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Boiyo, Duncan Kiboi, and Romeo Gamatham. "Optimization of flexible spectrum in optical transport networks." Thesis, Nelson Mandela Metropolitan University, 2017. http://hdl.handle.net/10948/14609.
Testo completoAbstract (sommario):
The ever-increasing demand for broadband services by end-user devices utilising 3G/4G/LTE and the projected 5G in the last mile will require sustaining broadband supply from fibre-linked terminals. The eventual outcome of the high demand for broadband is strained optical and electronic devices. The backbone optical fibre transport systems and techniques such as dense wavelength division multiplexing (DWDM), higher modulation formats, coherent detection and signal amplification have increased both fibre capacity and spectrum efficiency. A major challenge to fibre capacity and spectrum efficiency is fibre-faults and optical impairments, network management, routing and wavelength assignment (RWA). In this study, DWDM and flexible spectrum techniques such as wavelength assignment and adjustment, wavelength conversion and switching, optical add and drop multiplexing (OADM) and bitrate variable transmission have been experimentally optimized in a laboratory testbed for short- and long-haul optical fibre networks. This work starts by experimentally optimising different transmitters, fibre-types and receivers suitable for implementing cost effective and energy efficient flexible spectrum networks. Vertical cavity surface-emitting lasers (VCSELs) and distributed feedback (DFB) lasers have been studied to provide up to 10 Gb/s per channel in 1310 nm and 1550 nm transmission windows. VCSELs provide wavelength assignment and adjustment. This work utilises the non-return-to-zero (NRZ) on-off keying (OOK) modulation technique and direct detection due to their cost and simplicity. By using positive intrinsic negative (PIN) photo-receivers with error-free BER sensitivity of -18±1 dBm at the acceptable 10-9-bit error rate (BER) threshold level, unamplified transmission distances between 6 km and 76 km have been demonstrated using G.652 and G.655 single mode fibres (SMFs). For the first time, an all optical VCSEL to VCSEL wavelength conversion, switching, transmission at the 1550 nm window and BER evaluation of a NRZ data signal is experimentally demonstrated. With VCSEL wavelength conversion and switching, wavelength adjustments to a spectrum width of 4.8 nm (600 GHz) can be achieved to provide alternative routes to signals when fibre-cuts and wavelength collision occurs therefore enhancing signal continuity. This work also demonstrates a technique of removing and adding a wavelength in a bundle of DWDM and flexible channels using an OADM. This has been implemented using a VCSEL and a fibre Bragg grating (FBG) providing a wavelength isolation ratio of 31.4 dB and ~0.3 𝑑𝐵 add/drop penalty of 8.5 Gb/s signal. As a result, an OADM improves spectrum efficiency by offering wavelength re-use. Optical impairments such as crosstalk, chromatic dispersion (CD) and effects of polarization mode dispersion (PMD) have been experimentally investigated and mitigated. This work showed that crosstalk penalty increased with fibre-length, bitrate, interfering signal power and reduced channel spacing and as a result, a crosstalk-penalty trade-off is required. Effects of CD on a transmitted 10 Gb/s signal were also investigated and its mitigation techniques used to increase the fibre-reach. This work uses the negative dispersion fibres to mitigate the accumulated dispersion over the distance of transmission. A 5 dB sensitivity improvement is reported for an unamplified 76 km using DFB transmitters and combination of NZDSF true-wave reduced slope (TW-RS) and submarine reduced slope (TW-SRS) with + and – dispersion coefficients respectively. We have also demonstrated up to 52 km 10 Gb/s per channel VCSEL-based transmission and reduced net dispersion. Experimental demonstration of forward Raman amplification has achieved a 4.7 dB on-off gain distributed over a 4.8 nm spectral width and a 1.7 dB improvement of receiver sensitivity in Raman-aided 10 Gb/s per wavelength VCSEL transmission. Finally, 4.25-10 Gb/s PON-based point to point (P2P) and point to multipoint (P2MP) broadcast transmission have been experimentally demonstrated. A 10 Gb/s with a 1:8 passive splitter incurred a 3.7 dB penalty for a 24.7 km fibre-link. In summary, this work has demonstrated cost effective and energy efficient potential flexible spectrum techniques for high speed signal transmission. With the optimized network parameters, flexible spectrum is therefore relevant in short-reach, metro-access and long-haul applications for national broadband networks and the Square Kilometre Array (SKA) fibre-based signal and data transmission.
2
Liu, Jingjing. "Optically powered transceiver for optical wireless communications." Thesis, University of Oxford, 2009. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.509980.
Testo completo
3
Jin, Xian. "Integrated optical devices for free-space optical communications." Thesis, University of British Columbia, 2009. http://hdl.handle.net/2429/17406.
Testo completoAbstract (sommario):
Optical wireless communication technologies for free-space optical (FSO) transmission, distribution, and reception have numerous potential benefits. Such systems offer incredibly high data communication rates (in the same way that fibre optic technologies have revolutionized long-haul Terabit/second data transmission) together with the distributive benefits of multi-user wireless networking. Communication devices for these FSO technologies are presented in this thesis. A macroscopic passive retroreflective structure is introduced first for signal retroreflection over the full 4π steradians solid angle. Modulation is demonstrated with this structure through the use of liquid crystal switching elements. The FSO device work is then extended with an active retroreflective structure incorporating corner-cube-based retro-detection with integrated and orthogonal photodiodes. An actively-controlled differential triangulation process is demonstrated with this novel device to optimize the optical channel alignment in the FSO communication system. The proposed integrated retroreflective structures are ideally-suited to bi-directional (uplink and downlink) multi-nodal systems and have potential to be extended to ultrafast (picosecond) optical modulation in future work.
4
Diaz, Ariel Gomez. "Ultrafast indoor optical wireless communications." Thesis, University of Oxford, 2016. https://ora.ox.ac.uk/objects/uuid:2bd2257f-ae58-40f0-a10f-04e7b5336519.
Testo completoAbstract (sommario):
Traffic from wireless and mobile devices is predicted to increase 10-fold between 2014 and 2019, surpassing wired data traffic by 2016. Given the expected radio frequency (RF) capacity crunch, this growing wireless demand will have to be met using a variety of new technologies exploiting other parts of the electromagnetic spectrum. Promising research areas include the Millimetre Band as well as Optical Wireless Communications (OWC). Millimetre Band demonstrations have accomplished ultrafast multi-Gigabit links, making use of state-of-the-art fibre transmission systems. However, complex opto-electronic (OE) interfaces are required to convert the optical carrier into Millimetre wireless signals. To avoid these interfaces, an all-optical transparent network is proposed here, spanning over both the fibre and OWC domains, in order to deliver ultrahigh data rates to mobile end-users in indoor environments. This is supported by the recent deployment of fibre-to-the-home (FTTH) networks creating the potential for Terabit aggregate connections at the user's doorstep. Therefore, infrared fibre-wireless-fibre (FWF) links are studied to support data rates over 100 Gb/s in nomadic applications. The link coverage is achieved via narrow beam beamsteering over a wide field-of-view (FOV) using suitable localization and tracking techniques. The proposed model is inherently bidirectional and transparent, i.e. independent of the data rate and modulation format. In this thesis, the potential for ultrafast wide coverage OWCs using SMF-based transceivers and coherent transmission is demonstrated. A record data rate of 418 Gb/s and 209 Gb/s with a wide FOV of θ<sub>FOV</sub>=±30° and θ<sub>FOV</sub>=±20°, respectively, is shown at a free space range of 3 m. To the best of our knowledge, this is the fastest demonstration of an indoor wireless link that offers practical room-scale coverage. The automated alignment of this FWF link is also demonstrated with the design and implementation a mm-accurate localization and tracking system. Finally, architectures for point-to-multipoint communications are explored in order to adapt the system to multiple users.
5
Parand, Farivar. "Cellular optical wireless communications systems." Thesis, University of Oxford, 2002. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.270654.
Testo completo
6
Kim, Inwoong. "SYNCHRONIZATION IN ADVANCED OPTICAL COMMUNICATIONS." Doctoral diss., University of Central Florida, 2006. http://digital.library.ucf.edu/cdm/ref/collection/ETD/id/3564.
Testo completoAbstract (sommario):
All-optical synchronization and its application in advanced optical communications have been investigated in this dissertation. Dynamics of all-optical timing synchronization (clock recovery) using multi-section gain-coupled distributed-feedback (MS-GC DFB) lasers are discussed. A record speed of 180-GHz timing synchronization has been demonstrated using this device. An all-optical carrier synchronization (phase and polarization recovery) scheme from PSK (phase shift keying) data is proposed and demonstrated for the first time. As an application of all-optical synchronization, the characterization of advanced modulation formats using a linear optical sampling technique was studied. The full characterization of 10-Gb/s RZ-BPSK (return-to-zero binary PSK) data has been demonstrated. Fast lockup and walk-off of the all-optical timing synchronization process on the order of nanoseconds were measured in both simulation and experiment. Phase stability of the recovered clock from a pseudo-random bit sequence signal can be achieved by limiting the detuning between the frequency of free-running self-pulsation and the input bit rate. The simulation results show that all-optical clock recovery using TS-DFB lasers can maintain a better than 5 % clock phase stability for large variations in power, bit rate and optical carrier frequency of the input data and therefore is suitable for applications in ultrafast optical packet switching. All-optical timing synchronization of 180-Gb/s data streams has been demonstrated using a MS-GC DFB laser. The recovered clock has a jitter of less than 410 fs over a dynamic range of 7 dB. All-optical carrier synchronization from phase modulated data utilizes a phase sensitive oscillator (PSO), which used a phase sensitive amplifier (PSA) as a gain block. Furthermore, all-optical carrier synchronization from 10-Gb/s BPSK data was demonstrated in experiment. The PSA is configured as a nonlinear optical loop mirror (NOLM). A discrete linear system analysis was carried out to understand the stability of the PSO. Complex envelope measurement using coherent linear optical sampling with mode-locked sources is investigated. It is shown that reliable measurement of the phase requires that one of the optical modes of the sampling pulses be locked to the optical carrier of the data signal to be measured. Carrier-envelope offset (CEO) is found to have a negligible effect on the measurement. Measurement errors of the intensity profile and phase depend on the pulsewidth and chirp of the sampling pulses as well as the detuning between the carrier frequencies of the data signal and the center frequency of the sampling source. Characterization of the 10-Gb/s RZ-BPSK signal was demonstrated using the coherent detection technique. Measurements of the optical intensity profile, chirp and constellation diagram were demonstrated. A CW local oscillator was used and electrical sampling was performed using a sampling scope. A novel feedback scheme was used to stabilize homodyne detection.<br>Ph.D.<br>Other<br>Optics and Photonics<br>Optics
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Walker, N. G. "Multiport detection for optical communications." Thesis, University of Cambridge, 1986. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.383934.
