Integrated photonics is the field of shrinking and simplifying the fabrication of devices that guide and manipulate light. It not only offers to greatly lower the size and cost of systems used in optical communications it also offers a platform on which new physical phenomenon can be explored by being able to fabricate and manipulate structures on the scale of the wavelength of light. One such platform in integrated photonics is that of two-dimensional slab photonic crystals. These structures exhibit a photonic band-gap, a band of optical frequencies that are prohibited from propagating within the medium, that can be used to guide and confine light. When used to create photonic crystal waveguides these waveguides exhibit unique dispersion properties that demonstrate very low optical group velocities, so called "slow-light". This dissertation begins with the practical realization of design and fabrication of such waveguides using the silicon-on-insulator material system using conventional deep-UV photolithography fabrication techniques. It will detail and demonstrate the effect physical dimensions have on the optical transmission of these devices as well as their optical dispersion. These photonic crystal waveguides will then be used to demonstrate the enhancement of nonlinear optical phenomenon due to the slow-light phenomenon they exhibit. First spontaneous Raman scattering will be theoretically demonstrated to be enhanced by slow-light and then experimentally shown to be enhanced in a practical realization. The process of four-wave mixing will be demonstrated to be enhanced in these devices and be shown to be greatly affected by the unique optical dispersion within these structures. Additionally, we will examine the dispersion that exists in silicon nitride microring resonators and the effect it has on the use of these devices to generate optical frequency combs. This is done by leveraging the dispersion measurement methods used to characterize photonic crystal waveguides. We conclude this work by examining the avenues of future work that can be explored in the area of photonic crystal waveguides.

The possibility to manipulate electromagnetic radiation, as well as mechanical and acoustic waves has been an engaging topic since the beginning of the 20th century. Nowadays, thanks to the progress in technologies and the evolution of fabrication processes, realizing artificial materials that are able to interact with the environment in a desired fashion has become reality. The interest in micro/nanostructured metamaterials involves different field of research, ranging from optics to biology, through optoelectronics and photonics. Unfortunately, realizing experimentally these materials became highly challenging, since the size of the nanostructures are shrinking and the precision of the design became crucial for their effective operation. Disorder is, in fact, an intrinsic characteristic of fabrication processes and harnessing it by turning its unexpected effects in decisive advantages represents one of the ultimate frontiers in research. In this work we combine ab-initio FDTD simulations, fabrication process optimization and experimental results to show that, introducing disorder in metamaterials could constitute a key opportunity to enable many interesting capabilities otherwise locked. This could open up the way to novel applications in several fields, from smart network materials for solar cells and photo-electrochemical devices to all dielectric, highly-tunable structural colors.

Thesis advisor: Michael J. Naughton / Thesis advisor: Michael J. Burns / Recent progress in the study of the brain has been greatly facilitated by the development of new measurement tools capable of minimally-invasive, robust coupling to neuronal assemblies. Two prominent examples are the microelectrode array, which enables electrical signals from large numbers of neurons to be detected and spatiotemporally correlated, and optogenetics, which enables the electrical activity of cells to be controlled with light. In the former case, high spatial density is desirable but, as electrode arrays evolve toward higher density and thus smaller pitch, electrical crosstalk increases. In the latter, finer control over light input is desirable, to enable improved studies of neuroelectronic pathways emanating from specific cell stimulation. Herein, we introduce a coaxial electrode architecture that is uniquely suited to address these issues, as it can simultaneously be utilized as an optical waveguide and a shielded electrode in dense arrays. / Thesis (PhD) — Boston College, 2017. / Submitted to: Boston College. Graduate School of Arts and Sciences. / Discipline: Physics.

Thesis advisor: Torsten Fiebig / This dissertation introduces a new field of DNA photonics centering on the electronic properties of DNA, which emerges after the initial controversies regarding the long-range conductivity and wire-type behavior of DNA have been widely settled. DNA photonics study is not solely focused on charge transfer phenomena but encompasses all possible photophysical processes and their potentially complex interplays. For instance, ultrafast electronic energy migration, dissipation, and (de)localization on the femtosecond time scale are shown to be crucial for the description of light-induced dynamics in DNA and have been thoroughly investigated in this dissertation. In addition to measurements on natural single and double-stranded DNA, this dissertation also presents experimental data on a series of functionalized DNA systems (derivatized by stilbene, ethidium, 2-aminopurine, etc.), obtained by state-of-the-art femtosecond broadband pump–probe spectroscopy. The results illustrate the distance dependence of charge transfer, emphasize the role of the initial electronic excitation on energy transfer dynamics, and highlight the influence of structural factors on both processes in DNA. Finally, as one initial step towards DNA electronics application, a DNA mimicking system of tertiary arylureas were employed to demonstrate molecular wire behavior, implying its potential use in molecular electronics. Thus, both the experimental and theoretical research accumulated for DNA π–π coupling can be translated into designing and testing various molecular systems with similar π-stacked structures. / Thesis (PhD) — Boston College, 2008. / Submitted to: Boston College. Graduate School of Arts and Sciences. / Discipline: Chemistry.

