystal. Such self-frequency doubling (SFD) lasers involve fewer losses (absorption, reflection and scattering) than the intracavity frequency doubling lasers, which means that resonator designs are simpler and more compact.
Currently, efforts are focussed on the development of new noncentrosymmetric crystals with nonlinear optical properties to be used as a host for active laser ions, and mostly lanthanide ions. Nonlinear optical materials are able to double the frequency of the laser emission generated by the active ion hosted in it. Nonlinear crystals with suitable sites for lanthanide ions which emit in the infrared region around 1 m may be able to self-double the frequency, i.e. to reduce the wavelength to the half, =500 nm, which is in the blue or green spectral region.
The aim of this doctoral thesis is to synthesize and characterize the type III double phosphate of potassium and gadolinium, KGd(PO3)4 (KGP), either undoped or doped ordoped with ytterbium or neodymium, both of them emitting in the 1 m region.

The KGP crystal is noncentrosymmetric, so with the indispensable requirement to have nonlinear optical properties. We propose to use this crystal as a nonlinear host for alternatively ytterbium (Yb3+) or neodymium (Nd3+) to develop a new promising selffrequency doubling laser crystal to generate blue-green laser radiation.
As double phosphates of potassium and lanthanide melt incongruently, i.e. they decompose before melting, a high-temperature solution growth method has to be used to growth the crystals. This kind of growth methods allows growing the crystal under its melting point and so avoiding its decomposition. We use the top seeded solution growth-slow cooling (TSSG-SC) to grow the undoped and Yb- or Nd-doped KGP single crystals. This kind of growth method allows to freely growing the crystals in the solution by slowly cooling its temperature from the crystallization temperature. It allows obtaining bulk crystals with freely developed crystallographic forms determined by the crystals structure. By optimizing the growth process, we have successfully grown macrodefect-free crystals large enough for later characterizations and possible final application. The crystals have been structurally, physically, optically and spectroscopically characterized. Finally, laser operation with Yb:KGP has been proved for the first time. Although the low ion doping level in the crystal, the rather high slope efficiency obtained with this first sample is rather promising for the future.
In conclusion, single crystals of Yb:KGP and Nd:KGP can be regarded as a promising candidates to be applied as a self-frequency doubling crystals since it has been proved both the second harmonic generation ability and the laser operation.

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Sarkissian, Hakob. « APPLICATIONS OF LINEAR AND NONLINEAR OPTICAL EFFECTS IN LIQUID CRYSTALS ». Doctoral diss., University of Central Florida, 2006. http://digital.library.ucf.edu/cdm/ref/collection/ETD/id/2603.

