Photonic crystal interfaces: a design-driven approach

Photonic Crystal structures have been heralded as a disruptive technology for the miniaturization of opto-electronic devices, offering as they do the possibility of guiding and manipulating light in sub-micron scale waveguides. Applications of photonic crystal guiding - the ability to send light around sharp bends or compactly split signals into two or more channels have attracted a great deal of attention. Other effects of this waveguiding mechanism have become apparent, and attracted much interest - the novel dispersion surfaces of photonic crystal structures allow the possibility of “slow light” in a dielectric medium, which as well as the possibility of compact optical delay lines may allow enhanced light-matter interaction, and hence miniaturisation of active optical devices. I also consider a third, more traditional type of photonic crystal, in the form of a grating for surface coupling. In this thesis, I address many of the aspects of passive photonic crystals, from the underlying theory through applied device modelling, fabrication concerns and experimental results and analysis. Further, for the devices studied, I consider both the relative merits of the photonic crystal approach and of my work compared to that of others in the field. Thus, the complete spectrum of photonic crystal devices is covered. With regard to specific results, the highlights of the work contained in this thesis are as follows: Realisation of surface grating couplers in a novel material system demonstrating some of the highest reported fibre coupling efficiencies. Development of a short “injecting” taper for coupling into photonic crystal devices. Optimisation and experimental validation of photonic crystal routing elements (Y-splitter and bend). Exploration of interfaces and coupling for “slow light” photonic crystals

Sensor-Based Topological Coverage And Mapping Algorithms For Resource-Constrained Robot Swarms

Coverage is widely known in the field of sensor networks as the task of deploying sensors to completely cover an environment with the union of the sensor footprints. Related to coverage is the task of exploration that includes guiding mobile robots, equipped with sensors, to map an unknown environment (mapping) or clear a known environment (searching and pursuit- evasion problem) with their sensors. This is an essential task for robot swarms in many robotic applications including environmental monitoring, sensor deployment, mine clearing, search-and-rescue, and intrusion detection. Utilizing a large team of robots not only improves the completion time of such tasks, but also improve the scalability of the applications while increasing the robustness to systems’ failure. Despite extensive research on coverage, mapping, and exploration problems, many challenges remain to be solved, especially in swarms where robots have limited computational and sensing capabilities. The majority of approaches used to solve the coverage problem rely on metric information, such as the pose of the robots and the position of obstacles. These geometric approaches are not suitable for large scale swarms due to high computational complexity and sensitivity to noise. This dissertation focuses on algorithms that, using tools from algebraic topology and bearing-based control, solve the coverage related problem with a swarm of resource-constrained robots. First, this dissertation presents an algorithm for deploying mobile robots to attain a hole-less sensor coverage of an unknown environment, where each robot is only capable of measuring the bearing angles to the other robots within its sensing region and the obstacles that it touches. Next, using the same sensing model, a topological map of an environment can be obtained using graph-based search techniques even when there is an insufficient number of robots to attain full coverage of the environment. We then introduce the landmark complex representation and present an exploration algorithm that not only is complete when the landmarks are sufficiently dense but also scales well with any swarm size. Finally, we derive a multi-pursuers and multi-evaders planning algorithm, which detects all possible evaders and clears complex environments

Time-Optimal Trajectory Generation and Way-Point Sequencing for 5-Axis Laser Drilling

