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Title: LASER FILAMENT INTERACTION WITH AEROSOLS AND CLOUDS.
Creator: Jeon, Cheonha, Richardson, Martin, Vanstryland, Eric, Baudelet, Matthieu, Sigman, Michael, University of Central Florida
Abstract / Description: A high powered ultrashort laser pulse can propagate as a diffraction-free self-channeled structure called a filament, created by a combination of nonlinear processes. With its ability to convey extremely high intensity beams to distant targets, many applications such as remote sensing, cloud seeding, and discharge guiding are potentially possible. However, one of the main challenges of outdoor field applications is the laser propagation through the atmosphere where pressure fluctuations and...
Show moreA high powered ultrashort laser pulse can propagate as a diffraction-free self-channeled structure called a filament, created by a combination of nonlinear processes. With its ability to convey extremely high intensity beams to distant targets, many applications such as remote sensing, cloud seeding, and discharge guiding are potentially possible. However, one of the main challenges of outdoor field applications is the laser propagation through the atmosphere where pressure fluctuations and concentrations of aerosols may be present. The rationale behind the work presented in this dissertation is to evaluate the robustness of the filamentation, measure the interaction losses as well as understanding the modifications to (i) filament length (ii) supercontinuum generation, and (iii) the beam profile along propagation through perturbed media.Detailed studies of the interaction of a single filament with a single water droplet are presented. In addition, preliminary results on filament propagation through a cloud of aerosols are discussed. The effect of pressure on the beam profile along propagation and on the supercontinuum generated by the filament is studied. This document provides valuable insight into the complex nonlinear processes affecting the formation, propagation and post propagation of filaments under adverse atmospheric conditions.
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Date Issued: 2016
Identifier: CFE0006530, ucf:51368
Format: Document (PDF)
PURL: http://purl.flvc.org/ucf/fd/CFE0006530

Title: Cascaded plasmon resonances for enhanced nonlinear optical response.
Creator: Toroghi, Seyfollah, Kik, Pieter, Vanstryland, Eric, Kuebler, Stephen, Hagan, David, Belfield, Kevin, University of Central Florida
Abstract / Description: The continued development of integrated photonic devices requires low-power, small volume all-optical modulators. The weak nonlinear optical response of conventional optical materials requires the use of high intensities and large interaction volumes in order to achieve significant light modulation, hindering the miniaturization of all-optical switches and the development of lightweight transmission optics with nonlinear optical response. These challenges may be addressed using plasmonic...
Show moreThe continued development of integrated photonic devices requires low-power, small volume all-optical modulators. The weak nonlinear optical response of conventional optical materials requires the use of high intensities and large interaction volumes in order to achieve significant light modulation, hindering the miniaturization of all-optical switches and the development of lightweight transmission optics with nonlinear optical response. These challenges may be addressed using plasmonic nanostructures due to their unique ability to confine and enhance electric fields in sub-wavelength volumes. The ultrafast nonlinear response of free electrons in such plasmonic structures and the fast thermal nonlinear optical response of metal nanoparticles, as well as the plasmon enhanced nonlinear Kerr-type response of the host material surrounding the nanostructures could allow ultrafast all-optical modulation with low modulation energy. In this thesis, we investigate the linear and nonlinear optical response of engineered effective media containing coupled metallic nanoparticles. The fundamental interactions in systems containing coupled nanoparticles with size, shape, and composition dissimilarity, are evaluated analytically and numerically, and it is demonstrated that under certain conditions the achieved field enhancement factors can exceed the single-particle result by orders of magnitude in a process called cascaded plasmon resonance. It is demonstrated that these conditions can be met in systems containing coupled nanospheres, and in systems containing non-spherical metal nanoparticles that are compatible with common top-down nanofabrication methods such as electron beam lithography and nano-imprint lithography. We show that metamaterials based on such cascaded plasmon resonance structures can produce enhanced nonlinear optical refraction and absorption compared to that of conventional plasmonic nanostructures. Finally, it is demonstrated that the thermal nonlinear optical response of metal nanoparticles can be enhanced in carefully engineered heterogeneous nanoparticle clusters, potentially enabling strong and fast thermal nonlinear optical response in system that can be produced in bulk through chemical synthesis.
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Date Issued: 2014
Identifier: CFE0005556, ucf:50272
Format: Document (PDF)
PURL: http://purl.flvc.org/ucf/fd/CFE0005556

Title: Nonlinear integrated photonics on silicon and gallium arsenide substrates.
Creator: Ma, Jichi, Fathpour, Sasan, Hagan, David, Li, Guifang, Peale, Robert, University of Central Florida
Abstract / Description: Silicon photonics is nowadays a mature technology and is on the verge of becoming a blossoming industry. Silicon photonics has also been pursued as a platform for integrated nonlinear optics based on Raman and Kerr effects. In recent years, more futuristic directions have been pursued by various groups. For instance, the realm of silicon photonics has been expanded beyond the well-established near-infrared wavelengths and into the mid-infrared (3 (-) 5 (&)#181;m). In this wavelength range,...
Show moreSilicon photonics is nowadays a mature technology and is on the verge of becoming a blossoming industry. Silicon photonics has also been pursued as a platform for integrated nonlinear optics based on Raman and Kerr effects. In recent years, more futuristic directions have been pursued by various groups. For instance, the realm of silicon photonics has been expanded beyond the well-established near-infrared wavelengths and into the mid-infrared (3 (-) 5 (&)#181;m). In this wavelength range, the omnipresent hurdle of nonlinear silicon photonics in the telecommunication band, i.e., nonlinear losses due to two-photon absorption, is inherently nonexistent. With the lack of efficient light-emission capability and second-order optical nonlinearity in silicon, heterogeneous integration with other material systems has been another direction pursued. Finally, several approaches have been proposed and demonstrated to address the energy efficiency of silicon photonic devices in the near-infrared wavelength range. In this dissertation, theoretical and experimental works are conducted to extend applications of integrated photonics into mid-infrared wavelengths based on silicon, demonstrate heterogeneous integration of tantalum pentoxide and lithium niobate photonics on silicon substrates, and study two-photon photovoltaic effect in gallium arsenide and plasmonic-enhanced structures.Specifically, performance and noise properties of nonlinear silicon photonic devices, such as Raman lasers and optical parametric amplifiers, based on novel and reliable waveguide technologies are studied. Both near-infrared and mid-infrared nonlinear silicon devices have been studied for comparison. Novel tantalum-pentoxide- and lithium-niobate-on-silicon platforms are developed for compact microring resonators and Mach-Zehnder modulators. Third- and second-harmonic generations are theoretical studied based on these two platforms, respectively. Also, the two-photon photovoltaic effect is studied in gallium arsenide waveguides for the first time. The effect, which was first demonstrated in silicon, is the nonlinear equivalent of the photovoltaic effect of solar cells and offers a viable solution for achieving energy-efficient photonic devices. The measured power efficiency achieved in gallium arsenide is higher than that in silicon and even higher efficiency is theoretically predicted with optimized designs. Finally, plasmonic-enhanced photovoltaic power converters, based on the two-photon photovoltaic effect in silicon using subwavelength apertures in metallic films, are proposed and theoretically studied.
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Date Issued: 2014
Identifier: CFE0005373, ucf:50441
Format: Document (PDF)
PURL: http://purl.flvc.org/ucf/fd/CFE0005373