Testo completo
8
Kingsbury, Ryan W. "Optical communications for small satellites." Thesis, Massachusetts Institute of Technology, 2015. http://hdl.handle.net/1721.1/101444.
Testo completoAbstract (sommario):
Thesis: Ph. D., Massachusetts Institute of Technology, Department of Aeronautics and Astronautics, 2015.<br>This electronic version was submitted by the student author. The certified thesis is available in the Institute Archives and Special Collections.<br>Cataloged from student-submitted PDF version of thesis.<br>Includes bibliographical references (pages 115-124).<br>Small satellites, particularly CubeSats, have become popular platforms for a wide variety of scientific, commercial and military remote sensing applications. Inexpensive commercial o the shelf (COTS) hardware and relatively low launch costs make these platforms candidates for deployment in large constellations that can offer unprecedented temporal and geospatial sampling of the entire planet. However, productivity for both individual and constellations of CubeSats in low earth orbit (LEO) is limited by the capabilities of the communications subsystem. Generally, these constraints stem from limited available electrical power, low-gain antennas and the general scarcity of available radio spectrum. In this thesis, we assess the ability of free space optical communication (lasercom) to address these limitations, identify key technology developments that enable its application in small satellites, and develop a functional prototype that demonstrates predicted performance. We first establish design goals for a lasercom payload archi- tecture that offers performance improvements (joules-per-bit) over radio-frequency (RF) solutions, yet is compatible with the severe size, weight and power (SWaP) constraints common to CubeSats. The key design goal is direct LEO-to-ground downlink capability with data rates exceeding 10 Mbps, an order of magnitude better than COTS radio solutions available today, within typical CubeSat SWaP constraints on the space terminal, and with similar COTS and low-complexity constraints on the ground terminal. After defining the goals for this architecture, we identify gaps in previous implementations that limit their performance: the lack of compact, power-efficient optical transmitters and the need for pointing capability on small satellites to be as much as a factor of ten better than what is commonly achieved today. One approach is to address these shortcomings using low-cost COTS components that are compatible with CubeSat budgets and development schedules. In design trade studies we identify potential solutions for the transmitter and pointing implementation gaps. Two distinct transmitter architectures, one based on a high-power laser diode and another using an optical amplifier, are considered. Analysis shows that both configurations meet system requirements, however, the optical amplifier offers better scalability to higher data rates. To address platform pointing limitations, we dene a staged control framework incorporating a COTS optical steering mechanism that is used to manage pointing errors from the coarse stage (host satellite body-pointing). A variety of ne steering solutions are considered, and microelectromechanical systems (MEMS) tip-tilt mirrors are selected due to their advantage in size, weight and power. We experimentally validate the designs resulting from the trade studies for these key subsystems. We construct a prototype transmitter using a modified COTS fiber amplifier and a directly-modulated seed laser capable of producing a 200mW average power, pulse position modulated optical output. This prototype is used to confirm power consumption predictions, modulation rate scalability (10 Mbps to 100 Mbps), and peak transmit power (e.g., 24.6W for PPM-128). The transmitter optical output, along with a simple loopback receiver, is used to validate the sensitivity of the avalanche photodiode receiver used for the ground receiver in the flight experiment configuration. The MEMS fine steering mechanisms, which are not rated for space use, are characterized using a purpose-built test apparatus. Characterization experiments of the MEMS devices focused on ensuring repeatable behavior (+/-0:11 mrad, 3-[sigma]) over the expected operating temperature range on the spacecraft (0°C to 40°C). Finally, we provide an assessment of the work that remains to move from the prototype to flight model and into on-orbit operations. Space terminal packaging and integration needs, as well as host spacecraft interface requirements are detailed. We also describe the remaining ground station integration tasks and operational procedures. Having developed a pragmatic COTS-based lasercom architecture for CubeSats, and having addressed the need for a compact laser transmitter and optical ne steering mechanisms with both analysis and experimental validation, this thesis has set the stage for the practical use of lasercom techniques in resource-constrained CubeSats which can yield order-of-magnitude enhancements in communications link eciency relative to existing RF technologies currently in use.<br>by Ryan W. Kingsbury.<br>Ph. D.
9
Joshi, Harita. "Modulation for optical wireless communications." Thesis, University of Warwick, 2012. http://wrap.warwick.ac.uk/55521/.
Testo completo
10
Bandele, Jeremiah Oluwatosin. "Extended free-space optical communications." Thesis, University of Nottingham, 2016. http://eprints.nottingham.ac.uk/37961/.
Testo completoAbstract (sommario):
This thesis investigates the performance of free-space optical (FSO) communication systems in a turbulent atmosphere employing optical amplifiers (OAs) to extend transmission reach and wavelength-division multiplexing (WDM) to improve capacity. This system performance is considered in the presence of amplified spontaneous emission (ASE) noise, scintillation, beam spreading, atmospheric attenuation and interchannel crosstalk. In this work, the modulation scheme used is the on-off keying non-return-to-zero and the main performance metric employed is the average bit error rate (BER). Various performance evaluation methods are used to estimate system performance. Analysis of single link, cascaded OA and WDM FSO communication systems are given and the implications of using both adaptive (to channel state) and non-adaptive decision threshold schemes are analysed. The benefits of amplifier saturation, for example in the form of effective scintillation reduction when a non-adaptive decision threshold scheme is utilised at the receiver for different atmospheric turbulence regimes, are presented. Monte Carlo simulation techniques are used to model the probability distributions of system parameters such as the optical signal power, amplified spontaneous emission noise, optical signal to noise ratio and the average bit error rate due to scintillation. It is found that the performance of an adaptive decision threshold is superior to a non-adaptive decision threshold for both saturated and fixed gain preamplified receivers and the ability of a saturated gain OA to suppress scintillation is only meaningful for system performance when a non-adaptive decision threshold is used at the receiver. In a saturated gain preamplified system, the optimum non-adaptive decision threshold is investigated. An OA cascade can be successfully used to extend reach in FSO communication systems and specific system implementations are presented. The optimal cascade scheme with a non-adaptive receiver would use frequent low gain saturated amplification although this has a cost implication. Furthermore, a saturated gain amplified WDM FSO system with a non-adaptive decision threshold is superior to a non-amplified WDM FSO system with an adaptive decision threshold.
11
Almeida, Álvaro José Caseiro de. "Quantum communications in optical fibers." Doctoral thesis, Universidade de Aveiro, 2016. http://hdl.handle.net/10773/16306.
Testo completoAbstract (sommario):
Doutoramento em Engenharia Física<br>This thesis begins by proposing the implementation of a probabilistic photon source based on the stimulated four-wave mixing (FWM) process. This source was implemented experimentally and characterized in terms of its statistical distribution. Next, the impact of the stimulated FWM process in a co-propagating quantum signal was studied experimentally. Finally, the violation of Clauser-Horne-Shimony-Holt (CHSH) inequality was experimentally verified using polarization-entangled photon pairs, which were obtained from the spontaneous FWM process in a Sagnac loop. The experimental evolution of the quantum-bit error rate (QBER) in a system without control of polarization, using this degree of freedom to encode information, was studied. It was found out that the QBER increases with the length of the transmission fiber. It was also verified that the increase in the QBER was due to the random rotation of photon’s polarization. A model for the rigorous estimation of the QBER was derived and developed an automatic method to compensate the random rotations of polarization. The method was validated numerically and experimentally, in a transmission system with 40km, showing that it can compensate for the rotations that photons suffer during propagation in optical fibers. Finally, a quantum bit commitment (QBC) protocol between two untrusted entities was implemented. The encoding was performed using two nonorthogonal states of polarization (SOPs). As quantum channel between the two entities, it was first assumed that the transmitter and the receiver were side by side, and after that, they were separated by 8 km and finally, that they were 16km from each other. The implementation of the protocol was performed with a success rate in measurements exceeding 93%, well above the theoretical security limit of 85%. The best strategy for deceiving the commitment was also implemented, and its security experimentally confirmed with a confidence of 7 standard deviations.<br>Nesta tese começou-se por propor a realização de uma fonte de fotões probabilística baseada no processo estimulado de mistura de quatro ondas (FWM). Implementou-se essa fonte no laboratório e caracterizou-se experimentalmente a sua distribuição estatística. Depois, estudou-se experimentalmente o impacto do processo estimulado de FWM num sinal quântico que se propaga na mesma fibra ótica. Por fim, foi verificada experimentalmente a violação da desigualdade de ClauserHorne-Shimony-Holt (CHSH) usando pares de fotões entrelaçados, que foram obtidos a partir do processo espontâneo de FWM num ciclo de Sagnac. Estudou-se a evolução da taxa de erro de bits quânticos (QBER) num sistema sem controlo de polarização, quando este grau de liberdade é usado para codificar a informação. Verificou-se que a QBER aumenta com o comprimento da fibra de transmissão. Verificou-se ainda que o aumento da QBER era devido às variações aleatórias da polarização dos fotões. Derivou-se um modelo para a estimativa rigorosa da QBER e desenvolveu-se um método automático de compensação das rotações aleatórias da polarização. O método foi validado numericamente e experimentalmente, num sistema de transmissão com 40km, verificando se que consegue compensar as rotações que os fotões sofrem durante a sua propagação em fibras óticas. Finalmente, implementou-se um protocolo de compromisso quântico entre duas entidades não confiávéis. Na codificação foram usados dois estados de polarização (SOPs) não ortogonais. Como canal quântico entre as duas entidades foi primeiro considerado que o emissor e o recetor se encontravam lado a lado, depois que estes estavam separados por 8km e finalmente que se encontravam a 16km um do outro. A implementação do protocolo foi feita com uma taxa de sucesso nas medidas superior a 93%, muito acima do limite teórico mínimo de 85%. Implementou-se ainda a melhor estratégia para que o compromisso pudesse ser falseado, tendo sido confirmada experimentalmente a sua segurança com uma confiança de 7 desvios padrão.
