"The continually increasing speed of microprocessors over the past forty years has been due in large part to miniaturization. The smaller a transistor is made, the faster it can run, and the more can be packed onto a chip. More recently, the performance of the electrical interconnects, which are responsible for transporting data within the microprocessor and between the microprocessor and memory, has been unable to keep pace. As the interconnect is scaled down along with the transistors, its bandwidth decreases and its latency and power consumption increase. This not only decreases the bandwidth of the interconnect, but also increases both its latency and power consumption. Optical interconnects can directly address these problems by replacing electrical interconnects at the system level. In this work we outline the requirements for a successful optical interconnect, and show that the photonic crystal platform is ideal for optical interconnects. Specifically, we show how photonic crystals can be used to build one of the most basic components of an optical interconnect: the electro-optic modulator, which converts an electrical signal into the optical domain. We will first discuss the potential of photonic crystal slow light for modulation, and then introduce a new multi-channel slow light platform for improved bandwidth. Next we describe the design of a photonic crystal resonator that is embedded entirely in silicon dioxide, which is a fundamental requirement for chip compatibility. This resonator uses a graded cavity design and has a quality factor as high as 300,000. It can be coupled to standard strip waveguides, facilitating the integration of photonic crystal devices with other photonic devices. We will also describe a simplified model of photonic crystal line-defect cavities that can aid in their design. Finally, we propose a design for a low-energy electro-optic modulator based on this graded cavity. Due to the extremely small mode volume possible with photonic crystal resonators, the active region can be on the order of a single cubic wavelength in size. By optimizing a number of parameters, a theoretical switching energy as low as 1 fJ/ bit is possible using this design."--Leaves viii-ix

"Silicon photonics is the most promising candidate to achieve the high data transmission rates required for future telecommunications bandwidth demands, which require upgraded optical interconnects. Optical modulators, such as Mach-Zehnder modulators, are one of the most important sub-components in any optical communication system. Leveraging the complementary metal-oxide semiconductor (CMOS) fabrication processes, the integration of optical devices become more cost effective and energy efficient. Optical frequency comb has widespread applications in microwave photonics and optical communications as a multi-wavelength source for wavelength division multiplexing and orthogonal frequency division multiplexing systems. The most common approach to generate optical frequency comb is based on the use of optical modulators. On-chip optical frequency comb generation has great flexibility to tune the center frequency based on the frequency of the continuous wave laser, comb spacing, and the number of comb lines based on adjusting the RF signal frequency, power, and phase that is applied to the electro-optic modulator. The limitation of this technique lies in the high insertion loss, especially in cascaded modulators. In this thesis, we investigate two integrated cascaded electro-optic modulators in CMOS-compatible silicon-on-insulator for optical frequency comb generation. The first comprises cascaded push-pull traveling wave Mach-Zehnder modulators (MZM) while the second involves cascaded microring modulators (MRM). The 9 comb lines with a spacing up to 10 GHz and bandwidth of 90 GHz for the cascaded MZM, and 5 comb lines with a spacing up to 10 GHz and a bandwidth of 50 GHz for the cascaded MRM. The measured temporal waveforms corresponding to the generated quasi-rectangular combs match with the sinc-shaped Nyquist pulses which are well-known for its high spectral efficiency and have zero inter-symbol interference. Lastly, we summarize and compare the performance of both modulators"--

Abstract: The huge increments in data traffic and communication over the past few decades have pushed the conventional electronic communication systems to their physical limits in terms of data rate, bandwidth and capacity. The continuous shrinking of feature sizes, the increase in the microelectronic integrated circuits complexity, and the increasing demand for higher speeds and data rates have all stimulated seeking new technology to replace the currently present microelectronics industry rather than improving it. Photonics is one of the most likely candidates to answer this pursuit for its compatibility with the fiber optic industry, which has shown a great success in large-scale communication since around 50 years ago. Silicon photonics, in particular, is very interesting for the scientific community for its compatibility with the foundries which are the bases for microelectronic industries around the globe. Advancements in silicon photonic would rather enable the integration of both electronic and optical system components on the same chip, which is a very important step in the transition towards all-optical on-chip systems. The huge interest in silicon photonics over the past two decades has brought forth a number of applications in various fields, such as biosensing, displays, on- and off-chip interconnection, artificial intelligence, internet of things, big data centres, and telecommunications. In practice, there are many ways of realizing and fabricating on-chip silicon waveguides. Ion exchange process is one of the most commonly used techniques in fabricating glass waveguides as it offers ease of application, low cost, and low equipment requirements. Unfortunately, numerical constraints render the modelling of this process challenging due to the presence of computational instabilities at certain conditions. In the first part of this thesis, this issue is worked out by introducing a novel numerical model based on finite element method formulation. In the second part of the thesis, we concentrate on one of the promising applications of silicon photonics, which is the telecommunications. Optical communication systems include many components such as, light sources, photodetectors, multiplexers, filters, resonators, optical interconnects, switches, couplers, splitters, and modulators. The optical modulator is considered the most essential component in an optical communication system as it converts the incoming electric digital data into an optical data stream. Its acts as a binding link between both the optical and electronic domains on the chip. Therefore, electro-optical modulators have gained enormous attention during the past few years. Weak electro-optical effects in intrinsic silicon have stimulated the search for novel materials to be responsible for the modulation of the light beam. Surface plasmon polaritons, which propagate at a metal-dielectric interface, allow the confinement of light in subwavelength dimensions. However, they introduce large losses to the system. Transparent conducting oxides, especially indium tin oxide (ITO), provide metal-like response when exposed to a gating voltage while maintaining lower losses than noble metals. In the second part of the thesis, we propose two novel electro-optical on-chip integrated modulators based on the utilization of ITO as the active material.

