Contributions to adaptive equalization and timing recovery for optical storage systems

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Characterization And Optimization Of Avalanche Photodiodes Fabricated By Standard Cmos Process For High-Speed High-Speed Photoreceivers

A dissertation presented on the characterization and optimization of avalanche photodiodes fabricated by standard CMOS process (CMOS-APD) for high-speed photoreceivers, beginning with the theory and principle related to photodetector and avalanche photodiodes, followed by characterization,optimization, and wavelength dependence of CMOS-APD, and finally link up with the transimpedance amplifier. nMOS-type and pMOS-type silicon avalanche photodiodes were fabricated by standard 0.18 μm CMOS process, and the currentvoltage characteristic and the frequency response of the CMOS-APDs with and without the guard ring structure were measured. CMOS-APDs have features of high avalanche gain below 10 V, wide bandwidth over 5 GHz, and easy integration with electronic circuits. In CMOS-APDs, guard ring structure is introduced for high-speed operation with the role of elimination the slow photo generated carriers in a deep layer and a substrate. The bandwidth of the CMOS-APD is enhanced with the guard ring structure at a sacrifice of the responsivity. Based on comparison of nMOS-type and pMOS-type APDs, the nMOS-type APD is more suitable for high-speed operation. The bandwidth is enhanced with decreasing the spacing of interdigital electrodes due to decreased carrier transit time and with decreasing the detection area and the PAD size for RF probing due to decreased device capacitance. Thus, an nMOS-type APD with the electrode spacing of 0.84 μm, the detection area of 10 x 10 μm², the PAD size for RF probing of 30 x 30 μm² along with the guard ring structure was fabricated. As a results, the maximum bandwidth of 8.4 GHz at the avalanche gain of about 10 and the gain-bandwidth product of 280 GHz were achieved. Furthermore, the wavelength dependence of the responsivity and the bandwidth of the CMOS-APDs with and without the guard ring structure also revealed. At a wavelength of 520 nm or less, there is no difference in the responsivity and the frequency response because all the illuminated light is absorbed in the p+-layer and the Nwell due to strong light absorption of Si. On the other hand, a part of the incident light is absorbed in the Psubstrate and the photo-generated carriers in the P-substrate are eliminated by the guard ring structure for the wavelength longer than 520 nm, and then bandwidth was remarkably enhanced at the sacrifice of the responsivity. In addition, to achieve high-speed photoreceivers, two types of TIA which are common-source and regulated-cascode TIAs were simulated by utilizing the output of the CMOSAPDs.The figure of merits of gain-bandwidth product was used to find the ideal results of the transimpedance gain and bandwidth performance due to trade-offs between both of them. The common-source TIA produced the transimpedance gain of 22.17 dBΩ, the bandwidth of 21.21 GHz and the gain-bandwidth product of 470.23 THz × dBΩ. Besides that, the simulated results of the regulated-cascade TIA configuration demonstrate 79.45 dBΩ transimpedance gain, 10.64 GHz bandwidth, and 845.35 THz × dBΩ gain-bandwidth product. Both of these TIA results meet the target of this research and further encouraging this successful CMOS-APDs to realize high-speed photoreceivers

Three dimentional control of a diode based laser cutter

Includes bibliographical referencesLaser cutting is a widely used technology in many areas of industry and research. Conventional laser cutters only offer control of two axes and either cut through a material or rudimentary control of the third dimension is possible by varying the power, pulse rate and travel rate of the laser beam. These rudimentary three-dimensional systems (often called 2.5D laser cutters) do not incorporate any feedback mechanism to control the depth of cut. The idea of measuring distance using diode lasers (and other laser technologies) is a relatively mature technology and is common to various consumer and industrial products. Recently diode lasers have become powerful enough to perform as laser cutters allowing a merger of these technologies. The aim of this project is to verify the concept of using a laser diode to achieve both material processing and distance measurement. This would allow the creation of a full three-dimension laser cutting machine that is capable of accurate material processing in all three dimensions. This would also offer the ability to cut non-homogenous materials, such as timber, which current ‘2.5D’ laser cutters are unable to cut with any accuracy. A gantry system was designed and constructed, which was able to move the laser cutting toolhead in the x-y plane, using stepper motors and a belt-driven drive system. A 2W single emitter laser diode was used for both laser cutting and distance measurement. Optics were designed and assembled that focused the laser onto the workpiece and directed light reflected back from the workpiece onto a photodiode. Laser driver circuitry was constructed to control the DC current of the laser and to modulate the laser power at the high frequencies required for accurate phase shift measurements. A photodetector and phase shift measurement circuit was designed, simulated and constructed. The phase shift circuit amplified the signal from the light reflected off the workpiece and then compared that signal to a reference signal in order to determine the phase shift between the two. An Atmel® ATmega2560 microcontroller was used to control the gantry, laser driver circuitry and to measure the phase shift output of the phase detector circuitry. Software written in MATLAB® was used to command the microcontroller and to interpret the data received from the microcontroller The photo sensor circuit was not sensitive enough to detect the weak signals that were present when the workpiece had a low reflectivity but was able to be tested using reflective tape. On the other hand the laser diode was not powerful enough to cut reflective tape as it absorbs very little energy from the laser. Nevertheless, the same laser diode was used, without changing any configuration other than the workpiece material, to measure distance and to cut materials. Testing of both the materials processing ability and the distance measurement ability were carried out. Many aspects of each of these major functions were tested, individually and together, in order to determine the areas that performed well and those that need more research. In conclusion, this project was able to verify the concept of a three-dimensionally controlled diode powered laser cutter. Future work will be needed before a practical and useful laser cutter can be built but this project should prove a good starting point for any such future work

