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Bezdrátový optický spoj v sítích LAN a MAN / Wireless optical links in LAN and MAN networksŠporik, Jan January 2009 (has links)
The main aim of this thesis is the design of an optical wireless link that is transmitted in free space, in the atmosphere. The thesis describes the composition of heads of the atmospheric optical link. One part of this work focuses on the issue of the spread of optical beam in the atmosphere. The facts which have a major impact on the transmission of optical radiation in free space are pointed out here as well. In this work phenomena of absorption, refraction of light, turbulence and dispersion are discussed. Wavelengths spread in the atmosphere with different decline and therefore this thesis provides an analysis of the use of wavelengths between 750 and 1600 nm depending on the meteorological visibility. It describes the basis of the design of AOS through stationary model using power balance equation. It depicts the description of the statistical model, which makes possible to determine the availability on the basis of probability. Current possibilities of AOS are in general described in this work. The practical part of the work is focused on the design of simulation model of transmitter and receiver AOS in the program Pspice. The receiver and transmitter are designed to replace transiver in the media converter. The receiver plays a key role, and therefore big part of the thesis is given to it. Receiver model is composed of a photodiode and of an transimpedance amplifier. The receiver circuit has been tested. The model of transmitter shows the principle of modulating of current, which flows in laser diode. This work does not carried the model of atmosphere, which would serve as a link between the receiver and the transmitter. The circuit of the receiver is subjected to the noise analysis. Parameter NEP and SNR is designed. Link budget is calculated for models of the receivers and the transmitters. The maximum distance of heads is set based on the requirements for a BER error rate which combine this condition. The design of the practical implementation results from the models of transmitters and receivers. Printed circuit boards are designed in EAGLE. Within the frame of this thesis no curcuit diagram is carried out.
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Vysokorychlostní optický spoj pro krátké vzdálenosti / Low-range high-speed optical transceiverPučálka, Jan January 2013 (has links)
The diploma thesis deals with description and design of a low-cost free-space optical (FSO) link. First, general FSO theory is discussed including their common parameters, properties and topologies. Further, optical signal sources and detectors are proposed. Finally, the selected implementation is described including its design and realization. The proposed FSO consists of two identical segments (modules) to form a full-duplex link. The FSO utilizes LED as a light source, maximum speed data rate is 100 Mb/s with 100Base-TX interface.
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[en] FOG AND RAIN ATTENUATION MODELS FOR THE DESIGN OF FSO LINKS IN 5G+ / [pt] MODELOS DE ATENUAÇÃO DE NEBLINA E CHUVA PARA O PROJETO DE ENLACES FSO EM 5G+CLARA ELIZABETH VERDUGO MUNOZ 22 August 2022 (has links)
[pt] A óptica de espaço livre (FSO), inicialmente estudada na década de 60,
está atraindo atenção no contexto dos sistemas 5G+, que exige tecnologias de
back-hauling sem fio com taxas de dados extremamente altas em distâncias de
poucos quilômetros. A atual falta de um modelo global de perda de percurso
para FSO motiva o estudo do comportamento do enlace óptico sob diferentes
condições atmosféricas. Esta tese trata do desenvolvimento de modelos para
prever a atenuação devido a neblina e chuva para projetar enlaces FSO em
tecnologias 5G e além. Estudamos os bancos de dados de medições de superfície
disponíveis em todo o mundo como referência para analisar as respostas do
FSO considerando os dados disponíveis de longo prazo e descobrimos que o
maior impacto na visibilidade em todo o mundo é causado por neblina, neve e
chuva. Assim, selecionamos neblina e chuva como o foco deste estudo. Vários
modelos de perda de percurso, baseados na visibilidade, são avaliados através
de uma abordagem analítica. Propomos modelos de limite inferior e superior
para estimar a atenuação específica devido ao nevoeiro considerando incertezas
quanto à sensibilidade da atenuação específica, gama, em função da visibilidade em
1.550 micrômetros e o melhor ajuste aos resultados do modelo microfísico. Com relação
à atenuação causada pela chuva, estudamos modelos disponíveis na literatura
para enlaces de micro-ondas e os modificamos para aplicação em enlaces FSO.
Quando os efeitos de espalhamento múltiplo são considerados, foi encontrada
uma redução significativa na atenuação da chuva. Construímos a partir dos
modelos, um método para combinar estatisticamente a atenuação em enlaces
FSO causada por diferentes condições climáticas. O desempenho dos enlaces
ópticos é avaliado em termos do máximo comprimento do enlace em relação à
disponibilidade sob quatro condições climáticas: (i) somente chuva, (ii) somente
neblina, (iii) chuva e neblina, e (iv) e todas as condições. Finalmente, eventos
experimentais para os enlaces FSO e mmWave implementados no campus
Leonardo do Politecnico di Milano são classificados e analisados dependendo
do efeito atmosférico estudado: chuva estratiforme, chuva convectiva, chuva
leve, vento, neblina pesada, neve e outros. / [en] Free-space optics (FSO), initially studied in the 60s, is attracting attention in the frame of 5G+ systems, which demands wireless back-hauling
technologies with extremely high data rates over distances up to a few kilometers. The current lack of a global path loss model for FSO motivates studying
the optical link s behavior under different atmospheric conditions. This thesis deals with the development of models for predicting the attenuation due
to fog and rain for designing FSO links in 5G and beyond technologies. We
study extensive surface measurement databases worldwide as a benchmark for
analyzing FSO responses considering available long-term data. We find that
the highest impact on visibility worldwide is caused by fog, snow, and rain.
