Strategies for limiting interference and interception of free space optical communications

Thesis: M. Eng., Massachusetts Institute of Technology, Department of Electrical Engineering and Computer Science, 2013.This electronic version was submitted by the student author. The certified thesis is available in the Institute Archives and Special Collections.Cataloged from student-submitted PDF version of thesis.Includes bibliographical references (pages 167-168).Free space optical systems provide an attractive solution to communication needs that require inexpensive, easily deployable links capable of high data rate transmissions. A major challenge of free space optical communication is ensuring the integrity and confidentiality of the transmitted information. In an optical wireless network with close-in users, communication between two users could interfere with another link in the network. Such systems are also susceptible to eavesdropping, especially inside the main lobe of the transmitted beam. In this thesis, we propose a method of controlling the direction of energy propagation from an optical transmitter to maximize the power received by the remote terminal of a link while limiting the power received in a broadly defined region within the main lobe of the transmission. We consider specifically an optical transmitter comprised of an array of apertures with controllable amplitudes and phases, and we approximate the intended suppression region with a finite number of points. We assume the total transmitted power is held fixed. Via iterative numerical methods, we solve a nonlinear optimization problem for the weight vector that maximizes the intensity at the receiver while limiting the intensity at the specified suppression points to below some fraction of the intensity at the receiver. For a linear aperture array, we show that without overly limiting the power to the intended receiver, it is possible to suppress the signal intensity in a 1 beamwidth region located 0.2 beamwidths from the intended user down to one tenth of the intensity at the intended receiver. For a two dimensional array, we show that we can similarly suppress a !!!!! beamwidth region as close as 0.2333 beamwidths to the intended receiver. We further show that by increasing the number of suppression points used to approximate the suppression region, we can suppress a region much closer to the receiver, but at the cost of significantly lowering the intensity at the receiver. We also observe a tradeoff between the size of the suppression region and our ability to limit the signal intensity throughout the entire region. We show that our ability to successfully suppress power to the required region is limited by both our available transmit power and our uncertainty of the position of the eavesdropper or network user.by Manishika P. Agaskar.M. Eng

Integrated photonic structures for photon-mediated entanglement of trapped ions

Trapped atomic ions are natural candidates for quantum information processing and have the potential to realize or improve quantum computing, sensing, and networking. These applications often require the collection of individual photons emitted from ions into guided optical modes, in some cases for the production of entanglement between separated ions. Proof-of-principle demonstrations of such photon collection from trapped ions have been performed using high-numerical-aperture lenses and single-mode fibers, but integrated photonic elements in ion-trap structures offer advantages in scalability and manufacturabilty over traditional optics. In this paper we analyze structures monolithically fabricated with an ion trap for collecting single photons from ions, coupling them into integrated waveguides, and manipulating them via interference. We discuss practical considerations for realizing photon-mediated entanglement between trapped ions using these waveguide-based devices.Comment: 17 pages, 6 figures, 2 table

2022 Roadmap on integrated quantum photonics

AbstractIntegrated photonics will play a key role in quantum systems as they grow from few-qubit prototypes to tens of thousands of qubits. The underlying optical quantum technologies can only be realized through the integration of these components onto quantum photonic integrated circuits (QPICs) with accompanying electronics. In the last decade, remarkable advances in quantum photonic integration have enabled table-top experiments to be scaled down to prototype chips with improvements in efficiency, robustness, and key performance metrics. These advances have enabled integrated quantum photonic technologies combining up to 650 optical and electrical components onto a single chip that are capable of programmable quantum information processing, chip-to-chip networking, hybrid quantum system integration, and high-speed communications. In this roadmap article, we highlight the status, current and future challenges, and emerging technologies in several key research areas in integrated quantum photonics, including photonic platforms, quantum and classical light sources, quantum frequency conversion, integrated detectors, and applications in computing, communications, and sensing. With advances in materials, photonic design architectures, fabrication and integration processes, packaging, and testing and benchmarking, in the next decade we can expect a transition from single- and few-function prototypes to large-scale integration of multi-functional and reconfigurable devices that will have a transformative impact on quantum information science and engineering

Architectural constructs for time-critical networking in the smart city

Thesis: Ph. D., Massachusetts Institute of Technology, Department of Electrical Engineering and Computer Science, 2018.This electronic version was submitted by the student author. The certified thesis is available in the Institute Archives and Special Collections.Cataloged from student-submitted PDF version of thesis.Includes bibliographical references (pages 203-211).The rapid maturation of the Internet of Things and the advent of the Smart City present an opportunity to revolutionize emergency services as both reactive and preventative. A well-designed Smart City will synthesize data from multiple heterogeneous sensors, relay information to and between emergency responders, and potentially predict and even preempt crises autonomously. In this thesis, we identify distinctive characteristics and networking requirements of the Smart City and then identify and evaluate the architectural constructs necessary to enable time-critical Smart City operations. Two major goals inform our architectural analysis throughout this work. First, critical traffic must be served within a specified delay without excessive throttling of non-critical traffic. Second, surges in critical traffic from a geographically-concentrated region must be handled gracefully. To achieve these goals, we motivate, evaluate, and finally recommend: 1.) connecting local area Smart City networks to the existing metropolitan area networking infrastructure, 2.) standing up a dedicated municipal data center inside the metropolitan area served by the Smart City, 3.) deploying a contention-based priority reservation MAC protocol that guarantees latency and throughput for some specified maximum number of critical users per wireless access point, 4.) configuring MAN routers to provide non-preemptive priority service at output queues to critical Smart City traffic, 5.) offering dedicated optical paths from edge routers to the municipal hub in order to effectively form a virtual star topology atop a MAN mesh and significantly reduce switching delays in the network, 6.) processing select applications at dedicated fog servers adjacent to edge routers in order to reduce upstream congestion in the MAN, and 7.) setting up a network orchestration engine that monitors traffic into and out of the Smart City data center in order to preemptively detect critical traffic surges and to direct network reconfiguration (access point reassignment, load-balancing, and/or temporary resource augmentation) in anticipation.by Manishika Agaskar.Ph. D

Distributed Detection of Multi-Hop Information Flows With Fusion Capacity Constraints

The problem of detecting multihop information flows subject to communication constraints is considered. In a distributed detection scheme, eavesdroppers are deployed near nodes in a network, each able to measure the transmission timestamps of a single node. The eavesdroppers must then compress the information and transmit it to a fusion center, which then decides whether a sequence of monitored nodes are transmitting an information flow. A performance measure is defined based on the maximum fraction of chaff packets under which flows are still detectable. The performance of a detector becomes a function of the communication constraints and the number of nodes in the sequence. Achievability results are obtained by designing a practical distributed detection scheme, including a new flow finding algorithm that has vanishing error probabilities for a limited fraction of chaff packets. Converse results are obtained by characterizing the fraction of chaff packets sufficient for an information flow to mimic the distributions of independent traffic under the proposed compression scheme.National Science Foundation (U.S.) (Grant No. CCF-0635070)United States. Office of Naval Research (MURI W911NF-08-1-0238

Distributed recovery of a Gaussian source in interference with successive lattice processing

A scheme for recovery of a signal by distributed listeners in the presence of Gaussian interference is constructed by exhausting an "iterative power reduction" property. An upper bound for the scheme's achieved mean-squared-error distortion is derived. The strategy exposes a parameter search problem, which, when solved, causes the scheme to outperform others of its kind. Performance of a blocklength-one scheme is simulated and is seen to improve over plain source coding without compression in the presence of many interferers, and experiences less outages over ensembles of channels. Keywords: network information theory; distributed source coding; lattice code