A theoretical and experimental investigation of scatter from surface roughness and core refractive index fluctuations in planar waveguides was performed, with an emphasis placed on applications in solution-deposited SiO₂-TiO₂ (silica titania) planar waveguiding systems. A perturbation theory was used to model TE₀ mode scattering from surface and volume microstructure, and to predict attenuation when provided with the necessary waveguide and scattering parameters. Final forms for the equations predicting surface and volume scatter losses into the cover and substrate regions of the waveguides were provided. The rather complex perturbation theory model of surface scatter was compared to a very simple, intuitive model based on the Rayleigh criterion. The two models were shown to predict surface induced attenuation values which were in very close agreement when the guided mode propagation angle approached 90°. Thus, the simple model was shown to be adequate for predicting TE₀ mode surface scattering losses for waveguides which were very thick, and/or possessed a low refractive index. Considerable emphasis was placed on providing a simple, physical picture of guided mode scattering, utilizing rays to represent the scattered light. Following the development of this technique, it was utilized to explain the origins of interference peaks in surface scattered radiation at certain values of film thickness. Solution chemistry and processing methodologies for 50:50 mol% and 35:65 mol% SiO₂-TiO₂ sol-gel films, yielding high quality, amorphous, glass waveguides, were discussed. Attenuation in the 50:50 mol% films was 1-2 dB/cm, while attenuation in the 35:65 mol% films was 0.3-0.5 dB/cm, at λ = 0.6328 μm. Absorption in these films was negligible. Waveguide losses were measured by transferring the scattered streak to a remote image plane (using a coherent fiber bundle) and scanning it using an automated, stepper-motor controlled, apertured photomultiplier tube. Testing and calibration techniques were described in detail. We found that surface-induced scattering was the dominant loss mechanism in the 35:65 mol% SiO₂-TiO₂ films. Surface roughnesses of the sol-gel films, measured using Atomic Force Microscopy, ranged from about 2-5 A rms, with correlation lengths from about 0.05-0.75 μm.

This thesis encompasses a theoretical analysis, the fabrication, and optical characterization of a novel compact Bragg Slot Waveguide with a Cavity (BSWC). Strong light confinement in the low refractive index slot region formed by two silicon slabs on a silicon dioxide substrate [1] makes this structure useful for optofluidic, sensing, and optical trapping applications. The transmission spectrum of the BSWC can be engineered through the dimensional variations of the waveguide and through the refractive index change of the surrounding medium. BSWC is compact and can be integrated with various components on a chip for increased functionality. The results in this thesis show a good agreement between analytical and experimental results, while emphasizing the increasing importance of atomic-scale imperfections as a result of fabrication on the nano-scale. The impact of the slot width, slab width, and the cavity length on the waveguide transmission spectrum is investigated.

This thesis encompasses a theoretical analysis, the fabrication, and optical characterization of a novel compact Bragg Slot Waveguide with a Cavity (BSWC). Strong light confinement in the low refractive index slot region formed by two silicon slabs on a silicon dioxide substrate [1] makes this structure useful for optofluidic, sensing, and optical trapping applications. The transmission spectrum of the BSWC can be engineered through the dimensional variations of the waveguide and through the refractive index change of the surrounding medium. BSWC is compact and can be integrated with various components on a chip for increased functionality. The results in this thesis show a good agreement between analytical and experimental results, while emphasizing the increasing importance of atomic-scale imperfections as a result of fabrication on the nano-scale. The impact of the slot width, slab width, and the cavity length on the waveguide transmission spectrum is investigated.