Thus, we select fog and rain as the focus of this study. Several path loss models
based on visibility are assessed. We propose lower and upper-bound models to
estimate the specific attenuation, gamma, due to fog which considers uncertainties
as the sensitivity of gamma to the visibility at 1.550 µm and a micro-physical model
of fog. Regarding attenuation caused by rain, we study models available in the
literature for microwave links and modify them for application to FSO. When
the multiple scattering effects are considered, a significant reduction in the
rain attenuation has been found. From the findings, we build a method to statistically combine the attenuation effects on FSO caused by different weather
conditions. The performance of FSO links is assessed in terms of the maximum
link range against availability under four weather conditions: (i) rain only, (ii)
fog only, (iii) rain and fog, and (iv) all conditions. Finally, experimental events
for FSO and mmWave links implemented at Leonardo Campus of Politecnico
di Milano are classified and analyzed depending on the studied atmospheric
effects: stratiform rain, convective rain, light rain, wind, heavy fog, snow, and
others.
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The Pdf Of Irradiance For A Free-space Optical Communications Channel: A Physics Based ModelWayne, David 01 January 2010 (has links)
An accurate PDF of irradiance for a FSO channel is important when designing a laser radar, active laser imaging, or a communications system to operate over the channel. Parameters such as detector threshold level, probability of detection, mean fade time, number of fades, BER, and SNR are derived from the PDF and determine the design constraints of the receiver, transmitter, and corresponding electronics. Current PDF models of irradiance, such as the Gamma-Gamma, do not fully capture the effect of aperture averaging; a reduction in scintillation as the diameter of the collecting optic is increased. The Gamma-Gamma PDF of irradiance is an attractive solution because the parameters of the distribution are derived strictly from atmospheric turbulence parameters; propagation path length, Cn2, l0, and L0. This dissertation describes a heuristic physics-based modeling technique to develop a new PDF of irradiance based upon the optical field. The goal of the new PDF is three-fold: capture the physics of the turbulent atmosphere, better describe aperture averaging effects, and relate parameters of the new model to measurable atmospheric parameters. The modeling decomposes the propagating electromagnetic field into a sum of independent random-amplitude spatial plane waves using an approximation to the Karhunen-Loeve expansion. The scattering effects of the turbulence along the propagation path define the random-amplitude of each component of the expansion. The resulting PDF of irradiance is a double finite sum containing a Bessel function. The newly developed PDF is a generalization of the Gamma-Gamma PDF, and reduces to such in the limit. An experiment was setup and performed to measure the PDF of irradiance for several receiver aperture sizes under moderate to strong turbulence conditions. The propagation path was instrumented with scintillometers and anemometers to characterize the turbulence conditions. The newly developed PDF model and the GG model were compared to histograms of the experimental data. The new PDF model was typically able to match the data as well or better than the GG model under conditions of moderate aperture averaging. The GG model fit the data better than the new PDF under conditions of significant aperture averaging. Due to a limiting scintillation index value of 3, the new PDF was not compared to the GG for point apertures under strong turbulence; a regime where the GG is known to fit data well.
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Free space optical interconnects for speckled computingReardon, Christopher P. January 2009 (has links)
The aim of this project was to produce an integrate-able free space optical transceiver for Specks. Specks are tiny computing units that together can form a powerful network called a SpeckNet. The SpeckNet platform is developed by the SpeckNet consortium, which consists of five Scottish Universities and combines computer science, electrical engineering and digital signal processing groups. The principal goal of creating an optical transceiver was achieved by integrating in-house fabricated VCSELs (with lasing thresholds below 400 uA) and custom designed detectors on the SpeckNet platform. The transceiver has a very low power consumption (approximately 100 uW), which removes the need for synchronous communication through the SpeckNet thus making the network more efficient. I describe both static and dynamic beam control techniques. For static control, I used micro-lenses. I fabricated the lenses by greyscale electron beam lithography and integrated them directly on VCSEL arrays. I achieved a steering angle of 10 degrees with this design. I also looked at integrated gratings etched straight into a VCSEL and observed beam steering with an efficiency of 60% For dynamic control, I implemented a liquid crystal (LC) design. I built a LC cell with 30 individually controlled pixels, but I only achieved a steering angle of 1 degree. Furthermore, I investigated two different techniques for achieving beam steering by interference, using coupled VCSELs (a phased array approach). Firstly, using photonic crystals etched into the surface of the VCSEL, I built coupled laser cavities. Secondly, I designed and built bow-tie type VCSELs that were optically coupled but electrically isolated. These designs work by differential current injection causing an interference effect in the VCSELs far field. This technique is the first stepping stone towards realising a phased optical array. Finally, I considered signal detection. Using the same VCSEL material, I built a resonant-cavity detector. This detector had a better background rejection ratio than commercially available silicon devices.
