A Study of Synchronization Techniques for Optical Communication Systems

The study of synchronization techniques and related topics in the design of high data rate, deep space, optical communication systems was reported. Data cover: (1) effects of timing errors in narrow pulsed digital optical systems, (2) accuracy of microwave timing systems operating in low powered optical systems, (3) development of improved tracking systems for the optical channel and determination of their tracking performance, (4) development of usable photodetector mathematical models for application to analysis and performance design in communication receivers, and (5) study application of multi-level block encoding to optical transmission of digital data

Fluorescence Lifetime Imaging Camera: Image Analysis, Optimization and Enhancement

Fluorescence lifetime imaging microscopy (FLIM) is an imaging technique for producing an image based on differences in fluorescence lifetimes. The present thesis is devoted to analyzing a novel Fluorescence Lifetime Imaging Camera (FLI-Cam) system. The principle of the applied camera system is based on the Time-of-Flight (ToF) technique, which was originally designed for 3D depth scene imaging. Such a camera provides a high frame rate and realizes direct nanosecond-range fluorescence lifetime sensing. The main scope of this thesis is to deliver an optimized solution and rapid sophisticated algorithm for the FLI-Cam system with high accuracy. New time-gated schemes and heterodyne modulation scheme for FLIM using the pulse-based and continuous-wave-based (phase-based) ToF camera, respectively, are presented. In order to optimize the performance of the FLI-Cam system, a thorough statistical analysis is implemented and the photon economy of our FLIM techniques is investigated. Various operation modes and experimental parameters for the measurement have been studied and optimized. The presented theoretical result is validated by numerical simulations using the Monte Carlo method and real experiments. For the enhancement of the FLIM images from our system, the vector-valued total variation technique is applied to improve the quality of FLIM images for the first time. It shows better performance than other existing approaches

Wavelength-tunable picosecond optical pulse by self-seeding of a gain-switched fabry-perot laser diode.