An evolutionary stage model of outsourcing and competence destruction : a Triad comparison of the consumer electronics industry

Outsourcing has gained much prominence in managerial practice and academic discussions in the last two decades or so. Yet, we still do not understand the full implications of outsourcing strategy for corporate performance. Traditionally outsourcing across borders is explained as a cost-cutting exercise, but more recently the core competency argument states that outsourcing also leads to an increased focus, thereby improving effectiveness. However, no general explanation has so far been provided for how outsourcing could lead to deterioration in a firm‟s competence base. We longitudinally analyze three cases of major consumer electronics manufacturers, Emerson Radio from the U.S., Japan‟s Sony and Philips from the Netherlands to understand the dynamic process related to their sourcing strategies. We develop an evolutionary stage model that relates outsourcing to competence development inside the firm and shows that a vicious cycle may emerge. Thus it is appropriate to look not only at how outsourcing is influenced by an organization‟s current set of competences, but also how it alters that set over time. The four stages of the model are offshore sourcing, phasing out, increasing dependence on foreign suppliers, and finally industry exit or outsourcing reduction. The evolutionary stage model helps managers understand for which activities and under which conditions outsourcing across borders is not a viable option. Results suggest that each of these firms had faced a loss of manufacturing competitiveness in its home country, to which it responded by offshoring and then outsourcing production. When a loss of competences occurred, some outsourcing decisions were reversed

Discrete multitone modulation for short-range optical communications

As the need for higher information throughput increases, standard solutions such as copper lines and radio links seem to approach their limits. Therefore, optical solutions, after having conquered the long and medium-range networks, are nowadays also migrating into short-range data communication scenarios, offering the possibility of high capacity information transfer for both professional as well as consumer applications. The challenge is to offer cost-effective and robust optical solutions at relatively short (¿ 1 km) transmission distances, where traditional single-mode fiber for long-haul transmission systems are unsuitable. Solutions such as multimode glass fibers (MMF), plastic optical fibers (POF), using light-emitting diodes (LED) or low-cost vertical cavity surface emitting laser diodes (VCSEL), and optical wireless links (based on LEDs) are therefore being proposed and seem to be promising candidates. These solutions feature low costs, easy handling and installation, flexibility, and robustness, which are all very suitable characteristics for consumer needs. However, this comes at the expense of less bandwidth when compared to single-mode fiber systems. This thesis investigates the use of digital signal processing in order to overcome the bandwidth limitations in short-range optical communication systems, ensuring that such solutions are future-proof. In particular, discrete multitone (DMT) modulation is proposed and investigated in order to increase the capacity of such systems. Derived from the more general orthogonal frequency division multiplexing (OFDM), DMT is a baseband multicarrier modulation technique that is already widely employed in copper-based digital subscriber lines (DSL) systems such as asymmetrical DSL (ADSL) and very high data rate DSL (VDSL). By dividing a high-speed serial data stream into multiple parallel low-speed sub-streams and transmitting them simultaneously using different frequencies, DMT can be used to efficiently combat various signal impairments such as dispersion and narrowband interference. Due to the use of intensity-modulation and direct-detection (IM/DD) in low-cost optical systems, where only the intensity of light is modulated and not the phase, the application of DMT is different from standard electrical systems. Characteristics such as high crest factor, which is the ratio of the peak to root-mean-square amplitude value of the DMT signal, and clipping have different consequences and are studied in this thesis. After an introduction to the principles of DMT and rate-adaptive bit-loading, an analytical model of the optical IM/DD channel for short-range optical communications is presented. Making use of this model, the theoretical capacity of such a channel is derived for both a Gaussian and a first-order low-pass electrical-to-electrical channel response by means of the water-filling method. It is found that the crest factor of the modulation signal plays a dominant role in defining the capacity of the optical IM/DD channel. Furthermore, by including characteristics of DMT modulation such as clipping and quantization, it is shown that the calculated capacity values can be refined and optimum parameters for DMT transmission over an optical IM/DD channel exist. Following this, the optimum clipping values and number of subcarriers for maximizing DMT transmission performance over an optical IM/DD channel are investigated. It is shown that the optimum clipping value, which depends on various system parameters such as receiver noise power and modulation order, can be determined by using an analytical expression. In the case of the number of subcarriers, larger values generally lead to better performance when DMT with bit-loading is used. Additionally, various experiments to explore the system limits of DMT techniques have been performed and the results for POF, MMF, and optical wireless are presented. It is shown that record bit-rates of up to 47 Gbit/s can be achieved using DMT. Finally, an efficient way to implement DMT is presented, together with results regarding the implementation of a real-time DMT transmission system operating at 1.25 Gbit/s. System complexity issues of real-time hardware implementation are also discussed, showing that pipelining and parallelization are essential in high-speed designs, adding to the need of extra hardware resources. Moreover, it is verified that for DMT, the Fast Fourier Transform (FFT) operations require most hardware resources. After the presentation of some alternative modulation techniques such as pulse-amplitude-modulated DMT (PAM-DMT), which also were investigated by the author, this thesis ends with the conclusions and some recommendations for further research work

