We propose to develop a voltage-controllable multi-guide directional coupler in a planar nematic liquid crystal cell. The ITO grating-like electrodes are fabricated by the etching technique, and the director of liquid crystals will be aligned to the direction of applied electric field. Owing to the uniaxial property of liquid crystals, the difference of refractive index between two neighboring channels is increased with the applied voltage. Therefore, the coupling efficiency among grating-like multi-guide is also increased with the applied voltage. By using the combination of microscope and CCD system, the dynamic coupling can be observed under the distribution of grating-like electric field. The propagation of light in each channel can be selected by the controllable voltage between the electrodes of the individual channel. The intensity distribution of coupling in the transverse direction can be obtained by analyzing the image captured from the microscope and CCD system.

Analysis of dielectric straight bending waveguides has been a difficult problem in the past. Traditionally the task for computing bending of optical waveguides is carried out by the beam propagation method (BPM). However, due its assumptions on one-way propagation and paraxial approximation, BPM is unable to consider the reflection of dielectric straight-bent waveguides when the bending angles are large. In a straight-bent waveguide, two coordinate systems are needed to fully describe the ongoing complex scattering process in the transition region of the waveguide. It is extremely hard to analyze such an unbounded problems with two incompatible coordinate systems even for those general-purpose methods like the finite-difference, finite-element. In this thesis, we use the analytic continuity method (ACM) to deal with the boundary conditions that both the tangential electromagnetic field components must be continuous across the bending line. This method can handle the mismatch of two coordinate systems and decrease the amount of calculation and error for small bending angles. From the two coupled integral equation we can derive matrix equation via Galerkin least squared error method. The main part of this thesis contains the derivation of the approximate formula of the transmission and reflection matrices (scattering matrices) for a micro-bent waveguide. We show numerical results of various two-corner bends using cascading of these scattering matrices.

Tapered waveguides are often used as spot-size converters and power dividers. In general, radiation in these devices is hard to analyze by either BPM or FD-TD methods. We apply the full eigenmode expansion technique (FEMET) to study the propagation of an adiabatic dielectric tapered waveguide. We often assume that wave propagation in an ideal ¡§adiabatic¡¨ dielectric waveguide suffer no reflection nor radiation loss. It is especially true for the fundamental mode propagation in an ¡§adiabatic¡¨ dielectric waveguide. Thus, the fundamental mode of the input waveguides will be converted to the corresponding fundamental mode of the output waveguide whenever the two are connected by an adiabatically tapered waveguide. However, the higher-order modes do not always propagate through the tapered waveguide when the output waveguide does not support that particular guiding mode. It is interesting to predict such radiation phenomena and to observe them in a numerical experiment. In this thesis we consider the titled straight waveguide (TSR) as our test example. Since TSR has an exact solution in its natural coordinate system, we can study computational characteristics of FEMET via TSR examples. Using FEMET and FD-FD method, we carefully examine mode evolution, conversion radiation and reflection of many quasi-adiabatic tapered waveguides. Finally the apparent visual radiation angles are defined and computed as function of taper angle core/cladding indices and incident mode order for both TE and TM mode cases.

Present day optical integrated circuits contain many continuously bending waveguides making it important to study EM field profiles of bending waveguides. The mostly widely used numerical method for analyzing bending waveguides is the beam propagation method (BPM). Although it can calculate very fast, BPM results are not accurate enough in many wide-angle applications due to BPM¡¦s intrinsic paraxial approximation. Recently, full-wave based finite-difference time-domain technique has become quite popular and has been used to study many optical devices. Unfortunately it can not be used to study smoothly bending waveguides due to huge computational resource requirements needed for these large optical devices. In the absence of reflection in a bending waveguide, other one way, wide-angle methods can be applied. In this thesis we propose two such methods to analyze different kinds of bending waveguides. We use full eigen-mode expansion technique (FEMET) when reflection is negligible. In cases where reflection is strong, we propose a cylindrical couple transverse-mode integral-equation (C-CTMIE) to do the job. Both FEMET and CTMIE methods are built on complete sets of circular layered modes of the underlying structure. These modes are not easy to solve because the standard cylindrical mode solver requires extensive references to Bessel functions of complex arguments and orders. Here in this thesis, we proposed to expand cylindrical layered modes from planar layered modes of an equivalent structure. In essence, we renormalize the existing planar layered waveguide modes and turn them into desired circular layered modes. We show that using a matrix eigenvector formulation, this relatively simple technique is not only quite fast but also produces very accurate results. Finally using these circular modes various S-bend waveguides are analyzed. We also present a design to minimize the radiation loss of a circular waveguide using whisper gallery modes.

