This book discusses some research results for CMOS-compatible silicon-based optical devices and interconnections. With accurate simulation and experimental demonstration, it provides insights on silicon-based modulation, advanced multiplexing, polarization and efficient coupling controlling technologies, which are widely used in silicon photonics. Researchers, scientists, engineers and especially students in the field of silicon photonics can benefit from the book. This book provides valuable knowledge, useful methods and practical design that can be considered in emerging silicon-based optical interconnections and communications. And it also give some guidance to student how to organize and complete an good dissertation.

"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.

Optical Interconnects provides a fascinating picture of the state of the art in optical interconnects and a perspective on what can be expected in the near future. It is composed of selected reviews authored by world leaders in the field, and these reviews are written from either an academic or industrial viewpoint. An in-depth discussion of the path towards fully-integrated optical interconnects in microelectronics is presented. This book will be useful not only to physicists, chemists, materials scientists, and engineers but also to graduate students who are interested in the fields of microelectronics and optoelectronics.

Information processing requires interconnects to carry information from one place to another. Optical interconnects between electronics systems have attracted significant attention and development for a number of years because optical links have demonstrated potential advantages for high-speed, low-power, and interference immunity. With increasing system speed and greater bandwidth requirements, the distance over which optical communication is useful has continually decreased to chip-to-chip and on-chip levels. Monolithic integration of photonics and electronics will significantly reduce the cost of optical components and further combine the functionalities of chips on the same or different boards or systems. Modulators are one of the fundamental building blocks for optical interconnects. Previous work demonstrated modulators based upon the quantum confined Stark effect (QCSE) in SiGe p-i-n devices with strained Ge/SiGe multi-quantum-well (MQW) structures in the i region. While the previous work demonstrated the effect, it did not examine the high-speed aspects of the device, which is the focus of this dissertation. High-speed modulation and low driving voltage are the keys for the device's practical use. At lower optical intensity operation, the ultimate limitation in speed will be the RC time constant of the device itself. At high optical intensity, the large number of photo generated carriers in the MQW region will limit the performance of the device through photo carrier related voltage drop and exciton saturation. In previous work, the devices consist of MQWs configured as p-i-n diodes. The electric field induced absorption change by QCSE modulates the optical transmission of the device. The focus of this thesis is the optimization of MQW material deposition, minimization of the parasitic capacitance of the probe pads for high speed, low voltage and high contrast ratio operation. The design, fabrication and high-speed characterization of devices of different sizes, with different bias voltages are presented. The device fabrication is based on processes for standard silicon electronics and is suitable for mass-production. This research will enable efficient transceivers to be monolithically integrated with silicon chips for high-speed optical interconnects. We demonstrated a modulator, with an eye diagram of 3.125GHz, a small driving voltage of 2.5V and an f3dB bandwidth greater than 30GHz. Carrier dynamics under ultra-fast laser excitation and high-speed photocurrent response are also investigated.