Title: A Novel Nonlinear Mason Model and Nonlinear Distortion Characterization for Surface Acoustic Wave Duplexers.
Creator: Chen, Li, Wahid, Parveen, Malocha, Donald, Richie, Samuel, Briot, Jean-Bernard, University of Central Florida
Abstract / Description: Surface acoustic wave (SAW) technology has been in use for well over one century. In the last few decades, due to its low cost and high performance, this technology has been widely adopted in modern wireless communication systems, to build filtering devices at radio frequency (RF). SAW filters and duplexers can be virtually found inside every mobile handset. SAW devices are traditionally recognized as passive devices with high linear signal processing behavior. However, recent deployments of...
Show moreSurface acoustic wave (SAW) technology has been in use for well over one century. In the last few decades, due to its low cost and high performance, this technology has been widely adopted in modern wireless communication systems, to build filtering devices at radio frequency (RF). SAW filters and duplexers can be virtually found inside every mobile handset. SAW devices are traditionally recognized as passive devices with high linear signal processing behavior. However, recent deployments of third generation (3G) and fourth generation (4G) mobile networks require the handsets to handle an increasing number of frequency bands with more complex modulation /demodulation schemes and higher data rate for more subscribers. These requirements directly demand more stringent linearity specifications on the front end devices, including the SAW duplexers. In the past, SAW duplexer design was based on empirically obtained design rules to meet the linearity specifications. Lack of predictability and an understanding of the root cause of the nonlinearity have limited the potential applications of SAW duplexers. Therefore, research on the nonlinearity characterization and an accurate modeling of SAW nonlinearity for mobile device applications are very much needed.The Ph.D. work presented here primarily focuses on developing a general nonlinear model for SAW resonators/duplexers. Their nonlinear characteristics were investigated by measuring the harmonic and intermodulation distortions of resonators. A nonlinear Mason model is developed and the characterization results are integrated into SAW duplexer design flows to help to simulate the nonlinear effects accurately and improve the linearity performance of the products.In this dissertation, first, a novel nonlinear Mason equivalent circuit model including a third order nonlinear coefficient in the wave propagation is presented. Next, the nonlinear distortions of SAW resonators are analyzed by measuring large-signal harmonic and intermodulation spurious emission on resonators using a wafer probe station. The influence of the setups on the measurement reliability and reproducibility is discussed. Further, the nonlinear Mason model is validated by comparing its simulation results with harmonic and intermodulation measurements on SAW resonators and a WCDMA Band 5 duplexer. The Mason model developed and presented here is the first and only nonlinear physical model for SAW devices based on the equivalent circuit approach. By using this new model, good simulation measurement agreements are obtained on both harmonic and intermodulation distortions for SAW resonators and duplexers. These outcomes demonstrate the validity of the research on both the characterization and modeling of SAW devices. The result obtained confirms that the assumption of the representation of the 3rd order nonlinearity in the propagation by a single coefficient is valid.
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Date Issued: 2013
Identifier: CFE0004967, ucf:49565
Format: Document (PDF)
PURL: http://purl.flvc.org/ucf/fd/CFE0004967

Title: Nonlinear dispersive partial differential equations of physical relevance with applications to vortex dynamics.
Creator: VanGorder, Robert, Kaup, David, Vajravelu, Kuppalapalle, Nevai, Andrew, Mohapatra, Ram, Kassab, Alain, University of Central Florida
Abstract / Description: Nonlinear dispersive partial differential equations occur in a variety of areas within mathematical physics and engineering. We study several classes of such equations, including scalar complex partial differential equations, vector partial differential equations, and finally non-local integro-differential equations. For physically interesting families of these equations, we demonstrate the existence (and, when possible, stability) of specific solutions which are relevant for applications....
Show moreNonlinear dispersive partial differential equations occur in a variety of areas within mathematical physics and engineering. We study several classes of such equations, including scalar complex partial differential equations, vector partial differential equations, and finally non-local integro-differential equations. For physically interesting families of these equations, we demonstrate the existence (and, when possible, stability) of specific solutions which are relevant for applications. While multiple application areas are considered, the primary application that runs through the work would be the nonlinear dynamics of vortex filaments under a variety of physical models. For instance, we are able to determine the structure and time evolution of several physical solutions, including the planar, helical, self-similar and soliton vortex filament solutions in a quantum fluid. Properties of such solutions are determined analytically and numerically through a variety of approaches. Starting with complex scalar equations (often useful for studying two-dimensional motion), we progress through more complicated models involving vector partial differential equations and non-local equations (which permit motion in three dimensions). In many of the examples considered, the qualitative analytical results are used to verify behaviors previously observed only numerically or experimentally.
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Date Issued: 2014
Identifier: CFE0005272, ucf:50545
Format: Document (PDF)
PURL: http://purl.flvc.org/ucf/fd/CFE0005272