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Liquid crystals have been a major subject of research for the past decades. Aside from the variety of structures they can form, they exhibit a vast range of optical phenomena. Many of these phenomena found applications in technology and became an essential part of it. In this dissertation thesis we continue the line to propose a number of new applications of optical effects in liquid crystals and develop their theoretical framework. One such application is the possibility of beam combining using Orientational Stimulated Scattering in a nematic liquid crystal cell. Our numerical study of the OSS process shows that normally this possibility does not exist. However, we found that if a number of special conditions is satisfied efficient beam combining with OSS can be done. These conditions require a combination of special geometric arrangement of incident beams, their profiles, nematic material, and more. When these conditions are fulfilled, power of the beamlets can be coherently combined into a single beam, with high conversion efficiency while the shape and wave-front of the output beam are still of good quality. We also studied the dynamics of the OSS process itself and observed (in a numerical model) a number of notorious instabilities caused by effects of back-conversion iv process. Additionally, there was found a numerical solitary-wave solution associated with this back-conversion process. As a liquid crystal display application, we consider a nematic liquid crystal layer with the anisotropy axis modulated at a fixed rate in the transverse direction with respect to light propagation direction. If the layer locally constitutes a half-wave plate, then the thinscreen approximation predicts 100% -efficient diffraction of normal incident wave. If this diffracted light is blocked by an aperture only transmitting the zero-th order, the cell is in dark state. If now the periodic structure is washed out by applying voltage across the cell and light passes through the cell undiffracted, the light will pass through the aperture as well and the cell will be in its bright state. Such properties of this periodically aligned nematic layer suggest it as a candidate element in projection display cells. We studied the possibility to implement such layer through anchoring at both surfaces of the cell. It was found that each cell has a thickness threshold for which the periodic structure can exist. The anchored periodic structure cannot exist if thickness of the cell exceeds this threshold. For the case when the periodic structure exists, we found the structure distortion in comparison with the preferable ideal sinusoidal profile. To complete description of the electromechanical properties of the periodic cell, we studied its behavior at Freedericksz transition. Optical performance was successfully described with the coupled-mode theory. While influence of director distortion is shown to be negligibly small, the walk-off effects appear to be larger. In summary, there are good prospects for use of this periodically v aligned cell as a pixel in projection displays but experimental study and optimization need to be performed. In the next part we discuss another modulated liquid crystal structure in which the director periodically swings in the direction of light propagation. The main characteristic of such structure is the presence of bandgap. Cholesteric liquid crystals are known to possess bandgap for one of two circular polarizations of light. However, unlike the cholesterics the bandgap of the proposed structure is independent of polarization of normally incident light. This means that no preparation of light is needed in order for the structure to work in, for example, liquid crystal displays. The polarization universality comes at the cost of bandgap size, whose maximum possible value ∆ωPTN compared to that of cholesterics ∆ωCh is approximately twice smaller: ∆ωPTN ≈ 0.58∆ωCh if modulation profile is sinusoidal, and ∆ωPTN ≈ 0.64∆ωCh if it is rectangular. This structure has not yet been experimentally demonstrated, and we discuss possible ways to make it.
Ph.D.
Other
Optics and Photonics
Optics

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32

Webber, Kyle Grant. « Effect of Domain Wall Motion and Phase Transformations on Nonlinear Hysteretic Constitutive Behavior in Ferroelectric Materials ». Diss., Georgia Institute of Technology, 2008. http://hdl.handle.net/1853/22695.

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The primary focus of this research is to investigate the non-linear behavior of single crystal and polycrystalline relaxor ferroelectric PMN-xPT and PZN-xPT through experimentation and modeling. Characterization of single crystal and polycrystalline specimens with similar compositions was performed. These data give experimental insight into the differences that may arise in a polycrystal due to local interaction with inhomogeneities. Single crystal specimens were characterized with a novel experimental technique that reduced clamping effects at the boundary and gave repeatable results. The measured experimental data was used in conjunction with electromechanical characterizations of other compositions of single crystal specimens with the same crystallographic orientation to study the compositional effects on material properties and phase transition behavior. Experimental characterization provided the basis for the development of a model of the continuous phase transformation behavior seen in PMN-xPT single crystals. In the modeling it is assumed that a spatial chemical and structural heterogeneity is primarily responsible for the gradual phase transformation behavior observed in relaxor ferroelectric materials. The results are used to simulate the effects of combined electrical and mechanical loading. An improved rate-independent micromechanical constitutive model based on the experimental observations of single crystal and polycrystalline specimens under large field loading is also presented. This model accounts for the non-linear evolution of variant volume fractions. The micromechanical model was calibrated using single crystal data. Simulations of the electromechanical behavior of polycrystalline ferroelectric materials are presented. These results illustrate the effects of non-linear single crystal behavior on the macroscopic constitutive behavior of polycrystals.

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33

Sloanes, Trefor J. « Measurement and application of optical nonlinearities in indium phosphide, cadmium mercury telluride and photonic crystal fibres ». Thesis, University of St Andrews, 2009. http://hdl.handle.net/10023/723.

