Techniques to control dispersion in a medium have attracted much attention due to potential applications to devices such as ring laser gyroscopes, interferometric gravitational wave detectors, data buffers, phased array radars and quantum information processors. Of particular interest is an optical resonator containing a medium with an anomalous dispersion corresponding to fast-light, which behaves as a White Light Cavity (WLC). A WLC can be tailored to improve the sensitivity of sensing devices as well as to realize an optical data buffering system that overcomes the delay-bandwidth product of a conventional cavity. This dissertation describes techniques to tailor the dispersion for fast-light in intracavity media. We present first a demonstration of fast-light in a photorefractive crystal. When placed inside a cavity, such a medium could be used to enhance the bandwidth of a gravitational wave detector. We then describe how a superluminal laser can be realized by adding anomalously dispersive medium inside a ring laser. We identify theoretical conditions under which the sensitivity of the resonance frequency to a change in the cavity length is enhanced by as much as seven orders of magnitude. This paves the way for realizing a fast-light enhanced ring laser gyroscope, for example. This is followed by the development of a novel data buffering system which employs two WLC systems in series. In this system, a data pulse can be delayed an arbitrary amount of time, without significant distortion. The delay time is independent of the data bandwidth, and is limited only by the attenuation experienced by the data pulse as it bounces between two high-reflectivity mirrors. Such a device would represent a significant breakthrough in overcoming the delay-time bandwidth product limitation inherent in conventional data buffers. We then describe our experimental effort to create a fiber-based WLC by using stimulated Brillouin scattering (SBS). Experimental results, in agreement with our theoretical model presented here, show that the WLC effect is small under the conditions supported by current fiber optic technology. We conclude that future efforts to induce a large WLC effect would require fibers with high Brillouin coefficient and low transmission loss, as well as optical elements with very low insertion loss and high power damage thresholds.

With the industrial revolution, the world was acquainted with the concept of speed. &bdquo / Speed

Optics has the inherent advantages of parallelism and wide bandwidths in processing information. However, the need to interface with electronics creates a bottleneck that eliminates many of these advantages. The proposed research explores novel optical devices and techniques to overcome some of these bottlenecks. To address parallelism issues we take a specific example of a content-addressable memory that can recognize images. Image recognition is an important task that in principle can be done rapidly using the natural parallelism of optics. However in practice, when presented with incomplete or erroneous information, image recognition often fails to give the correct answer. To address this problem we examine a scheme based on free-space interconnects implemented with diffractive optics. For bandwidth issues, we study possible ways to eliminate the electronic conversion bottleneck by exploring all-optical buffer memories and all-optical processing elements. For buffer memories we examine the specific example of slow light delay lines. Although this is currently a popular research topic, there are fundamental issues of the delay-time-bandwidth product that must be solved before slow light delay lines can find practical applications. For all-optical processing we examine the feasibility of constructing circuit elements that operate directly at optical frequencies to perform simple processing tasks. Here we concentrate on the simplest element, a sub-wavelength optical wire, along with a grating coupler to interface with conventional optical elements such as lenses and fibers. Even such a simple element as a wire has numerous potential applications. In conclusion, information processing by all-optical devices are demonstrated with an associative memory using diffractive optics, an all-optical delay line using room temperature slow light in photorefractive crystals, and a subwavelength optical circuit by surface plasmon effects.

published_or_final_version / Education / Master / Master of Education

Networking research and development have historically focused on increasing network throughput and path resource utilization, which particularly helped bulk applications such as file transfer and video streaming. Recent over-provisioning in the core of the Internet has facilitated the use of interactive applications like interactive web browsing, audio/video conferencing, multi- player online gaming and financial trading applications. Although the bulk applications rely on transferring data as fast as the network permits, interactive applications consume rather little bandwidth, depending instead on low latency. Recently, there has been an increasing concern in reducing latency in networking research, as the responsiveness of interactive applications directly influences the quality of experience. To appreciate the significance of latency-sensitive applications for today's Internet, we need to understand their traffic pattern and quantify their prevalence. In this thesis, we quantify the proportion of potentially latency-sensitive traffic and its development over time. Next, we show that the flow start-up mechanism in the Internet is a major source of latency for a growing proportion of traffic, as network links get faster. The loss recovery mechanism in the transport protocol is another major source of latency. To improve the performance of latency-sensitive applications, we propose and evaluate several modifications in TCP. We also investigate the possibility of prioritization at the transport layer to improve the loss recovery. The idea is to trade reliability for timeliness. We particularly examine the applicability of PR-SCTP with a focus on event logging. In our evaluation, the performance of PR-SCTP is largely influenced by small messages. We analyze the inefficiency in detail and propose several solutions. We particularly implement and evaluate one solution that utilizes the Non-Renegable Selective Acknowledgments (NR-SACKs) mechanism, which has been proposed for standardization in the IETF. According to the results, PR-SCTP with NR-SCAKs significantly improves the application performance in terms of low latency as compared to SCTP and TCP. / Interactive applications such as web browsing, audio/video conferencing, multi-player online gaming and financial trading applications do not benefit (much) from more bandwidth. Instead, they depend on low latency. Latency is a key determinant of user experience. An increasing concern for reducing latency is therefore currently being observed among the networking research community and industry. In this thesis, we quantify the proportion of potentially latency-sensitive traffic and its development over time. Next, we show that the flow start-up mechanism in the Internet is a major source of latency for a growing proportion of traffic, as network links get faster. The loss recovery mechanism in the transport protocol is another major source of latency. To improve the performance of latency-sensitive applications, we propose and evaluate several modifications in TCP. We also investigate the possibility of prioritization at the transport layer to improve the loss recovery. The idea is to trade reliability for timeliness. We particularly examine the applicability of PR-SCTP with a focus on event logging. In our evaluation, the performance of PR-SCTP is largely influenced by small messages. We analyze the inefficiency in detail and propose several solutions. We particularly implement and evaluate one solution that utilizes the Non-Renegable Selective Acknowledgments (NR-SACKs) mechanism, which has been proposed for standardization in the IETF. According to the results, PR-SCTP with NR-SCAKs significantly improves the application performance in terms of low latency as compared to SCTP and TCP.