A low-loss polyimide/Ta2O5/SiO2 antiresonant reflecting optical waveguide (ARROW) at quasi-antiresonant condition is presented for the first time. The ARROW device was fabricated using both the organic and dielectric thin film technologies. It consisted of the fluorinated polyimide, tantalum pentoxide (Ta2O5) and silicon dioxide (SiO2) hybrid layers deposited on a Si substrate. For TE polarized light, the propagation loss of the waveguide as low as 0.4 dB/cm was obtained at 1.3 mm. The propagation loss for TM polarized light was 1.5 dB/cm. An ARROW waveguide fabricated using the polyimide/Ta2O5/polyimide material system is also presented for comparison. In addition, anisotropic etching of Si-V grooves were formed using the EDP solution, and room temperature sputtered Ta2O5 was used as the etching mask. At a etching temperature of 1200C, the under cut of the V-groove is 1.6mm

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A variable (0.2 to 5 MHz) repetition rate femtosecond laser was applied to delineate the role of thermal diffusion and heat accumulation effects in forming low-loss optical waveguides in borosilicate glass across a broad range of laser exposure conditions. For the first time, a transition from thermal diffusion-dominated transport at 200-kHz repetition rate to strong heat accumulation at 0.5 to 2 MHz was observed to drive significant variations in waveguide morphology, with rapidly increasing waveguide diameter that accurately followed a simple thermal diffusion model over all exposure variables tested. Amongst these strong thermal trends, a common exposure window of 200-mW average power and ~15-mm/s scan speed was discovered across the range of 200-kHz to 2-MHz repetition rates for minimizing insertion loss despite a 10-fold drop in laser pulse energy. Waveguide morphology and thermal modeling indicate that strong thermal diffusion effects at 200 kHz give way to a weak heat accumulation effect at ~1uJ pulse energy for generating low loss waveguides, while stronger heat accumulation effects above 1-MHz repetition rate offered overall superior guiding. The waveguides were shown to be thermally stable up to 800°C, showing promise for high temperature applications. Using a low numerical aperture (0.4) lens, the effect of spherical aberration was reduced, enabling similar low-loss waveguides over an unprecedented 520-um depth range, opening the door for multi-level, three-dimensional, optical integrated circuits. In contrast to borosilicate glass, waveguides written in pure fused silica under similar conditions showed only little evidence of heat accumulation, yielding morphology similar to waveguides fabricated with low repetition rate (1 kHz) Ti-Sapphire lasers. Despite the absence of heat accumulation in fused silica owing to its large bandgap and high melting point, optimization of the laser wavelength, power, repetition rate, polarization, pulse duration and writing speed resulted in uniform, high-index contrast waveguide structures with low insertion loss. Optimum laser exposure recipes for waveguide formation in borosilicate and fused silica glass were applied to fabricate optical devices such as wavelength-sensitive and insensitive directional couplers for passive optical networks, buried and surface microfluidic and waveguide networks for lab-on-a-chip functionality, and narrowband grating waveguides for sensing.

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Annealed proton-exchanged (APE) MgO:PPLN ridge waveguides have been successfully developed, and its optical properties have been researched. Nonlinear wavelength conversion experiments have been successfully conducted using the developed waveguide. The APE MgO:PPLN ridge waveguide has been proved suitable for high efficiency nonlinear optical conversions across its transparency spectrum from visible to mid-IR light. With distinctive features including flexibility, high efficiency and low cost, this new type of waveguide can find potential applications in various application fields. / Thesis / Candidate in Philosophy