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The two-photon absorption (TPA) coefficient is measured in indium phosphide (InP) using femtosecond pulses to be 45cm/GW at 1.32μm. Nanosecond pulses are subsequently used to find the free-carrier refractive index cross-section, σ_r, and the free-carrier absorption coefficient, σ_fca. The quantity βσ_r is measured to be -113x10⁻²ºcm⁴/GW at 1.064μm and -84x10⁻²ºcm⁴/GW at 1.534μm. At 1.064μm, with β assumed to be 22cm/GW, the value suggested by theory, σ_r is -5.1x10⁻²ºcm³. Similarly, at 1.534μm, assuming β to be 20cm/GW gives a σ_r value of -4.1x10⁻²ºcm³. Due to refraction affecting the measurements of σ_fca, only an upper limit of 1x10⁻¹⁵cm² can be put on its value. The free-carrier experiments are repeated on two samples of cadmium mercury telluride (CMT) having bandgaps of 0.89eV and 0.82eV. For the first sample, β_σr is measured to be -148x10⁻²ºcm⁴/GW. Assuming β to be 89cm/GW gives a σ_r value of -1.7x10⁻²ºcm³ whilst σ_fca is found to be at most 3x10⁻¹⁵cm². Significant linear absorption occurs in the second sample which generates a large free-carrier population. It is shown that this significantly enhances the nonlinearities. Finally, the results of the work are tested by modelling a nonlinear transmission experiment, and the results found in this work give a closer fit to experimental results than the result of theory. Four-wave mixing (FWM) in a photonic crystal fibre is exploited to create a high output power optical parametric amplifier (OPA). To optimise the OPA conversion efficiency, the fibre length has to be increased to 150m, well beyond the walk-off distance between the pump and signal/idler. In this regime, the Raman process can take over from the FWM process and lead to supercontinuum generation. The OPA exhibits up to 40% conversion efficiency, with the idler (0.9μm) and the signal (1.3μm) having a combined output power of over 1.5W.

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Manktelow, Kevin Lee. « Dispersion analysis of nonlinear periodic structures ». Diss., Georgia Institute of Technology, 2013. http://hdl.handle.net/1853/51936.

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The present research is concerned with developing analysis methods for analyzing and exploring finite-amplitude elastic wave propagation through periodic media. Periodic arrangements of materials with high acoustic impedance contrasts can be employed to control wave propagation. These systems are often termed phononic crystals or metamaterials, depending on the specific design and purpose. Design of these systems usually relies on computation and analysis of dispersion band structures which contain information about wave propagation speed and direction. The location and influence of complete (and partial) band gaps is a particularly interesting characteristic. Wave propagation is prohibited for frequencies that correspond to band gaps; thus, periodic systems behave as filters, wave guides, and lenses at certain frequencies. Controlling these behaviors has typically been limited to the manufacturing stage or the application of external stimuli to distort material configurations. The inclusion of nonlinear elements in periodic unit cells offers an option for passive tuning of the dispersion band structure through amplitude-dependence. Hence, dispersion analysis methods which may be utilized in the design of nonlinear phononic crystals and metamaterials are required. The approach taken herein utilizes Bloch wave-based perturbation analysis methods for obtaining closed-form expressions for dispersion amplitude-dependence. The influence of material and geometric nonlinearities on the dispersion relationship is investigated. It is shown that dispersion shifts result from both self-action (monochromatic excitation) and wave-interaction (multi-frequency excitation), the latter enabling dynamic anisotropy in periodic media. A particularly novel aspect of this work is the ease with which band structures of discretized systems may be analyzed. This connection enables topology optimization of unit cells with nonlinear elements. Several important periodic systems are considered including monoatomic lattices, multilayer materials, and plane stress matrix-inclusion configurations. The analysis methods are further developed into a procedure which can be implemented numerically with existing finite-element analysis software for analyzing geometrically-complex materials.

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35

Suizu, Koji, Kodo Kawase et 晃道川瀬. « Monochromatic-Tunable Terahertz-Wave Sources Based on Nonlinear Frequency Conversion Using Lithium Niobate Crystal ». IEEE, 2008. http://hdl.handle.net/2237/11170.

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Vieweg, Marius [Verfasser], et Harald [Akademischer Betreuer] Giessen. « Nonlinear optics in selectively fluid-filled photonic crystal fibers / Marius Vieweg. Betreuer : Harald Giessen ». Stuttgart : Universitätsbibliothek der Universität Stuttgart, 2012. http://d-nb.info/1025256271/34.