Field output factors (OF) for photon beams from a 6 MV medical accelerator were measured using five different detectors in a scanning water phantom. The measurements were taken for square field sizes of integral widths ranging from 1 cm to 10 cm for two reference source-to-surface distances (SSD) and depths in water. For the diode detectors, square field widths as small as 2.5 mm were also studied. The photon beams were collimated by using either the jaws or the multileaf collimators. Measured OFs are found to depend upon the field size, SSD, depth and also upon the type of beam collimation, size and type of detector used. For field sizes larger than 3 cm x 3 cm, the OF measurements agree to within 1% or less. The largest variation in OF occurs for jawsshaped field of size 1 cm x 1cm, where a difference of more than 18% is observed. / Includes bibliography. / Thesis (M.S.)--Florida Atlantic University, 2013.

The following thesis is comprised of four main areas of work. These are centred around the experimental observation of phenomena associated with both linear and non-linear optics in silicon photonic-wires. As a comparison, I also discuss a similar coupled-waveguide system; dual-core hollow-core photonic crystal fibre. To introduce the reader to this work, the first chapter will recap some undergraduate level theory; a general introduction to optical waveguides. It is not intended to be a complete theoretical picture, as many beautiful texts on optics already exist [1–3]. This chapter concerns itself only with the aspects of optics with which the author was intimately aware of throughout the completion of this thesis. Thereafter, the chapters become specific to the particular experiments undertaken. Each one follows a simple framework: examination of the relevant theory, extending upon that already discussed in the first chapter, a literature review and finally a discussion of the work I completed within this thesis. Chapter 2 is the only chapter not related to silicon based photonics. Here I discuss dual-core hollow-core photonic crystal fibres; including guidance mechanisms, fabrication methods and the numerical modelling techniques employed in my work. I will compare these numerical results to experimental results taken by colleagues at the university of Bath. Chapter 3 analyses linear propagation in arrays of silicon photonic wires. I extend the simple picture of light propagating in waveguides to discuss the di↵erent types of dispersion inherent in this system and how dispersion tailoring can be achieved; with reference to the other literature on this topic. Experimental results are examined and discussed. Chapters 4 and 5 discuss non-linear propagation in silicon photonic wire arrays; modulation instability and spatio-temporal solitons respectively. In each case I extend the ideas on non-linearity presented in Chapter 1 to explain both modulation instability and optical solitons. Detailed descriptions of the experiments undertaken, and associated numerical modelling completed are then discussed. Whilst the work I present is incomplete, I will discuss subsequent work performed by my colleagues at the University of Bath based on my initial work. Finally, Chapter 6 draws together my conclusions.

This thesis details work undertaken over the past three and a half years looking at the optical properties of silicon-on-insulator waveguide arrays and 1D photonic crystal microcavities. Chapter 1 contains relevant background information, while chapters 2, 3 and 4 contain results of experimental work. Chapter 5 summarises the results and conclusions of the preceding chapters and also suggests some directions for possible future research. Chapter 1 starts by introducing some of the fundamental aspects of guided wave optics and how these relate to silicon-on-insulator waveguides. The modes of single,uncoupled silicon waveguides are described, along with a brief description of how such waveguides can be fabricated. Following this a short introduction to optical cavities and the relevant parameters that can be used to describe them is provided. In Chapter 2 results are presented that experimentally confirm the presence of couplinginduced dispersion in an array consisting of two strongly-coupled silicon-on-insulator waveguides. This provides an additional mechanism to tailor dispersion and shows that it is possible to achieve anomalous dispersion at wavelengths where the dispersion of a single wire would be normal. In Chapter 3 the focus switches to the linear properties of 1D photonic crystal microcavities in silicon. The optical transmission of a number of different devices are examined allowing the identification of suitable microcavities for use in nonlinear measurements. Microcavities with Q-factors in excess of ∼40,000 were selected for use in the work presented in Chapter 4, whilst the possibility of thermally tuning the microcavity resonances is also investigated. A cavity resonance shift of 0.0770± 0.0004 nm K-1 is measured experimentally. Chapter 4 looks at the nonlinear transmission of those microcavities identified as suitable in Chapter 3. More specifically, the response of the microcavities to thermal and free carrier induced bistability is considered. Thermally induced bistability is observed at a threshold power of 240 μW for the particular cavity chosen, with a thermal time of 0.6 μs also measured. Free carrier induced bistability is then observed for pulses with nanosecond durations and milliwatt peak powers. Following that, the interplay of thermal and free carrier effects is observed using input pulses of a suitable duration.