"Global IP traffic will continue to grow in the foreseeable future. Different applications are driving demand for increased capacity such as cloud based services, video streaming services, and big data.Since 2008, most Internet traffic has originated or terminated in datacenters. As a result, datacenters have experienced unprecedented traffic increases, where datacenter traffic will reach more than 20.6 zettabytes by 2021, i.e., 3-fold increase since 2016. In response to demands to support capacity increases, there are significant worldwide research and commercialization efforts that are being directed toward developing high speed intra- and inter-datacenter optical interconnects (DCIs). Different material platforms are used to build optical transceivers including the silicon photonics (SiP) platform. The SiP platform has the potential to build compact, high yield, high performance, and low cost complementary metal oxide semiconductor (CMOS) compatible transceivers. In this thesis, we explore devices and circuits for optical DCIs. This thesis can be divided into three parts. In the first part, we develop and demonstrate passive and active SiP components which are essential in photonic integrated circuits (PICs) for optical transceivers. The first device is a 3-dB beam splitter based on multi-mode interference (MMI), where we present the device design and wafer-scale experimental results. Then, we include subwavelength gratings into an asymmetric MMI to enable compact, large bandwidth, and different splitting ratios. Using cascaded MMIs, we design a C-band polarization beam splitter for coherent PICs, where we demonstrate the advantages of using a cascaded MMI design in improving the device extinction ratio. Next, we present the detailed design and experimental results of a high yield and low insertion loss polarization splitter and rotator. Different variations of this design are demonstrated aiming at different performance metrics and operating bands. Finally, we present a variable optical attenuator based on a Mach-Zehnder interferometer structure where a substrate undercut is added to the design to enable low power consumption. In the second part, we present PICs for 200 Gb/s and 400 Gb/s intra-datacenter optical interconnects. First, a 4-lane SiP transmitter is demonstrated based on four parallel Mach-Zehnder modulators (MZMs). The crosstalk between the four MZMs is studied using small-signal and large-signal modulation. Driving the four MZMs simultaneously, 400 Gb/s aggregate rate can be achieved using relatively low voltage swing and simple digital signal processing (DSP). Then, we explore 200 Gb/s transmitters based on dual parallel multi-electrode MZMs (MEMZMs) to generate the PAM4 signal optically which results in a better signal to noise ratio compared to the electrical generation. Finally, we exploit the other polarization dimension by demonstrating a dual-polarization transmitter in a stokes vector direct detection experiment. More than 200 Gb/s can be achieved using this transmitter which doubles the capacity used for a classical intensity modulation/direct detection system and renders a better scalable approach for bitrates beyond 400 Gb/s. In the last part, we report system-level demonstrations targeting DCI applications. First, we present a single wavelength and polarization PAM4 transmission experiment using state of the art digital-to-analog converters (DACs), analog-to-digital converters (ADCs), and a lithium niobate MZM. Then, we present the first demonstration of a 400 Gb/s transmitter optical sub-assembly (TOSA) on the coarse wavelength division multiplexing (CWDM) grid. The TOSA performance is studied versus several parameters. Results show that we can achieve more than 600 Gb/s over 20 km of single mode fiber (SMF) without optical amplification"--

These proceedings describe processing, materials and equipment for CMOS front-end integration including gate stack, source/drain and channel engineering. Topics: strained Si/SiGe and Si/SiGe on insulator; high-mobility channels including III-V¿s, etc.; nanowires and carbon nanotubes; high-k dielectrics, metal and FUSI gate electrodes; doping/annealing for ultra-shallow junctions; low-resistivity contacts; advanced deposition (e.g. ALD, CVD, MBE), RTP, UV, plasma and laser-assisted processes.

The on-chip interconnect bandwidth limitation is becoming an increasingly critical challenge for integrated circuits (ICs) as device scaling continues to push the speed and density of ICs. Silicon photonics has the ability to solve this emerging problem due to its high speed, high bandwidth, low power consumption, and ability to be monolithically integrated on silicon. Most of the key devices for Si photonic ICs have already been demonstrated. However, a practical CMOS compatible coherent light source is still a major challenge. Germanium (Ge) has already been demonstrated to be a promising material for optoelectronic devices, such as photo-detectors and modulators. However, Ge is an indirect band gap semiconductor, which makes Ge-based light sources very inefficient and limits their practical use. Fortunately, the direct [uppercase Gamma] valley of the Ge conduction band is only 0.14 eV higher than the indirect L valley, suggesting that with band-structure engineering, Ge has the potential to become a direct band gap material and an efficient light emitter. In this dissertation, we first discuss our work on highly biaxial tensile strained Ge grown by molecular beam epitaxy (MBE). Relaxed step-graded InGaAs buffer layers, which are prepared with low temperature growth and high temperature annealing, are used to provide a larger lattice constant substrate to produce tensile strain in Ge epitaxial layers. Up to 2.3% in-plane biaxial tensile strained thin Ge epitaxial layers were achieved with smooth surfaces and low threading dislocation density. A strong increase of photoluminescence with highly tensile strained Ge layers at low temperature suggests that a direct band gap semiconductor has been achieved. This dissertation also presents our work on more than 9% Sn incorporation in epitaxial GeSn alloys using a low temperature MBE growth method. This amount of Sn is 10 times greater than the solid-solubility of Sn in crystalline Ge. Material characterization shows good crystalline quality without Sn precipitation or phase segregation. With increasing Sn percentage, direct band gap narrowing is observed by optical transmission measurements. The studies described in this dissertation will help enable efficient germanium based CMOS compatible coherent light sources. Other possible applications of this work are also discussed in the concluding chapter.