by Lee Yip-Chi.Thesis (M.Phil.)--Chinese University of Hong Kong, 1995.Includes bibliographical references (leaves [129]-[134]).AcknowledgmentsAbstractChapter Chapter 1. --- Introduction --- p.1-1Chapter 1.1) --- Recent approaches for wavelength-tunable optical pulse generation --- p.1 -2Chapter 1.2) --- Self-seeding a gain-switched Fabry-Perot laser diode --- p.1 -5Chapter 1.3) --- About this project --- p.1-8Chapter Chapter 2. --- Basic theory --- p.2-1Chapter 2.1) --- Basic mechanism of gain-switching --- p.2-1Chapter 2.2) --- Mechanism of self-seeding --- p.2-5Chapter 2.2.1) --- General principle --- p.2-5Chapter 2.2.2) --- Dynamics of singlemode formation --- p.2-7Chapter 2.2.3) --- Different cases of modal selection --- p.2-8Chapter 2.2.4) --- Reduction of turn-on delay time jitter of optical output --- p.2-10Chapter Chapter 3. --- Instrumentation --- p.3-1Chapter 3.1) --- Second harmonic autocorrelator --- p.3-1Chapter 3.1.1) --- Principle --- p.3-1Chapter 3.1.2) --- Description of the 2nd harmonic autocorrelator system --- p.3-3Chapter 3.1.3) --- Data acquisition --- p.3-4Chapter 3.1.4) --- Alignment and Measurement procedures --- p.3-5Chapter 3.1.5) --- Pulsewidth determination by curve fitting --- p.3-7Chapter 3.2) --- Optical pulse detection by high speed photodetector --- p.3-9Chapter 3.2.1) --- High speed photodetectors --- p.3-9Chapter 3.2.2) --- Data acquisition --- p.3-10Chapter 3.2.3) --- Deconvolution of the measured optical pulsewidth --- p.3-11Chapter Chapter 4 --- Self-seeding 830 nm laser diode using conventional grating method --- p.4-1Chapter 4.1) --- Introduction --- p.4-1Chapter 4.2) --- Design parameters --- p.4-2Chapter 4.2.1) --- External cavity length --- p.4-2Chapter 4.2.2) --- Grating orientation --- p.4-3Chapter 4.3) --- Experiment --- p.4-4Chapter 4.3.1) --- Experimental setup --- p.4-4Chapter 4.3.2) --- Equipment Description --- p.4-5Chapter 4.4) --- Results and discussion --- p.4-6Chapter Chapter 5. --- Self-seeding 1.3 μm LD using fiber-optic configuration --- p.5-1Chapter 5.1) --- Optimized operation of self-seeded laser diode --- p.5-1Chapter 5.1.1) --- General Description --- p.5-1Chapter 5.1.2) --- Components --- p.5-1Chapter 5.1.3) --- Experimental setup --- p.5-6Chapter 5.1.4) --- Feedback rate measurement --- p.5-8Chapter 5.1.5) --- Results and discussion --- p.5-9Chapter 5.2) --- Electrical bias dependence on the self-seeded LD --- p.5-15Chapter 5.3) --- An efficient scheme to improve tuning range and provide continuous tuning --- p.5-20Chapter 5.3.1) --- General Description --- p.5-20Chapter 5.3.2) --- Principle of thermal control scheme --- p.5-20Chapter 5.3.3) --- Experimental setup --- p.5-22Chapter 5.3.4) --- Results and Discussions --- p.5-23Chapter Chapter 6. --- A novel self-seeding configuration --- p.6-1Chapter 6.1) --- Principle --- p.6-1Chapter 6.2) --- Highly dispersion-shifted fiber --- p.6-2Chapter 6.3) --- Optical fiber-mirror --- p.6-3Chapter 6.3.1 --- Fabrication --- p.6-4Chapter 6.3.2) --- Characterization: --- p.6-6Chapter 6.4) --- Experiment --- p.6-10Chapter 6.5) --- Results --- p.6-12Chapter 6.6) --- Discussions --- p.6-27Chapter 6.6.1) --- Electrical tuning characteristic --- p.6-27Chapter 6.6.2) --- Sidemode supression ratio characteristics --- p.6-30Chapter 6.6.3) --- Thermal tuning characteristics --- p.6-33Chapter 6.7) --- Summary --- p.6-36Chapter Chapter 7. --- Half-period delayed dual-wavelength picosecond optical pulse generation using a self-seeded laser diode --- p.7-1Chapter 7.1) --- Introduction --- p.7-1Chapter 7.2) --- Principle --- p.7-2Chapter 7.3) --- Experiment --- p.7-4Chapter 7.4) --- Results and discussions --- p.7-5Chapter Chapter 8. --- A proposed self-seeding configuration for the programmable multi- wavelength optical pulse generation --- p.8-1Chapter Chapter 9. --- Conclusion --- p.9-1ReferencesAppendixList of accepted and submitted publication

Machine Learning in Digital Signal Processing for Optical Transmission Systems

The future demand for digital information will exceed the capabilities of current optical communication systems, which are approaching their limits due to component and fiber intrinsic non-linear effects. Machine learning methods are promising to find new ways of leverage the available resources and to explore new solutions. Although, some of the machine learning methods such as adaptive non-linear filtering and probabilistic modeling are not novel in the field of telecommunication, enhanced powerful architecture designs together with increasing computing power make it possible to tackle more complex problems today. The methods presented in this work apply machine learning on optical communication systems with two main contributions. First, an unsupervised learning algorithm with embedded additive white Gaussian noise (AWGN) channel and appropriate power constraint is trained end-to-end, learning a geometric constellation shape for lowest bit-error rates over amplified and unamplified links. Second, supervised machine learning methods, especially deep neural networks with and without internal cyclical connections, are investigated to combat linear and non-linear inter-symbol interference (ISI) as well as colored noise effects introduced by the components and the fiber. On high-bandwidth coherent optical transmission setups their performances and complexities are experimentally evaluated and benchmarked against conventional digital signal processing (DSP) approaches. This thesis shows how machine learning can be applied to optical communication systems. In particular, it is demonstrated that machine learning is a viable designing and DSP tool to increase the capabilities of optical communication systems