Silicon photonics is recognized as a disruptive technology that has the potential to reshape many application areas, for example, data center communication, telecommunications, high-performance computing, and sensing. The key capability that silicon photonics offers is to leverage CMOS-style design, fabrication, and test infrastructure to build compact, energy-efficient, and high-performance integrated photonic systems-on- chip at low cost. As the need to squeeze more data into a given bandwidth and a given footprint increases, silicon photonics becomes more and more promising. This work develops and demonstrates novel devices, methodologies, and architectures to resolve the challenges facing the next-generation silicon photonic transceivers. The first part of this thesis focuses on the topology optimization of passive silicon photonic devices. Specifically, a novel device optimization methodology - particle swarm optimization in conjunction with 3D finite-difference time-domain (FDTD), has been proposed and proven to be an effective way to design a wide range of passive silicon photonic devices. We demonstrate a polarization rotator and a 90◦ optical hybrid for polarization-diversity and phase-diversity communications - two important schemes to increase the communication capacity by increasing the spectral efficiency. The second part of this thesis focuses on the design and characterization of the next- generation silicon photonic transceivers. We demonstrate a polarization-insensitive WDM receiver with an aggregate data rate of 160 Gb/s. This receiver adopts a novel architecture which effectively reduces the polarization-dependent loss. In addition, we demonstrate a III-V/silicon hybrid external cavity laser with a tuning range larger than 60 nm in the C-band on a silicon-on-insulator platform. A III-V semiconductor gain chip is hybridized into the silicon chip by edge-coupling to the silicon chip. The demonstrated packaging method requires only passive alignment and is thus suitable for high-volume production. We also demonstrate all silicon-photonics-based transmission of 34 Gbaud (272 Gb/s) dual-polarization 16-QAM using our integrated laser and silicon photonic coherent transceiver. The results show no additional penalty compared to commercially available narrow linewidth tunable lasers. The last part of this thesis focuses on the chip-scale optical interconnect and presents two different types of reconfigurable memory interconnects for multi-core many-memory computing systems. These reconfigurable interconnects can effectively alleviate the memory access issues, such as non-uniform memory access, and Network-on-Chip (NoC) hot-spots that plague the many-memory computing systems by dynamically directing the available memory bandwidth to the required memory interface.

The continuous growth of electronic compute and memory nodes in terms of the number of I/O pins, bandwidth, and areal throughput poses major integration and packaging challenges associated with offloading multi-Tbit/s data rates within the few pJ/bit targets. While integrated photonics are already deployed in long and short distances such as inter and intra data centers communications, the promising characteristics of the silicon photonic platform set it as the future technology for optical interconnects in ultra short inter-chip distances. The high index contrast between the waveguide and the cladding together with strong thermo-optic and carrier effects in silicon allows developing a wide range of micro-scale and low power optical devices compatible with the CMOS fabrication processes. Furthermore, the availability of photonic foundries and new electrical and optical co-packaging techniques further pushes this platform for the next steps of commercial deployment. The work in this dissertation presents the current trends in high-performance memory and processor nodes and gives motivation for disaggregated and reconfigurable inter-chip network enabled with the silicon photonic layer. A dense WDM transceiver and broadband switch architectures are discussed to support a bi-directional network of ten hybrid-memory cubes (HMC) interconnected to ten processor nodes with an overall aggregated bandwidth of 9.6Tbit/s. Latency and energy consumption are key performance parameters in a processor to primary memory nodes connectivity. The transceiver design is based on energy-efficient micro-ring resonators, and the broadband switch is constructed with 2x2 Mach-Zehnder elements for nano-second reconfiguration. Each transceiver is based on hundreds of micro-rings to convert the native HMC electrical protocol to the optical domain and the switch is based on tens of hundreds of 2x2 elements to achieve non-blocking all-to-all connectivity. The next chapters focus on developing methods for controlling and monitoring such complex and highly integrated silicon photonic subsystems. The thermo-optic effect is characterized and we show experimentally that the phase of the optical carrier can be reliably controlled with pulse-width modulation (PWM) signal, ultimately relaxing the need for hundreds of digital to analog converters (DACs). We further show that doped waveguide heaters can be utilized as \textit{in-line} optical power monitors by measuring photo-conductance current, which is an alternative for the conventional tapping and integration of photo-diodes. The next part concerned with a common cascaded micro-ring resonator in a WDM transceiver design. We develop on an FPGA control algorithm that abstracts the physical layer and takes user-defined inputs to set the resonances to the desired wavelength in a unicast and multicast transmission modes. The associated sensitivities of these silicon ring resonators are presented and addressed with three closed-loop solutions. We first show a closed-loop operation based on tapping the error signal from the drop port of the micro-ring. The second solution presents a resonance wavelength locking with a single digital I/O for control and feedback signals. Lastly, we leverage the photo-conductance effect and demonstrate the locking procedure using only the doped heater for both control and feedback purposes. To achieve the inter-chip reconfigurability we discuss recent advances of high-port-count SiP broadband switches for reconfigurable inter-chip networks. To ensure optimal operation in terms of low insertion loss, low cross-talk and high signal integrity per routing path, hundreds of 2x2 Mach-Zehnder elements need to be biased precisely for the cross and bar states. We address this challenge with a tapless and a design agnostic calibration approach based on the photo-conductance effect. The automated algorithm returns a look-up table for all for each 2x2 element and the associated calibrated biases. Each routing scenario is then tested for insertion loss, crosstalk and bit-error rate of 25Gbit/s 4-level pulse amplitude modulation signals. The last part utilizes the Mach-Zehnder interferometers in WDM transceiver applications. We demonstrate a polarization insensitive four-channel WDM receiver with 40Gbit/s per channel and a transmitter design generating 8-level pulse amplitude modulation signals at 30Gbit/s.

No description available.