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Priyadarshi, Sanjay. "Optimal operating conditions and security considerations for optical chaos communications." Thesis, Bangor University, 2013. https://research.bangor.ac.uk/portal/en/theses/optimal-operating-conditions-and-security-considerations-for-optical-chaos-communications(63997d52-0808-47b1-a995-64e4dfebd099).html.
Testo completoAbstract (sommario):
This thesis details research on chaos-based optical communications using semiconductor lasers. Theoretical work has identified optimal operating condition of optical chaos communications systems without the need for re-adjustment of laser operating conditions in the field. In addition, an experimental investigation has been undertaken of one aspect of the security of message transmission using chaotic semiconductor lasers and specifically using Vertical-Cavity Surface-Emitting Laser (VCSEL). In optical chaos communications a message is masked in the noise-like broadband output of a chaotic transmitter laser, and message recovery is enabled through the synchronization of the transmitter and the (chaotic) receiver laser. Key issues are to identify the laser operating conditions which provide the highest quality synchronization conditions and those which provide optimized message extraction. In general such operating conditions are not coincident. In this thesis numerical simulations are performed with the aim of identifying a regime of operation where the highest quality synchronization and optimizing message extraction efficiency are achieved simultaneously for the analogue and digital message modulation. Use of such an operating regime will facilitate practical deployment of optical chaos communications systems without the need for re-adjustment of laser operating conditions in the field. In this way it has been found, for example, that in an optical chaos communication system an optimal configuration for 1 GHz modulation frequency may utilize a 2% modulation depth and 20% coupling rate from transmitter laser to receiver laser for analogue message modulation. Ideal operating conditions for digital message modulation, identified using the laser bias current as the control parameter, are found for 2GB/s message transmission and a modulation depth of about 2%. An experimental study has also been undertaken to determine the effect of time delay and concealment in the external cavity semiconductor laser systems. The time delay (TD) signature arises due to the external cavity round trip time of feedback in the external cavity semiconductor laser system. The identification of the time delay may affect the security of encoded messages. An external cavity VCSEL with variable optical-polarization-angle feedback has been explored experimentally in order to identify conditions for time delay concealment. In this work the VCSEL was subject not only to variable optical polarization angle of feedback but also variable optical feedback strength and bias current. The TD signature concealment is evaluated through the use of an autocorrelation function and an information theory-based permutation entropy function. It was found that the TD signature is concealed at low feedback strength of order –18 dB. At moderate feedback strengths, the TD signature is sensitive to the rotation of the polarization angle of the optical feedback with TD concealment being observed for polarization angles in the range from 45° to 90°.
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Mankong, Ukrit. "Gain clamped semiconductor optical amplifiers for optical communications applications." Thesis, University of Cambridge, 2008. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.612028.
Testo completo
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Tsonev, Dobroslav Antonov. "High speed energy efficient incoherent optical wireless communications." Thesis, University of Edinburgh, 2015. http://hdl.handle.net/1842/10571.
Testo completoAbstract (sommario):
The growing demand for wireless communication capacity and the overutilisation of the conventional radio frequency (RF) spectrum have inspired research into using alternative spectrum regions for communication. Using optical wireless communications (OWC), for example, offers significant advantages over RF communication in terms of higher bandwidth, lower implementation costs and energy savings. In OWC systems, the information signal has to be real and non-negative. Therefore, modifications to the conventional communication algorithms are required. Multicarrier modulation schemes like orthogonal frequency division multiplexing (OFDM) promise to deliver a more efficient use of the communication capacity through adaptive bit and energy loading techniques. Three OFDM-based schemes – direct-current-biased OFDM (DCO-OFDM), asymmetrically clipped optical OFDM(ACO-OFDM), and pulse-amplitude modulated discrete multitone (PAM-DMT) – have been introduced in the literature. The current work investigates the recently introduced scheme subcarrier-index modulation OFDM as a potential energy-efficient modulation technique with reduced peak-to-average power ratio (PAPR) suitable for applications in OWC. A theoretical model for the analysis of SIM-OFDMin a linear additive white Gaussian noise (AWGN) channel is provided. A closed-form solution for the PAPR in SIM-OFDM is also proposed. Following the work on SIM-OFDM, a novel inherently unipolar modulation scheme, unipolar orthogonal frequency division multiplexing (U-OFDM), is proposed as an alternative to the existing similar schemes: ACO-OFDMand PAM-DMT. Furthermore, an enhanced U-OFDMsignal generation algorithm is introduced which allows the spectral efficiency gap between the inherently unipolar modulation schemes – U-OFDM, ACO-OFDM, PAM-DMT – and the conventionally used DCO-OFDM to be closed. This results in an OFDM-based modulation approach which is electrically and optically more efficient than any other OFDM-based technique proposed so far for intensity modulation and direct detection (IM/DD) communication systems. Non-linear distortion in the optical front-end elements is one of the major limitations for high-speed communication in OWC. This work presents a generalised approach for analysing nonlinear distortion in OFDM-based modulation schemes. The presented technique leads to a closed-form analytical solution for an arbitrary memoryless distortion of the information signal and has been proven to work for the majority of the known unipolar OFDM-based modulation techniques - DCO-OFDM, ACO-OFDM, PAM-DMT and U-OFDM. The high-speed communication capabilities of novel Gallium Nitride based μm-sized light emitting diodes (μLEDs) are investigated, and a record-setting result of 3.5Gb/s using a single 50-μm device is demonstrated. The capabilities of using such devices at practical transmission distances are also investigated, and a 1 Gb/s link using a single device is demonstrated at a distance of up to 10m. Furthermore, a proof-of-concept experiment is realised where a 50-μm LED is successfully modulated using U-OFDM and enhanced U-OFDM to achieve notable energy savings in comparison to DCO-OFDM.
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Mysore, Sudhesh M. "Advances in optical power budgets and bandwidth capacity of broadband networks /." free to MU campus, to others for purchase, 1999. http://wwwlib.umi.com/cr/mo/fullcit?p9953885.
Testo completo
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Jedrkiewicz, Ottavia. "Theories of atom-field interaction in cavities and retrodiction for quantum communications." Thesis, University of Essex, 2001. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.340589.
Testo completo
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Yu, Zhenhua. "Optical wireless communications with optical power and dynamic range constraints." Diss., Georgia Institute of Technology, 2014. http://hdl.handle.net/1853/51784.
Testo completoAbstract (sommario):
Along with the rapidly increasing demand for wireless data while more and more crowded radio frequency (RF) spectrum, optical wireless communications (OWC) become a promising candidate to complement conventional RF communications, especially for indoor short and medium range data transmissions. Orthogonal frequency division multiplexing (OFDM) is considered for OWC due to its ability to boost data rates. However, the average emitted optical power and dynamic range of driving signals of LEDs are two major constraints in OWC. OFDM waveforms exhibits high upper and lower peak-to-average power ratios (PAPRs), which make OFDM signals optical power inefficient and easy to violate the dynamic range of LEDs, resulting clipping and nonlinear distortions. In this dissertation, we analyze and design optical power and dynamic range constrained OWC systems, for which OFDM is our major subject. We first derive distributions of upper PAPR and lower PAPR of OWC-OFDM signals. Then we analyze the clipped OFDM signals in term of error vector magnitude (EVM), signal-to-distortion ratio (SDR), and achievable data rates under both optical power and dynamic range constraints. The next part of this dissertation is the OFDM system design for visible light communications (VLC) considering illumination requirement. We investigate the illumination-to-communication efficiency (ICE) in VLC-OFDM, and design the brightness control and flickering mitigation schemes for VLC-OFDM. In the end, to reduce the complexity of driving circuits of LEDs , we propose using delta-sigma modulators in VLC-OFDM systems to convert continuous magnitude OFDM symbols into two-level LED driver signals without loss of the communication theory advantages of OFDM.
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Del, Portillo Barrios Iñigo. "Optimal locations for the ground segment of optical space communications networks." Thesis, Massachusetts Institute of Technology, 2016. http://hdl.handle.net/1721.1/105609.
