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Nonlinear and spatially multimode optical phenomena for use in optical and quantum communicationsJanuary 2020 (has links)
archives@tulane.edu / Quantum nonlinear optics has opened up avenues to defy the measurement, sensing, and amplification limits inherent in classical physics. Separately, the use of multimode or spatially structured states in light-based communications allows for remarkable increases in the amount of information that may be transferred by an individual communication or light pulse. In this dissertation, we apply these two boundary-pushing concepts to several experimental projects, with a primary goal to hasten and facilitate the implementation of quantum and classical free-space optical communications schemes into real-life scenarios. We start by applying neural networks to the optimization of spatially-structured and pulsed light communications in Chapter 2, wherein our networks successfully learn to predict distorted optical pulses and classify noisy light patterns carrying non-zero orbital angular momentum. Chapter 3 focuses on four-wave mixing, a nonlinear light-matter interaction in atomic vapor that we use to construct quantum-correlated light beams with nontrivial structures as well as a novel phase-sensitive amplifier. Finally, we continue to take advantage of the complex nonlinear response of atomic vapor in Chapter 4, this time to create "self-regenerating" light beams whose cross-sections resemble Bessel-Gauss functions. / 1 / Erin Knutson
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Acquisition time in laser inter-satellite link under satellite vibrationsLee, K., Mai, Vuong, Kim, H. 11 August 2024 (has links)
Yes / Pointing, acquisition, and tracking (PAT) is a major technical challenge of laser inter-satellite links (ISLs). For the fast establishment of laser link and the maximization of communication time, it is of importance to minimize the acquisition time. Satellite vibrations affect the PAT procedure adversely, and thus serve to increase the acquisition time. In this paper, we investigate through theoretical analysis the average acquisition time of laser ISLs in the presence of satellite vibrations. The analytic expression about the time taken from the beginning of spiral scan to the acquisition of the scan beam is provided in the presence of the pointing errors caused by vibrations. We also derive the optimum beam divergence angle for the acquisition time. The analyses are validated by Monte-Carlo computer simulations and a proof-of-concept experiment. The results show that the acquisition time can be minimized by adjusting the beam divergence angle adaptively to the link conditions. / Grant-in-aid of Hanwha Systems
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Radio-over-Free-Space Optical Fronthauling for Cloud Radio Access NetworksAhmed, Khaled January 2019 (has links)
The increasing demand on user rates in the fifth generation (5G) requires network architectures
that can support high data rates with acceptable reliability. In order to increase
the data rates in the presence of the current spectrum crisis, shrinking cells and reusing the
spectrum is a proposed solution. Conventional implementation of dense cells requires a
large number of expensive BSs to locally process and decode users’ signals. Another limiting
factor that degrades the performance in a dense network is the inter-cell interference.
A cloud radio access network (CRAN) is a promising solution to those cost, complexity,
and interference challenges. A typical CRAN architecture consists of simplified low-cost
base stations (BSs), termed radio units (RUs), that collect the radio frequency (RF) user
equipments’ (UEs) signals and forward them over the fronthaul links to the central office
(CO) where signal processing is done over shared resources. Besides the reduced cost and
complexity of a CRAN, the joint processing at the CO enables joint interference mitigation
techniques. However, the performance of CRANs depends critically on the availability of
reliable fronthaul links with large bandwidth that may be expensive. Analog optical fronthaul
links provide high data rates at lower cost and complexity since UEs’ signals are
optically analog-modulated without digitalization, however, they suffer from other channel
impairments and nonlinearities.
In this thesis, analog optical fronthaul topologies are considered in which radio signals are forwarded over free-space optical (FSO) links, termed radio-over-free-space optical
(RoFSO) links, and optical fiber (OF) links, termed radio-over-fiber (RoF) links.
Firstly, a CRAN with mixed RF/RoFSO fronthaul is considered to investigate the performance
improvement when RF fronthaul links are replaced one-by-one by RoFSO links.
A novel joint optimization problem is introduced for the given architecture in which the
weighted sum of UEs’ rates is maximized by jointly designing RF and RoFSO links. The
optimization problem is solved over different numbers of RF and RoFSO links and under
various weather conditions. Under favorable weather conditions, the replacement of 1 RF
link by a RoFSO link is shown to increase the 50th percentile of UEs’ rates by 7 times.
Secondly, the reliability of a CRAN with two-hop RoFSO/RoF fronthaul links is derived
along with other performance metrics such as the average bit-error rate and the cumulative
distribution function of UEs’ rates. For the given architecture, the Gaussian noise
model of fiber nonlinearity is applied and an optimal OF average optical power is derived
to minimize the outage probability. Using the optimal power, and under favorable weather
conditions, the 50th percentile of user rate exceeds 1:5 Gbps.