Laser drilling provides a highly productive method for producing arrays of holes on planar and freeform shaped components. Industrial applications include fuel injection nozzles, printed circuit boards (PCB’s), inkjet printer heads, pinholes and slits for scientific instrumentation, high-resolution circuitry, sensors, fiber-optic interconnects, medical devices, and gas turbine combustion chamber panels. This thesis deals with time-optimal trajectory planning for two mainstream laser drilling methods: on-the-fly drilling and percussion drilling, which are used in the aerospace industry. The research has been conducted in collaboration with the Canadian aero-engine producer, Pratt & Whitney Canada (P&WC). The algorithms developed have been tested in a target application involving the laser drilling of cooling hole arrays on gas turbine engine combustion chamber panels. On-the-fly drilling is an operation in which each hole receives one low powered shot at a time while the workpiece is in motion, and the beam focal point is continuously proceeding to the next hole location. The positioning sequence repeats itself until all holes are gradually opened up in small increments. Each hole location has ample time to cool down before the next shot is received. Thus, this process can yield favorable material properties in terms of preserving the desired crystal structure, and also hole quality in terms of dimensional (size) and form (shape) accuracy, due to the reduction of local thermal loading. However, there is no existing trajectory planner, in industry, or in literature, capable of generating time-optimized positioning trajectories for on-the-fly laser drilling. This thesis studies this problem and presents a new algorithm, capable of handling 5 degree-of-freedom (axis) positioning capability. The ability to generate spline-based smooth trajectories is integrated within a Traveling Salesman Problem (TSP) type sequencing algorithm. The sequencing algorithm optimizes both the order of the waypoints (i.e., hole locations) and also the timing levels in between, which affect the temporal (time-dependent) nature of the motions commanded to the laser drilling machine’s actuators. Furthermore, the duration between consecutive holes has to be an integer multiple of the laser pulsing period, considering a machine configuration in which the laser is firing at a constant frequency, and unused pulses are diverted away using a quick shutter. It is shown that the proposed algorithm is capable of generating 17-25% reduction in the beam positioning time spent during a manufacturing cycle, compared to some of the contemporary practices in industry. 17% reduction in the vibrations induced onto the laser optics is also observed, which helps prevent downtime due to the optics hardware gradually losing alignment. The second type of laser drilling operation for which optimized 5-axis trajectory planning has been developed is percussion drilling. In this process, a series of pulses are sent to each hole while the part is stationary. Once the hole is completely opened up, then positioning to the next hole proceeds. While percussion drilling is less advantageous in terms of local thermal loading and achievable part quality, it is used extensively in industry; due to its simplicity of automation compared to on-the-fly drilling. Thus, a TSP-style trajectory planning algorithm has also been developed for percussion laser drilling. The novelty, in this case, is concurrent planning of 5-axis time-optimal point-to-point movements within the sequencing algorithm, and direct minimization of the total travel time, rather than just distance (in two Cartesian axes); as is the method for which significant portion of TSP solvers and trajectory planners in literature have been developed. Compared to currently applied methods at P&WC, 32-36% reduction in the beam positioning time has been achieved. Also, 39-45% reduction in the peak magnitude of vibration has been realized. Limited benchmarking with state-of-the-art TSP solvers from combinatorial mathematics, considering only 2-axis Euclidean distance as the objective function, indicate that the proposed sequencing algorithm for percussion drilling is sub-optimal by 9-12%. Thus, it can still use further improvement in future research. Nevertheless, the two trajectory planners that have been developed in this thesis for on-the-fly drilling and percussion drilling have experimentally demonstrated very promising improvements in terms of motion time and smoothness. As more advanced Computer Numerical Control (CNC) systems and laser control electronics with deterministic execution and rapid synchronization capability become available, such algorithms are expected to facilitate significant production gains in laser drilling processes used in different industries

A novel scanned mask imaging system for high resolution solid state laser ablation

A technology gap has emerged between the sub-micron semiconductor manufacturing technologies used in the manufacture of integrated circuits and the semi-additive processes used to manufacture advanced chip packages which are currently limited to feature sizes greater than 10 µm. Embedding conductors in laser ablated circuit features is one of the proposed solutions to address this technology gap in the advanced chip packaging industry. Excimer laser systems are currently the only available production tools capable of the high throughput laser ablation of circuit features down to 2 µm. In this thesis I have developed an ablative, solid state laser, mask imaging system for the high volume 3D structuring of organic dielectrics. This system enables the ablation of circuit features down to 2 µm which are of comparable quality to excimer laser ablation. The system architecture has a throughput exceeding that of an excimer laser production system. I have developed an illumination system, which I have tested at both a feasibility stage and at a prototype stage, with custom designed optical components. The illumination system consists of a galvanometer scan head which is used to raster scan a solid state laser beam across a binary mask, the image of which is then projected onto the substrate. The system I present enables the use of multimode, UV, solid state lasers in well-developed and high resolution mask imaging optical systems. Through the use of a less expensive laser technology, the system I have developed has a cost of ownership estimated to be less than 50% of that of an excimer production system, thus reducing the cost of high resolution, high throughput laser ablation