Testo completoAbstract (sommario):
Thesis: S.M., Massachusetts Institute of Technology, Department of Aeronautics and Astronautics, 2016.<br>Cataloged from PDF version of thesis.<br>Includes bibliographical references (pages 123-126).<br>Optical communications are envisioned as a key technology for space communication in the near future. This transition to optical terminals is being pushed by the higher data volume demand of certain missions and by the spectrum encroachment in current RF bands. In addition, optical systems present multiple advantages with respect to RF terminals, such as their lower mass, size, and power, as well as the higher data-rate. However, one of the main issues of using optical systems is the space-to-ground link, as it is impossible for the laser beam to penetrate atmospheric clouds. Geographic diversity of ground stations has been proposed as an alternative to mitigate these effects. This thesis uses the systems architecture approach to analyze different architectures for the ground segment of an optical space communications network to serve low Earth orbit (LEO) missions. In particular, we analyze the tradespace characterized by three decisions: 1) number and location of optical ground stations, 2) use of geostationary relay satellites vs. the direct-to-Earth approach and 3) presence of crosslinks among relay satellites. Previous analyses studied the problem of mitigating cloud outage through site diversity both from a simulation perspective (working with point designs or a reduced tradespace composed of a fixed set of candidate locations), and from an analytical standpoint after assuming various simplifying hypotheses (independence of ground stations, uniform cloud conditions across the globe). This thesis expands those assumptions, presents a tool to analyze scenarios where no constraints are placed in the location and proposes a new cloud model to obtain first order approximations for the network availability. In order to analyze the availability of a network of optical ground stations, we use historical weather data from the National Oceanic and Atmospheric Administration (NOAA) and the cloud fraction dataset from Aqua's and Terra's MODIS instruments to characterize weather conditions across the globe. Next, we present the Optical Network Ground Segment Analyzer (ONGSA), a network simulator that incorporates the cloud models to simulate operations of the optical network. Finally we employ ONGSA to explore the aforementioned tradespace and analyze both cost and performance (in terms of availability) for each architecture. Results show that a maximum availability of 95.5 % can be achieved using an architecture similar to the actual system (the Tracking and Data Relay Satellite System) and 12 additional optical ground stations. Furthermore, an unconstrained optimization analysis identified the north of Mexico, southwest of Saudi Arabia, Morocco and central Australia as areas with high potential to construct new ground stations. Building new ground stations was identified to be a more cost-effective solution when the required level of availability is high, while using existing infrastructure is a better solution for systems when the required optical availability is low. Our analysis shows that inter-satellite links (ISL) are a cost-effective solution that adds an extra mitigation layer to combat the effects of cloud coverage. In particular, having ISL results in an increase in availability from 80% with six ground stations to 98.7% with the same number of ground stations.<br>by Iñigo del Portillo Barrios.<br>S.M.
19
Bond, Steven Winfred. "Through-silicon circuit optical communications links." Diss., Georgia Institute of Technology, 2001. http://hdl.handle.net/1853/15390.
Testo completo
20
Azizoḡlu, Murat. "Phase noise in coherent optical communications." Thesis, Massachusetts Institute of Technology, 1991. http://hdl.handle.net/1721.1/13463.
Testo completoAbstract (sommario):
Thesis (Ph. D.)--Massachusetts Institute of Technology, Dept. of Electrical Engineering and Computer Science, 1991.<br>Includes bibliographical references (p. 201-206).<br>by Murat AzizoÄlu.<br>Ph.D.
21
Fludger, Christopher Ronald Stephen. "Raman amplification for broadband optical communications." Thesis, University of Cambridge, 2002. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.620474.
Testo completo
22
Waegemans, R. "Digital electronic predistortion for optical communications." Thesis, University College London (University of London), 2010. http://discovery.ucl.ac.uk/20007/.
Testo completoAbstract (sommario):
The distortion of optical signals has long been an issue limiting the performance of communication systems. With the increase of transmission speeds the effects of distortion are becoming more prominent. Because of this, the use of methods known from digital signal processing (DSP) are being introduced to compensate for them. Applying DSP to improve optical signals has been limited by a discrepancy in digital signal processing speeds and optical transmission speeds. However high speed Field Programmable Gate Arrays (FPGA) which are sufficiently fast have now become available making DSP experiments without costly ASIC implementation possible for optical transmission experiments. This thesis focuses on Look Up Table (LUT) based digital Electronic Predistortion (EPD) for optical transmission. Because it is only one out of many possible implementations of EPD, it has to be placed in context with other EPD techniques and other distortion combating techniques in general, especially since it is possible to combine the different techniques. Building an actual transmitter means that compromises and decisions have to be made in the design and implementation of an EPD based system. These are based on balancing the desire to achieve optimal performance with technological and economic limitations. This is partly done using optical simulations to asses the performance. This thesis describes a novel experimental transmitter that has been built as part of this research applying LUT based EPD to an optical signal. The experimental transmitter consists of a digital design (using a hardware description language) for a pair of FPGAs and an analogue optical/electronic setup including two standard DAC integrated circuits. The DSP in the transmitter compensated for both chromatic dispersion and self phase modulation. We achieved transmission of 10.7 Gb/s non-return-to-zero (NRZ) signals with a +4 dBm launch power over 450 km keeping the required optical-signal-to-noise-ratio (OSNR) for a bit-error-rate of 2x10^{-3} below 11 dB. In doing so we showed experimentally, for the first time, that nonlinear effects can be compensated with this approach and that the combination of FPGA-DAC is a viable approach for an experimental setup.
23
Yuan, Wei Wen. "Optical wireless communications for micro-machines." Thesis, University of Oxford, 2011. http://ora.ox.ac.uk/objects/uuid:d0f2c779-fc66-4436-a831-fa65e1b36d5b.
Testo completoAbstract (sommario):
The main objective of this thesis is to develop a communication system that can minimize the micro-machine size and power consumption and maximize the link range and the number of micro-machines that can communicate simultaneously with the base station. Several possible communication systems are compared, including RF communications and active and passive free space optical communications. A directed, half duplex LOS link using a Ferroelectric liquid crystal (FLC) or multiple quantum well (MQW) modulating retroreflector-base passive uplink is then examined in more detail. Two potential geometries are described. In a broad-beam system, light from a source is broadcast to all micro-machines within the field of view (FOV). However, simulations show that the performance is unacceptable for most applications. In a narrow-beam system, light is holographically steered to active micro-machines within the same FOV. Therefore, the link budget has been improved. For a BER not exceeding 10-9, the 850 nm LC narrowbeam system can support maximum range of 146 m at a data rate of 10kbits/s, and the 1525 nm MQW narrowbeam system can support a maximum range of 34 m at a data rate of 10Mbits/s, when the transmitted power in the diffracted beam of the positive first order is 0.5 mW. Experiments have been carried out to verify the model. These were initially carried out with MQW Modulating RetroReflector (MRR). Results were then be used to modify the characteristics of these components in the model. Available components and discrete electronics have been used to set up a simple retro-reflecting link. Experiments have been performed at a limited data rate of 1 kbits/s over a limited range of 1m due to creating a uniform interrogation beam spot, and the active area of the receiver of 1 mm diameter. An algorithm to find the MQW MRR within the FOV is designed and tested.
24
Lin, Rui. "High-capacity short-reach optical communications." Doctoral thesis, KTH, Kommunikationssystem, CoS, 2016. http://urn.kb.se/resolve?urn=urn:nbn:se:kth:diva-196580.
Testo completoAbstract (sommario):
The global traffic is experiencing an exponential growth posing severe challenges to the communication networks in terms of capacity. As a future-proof technology fiber communication is widely implemented in different network segments, which can be categorized by transmission distance as long-haul and short-reach. This thesis focuses on the short-reach communication networks including fiber access network connecting the end users to the metro/core networks that covering tens of kilometers and optical datacenter network handling the traffic within the datacenter with distance up to a few kilometers. For fiber access networks, wavelength division multiplexing passive optical networks (WDM-PONs) assign a dedicated wavelength channel to each user guaranteeing high data rate. Dense channels enlarges the user count but makes the signals vulnerable to the wavelength drift. In this regard we propose two schemes based on optical frequency comb technique to generate stable carriers for WDM-PONs. Meanwhile, radio-over-fiber techniques allows the transmission of radio signals between central offices and the cells. Millimeter wave (MMW) over fiber, on the other hand, offer high bandwidth for future high capacity mobile access. We propose and experimentally demonstrate a palm-shaped spectrum generation where the high-power central carrier can be used for upstream transmission while multiple MMW bands are capable of transmitting different downstream data simultaneously. Regarding optical datacenter networks, passive optical interconnects (POIs) have been proposed as an energy-efficient solution since only passive optical components are used for server interconnection. However, the high insertion loss may result in a scalability problem. We develop a methodology that considers various physical-layer aspects, e.g., receiver types, modulation formats, to quantify the scalability of POIs. Both theoretical analyses and experimental measurements have been performed to assess the scalability of various coupler-based POIs.<br>Den globala datatrafiken växer exponentiellt, både på grund av nya bandbreddskrävande applikationer och ökningen av antalet användare. Detta innebär en utmaning för kommunikationsnätens kapacitet. Fiberoptisk kommunikation är en framtidssäker teknik för att möta detta kapacitetsbehov och används redan i stor utsträckning i olika delar av näten. Beroende på överföringsavstånd, kan fibernät kategoriseras som långdistansnät eller nät med kort räckvidd. Denna avhandling behandlar nät med kort räckvidd, innefattande dels 1) accessnät som förbinder slutanvändarna till stadsnätet/ huvudnätet och typiskt omfattar tiotals kilometer, dels 2) optiska datanätverk som hanterar den interna trafiken inom datacenter med överföringsavstånd upp till ett par kilometer.För fiberaccessnät är en av de lovande teknikerna våglängdsmultiplexade passiva optiska nät (WDM-PON), där en dedicerad våglängdskanal tilldelas varje användare vilket garanterar hög datahastighet. Genom ett litet kanalavstånd så kan antalet användare i WDM-PON utökas men det gör samtidigt systemet känsligt för våglängdsdrift hos lasrarna. För att råda bot på detta, föreslår vi två system baserade på optisk frekvenskams-teknik. Vi validerar experimentellt att de kan generera stabila optiska bärvågor för WDM-PON. Radio-över –fiber-tekniken gör samtidigt det möjligt att sända radiosignaler över en lång sträcka och används därför i mobilsystem för överföring mellan centralstationen och radiocellerna. Millimetervågor (MMW) över fiber erbjuder ännu större modulationsbandbredd och är lovande för framtidens mobilradiosystem med hög kapacitet. I denna avhandling föreslår vi, och demonstrerar experimentellt, generation av ett frekvenskams-spektrum som är format som en handflata, där en central bärare med hög effekt (långfingret på handflatan) kan användas i radiocellerna för uppströms överföring, medan multipla MMW band (övriga fingrar) samtidigt kan överföra olika data nedströms. När det gäller nätverk för optiska datacenter, har passiva optiska interconnects (POI) föreslagits som en energieffektiv lösning, där endast passiva optiska komponenter används för ihopkoppling av servrarna. Höga inkopplingsförluster hos passiva optiska komponenter kan emellertid leda till allvarliga skalbarhetsproblem. I denna avhandling presenterar vi en nyutvecklad metod för att kvantifiera skalbarheten, vilken tar hänsyn till olika faktorer i det fysiska lagret som t.ex. mottagartyp och modulationsformat. Både teoretiska analyser och experimentella mätningar har utförts för att utvärdera skalbarheten hos olika kopplarbaserade POI.<br><p>QC 20161117</p>
25
Alresheedi, Mohammed Thamer. "Adaptation techniques in optical wireless communications." Thesis, University of Leeds, 2013. http://etheses.whiterose.ac.uk/6396/.