Title: STUDY OF THE EXCITED-STATE ABSORPTION PROPERTIES OF POLYMETHINE MOLECULES.
Creator: Lepkowicz, Richard Stanley, Van Stryland, Eric W., University of Central Florida
Abstract / Description: This dissertation investigates excited-state nonlinearities in a series of polymethine dyes for the application of nanosecond optical limiting. Optical limiters are devices that for low intensity light exhibit a high linear transmittance, but for high intensity light strongly attenuate the incident radiation. These devices would serve to protect optical sensors from intense laser radiation by clamping the maximum energy allowed through an optical system below the damage threshold of the...
Show moreThis dissertation investigates excited-state nonlinearities in a series of polymethine dyes for the application of nanosecond optical limiting. Optical limiters are devices that for low intensity light exhibit a high linear transmittance, but for high intensity light strongly attenuate the incident radiation. These devices would serve to protect optical sensors from intense laser radiation by clamping the maximum energy allowed through an optical system below the damage threshold of the sensor. The search is ongoing for optical materials that are both broadband and have high damage thresholds to be effective materials for limiting applications. Polymethine dyes are promising compounds due to a strong and broad excited-state absorption (ESA) band in the visible region. However, the effectiveness of polymethine molecules as applied to optical limiting is hindered by a saturation of the ESA process at high fluences. Experiments and theoretical modeling are performed to determine the root causes of this saturation effect in both the picosecond and nanosecond time regime. The polymethine molecules studied have chromophore lengths from di- to pentacarbocyanine (2 to 5 -CH=CH- groups) with various bridge structures. This allows us to develop relationships between the molecular parameters of the polymethine molecules and overall nonlinear absorption performance. The experiments conducted included femtosecond white light continuum pump-probe experiments to measure ESA spectra, picosecond two-color polarization-resolved pump-probe to measure excited-state dynamics and the orientation of transition dipole moments, and picosecond and nanosecond optical limiting and z-scans. From these experiments we are able to develop energy level models that describe the nonlinear absorption processes in polymethines from the picosecond to nanosecond time regime. This work, along with the quantum chemical modeling performed at the Institute of Physics and National Academy of Sciences of Ukraine, has resulted in the creation of dyes that have improved photochemical stability with larger nonlinearities. These are useful not only for optical limiting but also for a wide variety of nonlinear optical applications.
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Date Issued: 2004
Identifier: CFE0000002, ucf:46115
Format: Document (PDF)
PURL: http://purl.flvc.org/ucf/fd/CFE0000002

Title: EXPERIMENTAL TECHNIQUES FOR NONLINEAR MATERIAL CHARACTERIZATION: A NONLINEAR SPECTROMETER USING A WHITE-LIGHT CONTINUUM Z-SCAN.
Creator: Balu, Mihaela, Van Stryland, Eric, University of Central Florida
Abstract / Description: The main goal of this dissertation is to introduce and demonstrate a new method for the rapid determination of the nonlinear absorption spectra and the dispersion of the nonlinear refraction of optical materials in the visible and near IR spectral regions. However, conventional methods like, white-light continuum pump-probe and Z-scan techniques were used to measure the peak 2PA cross-sections for a number of commercially available photoinitiators. In the new method mentioned above, a high...
Show moreThe main goal of this dissertation is to introduce and demonstrate a new method for the rapid determination of the nonlinear absorption spectra and the dispersion of the nonlinear refraction of optical materials in the visible and near IR spectral regions. However, conventional methods like, white-light continuum pump-probe and Z-scan techniques were used to measure the peak 2PA cross-sections for a number of commercially available photoinitiators. In the new method mentioned above, a high energy, broadband femtosecond white-light continuum is used to replace the single wavelength source conventionally used in a Z-scan experiment. In a Z-scan experiment, the transmittance of a focused beam through a sample is monitored as the sample travels through the focus, in the Z direction, along the focused beam. Providing the sample exhibits nonlinear absorption and/or refraction, the detector monitors a change in transmittance and/or a change in the beam divergence (if the energy is partially collected through an aperture in front of the detector). Replacing the single wavelength source with a white-light continuum allows for a much faster way of measuring nonlinear absorption/refraction spectra. This could eliminate the need for using other tunable sources (e.g. Optical Parameter Generators/Amplifiers) for nonlinear measurements. These sources made nonlinear spectroscopy using Z-scan experiments a time consuming task. This new source/method allows for rapid and simultaneous measurement of the nonlinear absorption spectrum and the dispersion of the nonlinear refraction. We have confirmed the functionality of the continuum as a source for nonlinear optical characterization of materials by using it to perform Z-scans on the well characterized semiconductors ZnSe and ZnS and on solutions of organic dyes.
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Date Issued: 2006
Identifier: CFE0001241, ucf:46934
Format: Document (PDF)
PURL: http://purl.flvc.org/ucf/fd/CFE0001241

