In the first part of this thesis, the stimulated Raman scattering (SRS) effect in optical time domain reflectometry (OTDR) on-line monitoring fiber transmission systems are investigated. We have investigated the distortion of baseband video picture arising from the 1.65 £gm OTDR-induced SRS effect in 1.55 £gm amplitude modulation with vestigial sideband (AM-VSB) cable television (CATV) transmission system. The baseband video-picture distortion in appearance with ¡§faintly white horizontal thins lines¡¨ on the TV picture is observed. The baseband video-picture distortion disappearing is demonstrated in the 1.31 £gm OTDR on-line monitoring 1.55

In this thesis, we investigate the OTDR on-line monitoring feasibility of forward- and backward-pumping distributed Raman fiber amplifiers (FRAs) transmission systems with different OTDR probe lights. In the experiments, we choose the large effect area fiber ( LEAF ) with 50 km long as gain medium of Raman amplifiers. Two different OTDR probe lights with 1.31£gm and 1.65£gm wavelengths are separately used for on-line monitoring forward- and backward-pumping distributed FRAs. We find that the OTDR probe lights affect the optical gain of the 1.55 mm data signal. In the experiments, for the forward-pumping scheme using 1.3£gm OTDR probe light on-line monitor, the optical gain of the 1.55 mm data signal increases 0.2 dB, but for the backward-pumping scheme, that only increases 0.1 dB. In the forward-pumping scheme using 1.65£gm OTDR probe light on-line monitor, the optical gain of the 1.55 mm data signal decreases 0.6 dB, but for the backward-pumping scheme, that only decreases 0.2 dB. We also find the OTDR on-line monitoring distribution fiber Raman amplifiers Systems makes OTDR traces distortion. In an aspect of system BER performance, the system power penalty on account of the OTDR monitoring in both 10 Gb/s forward- and backward-pumping schemes is trivial¡@. In the forward-pumping scheme using 1.3£gm OTDR probe light on-line monitor, the power penalty is about 0.1 dB, but for the backward-pumping scheme that is about 0.05 dB. As the forward-pumping scheme using 1.65£gm OTDR probe light, the power penalty is about 0.2 dB, but for the backward-pumping scheme that is about 0.07 dB.

In this thesis, I demonstrate a single­photon Light Detection And Ranging, (LiDAR)system operating at 1550 nm capable of reconstructing 3D environments live withmm resolution at a rate of 400 points per second using eye­safe laser pulses. Thesystem was built using off­-the-­shelf optical components and analysis was performedusing open-­source software. I utilise a single superconducting nanowire single photondetector (SNSPD) with 19 ps time jitter and 85% detection efficiency to achieve a 4 psdepth resolution in live measurements. I also show that by performing slightly moretime costly post analysis of the data it is possible to increase the details and smoothnessof the images. Furthermore, I show that the same LiDAR system and much of the algorithms usedfor 3D LiDAR can be used to perform Optical Time Domain reflectrometry (OTDR)measurements. I demonstrate that the system can identify interfaces between differentrefractive mediums such as fibre to fibre or fibre to air couplings with a depth resolutionof 9 mm along a single line. Using these reflections, I also show that the systemcan identify flaws in optical fibres as well as measure certain characteristics suchas absorption coefficient due to Rayleigh scattering or thermal expansion. Lastly, Idemonstrate that the same OTDR principles used in fibres can be applied to free­s-paceoptical setups and that the system can identify specific optical elements as well asmeasure the quality of the alignment of an optical system. / I detta projekt demonstrerar jag ett enstaka foton Light Detection And Ranging,(LiDAR) system som använder ljus med 1550 nm våglängd som är ofarliga för ögon.Systemet kan återskapa 3D miljöer i realtid med 400 punkter per sekund med mmprecision. Systemet är byggt med kommersiellt tillgängliga komponenter och all dataanalys utfördes med open­source mjukvaran ETA. Jag använder en superconductingnanowire single photon detector, (SNSPD) med 19 ps timing jitter och 85 % effektivitetför att uppnå en precision på 4 ps i mätningarna. Jag visar också att genom utföramer tidskrävande post­analys av datan så är det möjligt att öka upplösningen ochjämnheten i bilderna. Utöver detta visar jag att samma LiDAR system och algoritmer kan användas för attutföra Optical Time Domain reflectrometry, (OTDR) mätningar. Jag visar att systemetkan urskilja olika reflektioner från fiber till fiber och fiber till luft kopplingar. Med hjälpav dessa reflektioner visar jag också att det är möjligt att identifiera brister i optiskafiber samt mäta olika egenskaper av fibern som absorbtions koeffcient eller termiskkontraktion. Slutligen visar jag att samma principer av OTDR som används i fiber kantillämpas till free­-space optiska system och att det är möjligt att identifera olika optiskaelement samt bedömma linjeringen av det optiska systemet.