Testo completoAbstract (sommario):
The need for high-speed local area networks to meet the recent developments in multimedia and video transmission applications has recently focused interest on optical wireless communication. Optical wireless systems boast some advantages over radio frequency (RF) systems, including a large unregulated spectrum, freedom from fading, confidentiality and immunity against interference from electrical devices. They can satisfy the dual need for mobility and broadband networking. However, optical wireless links are not without flaws. They are affected by background noise (artificial and natural light sources) and suffer from multipath dispersion. The former can degrade the signal-to-noise ratio, while the latter restricts the maximum transmission rate available. The aim of this thesis is to investigate a number of techniques to overcome these drawbacks and design a robust high-speed indoor optical wireless system with full mobility. Beam delay and power adaptation in a multi-spot diffusing system is proposed in order to increase the received optical signal, reduce the delay spread and enable the system to operate at higher data rates. The thesis proposes employing angle diversity receivers and imaging diversity receivers as in order to reduce background noise components. Moreover, the work introduces and designs a high-speed fully adaptive optical wireless system that employs beam delay, angle and power adaptation in a multi-spot diffusing configuration and investigates the robustness of the link design in a realistic indoor office. Furthermore, a new adaptive optical wireless system based on a finite vocabulary of stored holograms is introduced. This method can effectively optimise the spots’ locations and reduce the design complexity of an adaptive optical wireless system. A fast adaptation approach based on a divide-andconquer methodology is proposed and integrated with the system to reduce the time required to identify the optimum hologram. The trade-off between complexity and performance enhancement of the adaptive finite holograms methods compared with the original beam power and angle adaptation is investigated.
26
Hattori, Haroldo Takashi. "Low Nonlinearity Optical Fibers for Broadband and Long-Distance Communications." Diss., Virginia Tech, 1998. http://hdl.handle.net/10919/29816.
Testo completoAbstract (sommario):
A class of low nonlinearity dispersion-shifted and dispersion-flattened fibers for
broadband and long haul applications is presented. The refractive index profiles of these
fibers assume a depressed-core multi-clad geometry in order to achieve effective-areas
much larger than those in conventional optical fibers.
A systematic approach for designing large effective-area dispersion-shifted fibers, using a
reference W-index profile to initiate the design, is presented. Transmission properties,
including effective-area, mode-field-diameter, dispersion, dispersion slope, cutoff
wavelength, and bending, microbending and splice losses are evaluated for several design
examples. To ascertain that the proposed fibers can be practically fabricated, the effects
of varying fiber dimensions and indices on effective-area, mode-field-diameter and
dispersion are assessed.
It is shown that there is a trade-off between effective-area and mode-field-diameter and,
generally, larger effective-areas are associated with larger mode-field-diameters. In other
words, less signal distortion due to fiber nonlinearity (larger effective-area) is associated
with higher power loss due to bending of fiber (larger mode-field-diameter). Thus, a large
effective-area and low bending loss are conflicting requirements. A parameter Q is
defined as a performance indicator, considering effective-area and mode-field-diameter.
Dispersion-shifted single-mode fiber designs with effective-areas of 78 mm
2 to 210 mm2 and the corresponding mode-field-diameter of 8.94 mm to 14.94 mm,
dispersion less than 0.07 ps/nm.km, and dispersion slope of about 0.05 ps/ nm2.km are
presented. Numerical simulations for propagation of pulses in few designed fibers are
performed.Designs of large effective-area dispersion-flattened fibers are also presented,
for the first time we believe. These fibers provide large effective-area and low dispersion
over an extended range of wavelengths. For our design, over the wavelength range of 1.48 mm <
l < 1.58 mm, the effective-area is 75 mm2 to 100 mm2, while the dispersion remains
below 0.7 ps/nm.km.<br>Ph. D.
27
Paquot, Yvan. "Novel linear and nonlinear optical signal processing for ultra-high bandwidth communications." Thesis, The University of Sydney, 2014. http://hdl.handle.net/2123/12408.
Testo completoAbstract (sommario):
The thesis is articulated around the theme of ultra-wide bandwidth single channel signals. It focuses on the two main topics of transmission and processing of information by techniques compatible with high baudrates. The processing schemes introduced combine new linear and nonlinear optical platforms such as Fourier-domain programmable optical processors and chalcogenide chip waveguides, as well as the concept of neural network. Transmission of data is considered in the context of medium distance links of Optical Time Division Multiplexed (OTDM) data subject to environmental fluctuations. We experimentally demonstrate simultaneous compensation of differential group delay and multiple orders of dispersion at symbol rates of 640 Gbaud and 1.28 Tbaud. Signal processing at high bandwidth is envisaged both in the case of elementary post-transmission analog error mitigation and in the broader field of optical computing for high level operations (“optical processor”). A key innovation is the introduction of a novel four-wave mixing scheme implementing a dot-product operation between wavelength multiplexed channels. In particular, it is demonstrated for low-latency hash-key based all-optical error detection in links encoded with advanced modulation formats. Finally, the work presents groundbreaking concepts for compact implementation of an optical neural network as a programmable multi-purpose processor. The experimental architecture can implement neural networks with several nodes on a single optical nonlinear transfer function implementing functions such as analog-to-digital conversion. The particularity of the thesis is the new approaches to optical signal processing that potentially enable high level operations using simple optical hardware and limited cascading of components.
28
Hao, Miin-Jong. "Performance evaluation of practival FSK, CPFSK, and ASK detection schemes for coherent optical fiber communication systems." Diss., Georgia Institute of Technology, 1995. http://hdl.handle.net/1853/15686.
Testo completo
29
West, Lamar. "Analysis and simulation of reverse path laser clipping in subcarrier multiplexed hybrid fiber coax networks." Diss., Georgia Institute of Technology, 1997. http://hdl.handle.net/1853/13301.
Testo completo
30
Males, Mladen. "Suppression of transient gain excursions in an erbium-doped fibre amplifier /." Connect to this title, 2006. http://theses.library.uwa.edu.au/adt-WU2007.0157.
Testo completo
31
Liu, Cheng. "Advanced system design and signal processing techniques for converged high-speed optical and wireless applications." Diss., Georgia Institute of Technology, 2013. http://hdl.handle.net/1853/49058.
Testo completoAbstract (sommario):
The ever-increasing data traffic demand drives the evolution of telecommunication networks, including the last-mile access networks as well as the long-haul backbone networks. This Ph.D. dissertation focuses on system design and signal processing techniques for next-generation converged optical-wireless access systems and the high-speed long-haul coherent optical communication systems. The convergence of high-speed millimeter-wave wireless communications and high-capacity fiber-optic backhaul networks provides tremendous potential to meet the capacity requirements of future access networks. In this work, a cloud-radio-over-fiber access architecture is proposed. The proposed architecture enables a large-scale small-cell system to be deployed in a cost-effective, power-efficient, and flexible way. Based on the proposed architecture, a multi-service reconfigurable small-cell backhaul network is developed and demonstrated experimentally. Additionally, the combination of high-speed millimeter-wave radio and fiber-optic backhaul is investigated. Several novel methods that enable high-spectral-efficient vector signal transmission in millimeter-wave radio-over-fiber systems are proposed and demonstrated through both theoretical analysis and experimental verification. For long-haul core networks, ultra-high-speed optical communication systems which can support 1Terabit/s per channel transmission will soon be required to meet the increasing capacity demand in the core networks. Grouping a number of tightly spaced optical subcarriers to form a terabit superchannel has been considered as a promising solution to increases channel capacity while minimizing the need for high-level modulation formats and high baud rate. Conventionally, precise spectral control at transmitter side is required to avoid strong inter-channel interference (ICI) at tight channel spacing. In this work, a novel receiver-side approach based on “super receiver” architecture is proposed and demonstrated. By jointly detecting and demodulating multiple channels simultaneously, the penalties associated with the limitations of generating ideal spectra can be mitigated. Several joint DSP algorithms are developed for linear ICI cancellation and joint carrier-phase recovery. Performance analysis under different system configurations is conducted to demonstrate the feasibility and robustness of the proposed joint DSP algorithms, and improved system performance is observed with both experimental and simulation data.
32
Angeh, Wolfgang Ondua. "Design and performance analysis of a survivable metropolitan area fiber optic communication network." Master's thesis, This resource online, 1990. http://scholar.lib.vt.edu/theses/available/etd-02022010-020030/.
Testo completo
33
Lee, Ho Tong. "Prism-coupled square optical micropillar resonator-based filters for optical communications /." View abstract or full-text, 2004. http://library.ust.hk/cgi/db/thesis.pl?ELEC%202004%20LEE.
Testo completoAbstract (sommario):
Thesis (M. Phil.)--Hong Kong University of Science and Technology, 2004.<br>Includes bibliographical references (leaves 134-138). Also available in electronic version. Access restricted to campus users.