Title: SYNTHESIS, CHARACTERIZATION, AND EVALUATION OF NEW REACTIVE TWO-PHOTON ABSORBING DYES FOR TWO-PHOTON EXCITED FLUORESCENCE IMAGING APPLICATIONS.
Creator: Hales, Katherine, Belfield, Kevin, University of Central Florida
Abstract / Description: Recent, cooperative advances in chemistry, computing, optics, and microelectronics have resulted in extraordinary developments in the biological sciences, resulting in the emergence of a novel area termed ¡¥biophotonics¡¦. The interdisciplinary nature of biophotonics cuts across virtually all disciplines, extending the frontiers of basic cellular, molecular, and biology research. This holds true for the development and application of the novel imaging modality utilizing...
Show moreRecent, cooperative advances in chemistry, computing, optics, and microelectronics have resulted in extraordinary developments in the biological sciences, resulting in the emergence of a novel area termed ¡¥biophotonics¡¦. The interdisciplinary nature of biophotonics cuts across virtually all disciplines, extending the frontiers of basic cellular, molecular, and biology research. This holds true for the development and application of the novel imaging modality utilizing multiphoton absorption and its extraordinary contribution to advances in bioimaging. Intimately involved in the revolution of nonlinear bioimaging has been the development of optical probes for probing biological function and activity. The focus of this dissertation is in the area of probe development, particularly ƒà-conjugated organic probes, optimized for efficient two-photon absorption followed by upconverted fluorescence for multiphoton bioimaging. Specifically, fluorene molecules, with enhanced two-photon absorbing (2PA) properties and high photostability, were prepared and characterized. Contemporary synthetic methods were utilized to prepare target fluorene derivatives expected to be highly fluorescent and, in particular, exhibit high two-photon absorptivity, suitable for two-photon excitation (2PE) fluorescence microscopy. The flexibility afforded through synthetic manipulation for integrating hydrophilic moieties into the fluorophore architecture to enhance compatibility with aqueous systems, more native to biological samples, was attempted. Incorporation of functional groups for direct covalent attachment onto biomolecules was also pursued to prepare fluorene derivatives as efficient 2PA reactive probes. Linear and two-photon spectroscopic characterizations on these novel compounds reveal they exhibit relatively high 2PA cross-sections on the order of ~100 GM units, which is greater than typical, commonly used fluorophores utilized in multiphoton bioimaging. Extensive photostability studies of representative fluorene compounds demonstrate these derivatives are photostable under one- and two-photon excitation conditions, exhibiting photodecomposition quantum yields on the order of 10-5. Additionally, preliminary cytotoxicity studies indicate these fluorene derivatives exhibit minimal cytotoxic effects on proliferating cells. Finally, their utility as high-performance, 2PA fluorescent probes in 2PE fluorescence microscopy imaging of biological samples was demonstrated in both fixed and live cells. Due to the low cytotoxicity, high photostability, efficient 2PA, and high fluorescence quantum yield, the probes were found suitable for relatively long-term, two-photon fluorescence imaging of live cells, representing a significant advance in biophotonics.
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Date Issued: 2005
Identifier: CFE0000685, ucf:46487
Format: Document (PDF)
PURL: http://purl.flvc.org/ucf/fd/CFE0000685

Title: OPTICAL WAVE PROPAGATION IN DISCRETE WAVEGUIDE ARRAYS.
Creator: Hudock, Jared, Christodoulides, Demetrios, University of Central Florida
Abstract / Description: The propagation dynamics of light in optical waveguide arrays is characteristic of that encountered in discrete systems. As a result, it is possible to engineer the diffraction properties of such structures, which leads to the ability to control the flow of light in ways that are impossible in continuous media. In this work, a detailed theoretical investigation of both linear and nonlinear optical wave propagation in one- and two-dimensional waveguide lattices is presented. The ability to...
Show moreThe propagation dynamics of light in optical waveguide arrays is characteristic of that encountered in discrete systems. As a result, it is possible to engineer the diffraction properties of such structures, which leads to the ability to control the flow of light in ways that are impossible in continuous media. In this work, a detailed theoretical investigation of both linear and nonlinear optical wave propagation in one- and two-dimensional waveguide lattices is presented. The ability to completely overcome the effects of discrete diffraction through the mutual trapping of two orthogonally polarized coherent beams interacting in Kerr nonlinear arrays of birefringent waveguides is discussed. The existence and stability of such highly localized vector discrete solitons is analyzed and compared to similar scenarios in a single birefringent waveguide. This mutual trapping is also shown to occur within the first few waveguides of a semi-infinite array leading to the existence of vector discrete surface waves. Interfaces between two detuned semi-infinite waveguide arrays or waveguide array heterojunctions and their possible applications are also considered. It is shown that the detuning between the two arrays shifts the dispersion relation of one array with respect to the other. Consequently, these systems provide spatial filtering functions that may prove useful in future all-optical networks. In addition by exploiting the unique diffraction properties of discrete arrays, diffraction compensation can be achieved in a way analogous to dispersion compensation in dispersion managed optical fiber systems. Finally, it is demonstrated that both the linear (diffraction) and nonlinear dynamics of two-dimensional waveguide arrays are significantly more complex and considerably more versatile than their one-dimensional counterparts. As is the case in one-dimensional arrays, the discrete diffraction properties of these two-dimensional lattices can be effectively altered depending on the propagation Bloch k-vector within the first Brillouin zone. In general, this diffraction behavior is anisotropic and as a result, allows the existence of a new class of discrete elliptic solitons in the nonlinear regime. Moreover, such arrays support two-dimensional vector soliton states, and their existence and stability are also thoroughly explored in this work.
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Date Issued: 2005
Identifier: CFE0000833, ucf:46687
Format: Document (PDF)
PURL: http://purl.flvc.org/ucf/fd/CFE0000833

Title: MOLECULAR STRUCTURE – NONLINEAR OPTICAL PROPERTY RELATIONSHIPS FOR A SERIES OF POLYMETHINE AND SQUARAINE MOLECULES.
Creator: Fu, Jie, Van Stryland, Eric, University of Central Florida
Abstract / Description: This dissertation reports on the investigation of the relationships between molecular structure and two-photon absorption (2PA) properties for a series of polymethine and squaraine molecules. Current and emerging applications exploiting the quadratic dependence upon laser intensity, such as two-photon fluorescence imaging, three-dimensional microfabrication, optical data storage and optical limiting, have motivated researchers to find novel materials exhibiting strong 2PA. Organic materials...
Show moreThis dissertation reports on the investigation of the relationships between molecular structure and two-photon absorption (2PA) properties for a series of polymethine and squaraine molecules. Current and emerging applications exploiting the quadratic dependence upon laser intensity, such as two-photon fluorescence imaging, three-dimensional microfabrication, optical data storage and optical limiting, have motivated researchers to find novel materials exhibiting strong 2PA. Organic materials are promising candidates because their linear and nonlinear optical properties can be optimized for applications by changing their structures through molecular engineering. Polymethine and squaraine dyes are particularly interesting because they are fluorescent and showing large 2PA. We used three independent nonlinear spectroscopic techniques (Z-scan, two-photon fluorescence and white-light continuum pump-probe spectroscopy) to obtain the 2PA spectra revealing 2PA bands, and we confirm the experimental data by comparing the results from the different methods mentioned. By systematically altering the structure of polyemthines and squaraines, we studied the effects of molecular symmetry, strength of donor terminal groups, conjugation length of the chromophore chain, polarity of solvents, and the effects of placing bridge molecules inside the chromophore chain on the 2PA properties. We also compared polymethine, squaraine, croconium and tetraon dyes with the same terminal groups to study the effects of the different additions inserted within the chromophore chain on their optical properties. Near IR absorbing squaraine dyes were experimentally observed to show extremely large 2PA cross sections ( 30000GM). A simplified three-level model was used to fit the measured 2PA spectra and detailed quantum chemical calculations revealed the reasons for the squaraine to exhibit strong 2PA. In addition, two-photon excitation fluorescence anisotropy spectra were measured through multiple 2PA transitions. A theoretical model based on four-levels with two intermediate states was derived and used for analysis of the experimental data.
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Date Issued: 2006
Identifier: CFE0001350, ucf:46967
Format: Document (PDF)
PURL: http://purl.flvc.org/ucf/fd/CFE0001350