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Alonso, Eva Vicente. « Nonlinear dynamics of a nematic liquid crystal in the presence of a shear flow ». Thesis, University of Southampton, 2000. https://eprints.soton.ac.uk/50628/.

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In this thesis we describe the complex array of behaviours of a homogeneous thermotropic nematic liquid crystal in the context of a Landau-de Gennes theory. There exist two parameters that control the behaviour of the system: the temperature and the shear rate, and by employing continuation and bifurcation theory we describe the different time dependent states for the two and three dimensional cases. For the two dimensional case we compute the steady state solution branches finding that the flow favours an in-plane nematic state at higher temperatures, while at lower temperatures it favours a nematic state with preferred direction of alignment perpendicular to the shear plane, the so-called log-rolling state. We have found excellent agreement between the numerical calculations and analytical results in the limit of very low and very large values of the shear rate. The existence of a Takens-Bogdanov bifurcation in the underlying bifurcation diagram organises the steady and the time dependent solutions in the state diagram. The periodic orbits can be either of the wagging type, at intermediate values of the shear rate or of the tumbling type at lower shear rates. We complete the analysis of the two dimensional case, by considering a general planar flow and studying the influences of strain and vorticity in the system. We provide a very detailed account of the behaviour of the liquid crystal in the three dimensional case, when the direction of alignment of the molecules that constitute the liquid crystal is allowed out of the shear plane. We establish that the only out-of-plane steady solution of the system is an anomalous continuum of equilibria, and therefore the Landau-de Gennes model that we are employing is structurally unstable. The time dependent solutions of the liquid crystal fall into one of the following categories: in plane periodic orbits, which are the tumbling and wagging solutions and out-of-plane periodic orbits, the so-called kayaking state. The use of bifurcation theory in the context of nematodynamics allows us to give a complete summary of the nonlinear behaviour of a nematic liquid crystal in a shear flow, for the two and three dimensional cases.

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Gokcen, Taner. « Molecular engineering of trigonal octupolar materials based on 2,4,6-diarylamino-1,3,5-triazines ». Link to electronic thesis, 2005. http://www.wpi.edu/Pubs/ETD/Available/etd-082405-155024/.

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39

Sloanes, Trefor James. « Measurement and application of optical nonlinearities in indium phosphide, cadmium mercury telluride and photonic crystal fibres / ». St Andrews, 2009. http://hdl.handle.net/10023/723.

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40

Wong, Tsz Chun. « Experimental and theoretical investigation of optical nonlinearity in one-dimensional photonic crystal with central defect mode / ». View abstract or full-text, 2009. http://library.ust.hk/cgi/db/thesis.pl?PHYS%202009%20WONG.

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MALAGUTI, Stefania. « Study, Modeling and Design of Semiconductor Photonic Crystal Based Devices ». Doctoral thesis, Università degli studi di Ferrara, 2011. http://hdl.handle.net/11392/2388821.

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This thesis is focused on the study of nonlinear e�ects in semiconductor materials. The aim is the design of e�cient optical devices able to supply ultra-fast high-performances all-optical signal processing. The goal is pur- sued by implementing di�erent tools, either theoretical models as well as numerical methods. The main achievement is the design of new topologies for photonic crystal based devices that implement various optical functional- ities such as optical conversion and switching. This work has provided some con�gurations for the manufacturing of a new generation of optical devices.

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42

Rady, Nicholas Henry. « Nonlinear UV Laser Build-up Cavity : An Efficient Design ». Thesis, University of North Texas, 2009. https://digital.library.unt.edu/ark:/67531/metadc9833/.

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Using the concept of the build-up cavity for second harmonic generation to produce 243nm laser light, an innovative cavity is theoretically explored using a 15mm length CLBO crystal. In order to limit the losses of the cavity, the number of effective optical surfaces is kept to only four and the use of a MgF2 crystal is adopted to separate the harmonic and fundamental laser beam from each other. The cavity is shown to have an expected round trip loss of five tenths of a percent or better, resulting in a conversion efficiency greater than 65%.