This thesis presents an investigation of the damping of spin waves in ferromagnetic Au(3 nm)/Ni(10 nm)/MgO(001) thin films using the time-resolved Magneto-optical Kerr Effect (TR-MOKE) and ferromagnetic resonance (FMR) techniques. In the optical measurements, a 150 fs, 800 nm laser beam pulse is split into pump and probe components. The pump pulse, containing most of the beam energy, thermally excites coherent spin precession. The weaker probe pulse, time-delayed by a variable beam path, captures the magnetization dynamics via the polar MOKE effect, and oscillations are observed as a function of external field amplitude and direction. The extracted precession frequency is consistent in both the optical and resonance techniques; however, additional damping is observed in the TR-MOKE measurements that is strongly correlated to the orientation of the magnetization with respect to the magnetic anisotropy. The damping is identical in TR-MOKE and FMR only when the external field is applied near the easy axis of magnetization. The enhanced damping in TR-MOKE is shown to be a consequence of pump-induced inhomogeneous broadening in the presence of magnetic anisotropy, a result of differing temperature recovery profiles for the magnetization and magnetic anisotropy. Finally, a simple model is developed which explains the anisotropic damping: mode broadening occurs in regions where the magnetization changes rapidly with respect to changes in the external field, as determined by the curvature of the magnetic free energy. We thus introduce a novel damping effect in TR-MOKE: pump-induced anisotropic damping (PIAD).

No description available.

Antenna systems play a significant role in today’s electronic communications. They are essential for cell phones, satellites, radio, and radar among many other important applications. This paper describes the design, assembly, and operation of an antenna demonstration system designed to instill interest in the field of antenna design among high school and undergraduate college students. The system is portable, supplied solely by DC power supplies, easily reproducible, and includes rotational axes to illustrate antenna performance limitations and requirements. It provides a visual indication of wireless signal strength and demonstrates several antenna performance characteristics including polarization, gain and directivity, radiation patterns - nulls and maximums, and spreading loss. Several antenna types used in present-day applications (embedded and reflector antennas), in addition to structural barriers encountered in typical operating environments, are used to define wireless system performance. Students gain insight on radiating structure and orientation effects on antenna system characteristics and hopefully develop interest in future wireless studies.

Thesis (Ph.D.)--City University of Hong Kong, 2009. / "Submitted to Department of Electronic Engineering in partial fulfillment of the requirements for the degree of Doctor of Philosophy." Includes bibliographical references.

Thesis (Ph. D.)--University of Chicago, Dept. of Chemistry, August 2001. / Includes bibliographical references. Also available on the Internet.

Light, at the length-scale on the order of its wavelength, does not simply behave as "light ray", but instead diffracts, scatters, and interferes with itself, as governed by Maxwell's equations. A profound understanding of the underlying physics has inspired the emergence of a new frontier of materials and devices in the past few decades. This thesis explores the concepts and approaches for manipulating light at the wavelength-scale in a variety of topics, including anti-reflective coatings, on-chip silicon photonics, optical microcavities and nanolasers, microwave particle accelerators, and optical nonlinearities. In Chapter 1, an optimal tapered profile that maximizes light transmission between two media with different refractive indices is derived from analytical theory and numerical modeling. A broadband wide-angle anti-reflective coating at the air/silicon interface is designed for the application of photovoltaics. In Chapter 2, a reverse design method for realizing arbitrary on-chip optical filters is demonstrated using an analytical solution derived from Chapter 1. Example designs are experimentally verified on a CMOS-compatible silicon-on-insulator (SOI) platform. Among this device’s many potential applications, the use for ultrafast on-chip pulse shaping is highlighted and numerically demonstrated. In Chapter 3, the concept of tapering is applied to the design of photonic crystal cavities. As a result, the scattering losses of cavities are suppressed, and light can be localized in a wavelength-scale volume for a long life-time. In Chapter 4, photonic crystal cavity-based nanolasers with low power consumption are demonstrated with two different prototypes-photonic crystal nanobeams and photonic crystal disks. The use of graphene is also explored in this chapter for the purpose of electrically-driven nanoscale light-emitting devices. In Chapter 5, photonic crystal cavities at millimeter wavelength for particle acceleration applications are developed. In Chapter 6, a novel design of dual-polarized mode photonic crystal cavities, and its potential for difference-frequency generations are examined. / Engineering and Applied Sciences

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