Title: SOLITARY WAVE FAMILIES IN TWO NON-INTEGRABLE MODELS USING REVERSIBLE SYSTEMS THEORY.
Creator: Leto, Jonathan, Choudhury, S. Roy, University of Central Florida
Abstract / Description: In this thesis, we apply a recently developed technique to comprehensively categorize all possible families of solitary wave solutions in two models of topical interest. The models considered are: a) the Generalized Pochhammer-Chree Equations, which govern the propagation of longitudinal waves in elastic rods, and b) a generalized microstructure PDE. Limited analytic results exist for the occurrence of one family of solitary wave solutions for each of these equations. Since, as mentioned...
Show moreIn this thesis, we apply a recently developed technique to comprehensively categorize all possible families of solitary wave solutions in two models of topical interest. The models considered are: a) the Generalized Pochhammer-Chree Equations, which govern the propagation of longitudinal waves in elastic rods, and b) a generalized microstructure PDE. Limited analytic results exist for the occurrence of one family of solitary wave solutions for each of these equations. Since, as mentioned above, solitary wave solutions often play a central role in the long-time evolution of an initial disturbance, we consider such solutions of both models here (via the normal form approach) within the framework of reversible systems theory. Besides confirming the existence of the known family of solitary waves for each model, we find a continuum of delocalized solitary waves (or homoclinics to small-amplitude periodic orbits). On isolated curves in the relevant parameter region, the delocalized waves reduce to genuine embedded solitons. For the microstructure equation, the new family of solutions occur in regions of parameter space distinct from the known solitary wave solutions and are thus entirely new. Directions for future work, including the dynamics of each family of solitary waves using exponential asymptotics techniques, are also mentioned.
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Date Issued: 2008
Identifier: CFE0002151, ucf:47930
Format: Document (PDF)
PURL: http://purl.flvc.org/ucf/fd/CFE0002151

Title: Navigation of an Autonomous Differential Drive Robot for Field Scouting in Semi-structured Environments.
Creator: Freese, Douglas, Xu, Yunjun, Lin, Kuo-Chi, Kauffman, Jeffrey L., Behal, Aman, University of Central Florida
Abstract / Description: In recent years, the interests of introducing autonomous robots by growers into agriculture fields are rejuvenated due to the ever-increasing labor cost and the recent declining numbers of seasonal workers. The utilization of customized, autonomous agricultural robots has a profound impact on future orchard operations by providing low cost, meticulous inspection. Different sensors have been proven proficient in agrarian navigation including the likes of GPS, inertial, magnetic, rotary...
Show moreIn recent years, the interests of introducing autonomous robots by growers into agriculture fields are rejuvenated due to the ever-increasing labor cost and the recent declining numbers of seasonal workers. The utilization of customized, autonomous agricultural robots has a profound impact on future orchard operations by providing low cost, meticulous inspection. Different sensors have been proven proficient in agrarian navigation including the likes of GPS, inertial, magnetic, rotary encoding, time of flight as well as vision. To compensate for anticipated disturbances, variances and constraints contingent to the outdoor semi-structured environment, a differential style drive vehicle will be implemented as an easily controllable system to conduct tasks such as imaging and sampling.In order to verify the motion control of a robot, custom-designed for strawberry fields, the task is separated into multiple phases to manage the over-bed and cross-bed operation needs. In particular, during the cross-bed segment an elevated strawberry bed will provide distance references utilized in a logic filter and tuned PID algorithm for safe and efficient travel. Due to the significant sources of uncertainty such as wheel slip and the vehicle model, nonlinear robust controllers are designed for the cross-bed motion, purely relying on vision feedback. A simple image filter algorithm was developed for strawberry row detection, in which pixels corresponding to the bed center will be tracked while the vehicle is in controlled motion. This incorporated derivation and formulation of a bounded uncertainty parameter that will be employed in the nonlinear control. Simulation of the entire system was subsequently completed to ensure the control capability before successful validation in multiple commercial farms. It is anticipated that with the developed algorithms the authentication of fully autonomous robotic systems functioning in agricultural crops will provide heightened efficiency of needed costly services; scouting, disease detection, collection, and distribution.
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Date Issued: 2018
Identifier: CFE0007401, ucf:52743
Format: Document (PDF)
PURL: http://purl.flvc.org/ucf/fd/CFE0007401

Title: Multi-level Optimization and Applications with Non-Traditional Game Theory.
Creator: Yun, Guanxiang, Zheng, Qipeng, Boginski, Vladimir, Karwowski, Waldemar, Yong, Jiongmin, University of Central Florida
Abstract / Description: We study multi-level optimization problem on energy system, transportation system and information network. We use the concept of boundedly rational user equilibrium (BRUE) to predict the behaviour of users in systems. By using multi-level optimization method with BRUE, we can help to operate the system work in a more efficient way. Based on the introducing of model with BRUE constraints, it will lead to the uncertainty to the optimization model. We generate the robust optimization as the...
Show moreWe study multi-level optimization problem on energy system, transportation system and information network. We use the concept of boundedly rational user equilibrium (BRUE) to predict the behaviour of users in systems. By using multi-level optimization method with BRUE, we can help to operate the system work in a more efficient way. Based on the introducing of model with BRUE constraints, it will lead to the uncertainty to the optimization model. We generate the robust optimization as the multi-level optimization model to consider for the pessimistic condition with uncertainty. This dissertation mainly includes four projects. Three of them use the pricing strategy as the first level optimization decision variable. In general, our models' first level's decision variables are the measures that we can control, but the second level's decision variables are users behaviours that can only be restricted within BRUE with uncertainty.
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Date Issued: 2019
Identifier: CFE0007881, ucf:52758
Format: Document (PDF)
PURL: http://purl.flvc.org/ucf/fd/CFE0007881

