Implementation and investigation of a real-time optical 16-QAM transmission system with FPGA-based coherent receiver

Diese Dissertation stellt die erste Echtzeitübertragung von 16-QAM mit FPGA-basierter DSPU vor. 2.5 Gb/s wurden dabei über 20 und 100 km übertragen und kohärent (heterodyn) in Echtzeit empfangen. Die Bitfehlerquote (BER) lag dabei unterhalb der Schwelle moderner Fehlervorwärtskorrekturverfahren mit 7% Overhead. Mit BPS (Blind Phase Search) und QPSK partitioning (QPSKP) wurden zwei unterschiedliche Techniken zur Phasenrückgewinnung implementiert und durch Echtzeitmessung verglichen. Der Einfluss der Auflösung der erforderlichen Analog-Digital-Umsetzer (ADC) wurde ebenfalls untersucht, welche ebenfalls eine Herausforderung für kohärente Echtzeitübertragung darstellt. Der Einfluss von Phasenrauschen wird hier auch gezeigt, welches vorwiegend von den verwendeten Lasern, optischen Verstärkern und nichtlinearen Effekten in den optischen Fasern abhängt. Darüber hinaus wurden verschiedene Arbeitspunkte des 16-QAM-Modulators in Echtzeit getestet und die optimalen Bedingungen für eine minimale Bitfehlerquote gefunden.In this dissertation the first published real-time implementation of a 16-QAM transmission system with FPGA-based DSP is presented. 2.5 Gb/s coherent 16-QAM data has been optically transmitted over 20 and 100 km and synchronously received by heterodyning in a real-time I&Q receiver, with BER below the threshold of a state-of-the-art FEC (7% overhead). Two techniques of feed-forward carrier phase recovery (Blind Phase Search (BPS) and QPSK partitioning (QPSKP)) were tested in a real-time transmission experiment and compared with each other. The influence of the required resolution of the analog-to-digital converter (ADC) has been investigated, which is a challenge of real-time coherent transmission systems. The influence of phase noise in 16-QAM, which is mainly contributed from laser sources, optical amplifiers, and nonlinear effects in optical fibers is also shown. Moreover, different operation points of a 16-QAM modulator were tested in real-time and an optimal condition is found which minimizes the BER.Tag der Verteidigung: 10.09.2013Paderborn, Univ., Diss., 201

DEVELOPMENT OF A VERSATILE HIGH SPEED NANOMETER LEVEL SCANNING MULTI-PROBE MICROSCOPE

The motivation for development of a multi-probe scanning microscope, presented in this dissertation, is to provide a versatile measurement tool mainly targeted for biological studies, especially on the mechanical and structural properties of an intracellular system. This instrument provides a real-time, three-dimensional (3D) scanning capability. It is capable of operating on feedback from multiple probes, and has an interface for confocal photo-detection of fluorescence-based and single molecule imaging sensitivity. The instrument platform is called a Scanning Multi-Probe Microscope (SMPM) and enables 45 microm by 45 microm by 10 microm navigation of specimen with simultaneous optical and mechanical probing with each probe location being adjustable for collocation or for probing with known probe separations. The 3D positioning stage where the specimen locates was designed to have nanometer resolution and repeatability at 10 Hz scan speed with either open loop or closed loop operating modes. The fine motion of the stage is comprises three orthogonal flexures driven by piezoelectric actuators via a lever linkage. The flexures design is able to scan in larger range especially in z axis and serial connection of the stages helps to minimize the coupling between x, y and z axes. Closed-loop control was realized by the capacitance gauges attached to a rectangular block mounted to the underside of the fine stage upon which the specimen is mounted. The stage's performance was studied theoretically and verified by experimental test. In a step response test and using a simple proportional and integral (PI) controller, standard deviations of 1.9 nm 1.8 nm and 0.41 nm in the x, y and z axes were observed after settling times of 5 ms and 20 ms for the x and y axes. Scanning and imaging of biological specimen and artifact grating are presented to demonstrate the system operation. For faster, short range scanning, novel ultra-fast fiber scanning system was integrated into the xyz fine stage to achieve a super precision dual scanning system. The initial design enables nanometer positioning resolution and runs at 100 Hz scan speed. Both scanning systems are capable of characterization using dimensional metrology tools. Additionally, because the high-bandwidth, ultra-fast scanning system operates through a novel optical attenuating lever, it is physically separate from the longer range scanner and thereby does not introduce additional positioning noise. The dual scanner provides a fine scanning mechanism at relatively low speed and large imaging area using the xyz stage, and focus on a smaller area of interested in a high speed by the ultra-fast scanner easily. Such functionality is beneficial for researchers to study intracellular dynamic motion which requires high speed imaging. Finally, two high end displacement sensor systems, a knife edge sensor and fiber interferometer, were demonstrated as sensing solutions for potential feedback tools to boost the precision and resolution performance of the SMPM

Sensorless vector control of surface mounted permanent magnet machines without restriction of zero frequency