Low computational SLAM for an autonomous indoor aerial inspection vehicle

The past decade has seen an increase in the capability of small scale Unmanned Aerial Vehicle (UAV) systems, made possible through technological advancements in battery, computing and sensor miniaturisation technology. This has opened a new and rapidly growing branch of robotic research and has sparked the imagination of industry leading to new UAV based services, from the inspection of power-lines to remote police surveillance. Miniaturisation of UAVs have also made them small enough to be practically flown indoors. For example, the inspection of elevated areas in hazardous or damaged structures where the use of conventional ground-based robots are unsuitable. Sellafield Ltd, a nuclear reprocessing facility in the U.K. has many buildings that require frequent safety inspections. UAV inspections eliminate the current risk to personnel of radiation exposure and other hazards in tall structures where scaffolding or hoists are required. This project focused on the development of a UAV for the novel application of semi-autonomously navigating and inspecting these structures without the need for personnel to enter the building. Development exposed a significant gap in knowledge concerning indoor localisation, specifically Simultaneous Localisation and Mapping (SLAM) for use on-board UAVs. To lower the on-board processing requirements of SLAM, other UAV research groups have employed techniques such as off-board processing, reduced dimensionality or prior knowledge of the structure, techniques not suitable to this application given the unknown nature of the structures and the risk of radio-shadows. In this thesis a novel localisation algorithm, which enables real-time and threedimensional SLAM running solely on-board a computationally constrained UAV in heavily cluttered and unknown environments is proposed. The algorithm, based on the Iterative Closest Point (ICP) method utilising approximate nearest neighbour searches and point-cloud decimation to reduce the processing requirements has successfully been tested in environments similar to that specified by Sellafield Ltd

The Emergence of De-facto Standards

Increasingly, companies compete on platform technologies that bring together groups of users in two-sided networks. Examples include smartphones and on-line search engines. In industries governed by platform technologies, it is common to see one emerging as the de-facto standard because they are especially prone to network externalities (i.e. when the benefit that can be derived from a technology increases exponentially with the number of users). Competitions for the de-facto standard are high-stakes games. These ‘winner-take-all’ markets demonstrate very different competitive dynamics than markets in which many competitors can coexist relatively peacefully, as they often have a single tipping point which shifts market adoption to one particular technology. The academic field lacks a robust clarification on how firms can shape the odds of their technology emerging as the de-facto standard. This study develops an integrative framework and corresponding methodology for understanding the process by which a technology becomes the de-facto standard. By applying the framework to several technology competitions, insight is provided in how firm-, technology- and market-related elements influence technology competitions. Results indicate that the emergence of every de-facto standard displays a unique path. This path can be divided into six phases, and can be influenced by 40 unique elements, of which 19 are subject to strategic decision making. Patterns between technology competitions indicate a common set of focal points per phase

Design and implementation of a control system for use of galvanometric scanners in laser micromachining applications

In the recent years, laser machining technology has been used widely in industrial applications usually with the aim of increasing the production capability of mass production lines - especially for fast marking, engraving type of applications where speed is an important concern - or manufacturing quality of a certain facility by increasing the level of accuracy in material processing applications such as drilling, cutting; or any scientific research oriented work where high precision machining of parts in sub millimeter scale might be required. A galvanometric scanner is a high precision device that is able to steer a laser beam with a mirror attached to a motor, whose rotor angular range is usually limited with tens of degrees in both directions of rotation; and position is controlled either by voltage or current. Due to their lightness, the rotor and the mirror can move very fast, allowing fast marking (burning out) operation with the laser beam. This can be evaluated as a great advantage compared to slower mechanical appliances used for cutting/machining of different materials. This study concentrates on the analysis of galvanometric scanner system components; and the design and implementation of a hardware and software based control system for a dual-axis galvo setup; and their adaptation for use in laser micromachining applications either as a standalone system or a modular subsystem. Analysis part of the thesis work contains: evaluation of dominant laser micromachining techniques, an overview of the galvanometric scanner system based approach and related components (e.g. electromechanical, electrical, optical), understanding of working principles and related simulation work, compatibility issues with the target micromachining applications. Design part of the thesis work includes: the design and implementation of electronic controller board, intermediate drive electronics stage, microcontroller programming for machining control algorithm, interfacing with graphical user interface based control software and production of necessary mechanical parts. The study has been finalized with experimental work and evaluation of obtained results. The results of these studies are promising and motivate the use of laser galvanometric scanner systems in laser micromachining applications