Title: Nonlinear Control Synthesis for Facilitation of Human-Robot Interaction.
Creator: Ding, Zhangchi, Behal, Aman, Pourmohammadi Fallah, Yaser, Haralambous, Michael, Boloni, Ladislau, Xu, Yunjun, University of Central Florida
Abstract / Description: Human-robot interaction is an area of interest that is becoming increasingly important in robotics research. Nonlinear control design techniques allow researchers to guarantee stability, performance, as well as safety, especially in cases involving physical human-robot interaction (PHRI). In this dissertation, we will propose two different nonlinear controllers and detail the design of an assistive robotic system to facilitate human-robot interaction. In Chapter 2, to facilitate physical...
Show moreHuman-robot interaction is an area of interest that is becoming increasingly important in robotics research. Nonlinear control design techniques allow researchers to guarantee stability, performance, as well as safety, especially in cases involving physical human-robot interaction (PHRI). In this dissertation, we will propose two different nonlinear controllers and detail the design of an assistive robotic system to facilitate human-robot interaction. In Chapter 2, to facilitate physical human-robot interaction, the problem of making a safe compliant contact between a human and an assistive robot is considered. Users with disabilities have a need to utilize their assistive robots for physical interaction during activities such as hair-grooming, scratching, face-sponging, etc. Specifically, we propose a hybrid force/velocity/attitude control for our physical human-robot interaction system which is based on measurements from a force/torque sensor mounted on the robot wrist. While automatically aligning the end-effector surface with the unknown environmental (human) surface, a desired commanded force is applied in the normal direction while following desired velocity commands in the tangential directions. A Lyapunov based stability analysis is provided to prove both convergence as well as passivity of the interaction to ensure both performance and safety. Simulation as well as experimental results verify the performance and robustness of the proposed hybrid force/velocity/attitude controller in the presence of dynamic uncertainties as well as safety compliance of human-robot interactions for a redundant robot manipulator.Chapter 3 presents the design, analysis, and experimental implementation of an adaptive control enabled intelligent algorithm to facilitate 1-click grasping of novel objects by a robotic gripper since one of the most common types of tasks for an assistive robot is pick and place/object retrieval tasks. But there are a variety of objects in our daily life all of which need different optimal force to grasp them. This algorithm facilitates automated grasping force adjustment. The use of object-geometry free modeling coupled with utilization of interaction force and slip velocity measurements allows for the design of an adaptive backstepping controller that is shown to be asymptotically stable via a Lyapunov-based analysis. Experiments with multiple objects using a prototype gripper with embedded sensing show that the proposed scheme is able to effectively immobilize novel objects within the gripper fingers. Furthermore, it is seen that the adaptation allows for close estimation of the minimum grasp force required for safe grasping which results in minimal deformation of the grasped object.In Chapter 4, we present the design and implementation of the motion controllerand adaptive interface for the second generation of the UCF-MANUSintelligent assistive robotic manipulator system. Based on usability testingfor the system, several features were implemented in the interface thatcould reduce the complexity of the human-robot interaction while alsocompensating for the deficits in different human factors, such as WorkingMemory, Response Inhibition, Processing Speed; , Depth Perception, SpatialAbility, Contrast Sensitivity. For the controller part, we designed severalnew features to provide the user has a less complex and safer interactionwith the robot, such as `One-click mode', `Move suggestion mode' and`Gripper Control Assistant'. As for the adaptive interface design, wedesigned and implemented compensators such as `Contrast Enhancement',`Object Proximity Velocity Reduction' and `Orientation Indicator'.
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Date Issued: 2019
Identifier: CFE0007798, ucf:52360
Format: Document (PDF)
PURL: http://purl.flvc.org/ucf/fd/CFE0007798

Title: THE LAST 2500 YEARS: DEFINING, DISSECTING AND DIRECTING THE LESS LINEAR MUSICAL.
Creator: Lewis, Andrew, Weaver, Earl, University of Central Florida
Abstract / Description: Since the first recorded theatrical events, theatre has been presented in a linear fashion. It is no surprise that the majority of American Musical Theatre also follows a linear plot conception. Musicals that blatantly defy linearity are often called Ã‚Â"conceptÃ‚Â" musicals. However, there is a small portion of concept musicals that do not abandon their linear plot altogether, but instead choose to skew the line in order to give the audience a unique...
Show moreSince the first recorded theatrical events, theatre has been presented in a linear fashion. It is no surprise that the majority of American Musical Theatre also follows a linear plot conception. Musicals that blatantly defy linearity are often called Ã‚Â"conceptÃ‚Â" musicals. However, there is a small portion of concept musicals that do not abandon their linear plot altogether, but instead choose to skew the line in order to give the audience a unique perspective of the story being told. This mass categorization does not accurately take into account the extreme difference in structure of the two types of concept musicals. For this purpose, I explored the notion of a new structural category, the Less Linear Concept Musical, in hopes of identifying the unique characteristics and challenges associated with this type of musical. Beginning with AristotleÃ‚Â's "The Poetics" and ending in modern day Musical Theatre, I examine key events in the shaping of this musical theatre form, as well as define the form itself. The application of this research culminated in a classroom presentation of Jason Robert BrownÃ‚Â's The Last Five Years, which I directed. I pose the question, Ã‚Â"Can sound direction conquer the pitfalls found within the Less Linear Concept Musical?Ã‚Â"
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Date Issued: 2010
Identifier: CFE0003361, ucf:48479
Format: Document (PDF)
PURL: http://purl.flvc.org/ucf/fd/CFE0003361