34
Zou, Ding, and Ivan B. Djordjevic. "FPGA-Based Rate-Compatible LDPC Codes for the Next Generation of Optical Transmission Systems." IEEE-INST ELECTRICAL ELECTRONICS ENGINEERS INC, 2016. http://hdl.handle.net/10150/621685.
Testo completoAbstract (sommario):
In this paper, we propose a rate-compatible forward error-correcting (FEC) scheme based on low-density-parity check (LDPC) codes together with its software reconfigurable unified field-programmable gate array (FPGA) architecture. By FPGA emulation, we demonstrate that the proposed class of rate-compatible LDPC codes based on puncturing and generalized LDPC coding with an overhead from 25% to 46% provides a coding gain ranging from 12.67 to 13.8 dB at a post-FEC bit-error rate (BER) of 10(-15). As a result, the proposed rate-compatible codes represent one of the strong FEC candidates of soft-decision FEC for both short-haul and long-haul optical transmission systems.
35
Ireeta, Winston Tumps. "Aerial optical fibres in telecommunication systems : SOP and PMD monitoring, and tolerance of modulation formats." Thesis, Nelson Mandela Metropolitan University, 2010. http://hdl.handle.net/10948/1478.
Testo completoAbstract (sommario):
The topic of this thesis is aerial optical fibres in telecommunication systems: state of polarization (SOP) and polarization mode dispersion (PMD) monitoring and tolerance of modulation formats. Errors in optical fibre telecommunication systems are introduced when these polarization effects (SOP and PMD) change. These changes are so intense especially in aerial optical fibres. Part of the backbone of South Africa’s national grid includes long distances of aerial optical fibre between transmission exchange stations. The work in this thesis can be divided into three parts which all deal with the major aspects of PMD in deployed aerial optical fibres: characterization, environmental effects plus other perturbations, and tolerance of different modulation formats. In our work, SOP and PMD field measurements revealed that they both fluctuate more rapidly in deployed aerial optical fibres especially on windy and hot days. The SOP and PMD changes in the aerial optical fibres showed a significant correlation with these environmental parameters. SOP and PMD are stochastic in nature due to changes in the properties of the optical fibres and its positions because of both intrinsic and extrinsic perturbations. In our work, with only 184 PMD values measured and obtained by use of the FTB-5700 single-ended dispersion analyzer, the predicted theoretical Gaussian fit was obtained with a mean of 0.47 ps and standard deviation of 0.08 ps. This small standard deviation was justification for its robustness and accuracy. The statistical distributions for first-order polarization mode dispersion (FO-PMD) and second-order polarization mode dispersion (SO-PMD) for the first time were experimentally confirmed when measured using the FTB-5700 single-ended dispersion analyzer instrument for deployed aerial optical fibres. We were also able to determine the time scale over which to compensate FO-PMD in deployed aerial fibres using the directional time drift autocorrelation function method. It is slightly higher than 390 s for SOP measurements made on a particular windy and hot day. This is due to the fact that the changes of the PMD vector are known to be slower than the SOP changes. vi We also investigated the theoretical statistical distribution that corresponds to output SOP variations. The SOP variations can either be with wavelength (for buried fibre) or with time (for aerial fibre). Our results showed that the statistics of the relative SOP changes approached the distribution proposed by Foschini et al. (2000). Advanced optical modulation formats have become a key ingredient in the design of modern state-of-the-art wavelength-division-multiplexed (WDM) optical transmission systems. In our work, we investigated which of these advanced modulation formats is best suited for the South African network especially on systems that have links of aerial optical fibres. Keywords: aerial optical fibre, polarization mode dispersion (PMD), principal states of polarization (PSP), state of polarization (SOP), first-order PMD, second-order PMD.
36
Flatten, Amy K. "Interaction of ultrasound with a polarization preserving optic fiber." Diss., Georgia Institute of Technology, 1993. http://hdl.handle.net/1853/30723.
Testo completo
37
Lai, Ming-fai, and 黎明輝. "All-optical signal processing based on optical parametric amplification." Thesis, The University of Hong Kong (Pokfulam, Hong Kong), 2008. http://hub.hku.hk/bib/B41508877.
Testo completo
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Lai, Ming-fai. "All-optical signal processing based on optical parametric amplification." Click to view the E-thesis via HKUTO, 2008. http://sunzi.lib.hku.hk/hkuto/record/B41508877.
Testo completo
39
Locquet, Alexandre Daniel. "Chaotic optical communications using delayed feedback systems." Available online, Georgia Institute of Technology, 2005, 2005. http://etd.gatech.edu/theses/available/etd-01102006-133806/.
Testo completoAbstract (sommario):
Thesis (Ph. D.)--Electrical and Computer Engineering, Georgia Institute of Technology, 2006.<br>Bertrand Boussert, Committee Member ; Douglas B. Williams, Committee Member ; William T. Rhodes, Committee Member ; Yves Berthelot, Committee Member ; David S. Citrin, Committee Chair.
40
Locquet, Alexandre Daniel. "Chaotic optical communications using delayed feedback systems." Diss., Georgia Institute of Technology, 2006. http://hdl.handle.net/1853/10431.
Testo completoAbstract (sommario):
Chaotic dynamics produced by optical delay systems have interesting applications in telecommunications. Optical chaos can be used to transmit secretly, in real-time, a message between an emitter and a receiver. The noise-like appearance of chaos is used to conceal the message, and the synchronization of the receiver with the chaotic emitter is used to decode the message. This work focuses on the study of two crucial topics in the field of chaotic optical communications.
The first topic is the synchronization of chaotic external-cavity laser diodes, which are among the most promising chaotic emitters for secure communications. It is shown that, for edge-emitting lasers, two drastically different synchronization regimes are possible. The regimes differ in terms of the delay time in the synchronization and in terms of the robustness of the synchronization with respect to parameter mismatches between the emitter and the receiver. In vertical-cavity surface-emitting lasers, the two linearly-polarized components of the electric field also exhibit isochronous and anticipating synchronization when the coupling between the lasers is isotropic. When the coupling is polarized, the linearly-polarized component that is parallel to the injected polarization tends to synchronize isochronously with the injected optical field, while the other component tends to be suppressed, but it can also be antisynchronized.
The second topic is the analysis of time series produced by optical chaotic emitters subjected to a delayed feedback. First, we verify with experimental data that chaos produced by optical delay systems is highly complex. This high complexity is demonstrated by estimating chaos dimension and entropy from experimental time series and from models of optical delay systems. Second, by analyzing chaotic time series, it is shown that the value of the delay of a single-delay system can always be identified, independently of the type of system used and of its complexity. Unfortunately, an eavesdropper can use this information on the delay value to break the cryptosystem. We propose a new cryptosystem with two delayed feedback loops that increases the difficulty of the delay identification problem.
41
Song, Xuegui. "Subcarrier optical wireless communications in atmospheric turbulence." Thesis, University of British Columbia, 2014. http://hdl.handle.net/2429/50010.
Testo completoAbstract (sommario):
In this thesis, we focus on performance study of subcarrier optical wireless communications (OWC) systems in atmospheric turbulence. Laser beam propagating through turbulence channel induces scintillation and phase aberration, which can result in significant performance degradation. The error rate performance of subcarrier OWC systems with lower order phase-shift keying (PSK) over the Gamma-Gamma turbulence channels is investigated using a direct integration method. Such analysis is generalized to M-ary PSK modulated OWC systems over strong atmospheric turbulence channels through a moment generating function approach. Since noncoherent or differentially coherent modulation schemes do not require carrier phase information at the receiver, such modulation schemes can be employed in scenarios where the carrier phase information cannot be tracked accurately. Error rate expressions of such OWC systems with noncoherent or differentially coherent modulation schemes over the Gamma-Gamma turbulence channels are also developed. Asymptotic relative performance of subcarrier OWC systems with noncoherent or differentially coherent modulation schemes with respect to those using coherent modulation schemes is quantified analytically.
Besides atmospheric turbulence, other sources can also introduce performance degradation to an outdoor OWC system. Through our analysis, it is shown that pointing errors can also degrade the performance of an OWC system significantly. The effect of pointing errors together with the Gamma-Gamma turbulence channel can be evaluated using the analytical tools we developed. As another performance impairment source, the effect of carrier phase synchronization error on performance of subcarrier binary PSK and quadrature PSK systems over atmospheric turbulence channels is also studied. In order to quantify the asymptotic noise reference loss for OWC systems over the lognormal channels, a novel auxiliary random variable technique is introduced.
Since the performance of outdoor subcarrier OWC systems is found to be impaired severely under strong turbulence conditions, spatial diversity techniques are introduced to mitigate the effects of turbulence induced fading. Multiple-input multiple-output OWC systems with repetition code and the Alamouti type orthogonal space-time block code are considered for the Gamma-Gamma turbulence channels. The performance analysis confirms that repetition code outperforms orthogonal space-time block code although both schemes achieve full diversity.<br>Applied Science, Faculty of<br>Engineering, School of (Okanagan)<br>Graduate
42
Jafar, Maysam. "Coherent systems for indoor optical wireless communications." Thesis, University of Oxford, 2005. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.427622.
Testo completo
43
Chamberlain, Adam W. "Integrated Surface-Plasmon Waveguides for Optical Communications." UKnowledge, 2005. http://uknowledge.uky.edu/gradschool_theses/258.
Testo completoAbstract (sommario):
Integrated optics present a potentially low cost and higher performance alternative to electronics in optical communication systems. Surface plasmon waveguides (SPWGs) offer a new approach for manipulating light in integrated optical chips. SPWGs provide several advantages over dielectric waveguides. In this study, a fabrication process for SPWGs is developed. SPWGs are fabricated with various lengths and bend radii to allow for study of absorption and bending losses in the waveguides at telecommunications wavelengths (~1550nm). Finite-element method models of straight, bent, and optically coupled waveguides are developed and analyzed.