Finally, a CRAN with passive all-optical two-hop fronthaul links is considered where
optical signals from the first RoFSO fronthaul hop are passively coupled into the RoF fronthaul
link. The fronthaul outage probability is derived in the context of network planning
to provide guidance on designing a set of system parameters. Those parameters include
coverage area radius, density of RUs, RoFSO gain, RoFSO optical power and RoF length. / Thesis / Doctor of Philosophy (PhD) / The upcoming generation of wireless communications, termed fifth generation (5G), promises
faster data rates and lower latency. In order to achieve this, more base stations (BSs) have
to be deployed which increases the cost and complexity of the network. A solution to
this challenge is to install simple BSs, i.e. radio units (RUs), that collect signals from
users and forward them to a central office (CO) for joint processing which is referred to
as a cloud radio access network (CRAN). The fronthaul network in a CRAN connects the
RUs to the CO and it can be implemented using different kinds of links. While there are
several fronthaul media (e.g., radio frequency (RF), free-space optical (FSO) links, copper
lines, satellite communications, and optical fiber (OF)), optical links provide high data
rates that are promising to achieve the 5G requirements. In this thesis, a novel architecture
of a CRAN is considered in which analog optical links, namely FSO links and OF
links, are used for fronthauling. Performance improvement in terms of rate and reliability
is investigated and optimized through different design tools. In response to the challenges
introduced by the proposed architecture, such as the nonlinearities of analog FSO and OF
links, various design parameters are proposed in the optimization problems to tackle those
challenges. Furthermore, a network planning framework is introduced to provide guidance
and insights on designing the network.
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Time-efficient simulation of free-space optical communication systems under atmospheric turbulence, pointing error, and angle-of-arrival fluctuationsNguyen, M.T., Mai, Vuong, Kim, H. 11 August 2024 (has links)
Yes / Computer simulation is a powerful and convenient tool for the design and performance evaluation of free-space optical (FSO) communication systems. In this article, we present two simulation frameworks that incorporate not only the effects of atmospheric turbulence but also the impact of the angular fluctuations of the transmitter and receiver in FSO systems. In the first framework, the waveform of the optical signal is calculated sequentially from the transmitter to the receiver. Thus, it takes very long to run the simulation numerous times to obtain the statistical performance of the system. This is because the vast majority of simulation time is spent on the split-step beam propagation. In the second framework, we propose to isolate the beam propagation through atmospheric channel from the other effects. We compare the two frameworks in terms of accuracy and simulation time. We show that the second framework reduces the simulation time by more than a factor of 10 without sacrificing the accuracy under various conditions. / 10.13039/501100003725-National Research Foundation of Korea HR&D Center Funded by the Ministry of Science and ICT (Grant Number: 2022M1A3C2069728)
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Comparative Analysis of Atmospheric Turbulence-induced Laser Power Fluctuations in a Monolithic and Tiled Optical Receiver SystemValero, Marcos E. 17 May 2021 (has links)
No description available.
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Lidar-Assisted Acquisition of Mobile Airborne FSO Terminals in a GPS-Denied EnvironmentLiu, Heyou 10 April 2023 (has links)
For acquisition of narrow-beam free-space optical (FSO) terminals, a Global Positioning System (GPS) is typically required for coarse localization of the terminal. However, the GPS signal may be shadowed, or may not be present at all, especially in rough or unnameable terrains. In this study, we propose a lidar-assisted acquisition of an unmanned aerial vehicle (UAV) for FSO communications in a poor GPS environment. Such an acquisition system consists of a lidar subsystem and an FSO acquisition subsystem: The lidar system is used for coarse acquisition of the UAV, whereas, the FSO system is utilized for fine acquisition to obtain the UAV’s accurate position. This study investigates the optimal allocation of energy between the lidar and FSO systems to minimize the acquisition time. Here, we minimize the average acquisition time, and maximize the cumulative distribution function of acquisition time for a fixed threshold. We learn that an optimal value of the energy allocation factor exists that provides the best performance of the proposed system.