Title: VARIATIONAL EMBEDDED SOLITONS, AND TRAVELING WAVETRAINS GENERATED BY GENERALIZED HOPF BIFURCATIONS, IN SOME NLPDE SYSTEMS.
Creator: Smith, Todd, Choudhury, Roy, University of Central Florida
Abstract / Description: In this Ph.D. thesis, we study regular and embedded solitons and generalized and degenerate Hopf bifurcations. These two areas of work are seperate and independent from each other. First, variational methods are employed to generate families of both regular and embedded solitary wave solutions for a generalized Pochhammer PDE and a generalized microstructure PDE that are currently of great interest. The technique for obtaining the embedded solitons incorporates several recent generalizations...
Show moreIn this Ph.D. thesis, we study regular and embedded solitons and generalized and degenerate Hopf bifurcations. These two areas of work are seperate and independent from each other. First, variational methods are employed to generate families of both regular and embedded solitary wave solutions for a generalized Pochhammer PDE and a generalized microstructure PDE that are currently of great interest. The technique for obtaining the embedded solitons incorporates several recent generalizations of the usual variational technique and is thus topical in itself. One unusual feature of the solitary waves derived here is that we are able to obtain them in analytical form (within the family of the trial functions). Thus, the residual is calculated, showing the accuracy of the resulting solitary waves. Given the importance of solitary wave solutions in wave dynamics and information propagation in nonlinear PDEs, as well as the fact that only the parameter regimes for the existence of solitary waves had previously been analyzed for the microstructure PDE considered here, the results obtained here are both new and timely. Second, we consider generalized and degenerate Hopf bifurcations in three different models: i. a predator-prey model with general predator death rate and prey birth rate terms, ii. a laser-diode system, and iii. traveling-wave solutions of twospecies predator-prey/reaction-diusion equations with arbitrary nonlinear/reaction terms. For speci c choices of the nonlinear terms, the quasi-periodic orbit in the post-bifurcation regime is constructed for each system using the method of multiple scales, and its stability is analyzed via the corresponding normal form obtained by reducing the system down to the center manifold. The resulting predictions for the post-bifurcation dynamics provide an organizing framework for the variety of possible behaviors. These predictions are veri ed and supplemented by numerical simulations, including the computation of power spectra, autocorrelation functions, and fractal dimensions as appropriate for the periodic and quasiperiodic attractors, attractors at in nity, as well as bounded chaotic attractors obtained in various cases. The dynamics obtained in the three systems is contrasted and explained on the basis of the bifurcations occurring in each. For instance, while the two predator-prey models yield a variety of behaviors in the post-bifurcation regime, the laser-diode evinces extremely stable quasiperiodic solutions over a wide range of parameters, which is very desirable for robust operation of the system in oscillator mode.
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Date Issued: 2011
Identifier: CFE0003634, ucf:48887
Format: Document (PDF)
PURL: http://purl.flvc.org/ucf/fd/CFE0003634

Title: Computationally Efficient Digital Backward Propagation for Fiber Nonlinearity Compensation.
Creator: Zhu, Likai, Li, Guifang, Schulzgen, Axel, Likamwa, Patrick, Wei, Lei, University of Central Florida
Abstract / Description: The next generation fiber transmission system is limited by fiber nonlinearity. A distributed nonlinearity compensation method, known as Digital Backward Propagation (DBP), is necessary for effective compensation of the joint effect of dispersion and nonlinearity. However, in order for DBP to be accurate, a large number of steps are usually required for long-haul transmission, resulting in a heavy computational load.In real time DBP implementation, the FIR filters can be used for dispersion...
Show moreThe next generation fiber transmission system is limited by fiber nonlinearity. A distributed nonlinearity compensation method, known as Digital Backward Propagation (DBP), is necessary for effective compensation of the joint effect of dispersion and nonlinearity. However, in order for DBP to be accurate, a large number of steps are usually required for long-haul transmission, resulting in a heavy computational load.In real time DBP implementation, the FIR filters can be used for dispersion compensation and account for most of the computation per step. A method of designing a complementary filter pair is proposed. The individual errors in the frequency response of the two filters in a complementary filter pair cancel each other. As a result, larger individual filter error can be tolerated and the required filter length is significantly reduced.Unequal step size can be used in DBP to minimize the number of steps. For unrepeatered transmission with distributed Raman amplification, the Raman gain as a function of the distance and the effective fiber length of each DBP step need to be calculated by solving the differential equations of Raman amplification. The split-step DBP is performed only for transmission where the signal power is high.In comparison with solving the nonlinear Schrodinger equation (NLSE) for the total field of the WDM signal, solving the coupled NLSE requires a smaller step number and a lower sampling rate. In addition, the phase-locking between the local oscillators is not necessary for solving the coupled NLSE. The XPM compensation of WDM long-haul transmission by solving the coupled NLSE is experimentally demonstrated.At the optimum power level of fiber transmission, the total nonlinear phase shift is on the order of 1 radian. Therefore, for transoceanic fiber transmission systems which consist of many ((>)100) amplified fiber spans, the nonlinear effects in each span are weak. As a result, the optical waveform evolution is dominated by the dispersion. Taking advantage of the periodic waveform evolution in periodically dispersion managed fiber link, the DBP of K fiber spans can be folded into one span with K times the nonlinearity. This method can be called (")distance-folded DBP("). Under the weakly nonlinear assumption, the optical waveform repeats at locations where accumulated dispersions are identical. Consequently, the nonlinear behavior of the optical signal also repeats at locations of identical accumulative dispersion. Hence for a fiber link with arbitrary dispersion map, the DBP steps can be folded according to the accumulated dispersion. Experimental results show considerable savings in computation using this (")dispersion-folded DBP(") method. Simulation results show that the dramatically reduced computational load makes the nonlinearity-compensated dispersion-managed fiber link a competitive candidate for the next-generation transmission systems.
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Date Issued: 2011
Identifier: CFE0004492, ucf:49272
Format: Document (PDF)
PURL: http://purl.flvc.org/ucf/fd/CFE0004492