Thanks to the development of silicon VLSI technology over the past several decades, we can now integrate far more transistors onto a single chip than ever before. However, this also imposes more stringent requirements, in terms of bandwidth, density, and power consumption, on the interconnect systems that link transistors. The interconnect system is currently one of the major hurdles for the further advancement of the electronic technology. Optical interconnect is considered a promising solution to overcome the interconnect bottleneck. The quantum-confined Stark effect in Ge/SiGe quantum well system paves the way to realize efficient optical modulation on Si in a fully CMOS compatible fashion. In this dissertation, we investigate the integration of Ge/SiGe quantum well waveguide modulators with silicon-on-insulator waveguides. For the first time, we demonstrate the selective epitaxial growth of Ge/SiGe quantum well structures on patterned Si substrates. The selective epitaxy exhibits perfect selectivity and minimal pattern sensitivity. Compared to their counterparts made using bulk epitaxy, the p-i-n diodes from selective epitaxy demonstrate very low reverse leakage current and high reverse breakdown voltage. Strong quantum-confined Stark effect (QCSE) is, for the first time, demonstrated in this material system in the telecommunication C-band at room temperature. A 3 dB optical modulation bandwidth of 2.8 THz is measured, covering more than half of the C-band. We propose, analyze, and experimentally demonstrate a novel approach to realize butt coupling between a SOI waveguide and a selectively grown Ge/SiGe quantum well waveguide modulator using a thin dielectric spacer. Through numerical simulation, we show that the insertion loss penalty for a thin 20 nm thick spacer can be as low as 0.13 dB. Such a quantum well waveguide modulator with a footprint of 8 [Mu]m2 has also been fabricated, demonstrating 3.2 dB modulation contrast with merely 1V swing at a speed of 16 Gpbs.

Many optoelectronic modulator designs use waveguides. Coupling light into waveguides requires a difficult alignment step. This dissertation will describe a number of optoelectronic modulators that do not have the tight alignment constraints associated with waveguide-based modulators. The eased alignment constraints may be important for the practical manufacturing and packaging of systems using optical interconnects.

On-chip optical interconnect is an emerging technology with great potentials to replace traditional electrical interconnects for large-data-operation and low-power-consumption communications of integrated circuit chips. The microring resonator-based modulator has prominent advantages such as compact footprint, low loss, high quality factor (Q-factor), integrating capability, and low power consumption to be a prime component in CMOS- compatible optical interconnect systems. In this thesis, a silicon carrier-depletion mode microring modulator is designed. The design methodology and simulation process are demonstrated in detail. To achieve the highest electro-optic phase modulation efficiency, a vertical doping structure is optimized for pn junction integrated waveguide of the microring modulator. The proposed microring modulator with a small ring radius of 3.7 [mu]m yields a high Q-factor higher than 8000. The simulated electro-optic phase efficiency is as high as 58 pm/V. The microring modulator is designed to achieve a critical coupling for the highest extinction ratio. When operated at low drive voltage from 0 V to -2 V bias, the modulation extinction ratio of the microring modulator reaches 35.56 dB when insertion loss is only about 3 dB. For the fabrication process definition, a simulation of the fabrication process, including implantation, etching, and annealing, is also be provided. Furthermore, a whole design and simulation process for a depletion-mode microdisk modulator with a vertical doping pn junction is also studied and demonstrated in Chapter 9. In the APPENDIX A, a high aspect-ratio through silicon vias fabrication process is demonstrated. Via applying a "hybrid Cu adhesion layer" deposited by E-beam system and sputtering in sequence, through silicon vias with an aspect ratio as high as 1: 15 is successfully achieved after electro-plating. In the APPENDIX B, a design and fabrication process of a 90° optical hybrid based on 150 nm Si3N4 platform is presented.