Η περιγραφή των αλληλεπιδράσεων που αναπτύσσονται μεταξύ ενός συνόλου σωμάτων που είτε είναι ακίνητα είτε κινούνται και ενός ρευστού, ρέοντος ή ηρεμούντος, βρίσκεται στον πυρήνα ενός μεγάλου αριθμού επιστημονικών προσπαθειών. Η μοντελοποίηση των αλληλεπιδράσεων αυτών μπορεί να γίνει με πολλούς τρόπους, καθένας από τους οποίους εμφανίζει πλεονεκτήματα και μειονεκτήματα, ανάλογα με το είδος του συστήματος στο οποίο επιχειρείται να εφαρμοστεί. Σκοπός της εργασίας αυτής είναι η ανάδειξη ενός εξ αυτών που είναι η Μέθοδος των Προτύπων Ροών. / The description of interactions between a number of solid particles, which may be in motion or fixed in space and a fluid which in turn may either be flowing or resting, is placed at the core of a large number of scientific publications. Modelling such interactions may follow a variety of approaches. Each approach has its own pros and cons, regarding the nature and the specific features of the system which is aimed to describe. Current thesis goal is to describe one of these approaches, which is the approach of Singularities or the Method of Elementary Flows.

No description available.

High-speed optical networks will require all-optical signalprocessing to avoid bottleneck due to optical-to-electrical (O/E)and electrical-to-optical (E/O) conversion. Enabling of opticalprocessing tasks such as optical buffering and data synchronizationwill require large tunable delay. Recently, slow-light physics gotwide attention to generate tunable delay. However, for a slow-lightsystem large delay comes at the expense of increased distortion.This dissertation presents a study of the slow-light systems andquantifies the limitations imposed on delay due to distortion andsystem resource constraints. Optimal designs for two- and three-lineBrillouin slow-light systems showed fractional pulse delay of up to1.7 compared to a single-line gain system. Optimal designs forbroadband Brillouin gain system showed upto 100\% delay improvementcompared to the Gaussian pump. Wavelength conversion and dispersionbased tunable delay systems showed bit delay of 15 bits. An opticalbuffer based on photorefractive medium for real-time data storagewas demonstrated by storing and retrieving a 7-bit data sequence.

Aim and tasks of the work. The aim of this work is to investigate insufficiently analyzed variants of the electrodynamic super-wide-band slow-wave structures, create their models, improve methods of analysis, analyze properties of the systems and reveal potentiality of the traveling-wave cathode-ray tubes, slow-wave structures. In order to achieve the aim it is necessary: 1. To improve method for evaluation of non-linear distortions in the traveling-wave cathode-ray tubes and reveal possibilities of reduction of non-linear distortions. 2. To create models of the insufficiently analyzed variants of slow-wave structures and reveal properties of the slow-wave structures. 3. To reveal influence of periodical non-homogeneities on properties of slow-wave structures, simulate and reveal influence of transitions to properties of slow-wave structures and traveling-wav cathode-ray tubes. 4. To make investigation of potentiality of slow-wave structures and traveling-wave cathode-ray tubes and select variants of slow-wave structures that can guarantee wide band and high operating speed of the traveling-wave cathode-ray tubes. Scientific novelty and practical value. Models of insufficiently simulated slow-wave structures were created and their properties were analyzed. According to analysis and modeling results, variants of systems were selected that can guarantee the wide pass-band and high operating speed of the traveling-wave cathode-ray tubes. Using finite element method calculation... [to full text]

Aim and tasks of the work. The aim of this work is to investigate insufficiently analyzed variants of the electrodynamic super-wide-band slow-wave structures, create their models, improve methods of analysis, analyze properties of the systems and reveal potentiality of the traveling-wave cathode-ray tubes, slow-wave structures. In order to achieve the aim it is necessary: 1. To improve method for evaluation of non-linear distortions in the traveling-wave cathode-ray tubes and reveal possibilities of reduction of non-linear distortions. 2. To create models of the insufficiently analyzed variants of slow-wave structures and reveal properties of the slow-wave structures. 3. To reveal influence of periodical non-homogeneities on properties of slow-wave structures, simulate and reveal influence of transitions to properties of slow-wave structures and traveling-wav cathode-ray tubes. 4. To make investigation of potentiality of slow-wave structures and traveling-wave cathode-ray tubes and select variants of slow-wave structures that can guarantee wide band and high operating speed of the traveling-wave cathode-ray tubes. Scientific novelty and practical value. Models of insufficiently simulated slow-wave structures were created and their properties were analyzed. According to analysis and modeling results, variants of systems were selected that can guarantee the wide pass-band and high operating speed of the traveling-wave cathode-ray tubes. Using finite element method calculation... [to full text]