Optical fibre communication over a noisy partially coherent channel

As global IP traffic grows unceasingly, optical networks demand for technology upgrades in order to keep the feared “capacity crunch” away. The most celebrated technologies of coherent detection and wavelength-division multiplexing (WDM), widely deployed in long-haul links, are gaining ground in access networks, which is particularly challenging due to the shared-cost requirements, leading to denser channel spacings and the use of cheaper devices that tend to be noisier. In order to make the most of this technology combination, it is crucial to have a model of the channel that accurately describes all the present sources of noise. Traditionally, the most used model has been the additive white Gaussian noise (AWGN) channel, which, although only accounting for a linear contribution of complex noise and being insensitive to rotational phenomena, has shown its validity in numerous studies, as well as in commercial equipment. In this thesis, however, it is observed that the adoption of coherent detection and WDM, with lower-grade semiconductor lasers showing a moderate linewidth, yields scenarios where a phase-sensitive model becomes a must. The partially coherent AWGN (PCAWGN) channel is a popular choice that fulfils this need, but its high complexity due to non-trivial functions involved, deprives it from being suitable in high-speed digital circuits. The main goal of this thesis is to describe a reduced-complexity approximation in polar coordinates, accurate enough to find its applicability in modern systems. Furthermore, this works explores some possible end-to-end applications, like channel capacity estimation or symbol detection, assessing its performance by means of extensive simulations. Lastly, the emerging field of complex modulation of directly modulated lasers is revisited, with a special interest in how the proposed approximation can help to improve the performance of previously reported techniques, as well as proposing a new way to design spiral-shaped constellations aimed to maximise the channel capacity

Spatial statistics and analysis of earth's ionosphere

Thesis (Ph.D.)--Boston UniversityThe ionosphere, a layer of Earths upper atmosphere characterized by energetic charged particles, serves as a natural plasma laboratory and supplies proxy diagnostics of space weather drivers in the magnetosphere and the solar wind. The ionosphere is a highly dynamic medium, and the spatial structure of observed features (such as auroral light emissions, charge density, temperature, etc.) is rich with information when analyzed in the context of fluid, electromagnetic, and chemical models. Obtaining measurements with higher spatial and temporal resolution is clearly advantageous. For instance, measurements obtained with a new electronically-steerable incoherent scatter radar (ISR) present a unique space-time perspective compared to those of a dish-based ISR. However, there are unique ambiguities for this modality which must be carefully considered. The ISR target is stochastic, and the fidelity of fitted parameters (ionospheric densities and temperatures) requires integrated sampling, creating a tradeoff between measurement uncertainty and spatio-temporal resolution. Spatial statistics formalizes the relationship between spatially dispersed observations and the underlying process(es) they represent. A spatial process is regarded as a random field with its distribution structured (e.g., through a correlation function) such that data, sampled over a spatial domain, support inference or prediction of the process. Quantification of uncertainty, an important component of scientific data analysis, is a core value of spatial statistics. This research applies the formalism of spatial statistics to the analysis of Earth's ionosphere using remote sensing diagnostics. In the first part, we consider the problem of volumetric imaging using phased-array ISR based on optimal spatial prediction ("kriging"). In the second part, we develop a technique for reconstructing two-dimensional ion flow fields from line-of-sight projections using Tikhonov regularization. In the third part, we adapt our spatial statistical approach to global ionospheric imaging using total electron content (TEC) measurements derived from navigation satellite signals

Engineering of reconfigurable integrated photonics for quantum computation protocols

Over the last decade, integrated optics has emerged as one of the main technologies for quantum optics and more generally quantum computation, quantum cryptography and communication. In particular, it is fundamental for the construction of reconfigurable interferometers with a high number of optical modes. In this thesis we present, on the one hand, the development of a new geometry for the creation of integrated reconfigurable devices with a high number of modes and, on the other hand, the development of quantum computation protocols to be realized in integrated photonic chips. In the first part, two algorithms are proposed for the characterization of integrated circuits in terms of implemented unitary matrix. The first uses a so-called Black Box approach, i.e. one that makes no assumptions about the internal structure of the device under consideration, and it is based on second-order correlation measurements with coherent light. The second is specific to a planar rectangular geometry, first proposed by Clements et al., which has a variety of applications in the literature and is also employed in this thesis. Subsequently, we present the realization of a new 32-mode reconfigurable integrated photonic device with a continuously coupled three-dimensional geometry. Its potential in terms of reconfigurability is tested and a Boson sampling experiment with three and four photons is carried out to show its potential in the field of quantum computation. In the second part, we propose the application of integrated photonic devices to two quantum computation protocols. The first was recently proposed and is the quantum extension of a problem called Bernoulli factory. It consists in the construction of a qubit from $n$ qubits in the same unknown state so that there is a predetermined exact relation between the output and input states. In the thesis, we theoretically analyze the computational complexity of the problem in terms of the qubits used and the success probability of the problem. Furthermore, a photonic implementation is proposed and experimentally tested for correctness and resilience to experimental noise. The second application consists of the experimental implementation of a quantum metrology protocol in which three distinct phases are estimated simultaneously, showing that the use of indistinguishable photons leads to an advantage in terms of the variance of the estimates