44
Mirshafiei, Mehrdad. "Ultra-wideband Indoor Communications Using Optical Technology." Thesis, Université Laval, 2013. http://www.theses.ulaval.ca/2013/29408/29408.pdf.
Testo completoAbstract (sommario):
La communication ultra large bande (UWB) a attiré une énorme quantité de recherches ces dernières années, surtout après la présentation du masque spectral de US Federal Communications Commission (FCC). Les impulsions ultra-courtes permettent de très hauts débits de faible puissance tout en éliminant les interférences avec les systèmes existants à bande étroite. La faible puissance, cependant, limite la portée de propaga- tion des radios UWB à quelques mètres pour la transmission sans fil à l’intérieur d’une pièce. En outre, des signaux UWB reçu sont étendus dans le temps en raison de la propagation par trajet multiple qui résulte en beaucoup d’interférence inter-symbole (ISI) à haut débit. Le monocycle Gaussien, l’impulsion la plus commune dans UWB, a une mauvaise couverture sous le masque de la FCC. Dans cette thèse, nous démontrons des transmet- teurs qui sont capables de générer des impulsions UWB avec une efficacité de puissance élevée. Une impulsion efficace résulte dans un rapport de signal à bruit (SNR) supérieur au récepteur en utilisant plus de la puissance disponible sous le masque spectral de la FCC. On produit les impulsions dans le domaine optique et utilise la fibre optique pour les transporter sur plusieurs kilomètres pour la distribution dans un réseau optique pas- sif. La fibre optique est très fiable pour le transport des signaux radio avec une faible consommation de puissance. On utilise les éléments simples comme un modulateur Mach-Zehnder ou un résonateur en anneau pour générer des impulsions, ce qui permet l’intégration dans le silicium. Compatible avec la technologie CMOS, la photonique sur silicium a un potentiel énorme pour abaisser le coût et l’encombrement des systèmes optiques. La photodétection convertit les impulsions optiques en impulsions électriques avant la transmission sur l’antenne du côté de l’utilisateur. La réponse fréquentielle de l’antenne déforme la forme d’onde de l’impulsion UWB. Nous proposons une technique d’optimisation non-linéaire qui prend en compte la dis- torsion d’antenne pour trouver des impulsions qui maximisent la puissance transmise, en respectant le masque spectral de la FCC. Nous travaillons avec trois antennes et con- cevons une impulsion unique pour chacune d’entre elle. L’amélioration de l’énergie des impulsions UWB améliore directement la SNR au récepteur. Les résultats de simulation montrent que les impulsions optimisées améliorent considérablement le taux d’erreur (BER) par rapport au monocycle Gaussien sous propagation par trajet multiple. Notre autre contribution est l’évaluation d’un filtre adapté pour recevoir efficace- ment des impulsions UWB. Le filtre adapté est synthétisé et fabriqué en technologie microstrip, en collaboration avec l’Université McGill comme un dispositif de bande interdite électromagnétique. La réponse fréquentielle du filtre adapté montre une ex- cellente concordance avec le spectre ciblé de l’impulsion UWB. Les mesures de BER confirment la performance supérieure du filtre adapté par rapport à un récepteur à conversion directe. Le canal UWB est très riche en trajet multiple conduisant à l’ISI à haut débit. Notre dernière contribution est l’étude de performance des récepteurs en simulant un système avec des conditions de canaux réalistes. Les résultats de la simulation montrent que la performance d’un tel système se dégrade de façon significative pour les hauts débits. Afin de compenser la forte ISI dans les taux de transfert de données en Gb/s, nous étudions l’algorithme de Viterbi (VA) avec un nombre limité d’états et un égaliseur DFE (decision feedback equalizer). Nous examinons le nombre d’états requis dans le VA, et le nombre de coefficients du filtre dans le DFE pour une transmission fiable de UWB en Gb/s dans les canaux en ligne de vue. L’évaluation par simulation de BER confirme que l’égalisation améliore considérablement les performances par rapport à la détection de symbole. La DFE a une meilleure performance par rapport à la VA en utilisant une complexité comparable. La DFE peut couvrir une plus grande mémoire de canal avec un niveau de complexité relativement réduit.<br>Ultra-wideband (UWB) communication has attracted an enormous amount of research in recent years, especially after the introduction of the US Federal Communications Commission (FCC) spectral mask. Ultra-short pulses allow for very high bit-rates while low power eliminates interference with existing narrowband systems. Low power, however, limits the propagation range of UWB radios to a few meters for indoors wireless transmission. Furthermore, received UWB signals are spread in time because of multipath propagation which results in high intersymbol interference at high data rates. Gaussian monocycle, the most commonly employed UWB pulse, has poor coverage under the FCC mask. In this thesis we demonstrate transmitters capable of generating UWB pulses with high power efficiency at Gb/s bit-rates. An efficient pulse results in higher signal-to-noise ratio (SNR) at the receiver by utilizing most of the available power under the FCC spectral mask. We generate the pulses in the optical domain and use optical fiber to transport the pulses over several kilometers for distribution in a passive optical network. Optical fiber is very reliable for transporting radio signals with low power consumption. We use simple elements such as a Mach Zehnder modulator or a ring resonator for pulse shaping, allowing for integration in silicon. Being compatible with CMOS technology, silicon photonics has huge potential for lowering the cost and bulkiness of optical systems. Photodetection converts the pulses to the electrical domain before antenna transmission at the user side. The frequency response of UWB antennas distorts the UWB waveforms. We pro- pose a nonlinear optimization technique which takes into account antenna distortion to find pulses that maximize the transmitted power, while respecting the FCC spectral mask. We consider three antennas and design a unique pulse for each. The energy improvement in UWB pulses directly improves the receiver SNR. Simulation results show that optimized pulses have a significant bit error rate (BER) performance improvement compared to the Gaussian monocycle under multipath propagation. Our other contribution is evaluating a matched filter to receive efficiently designed UWB pulses. The matched filter is synthesized and fabricated in microstrip technology in collaboration with McGill University as an electromagnetic bandgap device. The frequency response of the matched filter shows close agreement with the target UWB pulse spectrum. BER measurements confirm superior performance of the matched filter compared to a direct conversion receiver. The UWB channel is very rich in multipath leading to ISI at high bit rates. Our last contribution is investigating the performance of receivers by simulating a system employing realistic channel conditions. Simulation results show that the performance of such system degrades significantly for high data rates. To compensate the severe ISI at gigabit rates, we investigate the Viterbi algorithm (VA) with a limited number of states and the decision feedback equalizer (DFE). We examine the required number of states in the VA, and the number of taps in the DFE for reliable Gb/s UWB trans- mission for line-of-sight channels. Non-line-of-sight channels were also investigated at lower speeds. BER simulations confirm that equalization considerably improves the performance compared to symbol detection. The DFE results in better performance compared to the VA when using comparable complexity as the DFE can cover greater channel memory with a relatively low complexity level.
45
Parish, Amanda Jane. "High Birefringence Liquid Crystals for Optical Communications." Master's thesis, University of Central Florida, 2007. http://digital.library.ucf.edu/cdm/ref/collection/ETD/id/3199.
Testo completoAbstract (sommario):
High birefringence ([delta]n>0.4) nematic liquid crystals are particularly attractive for infrared applications because they enable a thinner cell gap to be used for achieving fast response time and improved diffraction efficiency. In this thesis, the mesomorphic and electro-optic properties of several new fluorinated isothiocyanate (NCS) terphenyl and phenyl tolane single compounds and mixtures are reported. The single compounds demonstrated [delta]n~0.35-0.52 in the visible spectral region at room temperature and exhibit relatively low viscosity. It was found that lateral fluorine substitutions and short alkyl chains eliminate smectic phase and lower the melting temperature of the single compounds. However, the consequence of using highly conjugated compounds to improve electro-optic properties is that the nematic phase is exhibited at high temperatures, over 100[degrees]C, and therefore single compounds cannot be used for device applications. Therefore, several mixtures based on the terphenyl and phenyl-tolane compounds were formulated and evaluated. The purpose of mixtures is to find the optimum balance between electro-optic performance and the mesomorphic properties that determine the operating temperature range. It was found that mixture formulations greatly improved mesomorphic properties to produce nematic phase at or near room temperature and suppressed smectic phase to below 0[degrees]C or eliminating completely. The analysis presented evaluates the benefits of lowering the operating temperature versus the consequence of degrading the electro-optic properties.<br>M.S.<br>Optics and Photonics<br>Optics and Photonics<br>Optics MS
46
SANTOS, ALEXANDRE BESSA DOS. "POLARIZATION EFFECTS IN OPTICAL FIBER COMMUNICATIONS SYSTEMS." PONTIFÍCIA UNIVERSIDADE CATÓLICA DO RIO DE JANEIRO, 2005. http://www.maxwell.vrac.puc-rio.br/Busca_etds.php?strSecao=resultado&nrSeq=7013@1.
Testo completoAbstract (sommario):
CONSELHO NACIONAL DE DESENVOLVIMENTO CIENTÍFICO E TECNOLÓGICO<br>Os efeitos que causam limitações nas comunicações ópticas
referentes a
polarização se resumem essencialmente na Dispersão dos
Modos de Polarização
(PMD), nas Perdas Dependentes da Polarização (PDL), e no
Ganho Dependente
da Polarização (PDG). Estes efeitos podem aparecer na
transmissão de forma
isolada ou combinada, gerando distorções no sinal.