Permanent magnet motors have a series of characteristics that make them attractive for the use in industrial drives: low maintenance, high dynamics, small size and mass to power ratio. In particular its higher efficiency means that permanent magnet synchronous motors may be used instead of electro-magnetically exited motors (such induction machines or commutator DC motors) in applications where the energy savings compensate the higher initial cost. Nevertheless, the need for a shaft mounted position measurement to perform the orientation of the control of the synchronous machine is of concern, because it increases the total drive cost and reduces reliability. In this work the sensorless vector control of a surface mounted permanent magnet machine is presented. The emphasis is in the control at low and zero speed, including position control, by means of saturation saliency tracking. Two different strategies for rotor position detection used in salient synchronous machines and in induction machines are analysed. These are hf voltage injection in the stationary, stator, reference frame of the machine (α-ß injection) and hf voltage injection on the estimated rotor axis (so called d-axis or pulsating injection). These two methods are optimised for its application to the surface mounted PM machine. The small magnitude of the saliency present difficulties and disturbances are significant. A commissioning based method (SMP) is used for enhanced rotor position estimation by the α-ß rotating injection. The two methods are implemented on a 4 kW experimental rig and the sensorless controlled results are compared and discussed. A hybrid structure combining the saliency tracking method with a flux-observer is also presented and provides sensorless control capability over the whole speed range

Compensation of fibre impairments in coherent optical systems

Tese de mestrado integrado. Engenharia Electrotécnica e de Computadores. Faculdade de Engenharia. Universidade do Porto. 201

Multi-gigabit CMOS analog-to-digital converter and mixed-signal demodulator for low-power millimeter-wave communication systems

The objective of the research is to develop high-speed ADCs and mixed-signal demodulator for multi-gigabit communication systems using millimeter-wave frequency bands in standard CMOS technology. With rapid advancements in semiconductor technologies, mobile communication devices have become more versatile, portable, and inexpensive over the last few decades. However, plagued by the short lifetime of batteries, low power consumption has become an extremely important specification in developing mobile communication devices. The ever-expanding demand of consumers to access and share information ubiquitously at faster speeds requires higher throughputs, increased signal-processing functionalities at lower power and lower costs. In today’s technology, high-speed signal processing and data converters are incorporated in almost all modern multi-gigabit communication systems. They are key enabling technologies for scalable digital design and implementation of baseband signal processors. Ultimately, the merits of a high performance mixed-signal receiver, such as data rate, sensitivity, signal dynamic range, bit-error rate, and power consumption, are directly related to the quality of the embedded ADCs. Therefore, this dissertation focuses on the analysis and design of high-speed ADCs and a novel broadband mixed-signal demodulator with a fully-integrated DSP composed of low-cost CMOS circuitry. The proposed system features a novel dual-mode solution to demodulate multi-gigabit BPSK and ASK signals. This approach reduces the resolution requirement of high-speed ADCs, while dramatically reducing its power consumption for multi-gigabit wireless communication systems.PhDGee-Kung Chang - Committee Chair; Chang-Ho Lee - Committee Member; Geoffrey Ye Li - Committee Member; Paul A. Kohl - Committee Member; Shyh-Chiang Shen - Committee Membe

nEUCLID: a new homodyne interferometer with space applications

The objective of this project was to design a low-mass, low-power interferometer to be used for space applications. It had to be capable of remaining tilt-immune whilst working at a distance of at least 1 m. This thesis describes the design and subsequent building of a 1550 run homodyne interferometer. Known as nEUCLID, it has a working distance of 660 mm and a working range of± 120 mm. These large distances are made possible by the novel cat's eye design within the interferometer, which also allows tilt immunity of± 0.35° of the target mirror (at the sweet plane). The thesis explains in detail the theory and design of the cat's eye, known as a PCE in the text. The interferometer, nEUCLID, has a sensitivity of 420 pm/√Hz, at 1 Hz in air, tested at the working distance of the current design. It has a mass of 2 kg and an overall power of 1.8 W. Both of these values are due to using standard, off-the-shelf components in the design, and could be reduced with further development. Within this thesis ground-based and space-based applications for nEUCLID within the space industry are discussed and compared with existing technologies

Microwave resonant sensors

Microwave resonant sensors use the spectral characterisation of a resonator to make high sensitivity measurements of material electromagnetic properties at GHz frequencies. They have been applied to a wide range of industrial and scientific measurements, and used to study a diversity of physical phenomena. Recently, a number of challenging dynamic applications have been developed that require very high speed and high performance, such as kinetic inductance detectors and scanning microwave microscopes. Others, such as sensors for miniaturised fluidic systems and non-invasive blood glucose sensors, also require low system cost and small footprint. This thesis investigates new and improved techniques for implementing microwave resonant sensor systems, aiming to enhance their suitability for such demanding tasks. This was achieved through several original contributions: new insights into coupling, dynamics, and statistical properties of sensors; a hardware implementation of a realtime multitone readout system; and the development of efficient signal processing algorithms for the extraction of sensor measurements from resonator response data. The performance of this improved sensor system was verified through a number of novel measurements, achieving a higher sampling rate than the best available technology yet with equivalent accuracy and precision. At the same time, these experiments revealed unforeseen applications in liquid metrology and precision microwave heating of miniature flow systems.EThOS - Electronic Theses Online ServiceGBUnited Kingdo