Master thesis is focused on creating graphical user interface for the sensorical system based on Phase-OTDR. Theoretical part describes optical fibers, explains the principle of Bragg gratings, their production and their use in sensors. Methods of optical fiber attenuation and phase OTDR measurement are also described. Other part is focused on LabVIEW programming software and utilization of sensorical system and its components. Practical part deals with the user interface itself, which consists of two tabs. The first tab is designed for evaluation and display of measured data. The second tab is used to control and set up system components. Both of these tabs are further subdivided into other subtabs. Regarding the conclusion, further development of the program and options of hardware replacement for improving this sensorical system in the future will be discussed.

A distributed fiber optic intrusion sensor capable of detecting intruders from the pressure of their weight on the earth's surface was investigated in the laboratory and in field tests. The presence of an intruder above or in proximity to the buried sensor induces a phase shift in light propagating along the fiber which allows for the detection and localization of intrusions. Through the use of an ultra-stable erbium-doped fiber laser and phase sensitive optical time domain reflectometry, disturbances were monitored in long (several km) lengths of optical fiber. Narrow linewidth and low frequency drift in the laser were achieved through a combination of optical feedback and insulation of the laser cavity against environmental effects. The frequency drift of the laser, characterized using an all-fiber Mach Zehnder interferometer, was found to be less than 1 MHz/min, as required for operation of the intrusion detection system. Intrusions were simulated in a laboratory setting using a piezoelectric transducer to produce a controllable optical phase shift at the 2 km point of a 12 km path length. Interrogation of the distributed sensor was accomplished by repetitively gating light pulses from the stable laser into the sensing fiber. By monitoring the Rayleigh backscattered light with a photodetector and comparing traces with and without an induced phase shift, the phase disturbances were detected and located. Once the feasibility of such a sensor was proven in the laboratory, the experimental set up was transferred to Texas A&M's Riverside Campus. At the test site, approximately 40 meters of fiber optic cable were buried in a triangle perimeter and then spliced into the 12 km path length which was housed inside the test facility. Field tests were conducted producing results comparable to those found in the laboratory. Intrusions over this buried fiber were detectable on the φ-OTDR trace and could be localized to the intrusion point. This type of sensor has the potential benefits of heightened sensitivity, covertness, and greatly reduced cost over the conventional seismic, acoustic, infrared, magnetic, and fiber optic sensors for monitoring long (multi-km) perimeters.

