[pt] Um estudo sistemático da metodologia de determinação da probabilidade do DGD ultrapassar um determinado valor máximo foi apresentado. A metodologia foi discutida sob o ponto de vista teórico, obtendo-se o resultado a partir de uma base de dados recebidos de fabricantes de cabos de fibra óptica. Efetuou-se a comparação com os dados coletados destes mesmos cabos, porém já implantados em backbone. O resultado deste comparativo sistemático, foi apresentado sob a forma de estatística do valor de DGD ultrapassar o valor máximo estabelecido na norma ITU-T, para sistemas de 10 e 40Gbps. A partir dos resultados obtidos foi importante a identificação de erros que remontam a origem do processo de fabricação de cabos de fibras ópticas, a restrição na sensibilidade dos equipamentos de medição o que leva a uma superestimação da probabilidade do DGD ultrapassar um certo valor máximo e o próprio conceito do guia TIA/EIA TSB107, que define o método para a obtenção destes resultados. A criticidade destes resultados pode levar a um erro na escolha de um sistema óptico de transmissão podendo gerar prejuízos muito significativos, sejam financeiro ou temporal. Foram propostas três recomendações para direcionar a metodologia a uma previsão mais confiável dos resultados obtidos a partir do método 2 TIA/EIA TSB107, gerando mais conforto para o projeto de sistemas de alta capacidade. / [en] A systematic study of the methodology that determines the probability of the DGD overcomes a settled maximum value was presented. The methodology was discussed in a theoretical way; the values were based on a database received from optical fibers manufacturers/cablers. A comparison was conducted taking in consideration these same cables already installed in two backbones. The result of this systematic comparison was presented, as a statistic of the DGD value exceeds certain maximum value established by the standard ITU-T for systems from 10 to 40Gbps. Based on these results, the identification of mistakes that ascends the beginning of manufacture process of the optical fiber cables was important. The restriction of the sensibility of measurement devices leads to a overestimation of the probability of the DGD exceeds a given maximum value and the concept of the guideline TIA/EIA TSB107, that defines the methodology of acquisition of these results. These critical results could lead to a mistake choosing the optical system transmission and cause loss profit as well as time delay in a project. There were proposed three recommendations in order to guide the methodology for a trustful preview of the obtained results from TIA/EIA method 2, offering more comfort for optical high capacity system design.

[pt] Este trabalho propõe um estudo da PMD (Polarization Mode Dispersion) para um sistema com múltiplos comprimentos de onda. Para tanto, apresenta uma ferramenta computacional que permite simulações do comportamento do DGD (Dispersion Group Delay) em função da variação contínua temporal. Estes dados são validados através da comparação com simulações convencionais, em função do comprimento de onda. Também são apresentados métodos de controle de polarização e compensação de PMD utilizando o simulador temporal desenvolvido. Foram realizadas medidas experimentais analisando o sinal de potência de RF de saída e a polarização de saída do sinal para diferentes canais WDM (Wavelength Division Multiplex). / [en] This work proposes a PMD (Polarization Mode Dispersion) study in WDM communications systems. A simulation tool for the calculation of the statistics and correlations of PMD-related variables in time domain is presented here. Calculations are performed in time domain, allowing the simulation of the temporal evolution of differential group delay (DGD), principal states of polarization (PSP) among others. Results are validated with predictions from spectral calculations. A polarization control and a PMD mitigation scheme are also presented.

This thesis firstly theoretically describes phenomena which appear in optical fiber transmission. The theoretical part of the thesis deals with linear and non-linear phenomena, and later on proceeds to dispersions with a more significant effect on the optical transmission quality. It puts polarization to the centre of the phenomenon called Polarization mode dispersion (PMD), which is the main object of our interest. It leads to a deep PMD description from the point of view of polarization states, limit values, compensation methods, and methods of measurement. The practical part of this thesis deals with a draft of PMD measurement via Fixed Analyzer method. For the purposes of this measurement, we used the optical spectral analyzer MS9740A. In order to compare measured values, the proposed idea then proceeds to the reference measurement by using a modular platform EXFO FTB--200 in combination with CD/PMD module EXFO FTB-5700. Results of measurements have been evaluated for the limit values defined by the standard. In the last chapter of this thesis, the reference measurements are compared to the Fixed Analyzer method. All the advantages and disadvantages of individual measurement methods are identified at the end of this chapter too.