Stacked Modulation Formats Enabling Highest-Sensitivity Optical Free-Space Communications

Die vorliegende Arbeit befasst sich mit hochempfindlichen optischen Kommunikationssystemen, wie sie z.B. bei Intersatellitenlinks verwendet werden. Theoretische Überlegungen zur Steigerung der Empfängerempfindlichkeit werden mit Simulations- und Messergebnissen ergänzt und verifiziert. Auf Grund der steigenden Nachfrage nach optischen Links zwischen Satelliten stellt sich die Frage, was sind geeignete Eckparameter, um ein solches System zu beschreiben. Die gigantischen Datenmengen, die von diversen Messgeräten, wie z.B. hochauflösende Kameras auf einem Satelliten generiert werden, bringen die Kapazitäten klassischer HF-Datenlinks an ihre Grenzen. Hier können optische Kommunikationssysteme auf Grund ihrer hohen Trägerfrequenz im Infrarotbereich sehr hohe Datenraten im Terabit/s Bereich ermöglichen. Systeme mit Radiowellen im GHz Bereich als Trägerfrequenz sind hier deutlich limitierter. [7] Linkdistanz, verfügbare Leistung, Pointinggenauigkeit und verfügbare Antennengröße sind einige Parameter, die einen wichtigen Einfluss auf die Leistungsfähigkeit des Systems haben. Je größer die Distanz und desto kleiner die verfügbare Antennengröße sowohl am Sender als auch am Empfänger sind, desto weniger Signalleistung wird den Detektor erreichen. Nimmt man dann noch ungenaues Pointing hinzu, d.h. Sender und Empfänger sind nicht exakt aufeinander ausgerichtet, treten zusätzliche Verluste auf. [7] Ziel dieser Arbeit ist es, ein vereinfachtes System zu implementieren und zu testen, das mit möglichst wenigen Photonen pro Bit bei einer gegebenen Bitfehlerwahrscheinlichkeit bei einer möglichst hohen Datenrate arbeiten kann. Hierfür werden alle Freiheitsgrade einer optischen Welle zur Modulation verwendet, um mit sog. „Stapeln“ von Modulationsformaten eine Empfindlichkeitssteigerung zu erreichen. Die Amplitude des Signals wird durch Pulspositionsmodulation (PPM) moduliert, wobei das zeitlich variable Vorhandensein eines Pulses innerhalb des Symbols die Information enthält. Dieses Modulationsformat weist bis dato die höchste Empfindlichkeit in Literatur und Experimenten auf [4]. Je mehr Möglichkeiten es gibt, einen Puls in einem Symbol zu platzieren, desto höher ist die zu erwartende Empfindlichkeit des Systems. Mit anderen Worten: Steigert man die zeitliche Dauer eines PPM-Symbols, so wächst ebenfalls die Empfängerempfindlichkeit. Da bei diesem Ansatz die Datenrate sinkt, wird in dieser Arbeit eine andere Methode vorgestellt, die Empfindlichkeit eines Übertragungssystems zu steigern, ohne die Symbollänge unnötig in die Länge zu ziehen. Diese Arbeit befasst sich mit dem Stapeln (sog. „Stacking“) von Modulationsformaten, in dem neben der Amplitudenmodulation weitere Freiheitsgrade, wie die Frequenz, Phase und Polarisation geschickt genutzt werden. Bei der Frequenzumtastung (FSK) wird die optische Frequenz je nach Symbol um ein gewisses Maß verschoben. Bei der polarisations-geschalteten Quadratur-Phasenumtastung (PS-QPSK) werden sowohl die Phase, als auch die Polarisation der optischen Welle moduliert [12]. Als Endergebnis erhält man PPM-FSK-PS-QPSK als Modulationsformat mit hoher Empfindlichkeit. Gegenüber dem reinen PPM wird eine theoretische Empfindlichkeitssteigerung von mehr als 1 dB erreicht. Sowohl Simulations- als auch Messergebnisse bestätigen den Empfindlichkeitsgewinn