Dense wavelength-division multiplexing (DWDM) technology are the provide solutions to increase the capacity of network. With the growth of using the OADM in DWDM system, it is more and more important to research the fault-locating fiber-link in-service supervisory technique for enhance the system reliability. Optical Time Domain Reflectometer (OTDR) is a popular tool to offer an in-service fault-locating of fiber link in fiber-optic transmission systems. But in the DWDM network, this technique is never be used for in-service supervisory application on the system. Are different OADM structures will affect the in-service OTDR monitoring? Since OTDR operates with high peak powers, the stimulated Raman scattering (SRS) effect in the conventional transmission fiber gives rise to power depletion of the data signal, and may degrade the bit-error-rate (BER) performance. In this work, we investigate the in-service 1.65-£gm OTDR monitoring supported FBG-based OADM structures. We improved FBG sandwiched between a pair of three-port optical circulator and multi-port optical circulator (MOC) FBG-based OADM to support OTDR monitoring, and research the technique of in-service OTDR monitoring for FBG-based, MZ-FBG based OADM system. The system bit-error-rate due to the OTDR monitoring a 10-Gb/s long (> 80 km) distance fiber link is examined. Negligible system power penalty, due to the OTDR monitoring, of both structures in 10 Gb/s dense wavelength division multiplexing (DWDM) link is achieved. That is mean the system with OTDR monitoring should have the in-service fault-location monitoring capability to enhance network reliability. We also investigate the in-service OTDR 1.65-£gm OTDR monitoring on the distributed Raman application system.

The statistics of the phase dependent optical time-domain reflectometer have been analyzed. The optical fiber is modeled by the use of a discrete set of reflectors positioned randomly along the fiber. The statistics of the reflected light from a traveling pulse are derived. The statistics of the signal are used to calculate the characteristics of shot noise in the photodetector, and the probability that noise of certain intensity will occur. An estimation of the backscattered power is made by calculating the fraction of the backscattered power that is captured in a guiding mode. Upper power limits are calculated by considering nonlinear optical effects. An estimation of noise from thermally excited sound waves, amplified by Brillouin scattering, is derived. This noise considers the parameters of a photodetector, giving a model for the noise in the measurable photocurrent. Two models are used to describe the fading probability of the signal. The first model, based on the Fabry-Perot interferometer with a random phase perturbation in the middle, is used to calculate the probability that the whole signal vanishes for any value of phase perturbation. The second model, by calculating the correlation between two signals, one perturbed and one unperturbed, predicts the fading of the signal of interest. The present work gives the theoretical basis for the phase dependant Optical Time Domain Reflectometry, allowing its optimization and setting the fundamental limitations to the performance of the system.

A distributed fiber optic intrusion sensor capable of detecting intruders from the pressure of their weight on the earth's surface was investigated in the laboratory and in field tests. The presence of an intruder above or in proximity to the buried sensor induces a phase shift in light propagating along the fiber which allows for the detection and localization of intrusions. Through the use of an ultra-stable erbium-doped fiber laser and phase sensitive optical time domain reflectometry, disturbances were monitored in long (several km) lengths of optical fiber. Narrow linewidth and low frequency drift in the laser were achieved through a combination of optical feedback and insulation of the laser cavity against environmental effects. The frequency drift of the laser, characterized using an all-fiber Mach Zehnder interferometer, was found to be less than 1 MHz/min, as required for operation of the intrusion detection system. Intrusions were simulated in a laboratory setting using a piezoelectric transducer to produce a controllable optical phase shift at the 2 km point of a 12 km path length. Interrogation of the distributed sensor was accomplished by repetitively gating light pulses from the stable laser into the sensing fiber. By monitoring the Rayleigh backscattered light with a photodetector and comparing traces with and without an induced phase shift, the phase disturbances were detected and located. Once the feasibility of such a sensor was proven in the laboratory, the experimental set up was transferred to Texas A&M's Riverside Campus. At the test site, approximately 40 meters of fiber optic cable were buried in a triangle perimeter and then spliced into the 12 km path length which was housed inside the test facility. Field tests were conducted producing results comparable to those found in the laboratory. Intrusions over this buried fiber were detectable on the φ-OTDR trace and could be localized to the intrusion point. This type of sensor has the potential benefits of heightened sensitivity, covertness, and greatly reduced cost over the conventional seismic, acoustic, infrared, magnetic, and fiber optic sensors for monitoring long (multi-km) perimeters.