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Bezdrátové spoje pro metropolitní sítě / Wireless connections for metropolitan networksSvoboda, Jan January 2011 (has links)
This Master’s thesis analizes technologies suitable for metropolitan area networks. In this thesis there are mentioned technologies used for wireless transfer with speeds above 1 Gbps. There are described basic features and parameters of microwave radio relay links in 70/80GHz range and free space optic links. These technologies are compared with classic optical networks. Practical part of thesis was focused on development of application which calculates signal attenuation caused by the passage of the atmosphere for both technologies. Results gained from this application are mentioned in this Master’s thesis.
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[pt] CONTAGEM DE FÓTONS NO INFRAVERMELHO PRÓXIMO E MÉDIO VIA CONVERSÃO DE FREQÜÊNCIAS APLICADA A COMUNICAÇÕES QUÂNTICAS / [en] SINGLE PHOTON COUNTING IN THE NEAR- AND MID-INFRARED VIA FREQUENCY UP-CONVERSION APPLIED TO QUANTUM COMMUNICATIONS06 September 2007 (has links)
[pt] Dois dispositivos de contagem de fótons únicos, sensíveis
a comprimentos
de onda no infravermelho próximo e médio, são propostos e
experimentalmente
investigados. Ambos utilizam uma técnica de dois estágios,
composta de uma
etapa inicial de conversão de freqüências em um cristal
não-linear seguida de
detecção por um fotodiodo avalanche de silício. Enquanto o
primeiro projeto é
voltado à detecção de fótons únicos a 1.55 μm para
comunicações quânticas via
fibra óptica, usando um processo intra-cavidade, o segundo
projeto prevê o
desenvolvimento de um contador de fótons operando a 4.65
μm para sistemas de
espaço livre. Neste caso, um estudo de viabilidade para um
sistema prático de
criptografia quântica operando em um comprimento de onda
no infravermelho
médio é realizado. Os resultados mostram que, usando a
tecnologia disponível na
atualidade, tal sistema pode ser construído, embora sua
utilidade se mostre restrita
a enlaces possuindo certas condições meteorológicas
específicas. / [en] Two single photon counting devices, operating at near- and
mid-infrared
wavelengths, are introduced and experimentally
investigated. Both use a twostage
technique, comprised of an initial frequency up-conversion
procedure inside
a nonlinear crystal followed by a silicon avalanche
photodiode. Whereas the first
project consists on detection of single photons at 1.55 ìm
for fiber-optic-based
quantum communications, using a cavity-enhanced procedure,
the second project
envisions the development of a single-photon counter
operating at 4.65 ìm for
free-space systems. In this case, a feasibility study for
a practical quantum key
distribution system operating in a mid-infrared wavelength
is performed. The
results show that, using present-day technology, such a
system can be constructed,
albeit its usefulness would be restricted to operation
under very specific weather
conditions.
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Vliv atmosférických turbulencí na optický svazek / Influence of atmospheric turbulences on the optical beamBárta, Miroslav January 2009 (has links)
The aim of this thesis is to study a free space optics and its application in communication technologies. It describes possible interrupting impacts on the beamed optical signal, which are signal noise, attenuation of the atmosphere and atmospheric turbulence. The basis of the thesis is to describe the impact of the atmospheric turbulences on the optical beam. Fluctuation of optical intensity in the optical beam has been measured and index of refraction structure parameter calculated. With its assistance, turbulence rate has been determined.
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Bezdrátový optický spoj / Free-Space Optics data linkŠála, Jakub January 2010 (has links)
In this thesis, shows a current issue for free space optics, limiting their use in practice with regard to the availability and reliability. They conducted measurements on wireless optical links and the observed values is calculated by the availability of the connection. Subsequently, measurements are performed on alternate versions of wireless and copper connections. Observed values were compared with a wireless optical link. It is made of optical design of wireless connections at home.
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CHYBOVOST A DOSTUPNOST ATMOSFÉRICKÝCH OPTICKÝCH SPOJŮ / BIT ERROR RATE AND AVAILABILITY OF THE ATMOSPHERIC OPTICAL LINKSKvíčala, Radek January 2009 (has links)
This dissertation deals with the problematic of the free space optical link availability determination. For the presumption of the free space optical link unavailability we have to know statistical distribution of the atmospheric attenuations. In this work is also presented the measurement of these atmospheric attenuations with the specially designed optical link. Measurement is using switching of the two separate transmitters with wavelengths of 830 nm and 1550 nm. Presented statistic distribution let us determine the suitability of the link in the chosen locality during its design. Comparison of our measurement with other models like model based on the meteorological visibility is also presented. The last part of this work is focused on the preconditions for the hi-speed network bit error rate determination. Sample of the bit error rate measurement obtained by our designed bit error rate tester is attached.
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