Recent progress in combing multiple materials with distinct optical, electronic, and thermomechanical properties monolithically in a kilometer-long fiber drawn from a preform offers unique multifunctionality at a low cost. A wide range of unique in-fiber devices have been developed in fiber form-factor using this strategy. Here, I summary my recent results in this nascent field of 'multimaterial fibers'. I will focus on my achievements in producing robust infrared optical fibers and in appropriating optical fiber production technology for applications in nanofabrication. The development of optical components suitable for the infrared (IR) is crucial for applications in this spectral range to reach the maturity level of their counterparts in the visible and near-infrared spectral regimes. A critical class of optical components that has yet to be fully developed is that of IR optical fibers. Here I will present several unique approaches that may result in low-cost, robust IR fibers that transmit light from 1.5 microns to 15 microns drawn from multimaterial preforms. These preforms are prepared exploiting the newly developed procedure of multimaterial coextrusion, which provides unprecedented flexibility in material choices and structure engineering in the extruded preform. I will present several different 'generations' of multimaterial extrusion that enable access to a variety of IR fibers. Examples of the IR fibers realized using this methodology include single mode IR fibers, large index-contrast IR fibers, IR imaging fiber bundles, IR photonic crystal and potentially photonic band-gap fibers. The complex structures produced in multimaterial fibers may also be used in the fabrication of micro- and nano-scale spherical particles by exploiting a recently discovered in-fiber Plateau-Rayleigh capillary instability. Such multimaterial structured particles have promising application in drug delivery, optical sensors, and nanobiotechnology. The benefits accrued from the multimaterial fiber methodology allow for the scalable fabrication of micro- and nano-scale particles having complex internal architectures, such as multi-shell particles, Janus-particles, and particles with combined control over the radial and azimuthal structure. Finally, I will summarize my views on the compatibility of a wide range of amorphous and crystalline materials with the traditional thermal fiber drawing process and with the more recent multimaterial fiber strategy.

Symmetry plays a crucial role in exploring the laws of nature. By exploiting some of the underlying analogies between the mathematical formalism of quantum mechanics and that of electrodynamics, in this dissertation we show that optics can provide a fertile ground for studying, observing, and utilizing some of the peculiar symmetries that are currently out of reach in other areas of physics. In particular, in this work, we investigate two important classes of symmetries, parity-time symmetry (PT) and supersymmetry (SUSY), within the context of classical optics. The presence of PT symmetry can lead to entirely real spectra in non-Hermitian systems. In optics, PT-symmetric structures involving balanced regions of gain and loss exhibit intriguing properties which are otherwise unattainable in traditional Hermitian systems. We show that selective PT symmetry breaking offers a new method for achieving single mode operation in laser cavities. Other interesting phenomena also arise in connection with PT periodic structures. Along these lines, we introduce a new class of optical lattices, the so called mesh lattices. Such arrays provide an ideal platform for observing a range of PT-related phenomena. We show that defect sates and solitons exist in such periodic environments exhibiting unusual behavior. We also investigate the scattering properties of PT-symmetric particles and we show that such structures can deflect light in a controllable manner. In the second part of this dissertation, we introduce the concept of supersymmetric optics. In this regard, we show that any optical structure can be paired with a superpartner with similar guided wave and scattering properties. As a result, the guided mode spectra of these optical waveguide systems can be judiciously engineered so as to realize new families of mode filters and mode division multiplexers and demultiplexers. We also present the first experimental demonstration of light dynamics in SUSY ladders of photonic lattices. In addition a new type of transformation optics based on supersymmetry is also explored. Finally, using the SUSY formalism in non-Hermitian settings, we identify more general families of complex optical potentials with real spectra.

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 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.