Title: Non-Reciprocal Wave Transmission in Integrated Waveguide Array Isolators.
Creator: Ho, Yat, Likamwa, Patrick, Christodoulides, Demetrios, Vanstryland, Eric, Kaup, David, University of Central Florida
Abstract / Description: Non-reciprocal wave transmission is a phenomenon witnessed in certain photonic devices when the wave propagation dynamics through the device along one direction differs greatly from the dynamics along the counter-propagating direction. Specifically, it refers to significant power transfer occurring in one direction, and greatly reduced power transfer in the opposite direction. The resulting effect is to isolate the directionality of wave propagation, allowing transmission to occur along one...
Show moreNon-reciprocal wave transmission is a phenomenon witnessed in certain photonic devices when the wave propagation dynamics through the device along one direction differs greatly from the dynamics along the counter-propagating direction. Specifically, it refers to significant power transfer occurring in one direction, and greatly reduced power transfer in the opposite direction. The resulting effect is to isolate the directionality of wave propagation, allowing transmission to occur along one direction only.Given the popularity of photonic integrated circuits (PIC), in which all the optical components are fabricated on the same chip so that the entire optical system can be made more compact, it is desirable to have an easily integrated optical isolator. Common free-space optical isolator designs, which rely on the Faraday effect, are limited by the availability of suitable magnetic materials. This research proposes a novel integrated optical isolator based on an array of closely spaced, identical waveguides. Because of the nonlinear optical properties of the material, this device exploits the differing behaviors of such an array when illuminated with either a high power or a low power beam to achieve non-reciprocal wave transmission in the forwards and backwards directions, respectively. The switching can be controlled electro-optically via an integrated gain section which provides optical amplification before the input to the array. The design, fabrication, characterization and testing of this optical isolator are covered in this dissertation. We study the switching dynamics of this device and present its optimum operating conditions. ?
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Date Issued: 2012
Identifier: CFE0004305, ucf:49495
Format: Document (PDF)
PURL: http://purl.flvc.org/ucf/fd/CFE0004305

Title: RESPONSE SENSITIVITY OF HIGHWAY BRIDGES TO RANDOM MULTI-COMPONENT EARTHQUAKE EXCITATION.
Creator: Cronin, Kyle, Mackie, Kevin, University of Central Florida
Abstract / Description: Highway bridges provide a critical lifeline during extreme seismic events and must maintain serviceability under a large range of earthquake intensities. Consequently, the advent of more computational power has allowed more advanced analysis approaches for predicting performance and vulnerability of highway bridges under these seismic loads. In traditional two-dimensional finite element analyses, it has been demonstrated that the incidence angle of the ground motion can play a significant...
Show moreHighway bridges provide a critical lifeline during extreme seismic events and must maintain serviceability under a large range of earthquake intensities. Consequently, the advent of more computational power has allowed more advanced analysis approaches for predicting performance and vulnerability of highway bridges under these seismic loads. In traditional two-dimensional finite element analyses, it has been demonstrated that the incidence angle of the ground motion can play a significant role in structural response. As three-dimensional nonlinear time history analyses are used more frequently in practice, ground motions are still usually applied along a single bridge axis. It is unknown how three orthogonal components of ground motion excitation should be applied to the structure to best represent the true response. In this study, the fundamental behavior of three-dimensional ground motion was studied using single-degree-of-freedom elastic spectra. Mean spectra computed from various orientation techniques were found indistinguishable when the orthogonal components were combined. The effect of incidence angle on the nonlinear structural response of highway bridges was then investigated through extensive statistical simulation. Three different bridge models were employed for this study implementing a suite of 180 multi-component ground motion records of various magnitude-distance-soil bins. Probabilistic seismic demand models for various response parameters are presented comparing the effects of random incidence angle to that of recorded directions. Although there are instances where the angle of incidence can significantly amplify response, results indicated that incidence angle had negligible effect on average ensemble response. This is consistent with results from the spectral analysis, although existing literature has emphasized incidence angle as a significant parameter of multi-component analysis.
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Date Issued: 2009
Identifier: CFE0002933, ucf:47973
Format: Document (PDF)
PURL: http://purl.flvc.org/ucf/fd/CFE0002933

Title: NONLINEAR STABILIZATION AND CONTROL OF MEDIUM RANGE SURFACE TO AIR INTERCEPTOR MISSILES.
Creator: Snyder, Mark, Qu, Zhihua, University of Central Florida
Abstract / Description: Nonlinear stabilization and control autopilots are capable of sustaining nominal performance throughout the entire fight envelope an interceptor missile may encounter during hostile engagements and require no gain scheduling to maintain autopilot stability. Due to non minimum phase conditions characteristic of tail controlled missile airframes, a separation of time scales within the dynamic equations of motion between rotational and translational differential equations was enforced to...
Show moreNonlinear stabilization and control autopilots are capable of sustaining nominal performance throughout the entire fight envelope an interceptor missile may encounter during hostile engagements and require no gain scheduling to maintain autopilot stability. Due to non minimum phase conditions characteristic of tail controlled missile airframes, a separation of time scales within the dynamic equations of motion between rotational and translational differential equations was enforced to overcome unstable effects of non minimum phase. Dynamic inversion techniques are then applied to derive linearizing equations which, when injected forward into the plant result in a fully controllable linear system. Objectives of the two time scale control architecture are to stabilize vehicle rotational rates while at the same time controlling acceleration within the lateral plane of the vehicle under rapidly increasing dynamic pressure. Full 6 degree of freedom dynamic terms including all coriolis accelerations due to translational and rotational dynamic coupling have been taken into account in the inversion process. The result is a very stable, nonlinear autopilot with fixed control gains fully capable of stable nonlinear missile control. Several actuator systems were also designed to explore the destabilizing effects second order nonlinear actuator characteristics can have on nonlinear autopilot designs.
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Date Issued: 2009
Identifier: CFE0002566, ucf:48268
Format: Document (PDF)
PURL: http://purl.flvc.org/ucf/fd/CFE0002566

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non-linear muscle model (2)	+ -
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silicon photonics (2)	+ -
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