First NASA Advanced Composites Technology Conference, Part 2

Presented here is a compilation of papers presented at the first NASA Advanced Composites Technology (ACT) Conference held in Seattle, Washington, from 29 Oct. to 1 Nov. 1990. The ACT program is a major new multiyear research initiative to achieve a national goal of technology readiness before the end of the decade. Included are papers on materials development and processing, innovative design concepts, analysis development and validation, cost effective manufacturing methodology, and cost tracking and prediction procedures. Papers on major applications programs approved by the Department of Defense are also included

Optical coupler design and experimental demonstration for 2.5D/3D heterogeneous integrated electronics

The objective of the dissertation is to theoretically design and experimentally demonstrate optical couplers for 2.5D/3D heterogeneous integrated electronics. In the first part, a new concept, "Equivalent Index Slab (EIS)" method, is proposed to extend the application of Rigorous Coupled-Wave Analysis (RCWA) to rectangular waveguide grating diffraction involving surface waves. RCWA-EIS method can be applied to optimize rectangular grating couplers with arbitrary profiles and to analyze the effects of angular misalignments on the coupling efficiency. In the second part, a fundamentally new coupling structure, Grating-Assisted-cylindrical-Resonant-Cavities (GARC) coupler, is introduced to achieve efficient and broadband interlayer coupling. GARC coupler is based on evanescent field coupling between waveguides and the interconnecting via, and the via serves as a cylindrical resonant cavity which is further assisted by the circular gratings to enhance the field. In the third part, a passive fiber alignment and assembly approach, Fiber-Interconnect Silicon Chiplet Technology (FISCT), is demonstrated using a combination of silicon micromachining and 3D printing to achieve efficient and convenient near-vertical fiber-to-chip coupling.Ph.D

Proceedings of the 22nd Conference on Formal Methods in Computer-Aided Design – FMCAD 2022

The Conference on Formal Methods in Computer-Aided Design (FMCAD) is an annual conference on the theory and applications of formal methods in hardware and system verification. FMCAD provides a leading forum to researchers in academia and industry for presenting and discussing groundbreaking methods, technologies, theoretical results, and tools for reasoning formally about computing systems. FMCAD covers formal aspects of computer-aided system design including verification, specification, synthesis, and testing

Proceedings of the 22nd Conference on Formal Methods in Computer-Aided Design – FMCAD 2022

The Conference on Formal Methods in Computer-Aided Design (FMCAD) is an annual conference on the theory and applications of formal methods in hardware and system verification. FMCAD provides a leading forum to researchers in academia and industry for presenting and discussing groundbreaking methods, technologies, theoretical results, and tools for reasoning formally about computing systems. FMCAD covers formal aspects of computer-aided system design including verification, specification, synthesis, and testing

Guiding the Self-Assembly of Block Copolymers in 2D and 3D with Minimal Patterning

Directed self-assembly (DSA) of block copolymers (BCPs) based on topographic patterns is one of the most promising strategies for overcoming resolution limitations in the current lithographic process and fabricating the next generation data storage devices. While the DSA of BCPs with deep topographic patterning has been extensively studied both experimentally and theoretically over the past two decades, less attention has been paid to the development of the DSA process using minimal topographic patterning. This dissertation focuses on understanding the effect of minimal topographic patterning on guiding the self-assembly of BCPs in 2D and 3D. We demonstrate that minimal trench patterns can be used to achieve highly ordered hexagonal arrays or unidirectionally aligned line patterns over large areas. By preparing BCP thin films on a series of minimal single trench with different dimensions, we study the minimum amount of topographic patterning necessary to successfully guide the self-assembly of BCPs. This approach provides insight into the minimum pitch of the trench necessary to fully order BCP microdomains. We develop a simple and robust method for the generation of macroscopically ordered xi hexagonal arrays from the DSA of BCPs based on minimal trench patterns with solvent vapor annealing. The use of minimal trench patterns allows us to elucidate the morphological characteristics and lateral ordering of hexagonal array using grazing incidence small angle X-ray scattering (GISAXS). Moreover, using minimal trench patterns, we describe the generation of BCP line patterns oriented orthogonal to the trench direction over arbitrarily macroscopic distances. Beyond 2D BCP nanostructures, we explore the fabrication of 3D BCP architectures over large areas using simple woodpile structures as 3D guiding templates. We can also produce 3D networks of metallic nanostructures within the woodpile structures using a metal salt infiltration technique. In the last part, we conclude this dissertation and propose an outlook