Primeiramente estes efeitos
foram estudados individualmente, cada efeito sendo
analisado e quantificado sob
diversos aspectos. Através de uma analise teórica e
experimental foi proposto
uma nova técnica de medida de penalidade de potência
envolvendo os efeitos
estudados. Depois de um estudo detalhado sobre os efeitos
isolados, analisou-se
os efeitos combinados de PMD e PDL. Diversos emuladores de
PMD, elementos
com PDL variável e emuladores de PMD e PDL fizeram parte
de um longo
estudo sobre estes efeitos combinados. Procurou-se
ressaltar a importância e os
cuidados necessários que se deve tomar para a construção
de um emulador de
PMD. Na última etapa, foram estudados os efeitos de PMD e
PDG oriundos de
um sistema utilizando amplificação Raman. Desta forma foi
possível evidenciar,
caracterizar e relacionar os efeitos da polarização nas
fibras ópticas.<br>The polarization effects that cause limitations in optical
communications
are essentially the Polarization Mode Dispersion (PMD),
the Polarization
Dependent Loss (PDL), and the Polarization Dependent Gain
(PDG). These
effects can appear either isolated or in combinations,
generating signal
distortion. These effects were first investigated
individually under different
experimental situations and then combined effects were
studied. A new
technique for measuring the power penalties corresponding
to these effects was
proposed. The combined effects of PMD and PDL in PMD
emulators were
evaluated and quantified. Thumb rules for the manufacture
of PDL-free
emulators were proposed. The effects of PMD and PDG
originated from Raman
amplification were also studied and compared with
theoretical predictions.
47
XAVIER, GUILHERME BARRETO. "PRACTICAL ASSETS FOR FIBER OPTICAL QUANTUM COMMUNICATIONS." PONTIFÍCIA UNIVERSIDADE CATÓLICA DO RIO DE JANEIRO, 2009. http://www.maxwell.vrac.puc-rio.br/Busca_etds.php?strSecao=resultado&nrSeq=14226@1.
Testo completoAbstract (sommario):
COORDENAÇÃO DE APERFEIÇOAMENTO DO PESSOAL DE ENSINO SUPERIOR<br>CONSELHO NACIONAL DE DESENVOLVIMENTO CIENTÍFICO E TECNOLÓGICO<br>As comunicações quânticas estão rapidamente integrando-se às redes de fibras
ópticas, entretanto muitos desafios de engenharia ainda existem para essa
aglutinação. Esta tese discute algumas soluções práticas para a melhoria de
aplicações reais em comunicações quânticas em fibras ópticas. No primeiro
experimento uma fonte de pares de fótons emaranhados não-degenerados, de
banda-estreita, empregando conversão espontânea paramétrica descendente
(CEPD) é utilizada para demonstrar a viabilidade da distribuição quântica de
chaves (DQC) através de 27 km de fibras ópticas, com o canal de sincronismo
presente na mesma fibra com uma separação de 0.8 nm em comprimento de onda.
A outra demonstração utilizou uma fonte heráldica de fótons únicos também
baseada em CEPD para a realização de DQC através de 25 km de fibras ópticas
com a utilização do protocolo de decoy states pela primeira vez. Houve também
um estudo dos impactos gerados por ruído Raman espontâneo causado por um
canal óptico clássico presente na mesma fibra que o canal quântico. Um protocolo
para gerar números verdadeiramente aleatórios em um sistema de DQC
independente da taxa de transmissão do sistema é proposto, e um experimento
prova-de-princípio demonstra a idéia. Finalmente um sistema de controle
automático de polarização é utilizado para a realização de uma sessão de DQC
através de 16 km de fibras ópticas utilizando codificação em polarização, mesmo
sob a presença de um embaralhador rápido do estado de polarização.<br>Quantum communications is quickly becoming integrated within fiber optical
networks and still many engineering challenges remain towards this interweaving.
This thesis deals with some practical solutions toward improving real-world
applications in quantum communications within optical fibers. In the first
experiment, a non-degenerate narrowband entangled pair single-photon source
based on spontaneous parametric down-conversion (SPDC) is used to show the
feasibility of performing quantum key distribution (QKD) through 27 km of
optical fiber, with the synchronization channel wavelength multiplexed in the
same fiber with a channel spacing of just 0.8 nm. A second experiment uses a
heralded single-photon source also based on SPDC to perform QKD over 25 km
of optical fiber with the decoy state modification for the first time. Then there is a
study of the problems caused by spontaneous Raman induced noise due to the
presence of a classical signal in the same fiber as the quantum channel. A protocol
to generate truly random numbers in a QKD setup independent of the system s
transmission rate is proposed, and a proof-of-principle experiment demonstrates
the idea. Finally an automatic polarization control system is used to perform a
QKD session over 16 km of optical fiber using polarization encoding, even in the
presence of a fast polarization scrambler.
48
Chi, Danny T., and Nien-Lou Li. "DPPM Optical Communications and Reed-Solomon Codes." International Foundation for Telemetering, 1992. http://hdl.handle.net/10150/608918.
Testo completoAbstract (sommario):
International Telemetering Conference Proceedings / October 26-29, 1992 / Town and Country Hotel and Convention Center, San Diego, California<br>Pulse position modulation (PPM) has many attractions for optical communication over
deep space and for intersatellite communications. This paper describes a variate of PPM,
known as differential pulse position modulation (DPPM) which can double the data
throughput relative to PPM. We begin this paper with a survey of various laser sources and
laser modulation techniques used in modem space optical communications. We then
discuss the advantages of the combination of DPPM and Reed-Solomon (RS) codes.
49
Chitnis, Danial. "Single photon avalanche diodes for optical communications." Thesis, University of Oxford, 2013. http://ora.ox.ac.uk/objects/uuid:5fd582dd-8167-4fe4-88f8-871ba905ade1.
Testo completoAbstract (sommario):
In order to improve the sensitivity of an optical receiver, the gain and the collection area of the photo-detectors within the receiver should be increased. Detectors with internal gain such as avalanche photodiodes (APD) are usually used to increase the sensitivity of the receiver. One problem with APDs is the sensitivity of their gain to their bias voltage, which makes them challenging to be fabricated in a standard CMOS process due to variations in their gain. However, when an APD is biased over its breakdown voltage, it is sensitive to a single photon, hence, referred to as a single photon avalanche diodes (SPAD). The SPADs are photon-counting detectors, which are less sensitive to their bias voltage, and can be integrated with rest of the electronic circuitry that form an optical receiver. An avalanche diode requires dedicated circuits to be operated in the SPAD mode. These circuits make the diode insensitive to an incident photon for a duration that is known as deadtime. Unfortunately, The collection area of the PD, APD, and SPADs are limited to their capacitance. Hence, a large photo-detector leads to a larger capacitance, which reduces the bandwidth of the receiver. In this thesis, a photon counting optical receiver based on an array of SPADs is proposed which increases the collection area with a low output capacitance. The avalanche diode and peripheral circuits which operate and readout-out the SPAD array are fabricated in the commercially available UMC 0.18 μm CMOS process. Initially, the avalanche diode is tested and characterised. A high performance circuit is then designed and tested which is able to achieve short deadtimes up to 4 ns. Once the photon counting operation of the SPAD is verified, a numerical model is developed to investigate the influence of several factors, including the deadtime, on the performance of the photon-counting detector in a communication link. Based on the simulation results, which show the advantages of an array over a single detector, a prototype detector array of 64 asynchronous SPADs is designed and tested. This array uses a high-speed readout mechanism which is inspired by the current steering digital-to-analogue converters. Bit error ratio tests (BERT) verify the photon counting capability of the proposed detector, and a bit error rate of 1E-3 has been achieved at data rate of 100 Mbps. In addition, the array of SPAD is compatible with a front-end of conventional optical receiver which uses a photodiode as a photo detector.
50
Tran, Tuan-Anh. "Multiple-input multiple-output optical wireless communications." Thesis, University of Oxford, 2013. http://ora.ox.ac.uk/objects/uuid:094fbe23-88c3-49c4-b64b-a1de40674123.
Testo completoAbstract (sommario):
Visible-light optical wireless communications (OWC) is a potential technology that can help resolve the crowdedness of the radio-frequency bands, whilst conveniently exploiting energy-saving light-emitting diodes (LEDs) as transmitters for both illumination and communications. Since there usually are many LEDs in a lighting unit, OWC has a multi- input multi-output (MIMO) geometry which, thanks to its channel diversity, can offer wireless local networks at data-rates many times higher than possible with single-channel systems. In such systems, MIMO-detection methods to separate the different optical channels play an important role in improving the system performance by helping reduce cross-talk between channels. To measure the performance of a particular geometry for MIMO communications, a simulation study, reported in this thesis, found that, amongst the signal- independent metrics, the condition number may be used as a rough predictor of the performance, whilst the channel Signal-to-Interference-and-Noise Ratio (SINR) is the most appropriate for geometry assessment. Combined with the fact that the overall performance of a MIMO system is mostly dominated by its worst channel, this indicates that the most effective way to improve the system performance is to maximise the worst channel’s SINR. One of the possible solutions to improving the SINRs is to use holograms to steer the transmitter images such that their distributions over the photo-detectors reduce overlaps. As LEDs emit partially-coherent light, the beam steering has to be carried out with partially- coherent illumination. By using two lenses to parallelise and collect partially-coherent light before and after the hologram, respectively, the source and image intensity distributions, and the autocorrelation of the hologram can be related in a succinct mathematical relationship. This leads to the development of three computational algorithms based on the autocorrelation function to obtain a quantised hologram with the desired beam-steering capability. These algorithms have their cost functions and performance comparison done at the hologram plane instead of the image plane, which therefore takes less time than traditional image-based methods. Specifically, one of these algorithms is able to save significant time over both the other autocorrelation-based algorithms and the direct binary-search, by 33% and by 50% respectively. A simulation-based study and a corresponding experiment, both reported in this thesis, found that the one of the proposed algorithms had poor power efficiency, whilst the other two were both highly effective in generating digital holograms with precise and power-efficient beam-steering performance. Of these two algorithms, one had superior time performance and was likely the best of the three proposed autocorrelation-based algorithms for generating beam-steering holograms. MIMO-OWC simulation also demonstrated the capability of using beam-steering holograms to design the channel and improve the system performance. Combining reported findings, a strategy can be devised to optimise the throughput of an imaging MIMO-OWC system for a given transmitted power.