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Measurement and Modelling of a Free-Space Optical Link and In-Field OFDM ExperimentMostafa, Ayman 04 1900 (has links)
<p>Free-space optical (FSO) communication is a potential technology for last-mile applications. Key advantages are the unlicensed spectrum, high transmission rates, and inherent security. Moreover, Radio-over-FSO (RoFSO) allows seamless integration between the incompatible radio frequency (RF) and optical networks. Such advantages qualify FSO systems to take a front seat in next-generation broadband communication networks. However, the main challenge for FSO systems is the performance degradation imposed by the atmospheric attenuation and turbulence. To exploit the advantages of FSO systems, accurate and computationally-efficient channel models are required. This thesis represents in-field experimental work related to FSO channel measurement as well as the transmission of orthogonal frequency division multiplexing (OFDM) over the FSO channel. A 1.87-km FSO link installed at McMaster University is employed. A high-speed field-programmable gate array (FPGA)-based digitizer board is used as the underlying hardware platform for interface with the link. A system-on-three-FPGAs is implemented to act as a universal transceiver for signals composed using MATLAB. A new technique is developed for conducting the FSO channel measurement. An optical signal intensity-modulated by a high frequency sinusoid is transmitted. The received signal undergoes a fast-Fourier transform (FFT) to filter out a large portion of the interfering noise providing more accurate measurements. Fitting with the log-normal distribution is investigated. A finite-state Markov model is also derived and its accuracy is verified by the simulation results. The first realization of an in-field OFDM over FSO transmission system is implemented and tested over the link. The received signal is investigated on the symbol level and constellation diagrams are visualized. Transmission rates up to 300 Mbps are achieved with average symbol-error rate (SER) on the order of 10<sup>-6</sup>.</p> / Master of Applied Science (MASc)
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Cooperative MIMO techniques for outdoor optical wireless communication systems / Techniques MIMO coopératives pour les systèmes de communication optique sans fil en espace libreAbaza, Mohamed 01 December 2015 (has links)
Au cours de la dernière décennie, les communications optiques en espace libre (FSO) ont pris de l’ampleur dans les deux domaines académiques et industriels. L’importance de FSO s’appuie sur la possibilité de faire un système de transmission économique et écologique avec un débit élevé et sans licence à l’opposition des systèmes de transmission radiofréquences (RF). Dans la plupart des travaux antécédents sur les systèmes multi-émetteurs, seulement les canaux décorrélés ont été considérés. Un canal décorrélé nécessite un espace suffisant entre les émetteurs. Cette condition devient difficile et non-réalisable dans certaines applications. Pour cette raison, nos études se focalisent sur les performances des codes à répétition RC (Repitition Codes) et les codes OSTBC (Orthogonal Space-Time Block Codes) dans des canaux log-normaux corrélés en utilisant une modulation d’intensité et une détection directe (IM/DD). En addition, les effets des différentes conditions météorologiques sur le taux d’erreur moyen (ABER) sont étudiés. Les systèmes FSO à multi-entrées/ multi-sorties MIMO (Multiple-Input Multiple-Output) avec une modulation SSK (Space Shift Keying) ont été abordés. Les résultats obtenus montrent que la SSK est supérieure aux RC avec une modulation d’impulsion (Multiple Pulse Amplitude Modulation) pour toute efficacité spectrale égale ou supérieure à 4 bit/s/Hz. Nous avons aussi analysé les performances d’un système à sauts multiples (Multi-Hop) et des relais à transmission directe (forward relays). Nos simulations montrent que le système ainsi considéré est efficace pour atténuer les effets météorologiques et les pertes géométriques dans les systèmes de communication FSO. Nous avons montré qu’un tel système avec plusieurs entrées et une sortie (MISO, i.e. multiple-input single-output) à sauts multiples est supérieur à un système MISO avec un lien direct (direct link) avec une forte atténuation. Pour satisfaire la demande croissante des réseaux de communication à débits élevés, la communauté scientifique s'intéresse de plus en plus aux systèmes FSO avec des relais full-duplex (FD). Pour ces derniers systèmes, nous avons étudié la probabilité d'erreur moyenne (ABER) et nous avons analysé leurs performances. En considérant des différentes conditions de transmission, les performances de relais FD ont été comparées à celles d'un système avec un lien direct ou des relais half-duplex. Les résultats obtenus montrent que les relais FD ont le minimum ABER. En conséquence, les résultats obtenus dans cette thèse sont très prometteurs pour la prochaine génération de FSO. / Free-space optical (FSO) communication has been the subject of ongoing research activities and commercial attention in the past few years. Such attention is driven by the promise of high data rate, license-free operation, and cheap and ecological friendly means of communications alternative to congested radio frequency communications. In most previous work considering multiple transmitters, uncorrelated channel conditions have been considered. An uncorrelated channel requires sufficient spacing between transmitters. However, this can be difficult and may not be always feasible in some applications. Thereby, this thesis studies repetition codes (RCs) and orthogonal space-time block codes performance in correlated log-normal FSO channels using intensity modulation and direct detection (IM/DD). Furthermore, the effect of different weather conditions on the average bit error rate (ABER) performance of the FSO links is studied. Multiple-input multiple-output (MIMO) FSO communication systems using space shift keying (SSK) modulation have been also analyzed. Obtained results show that SSK is a potential technique for spectral efficiencies equal or greater than 4 bits/s/Hz as compared to RCs with multiple pulse amplitude modulations. The performance analysis of a multi-hop decode and forward relays for FSO communication system using IM/DD is also considered in this thesis. It is shown that multi-hop is an efficient technique to mitigate atmospheric turbulence and different weather attenuation effects and geometric losses in FSO communication systems. Our simulation results show that multiple-input single-output (MISO) multi-hop FSO systems are superior to direct link and MISO systems over links exhibiting high attenuation. Meeting the growing demand for higher data rates communication networks, a system with full-duplex (FD) relays is considered. For such a system, the outage probability and the ABER performance are analyzed under different turbulence conditions, misalignment error and path loss effects. FD relays are compared with the direct link and half-duplex relays. Obtained results show that FD relays have the lowest ABER and the outage probability as compared to the two other systems. Finally, the obtained results in this thesis are very promising towards the next generation of FSO systems.
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