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43

Schulz, Sebastian Andreas. « Propagation loss in slow light photonic crystal waveguides ». Thesis, University of St Andrews, 2012. http://hdl.handle.net/10023/2837.

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The field of nanophotonics is a major research topic, as it offers potential solutions to important challenges, such as the creation of low power, high bandwidth interconnects or optical sensors. Within this field, resonant structures and slow light waveguides are used to improve device performance further. Photonic crystals are of particular interest, as they allow the fabrication of a wide variety of structures, including high Q-factor cavities and slow light waveguides. The high scattering loss of photonic crystal waveguides, caused by fabrication disorder, however, has so far proven to be the limiting factor for device applications. In this thesis, I present a detailed study of propagation loss in slow light photonic crystal waveguides. I examine the dependence of propagation loss on the group index, and on disorder, in more depth than previous work by other authors. I present a detailed study of the relative importance of different components of the propagation loss, as well as a calculation method for the average device properties. A new calculation method is introduced to study different device designs and to show that photonic crystal waveguide propagation loss can be reduced by device design alone. These “loss engineered” waveguides have been used to demonstrate the lowest loss photonic crystal based delay line (35 dB/ns) with further improvements being predicted (< 20 dB/ns). Novel fabrication techniques were investigated, with the aim of reducing fabrication disorder. Initial results showed the feasibility of a silicon anneal in a nitrogen atmosphere, however poor process control led to repeatability issues. The use of a slow-fast-slow light interface allowed for the fabrication of waveguides spanning multiple writeﬁelds of the electron-beam lithography tool, overcoming the problem of stitching errors. The slow-fast-slow light interfaces were combined with loss engineering waveguide designs, to achieve an order of magnitude reduction in the propagation loss compared to a W1 waveguide, with values as low as 130 dB/cm being achieved for a group index around 60.

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Mak, Ka Fai [Verfasser], et Philip [Akademischer Betreuer] Russell. « Nonlinear optical effects in gas-filled hollow-core photonic-crystal fibers / Ka Fai Mak. Gutachter : Philip Russell ». Erlangen : Friedrich-Alexander-Universität Erlangen-Nürnberg (FAU), 2015. http://d-nb.info/1075479037/34.

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Schmidberger, Michael J. [Verfasser], Nicolas Y. [Akademischer Betreuer] Joly et Ben [Akademischer Betreuer] Fabry. « Nonlinear Dynamics in Photonic Crystal Fibre Ring Cavities / Michael J. Schmidberger. Gutachter : Nicolas Y. Joly ; Ben Fabry ». Erlangen : Friedrich-Alexander-Universität Erlangen-Nürnberg (FAU), 2014. http://d-nb.info/1065045115/34.

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46

Baselt, Tobias, Christopher Taudt, Bryan Nelsen, Andrés Fabián Lasagni et Peter Hartmann. « Experimental study of supercontinuum generation in an amplifier based on an Yb3+ doped nonlinear photonic crystal fiber ». SPIE, 2016. https://tud.qucosa.de/id/qucosa%3A35094.

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The use of supercontinuum light sources in different optical measurement methods, like microscopy or optical coherence tomography, has increased significantly compared to classical wideband light sources. The development of various optical measurement techniques benefits from the high brightness and bandwidth, as well as the spatial coherence of these sources. For some applications, only a portion of the broad spectral range can be used. Therefore, an increase of the spectral power density in limited spectral regions would provide a clear advantage over spectral filtering. This study describes a method to increase the spectral power density of supercontinuum sources by amplifying the excitation wavelength inside a nonlinear photonic crystal fiber (PCF). An ytterbium doped photonic crystal fiber was manufactured by a nanopowder process (drawn by the company fiberware) and used in a fiber amplifier setup as the nonlinear fiber medium. In order to characterize the fiber’s optimum operational characteristics, group-velocity dispersion (GVD) measurements were performed on the fiber during the amplification process. For this purpose, a notch-pass mirror was used to launch the radiation of a stabilized laser diode at 976 nm into the fiber sample for pumping. The performance of the fiber was compared with a conventional PCF. Finally, the system as a whole was characterized in reference to common solid state-laser-based photonic supercontinuum light sources. An improvement of the power density up to 7.2 times was observed between 1100 nm to 1380 nm wavelengths.