For the past few decades, tremendous progress has been made on liquid crystal display (LCD) technologies in terms of stability, resolution, contrast ratio, and viewing angle. The remaining challenge is response time. The state-of-the-art response time of a nematic liquid crystal is a few milliseconds. Faster response time is desirable in order to reduce motion blur and to realize color sequential display using RGB LEDs, which triples the optical efficiency and resolution density. Polymer-stabilized blue phase liquid crystal (PS-BPLC) is a strong candidate for achieving fast response time because its self-assembled cubic structure greatly reduces the coherence length. The response time is typically in the submillisecond range and can even reach microsecond under optimized conditions. Moreover, it exhibit several attractive features, such as no need for surface alignment layer, intrinsic wide viewing angle, and cell gap insensitivity if an in-plane-switching (IPS) cell is employed. In this dissertation, recent progresses in polymer-stabilized blue phases, or more generally optically-isotropic liquid crystals, are presented. Potential applications in display and photonic devices are also demonstrated. In Chapter 1, a brief introduction of optically isotropic liquid crystals is given. In Chapter 2, we investigate each component of polymer-stabilized blue phase materials and provide guidelines for material preparation and optimization. In Chapter 3, the electro-optical properties of PS-BPLCs, including electric-field-induced birefringence and dynamic behaviors are characterized. Theoretical models are proposed to explain the physical phenomena. Good agreements between experimental data and models are obtained. The proposed models also provide useful guidelines for both material and device optimizations. Four display and photonic devices using PS-BPLCs are demonstrated in Chapter 4. First, by red-shifting the Bragg reflection and using circular polarizers, we reduce the LCD driving voltage by 35% as compared to a short-pitch BPLC while maintaining high contrast ratio and submillisecond response time. Second, a turning film which is critically needed for widening the viewing angle of a vertical field switching (VFS) BPLC mode is designed. With this film, the viewing angle of VFS is widened to [plus or minus] 80[degrees] in horizontal direction and [plus or minus] 50[degrees] in vertical direction. Without this turning film, the viewing angle is only [plus or minus]30[degrees], which is too narrow for most applications. Third, a reflective BPLC display with vivid colors, submillisecond response time, and natural grayscales is demonstrated for the first time. The proposed BPLC reflective display opens a new gateway for 3D reflective displays; it could make significant impact to display industry. Finally, we demonstrate a tunable phase grating with a high diffraction efficiency of 40% and submillisecond response time. This tunable grating exhibits great potential for photonic and display applications, such as optical interconnects, beam steering, and projection displays.

This thesis studies the center wavelength accuracy of a Fiber Bragg Grating Sensor system that has a large number of sensor elements both as a function of wavelength and as a function of position. Determining the center wavelength of each of the fiber optic sensors is a critical parameter that ultimately determines sensor accuracy. The high density environment can result in degradation of accuracy of the center wavelength measurement. This thesis aims to quantify this measurement error both with theoretical and experimental studies. There are many sensing applications where optical fiber sensors are preferred over electrical sensors, such as the oil and gas industry where fiber optic sensors are used to monitor wells and pipelines due to their low signal degradation over long distances and immunity to harsh physical environments. Fiber Bragg grating (FBG) sensors in particular have widespread use because of their versatility, measurement sensitivity, and distributed multiplexing abilities. In conventional wavelength multiplexing, up to 50 FBG sensors are spread out over a band of 100nm, each with a center wavelength difference large enough so that each element can be individually measured. However, numerous sensing applications require several hundred to over a thousand sensors cascaded together on a single fiber. These sensor arrays use a combination of WDM and TDM for measurements, where many FBG sensors with the same center wavelength are separated by a long enough length of fiber so that the reflected signals are separated in time. These Wavelength-to-Time Domain Multiplexing (W-TDM) measurements are enabled by Insight Photonic’s new ‘akinetically’ swept, all-semiconductor laser. This laser is a Vernier-Tuned Distributed Bragg Reflector (VT-DBR) device, capable of rapidly sweeping through different wavelengths without any moving parts. Attributes that make this laser superior to mechanically-swept lasers include: 1) short and long term consistent sweep-sweep reliability, 2) availability at many wavelengths, 3) a narrow linewidth with single longitudinal mode, and 4) the ability to do non-traditional sweep patterns that facilitate measurement of high-density sensor networks. In this thesis, experiments will be performed in the lab with the Insight VT-DBR laser to determine how accurately the center wavelength of a single Fiber Bragg grating can be measured. Experiments will also be performed with two and three FBGs to compare different algorithmic approaches to measurements. The second part of the thesis will simulate both single and multiple FBG sensor environments, comparing the center wavelength measurement accuracy results for different parameters including signal-to-noise ratios, wavelength point density, FBG loss and width, and multiple algorithmic approaches. The results of these experiments and simulations will demonstrate how accurate a FBG sensor system is at particular parameters, which will be useful to those designing a sensor network or performing similar experiments.