[pt] Apesar da alta sensibilidade alcançada por Fotodetectores comercialmente disponíveis, a implementação de circuitos de gerenciamento é capaz de fortalecer a robustez das medidas, criando um aparato com mais recursos em aplicações específicas. Duas aplicações práticas dessa hipótese são apresentadas em contextos diferentes, Criptografia Quântica e Monitoramento de Fibras Ópticas fazendo uso da plataforma FPGA. / [en] Despite the high sensitivity reached by Photon Detectors so far, the implementation of a background managing system often enforces the robustness of measurements thus creating a resourceful apparatus for specific applications. In this document, the management tools offered by Software Defined Hardware (SDHs) is put to test. By associating the power of FPGAs and Photon Detectors, enhanced measurement stations were assembled. Two different applications, a Bell State Projection Analysis Station and a Photon Counting Optical Time Domain Reflectometry (v-OTDR)Automatic Setup, are presented. Even though both experiments involve the detection of single photons, the background technologies differ drastically.

[pt] A crescente demanda do uso de sistemas de comunicação óptica, seja pelo aumento do número de usuários ou pela quantidade de informação enviada, requer um aumento substancial na necessidade de desenvolvimento de novos sistemas e componentes. A reectometria óptica no domínio do tempo (OTDR) é a técnica mais empregada para detecção de falhas em enlaces de fibra óptica. Em alguns tipos de rede óptica, como é o caso das redes ópticas passivas (PONs), as perdas nos enlaces são muito elevadas devido à presença de splitters, que dividem o sinal para cada usuário (no cenário FTTH) ou cada grupo de usuários (FTTB / FTTA), o que diminui consideravelmente a máxima distância atingida pelo OTDR. Em termos de componentes aplicados à comunicação óptica, aqueles utilizados para a amplificação óptica são de grande importância. Entre eles estão presentes os amplificadores ópticos de semicondutores. Uma forma de vencer as limitações impostas pelas altas perdas está no emprego de um amplificador óptico semicondutor (SOA), que ao mesmo tempo amplifica o sinal e funciona como uma chave, inibindo a emissão de ASE nos intervalos entre os pulsos do OTDR. Ainda assim, o ganho adicional pode ser insuficiente devido à baixa potência de saturação do SOA. Neste trabalho, será desenvolvido experimentalmente um método para superar a limitação de saturação de um SOA e permitir maiores ganhos de amplificação para pulsos de OTDR. O conceito básico consiste em se aproveitar do fato de que o ciclo de uso de um OTDR é relativamente baixo, o que permite subdividir os pulsos em sub-pulsos, amplificá-los um a um e depois recombiná-los, de forma transparente ao OTDR. Com base na ideia proposta acima, nesta dissertação de mestrado terão avaliados métodos usando a polarização e o comprimento de onda dos pulsos. / [en] The growing demand of using optical communication systems, either by increasing the number of users or the amount of information sent, requires a substantial increase in the need to develop new systems and components. The optical time domain re ectometry (OTDR) is the most common technique for detecting faults in fiber optic links. In some types of optical network, such as passive optical networks (PONs), losses in the links are very high due to the presence of splitters that divide the signal to each user (in FTTH scenario) or each user group ( FTTB / FTTA), which considerably reduces the maximum distance reached by the OTDR. In terms of components used for optical communication, those used for optical amplification is of great importance. Among them are present optical semiconductor amplifiers. One way to overcome the limitations imposed by high losses is the use of a semiconductor optical amplifier (SOA), which at the same time amplifies the signal and acts as a key, inhibiting the emission ASE in the intervals between the OTDR pulses. Still, the additional gain may be insufficient due to low saturation power SOA. This work will develop experimentally a method to overcome the limitation of saturation of an SOA and allow higher amplification gains for OTDR pulse. The basic concept is to take advantage of the fact that the use of an OTDR cycle is relatively low, which allows to split the pulses into sub-pulses, amplify them one by one and then recombine them in a transparent manner to the OTDR. Based on the idea proposed above, this master thesis will be evaluated using methods polarization and wavelength of the pulses.