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47

Wu, Yeheng. « Photonic Crystals with Active Organic Materials ». Cleveland, Ohio : Case Western Reserve University, 2010. http://rave.ohiolink.edu/etdc/view?acc_num=case1269618198.

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Thesis(Ph.D.)--Case Western Reserve University, 2010
Title from PDF (viewed on 2010-04-12) Department of Physics Includes abstract Includes bibliographical references and appendices Available online via the OhioLINK ETD Center

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48

Hou, Wenbo. « Crystal growth of an organic non-linear optical material from the vapour phase ». Thesis, University of Strathclyde, 1999. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.366941.

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49

Schelew, Ellen N. « Nonlinear optical response of triple-mode silicon photonic crystal microcavities coupled to single channel input and output waveguides ». Thesis, University of British Columbia, 2017. http://hdl.handle.net/2429/63353.

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Optical and opto-electronic components play important roles in both classical and quantum information processing technologies. Despite fundamental differences in these technologies, both stand to benefit greatly from moving away from bulky, individually packaged components, toward a scalable platform that supports dense integration of low power consumption devices. Planar photonic circuits, composed of devices etched in a thin slab of high refractive index material, are considered an excellent candidate, and have been used to realize many key components, including low-loss waveguides, light sources, detectors, modulators, and spectral filters. In this dissertation, a novel triple-microcavity structure was designed, externally fabricated, and its linear and nonlinear optical properties were thoroughly characterized. The best of the structures exhibited both high four-wave mixing conversion efficiencies and low threshold optical bistability, which are relevant to frequency conversion and all-optical switching applications. The device consisted of three coupled photonic crystal (PC) microcavities with three nearly equally spaced resonant frequencies near telecommunication wavelengths (λ ~ 1.5 μm), with high quality factors (~ 10⁵, 10⁴ and 10³). The microcavity system was coupled to independent input and output PC waveguides, and the cavity-waveguide coupling strengths were engineered to maximize the coupling of the input waveguide to the central mode, and the output waveguide to the two modes on either side. A novel and sophisticated measurement and analysis protocol was developed to characterize the devices. This involved measuring and modelling the linear and nonlinear transmission characteristics of each of the modes separately with a single tunable laser, as well as the frequency conversion efficiency (via stimulated four-wave mixing) when two tunable lasers pumped two of the modes, and the power generated in the third mode was monitored. Comparisons of the entire set of model and experimental results led to the conclusion that this structure can be used to achieve both low-power-threshold optical switching and high efficiency four-wave-mixing-based frequency conversion. The advantages of this structure over others in the literature are its small footprint, multi-mode functionality and independent input and output channels. The main disadvantage that requires further refinement, has to do with its sensitivity to fabrication imperfections.
Science, Faculty of
Physics and Astronomy, Department of
Graduate

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Reinke, Charles M. « Design, simulation, and characterization toolset for nano-scale photonic crystal devices ». Diss., Georgia Institute of Technology, 2009. http://hdl.handle.net/1853/33932.

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The objective of this research is to present a set of powerful simulation, design, and characterization tools suitable for studying novel nanophotonic devices. The simulation tools include a three-dimensional finite-difference time-domain code adapted for parallel computing that allows for a wide range of simulation conditions and material properties to be studied, as well as a semi-analytical Green's function-based complex mode technique for studying loss in photonic crystal waveguides. The design tools consist of multifunctional photonic crystal-based template that has been simulated with nonlinear effects and measured experimentally, and planar slab waveguide structure that provides highly efficient second harmonic generation is a chip-scale device suitable for photonic integrated circuit applications. The characterization tool is composed of a phase-sensitive measurement system using a lock-in amplifier and high-precision optical stages, suitable for probing the optical characteristics of nanoscale devices. The high signal-to-noise ratio and phase shift data provided by the lock-in amplifier allow for accurate transmission measurements as well as a phase spectrum that contains information about the propagation behavior of the device beyond what is provided by the amplitude spectrum alone.

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