<p>The rapid development of fiber optic communication systems requires higher transmission data rate and longer reach. This thesis deals with the limiting factors in design of long-haul fiber optic communication systems and the techniques used to suppress their resulting impairments. These impairments include fiber chromatic dispersion, the Ker nonlinearity and nonlinear phase noise due to amplified spontaneous emission.</p> <p>In the first part of this thesis, we investigate the effect of amplified spontaneous noise in quasi-linear systems. In quasi-linear systems, inline optical amplifiers change the amplitude of the optical field envelope randomly and fiber nonlinear effects such as self phase modulation (SPM) convert the amplitude fluctuations to phase fluctuations which is known as nonlinear phase noise. For M-ary phase shift keying (PSK) signals, symbol error probability is determined solely by the probability density function (PDF) of the phase. Under the Gaussian PDF assumption, the phase variance can be related to the symbol error probability for PSK signals. We implemented the simulation based on analytical phase noise variance and Monte-Carlo simulation, and it is found that the analytical approximation is in good agreement with numerical simulations. We have developed analytical expressions for the linear and nonlinear phase noise variance due to SPM using second-order perturbation theory. It is found that as the transmission reach and/or lunch power increase, the variance of the phase noise calculated using first order perturbation theory becomes inaccurate. However, the variance calculated using second order perturbation theory is in good agreement with numerical simulations. We have also showed that the analytical formula given in this chapter for the variance of nonlinear phase noise can be used as a design tool to investigate the optimum system design parameters such as average power and dispersion maps for coherent fiber optic systems based on phase shift keying due to the fact that the numerical simulation of nonlinear Schrodinger (NLS) equation is time consuming, however, the analytical method based on solving NLS equation using perturbation approximation is quite efficient and therefore the analytical variance can be obtained more easily without requiring extensive computational efforts, and also with fairly good accuracy.</p> <p>In the second part of this thesis, an improved optical signal processing using highly nonlinear fibers is studied. This technique, optical backward propagation (OBP), can compensate for the fiber dispersion and nonlinearity using optical nonlinearity compensators (NLC) and dispersion compensating fibers (DCF), respectively. In contrast, digital backward propagation (DBP) uses the high-speed digital signal processing (DSP) unit to compensate for the fiber nonlinearity and dispersion digital domain. NLC imparts a phase shift that is equal in magnitude to the nonlinear phase shift due to Fiber propagation, but opposite in sign. In principle, BP schemes could undo the deterministic (bit-pattern dependent) nonlinear impairments, but it can not compensate for the stochastic nonlinear impairments such as nonlinear phase noise. We also introduced a novel inline optical nonlinearity compensation (IONC) technique. Our Numerical simulations show that the transmission performance can be greatly improved using OBP and IONC. Using IONC, the transmission reach becomes almost twice of DBP. The advantage of OBP and IONC over DBP are as follows: OBP/IONC can compensate the nonlinear impairments for all the channels of a wavelength division multiplexed system (WDM) in real time while it would be very challenging to implement DBP for such systems due to its computational cost and bandwidth requirement. OBP and IONC can be used for direct detection systems as well as for coherent detection while they provide the compensation of dispersion and nonlinearity in real time, but DBP works only for coherent detection and currently limited to off-line signal processing.</p> / Master of Applied Science (MASc)

<p>A new model, referred to as the Rational Dispersion Model is proposed for modeling of dispersive materials in wide wavelength range using the Finite-Difference Time-Domain(FDTD) method. A hardware-accelerated FDTD method combined with the matrix pencil method is proposed to solve both guided and leaky modes. A circuit model based on the complex mode theory is proposed for analysis of large scale structures with non-negligible radiation effects.</p> / Doctor of Philosophy (PhD)

<p>Optical waveguide is a very important component in numerous optical structures, devices and photonic circuits. With the rapid development of fabrication technologies, increasing integrated complexity and different materials characteristics, there is higher demand on high-index contrast waveguide with arbitrary cross section and anisotropic material, which indicates the need to develop an efficient, high-performance mode solver to analyze optical waveguides to reduce the fabrication cycle and total cost. Modeling and simulation methods, including Finite Difference Time-Domain (FDTD) method, Finite Element Method (FEM), Beam Propagating Method (BPM), Mode Matching Method (MMM) and Couple Mode Theory (CMT), etc, have been popular for years. Among those methods, FEM is a good and efficient method, especially for its superiority on arbitrary meshes.</p> <p>In this thesis, both scalar and vectorial FEM mode solvers are implemented with an emphasis on dealing with the radiation and evanescent modes by enclosing the whole region with the Perfect Matched Layer (PML) and Perfect Reflecting Boundary (PRB). Thus, the unbounded and continuous radiation modes together with evanescent modes are replaced by what we called "complex modes", but still keeping the completeness and orthogonality properties.</p> / Master of Applied Science (MASc)

published_or_final_version / abstract / Electrical and Electronic Engineering / Master / Master of Philosophy

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