Advanced adaptive compensation system for free-space optical communications

Massive amounts of information are created daily in commercial fields like earth observation, that must be downloaded to earth ground stations in the short time of a satellite pass. Today, much of the collected information must be dropped due to lack of bandwidth, and laser downlinks can offer tenths of gigabits throughput solving this bottleneck limitation. In a down-link scenario, the performance of laser satellite communications is limited due to atmospheric turbulence, which causes fluctuations in the intensity and the phase of the received signal leading to an increase in bit error probability. In principle, a single-aperture phase-compensated receiver, based on adaptive optics, can overcome atmospheric limitations by adaptive tracking and correction of atmospherically induced aberrations. However, under strong-turbulence situations, the effectiveness of traditional adaptive optics systems is severely compromised. In such scenarios, sensor-less techniques offer robustness, hardware simplicity, and easiness of implementation and integration at a reduced cost, but the state-of-the-art approaches still require too many iterations to perform the correction, exceeding the temporal coherence of the field and thus falling behind the field evolution. This thesis proposes a new iterative AO technique for strong turbulence compensation that reduces the correction time, bridging the limitation of similar systems in lasercom applications. It is based on the standard sensor-less system design, but it additionally uses a short-exposure focal intensity image to accelerate the correction. The technique combines basic principles of Fourier optics, image processing, and quadratic signal optimization to correct the wave-front. This novel approach directly updates the phases of the most intense focal-plane speckles, maximizing the power coupled into a single-mode fiber convexly. Numerical analyses show that this method has a robust and excellent performance under very strong turbulence. Laboratory results confirm that a focal speckle pattern can be used to accelerate the iterative compensation. This technique delivers nearly twofold bandwidth reduction compared with standard methods, and sufficient signal gain and stability to allow high throughput data transmission with nearly error-free performance in emulated satellite downlink scenarios. A property highlight is the in-advance knowledge of the required number of iterations, allowing on-demand management of the loop bandwidth in different turbulent regimes. Besides remaining conceptually and technically simple, it opens a new insight to iterative solutions that may lead to the development of new methods. With further refinement, this technique can surely contribute to making possible the use of iterative solutions in laser communicationsSatélites de observación de la tierra diariamente generan gigantescas cantidades de datos que deben ser enviados a estaciones terrenas. La mayoría de la información recolectada debe desecharse debido al reducido tiempo visible de un satélite en movimiento y el limitado ancho de banda de transmisión. Enlaces ópticos pueden solucionar esta limitación ofreciendo multi-gigabit de ancho de banda. Sin embargo, el desempeño de un downlink laser está limitado por la turbulencia atmosférica, la cual induce variaciones en la intensidad y la fase de la señal recibida incrementando la probabilidad de error en los datos recibidos. En principio, un receptor basado en una apertura simple utilizando óptica adaptativa puede corregir las aberraciones de fase inducidas por la atmósfera, mejorando el canal de transmisión. Sin embargo, la eficiencia de los sistemas de óptica adaptativa tradicionales se ve seriamente reducida en situaciones de turbulencia fuerte. En tales escenarios, técnicas iterativas ofrecen mayor robustez, simplicidad de diseño e implementación, así como también facilidad de integración a un costo reducido. Desafortunadamente, dicha tecnología aún requiere demasiadas iteraciones para corregir la fase distorsionada, excediendo el tiempo de coherencia del frente de onda. Esta tesis propone una nueva técnica iterativa de óptica adaptativa capaz de reducir el tiempo de convergencia en escenarios de turbulencia fuerte. La técnica utiliza el diseño tradicional de los sistemas de corrección iterativos, agregando el uso de una imagen focal de intensidad para acelerar el proceso de corrección del campo distorsionado. En dicha técnica se combinan principios básicos de óptica de Fourier, procesamiento de imagen, y optimización cuadrática de la señal para corregir el frente de onda. De esta forma, la fase de los puntos focales de mayor intensidad (speckles) puede modificarse directamente y con ello maximizar de forma convexa la potencia acoplada en fibra. Los análisis numéricos demuestran robustez y un excelente desempeño en escenarios de turbulencia fuerte. Los resultados de laboratorio confirman que el moteado de intensidad puede utilizarse para acelerar la corrección iterativa. Esta técnica utiliza la mitad del ancho de banda requerido con la técnica tradicional, al mismo tiempo que ofrece suficiente ganancia y estabilidad de la señal para lograr enlaces ópticos con muy baja probabilidad de error. Al mismo tiempo, la técnica propuesta permite conocer con anticipación el número total de iteraciones y posibilita la administración bajo demanda del ancho de banda requerido en diferentes escenarios de turbulencia. Esta tesis ofrece una mirada diferente a los métodos iterativos, posibilitando el desarrollo de nuevos conceptos y contribuyendo al uso de soluciones iterativas en comunicaciones laser por espacio libre.Postprint (published version