The master thesis discusses physical causes of light polarization and problems brought by nascence of Polarization Mode Dispersion (PMD). These problems occur especially by high speed systems on optical cable traces. The thesis deals with actuation of transmitted signal by influence of Inter Symbol Interference and it also deals with methods for its measuring and compensation. As a results of measurements are in text presented data provided by EXFO Electro-Optical Engineering Inc. Company. Significant part of the thesis focuses on optical link Bit Error Rate (BER) which is connected with Signal to Noise Ratio (SNR) and signal quality (Q-factor). Further on it is possible to find in text about so called eye diagram which is display mode that shows influence of communication channel on shape of the transmitted signal. To this diagram is related another one called constellation diagram which describes modulation mode and makes it possible to map dispersion of signal points around their nominal values. In connection with so called trajectory it makes vector diagram. Practical part includes depiction of these diagrams in MATLAB development environment.

Master’s thesis engages in the impact of polarization mode dispersion on optical communication system. Polarization mode dispersion is mathematically described by Stoke’s and Jone’s space and ensure the theoretic causes of the rise of polarization mode dispersion that are divided on the external and internal effects. On the basis of these effects grow up a differential group delay (DGD) which makes causes that individual polarization modes have between them a time delay and limitation of maximum bit rate. Then master´s thesis analyses the influence of the polarization mode dispersion on the pulse enlargement and on the modulation signal. In this work, there are described the most applicated optical modulation formats. Polarization mode dispersion has also influence on the bit error rate of optical fibre link and closing of eye diagram too. Eye diagram is used to view the transmission characteristics and diagnoses the channel errors. Eye diagram is connected with the definitions as a bit error rate (BER) and signal-to-noise ratio (SNR) that are explained in this work too. Following the gained experiences it was designed an useful graphic interface to display the effect of the polarization mode dispersion on the transmitted signal. Realization of the graphic interface is created in the program MATLAB. In Matlab-Simulink are created six models according to the kind of modulations with characteristic AWGN (Additive White Gaussian Noise) channel. Program was tested for a typical values. In all calculations it is counted only with the losses that are caused by the polarization mode dispersion. It is not calculated with the losses that are caused by a chromatic dispersion and attenuation. At the end of this work are evaluated all types of modulation formats depending on the polarization mode dispersion, optical fibre length, price and complexity of the realization. Atteined results of my master’s thesis are compared with two foreign articles.

The dusky grouper Epinephelus marginatus (Lowe 1834), is a protogynous sequential hermaphrodite and is considered to be one of the most important fish species in the Mediterranean Sea. It is a K-strategist, being slow growing and late maturing, and this, coupled with its reproductive biology and relatively sedentary behaviour, has made it extremely sensitive to overexploitation, leading it to be classified by the IUCN as an endangered fish species. Wild dusky grouper have suffered from disease outbreaks in the past decade, leading to mass mortalities across the Mediterranean Sea, including Libyan coastal waters. These mortalities have mostly been attributed to Nodavirus infections. In Europe and Brazil, efforts are in place to culture this fish for commercial grow-out and stock enhancement programmes. In Libya, the dusky grouper is consumed regularly and is considered a prime-eating fish. Its importance for the Libyan internal market, as well as its potential for export, makes it an ideal candidate for future Libyan aquaculture activities. Given the scarce literature regarding the dusky grouper in Libya, this study aimed first to assess dusky grouper fisheries, spawning seasons and to identify the main threats that the fishing sector poses for wild stocks. Second this study aimed to determine the health status of wild dusky grouper offered at a local fish market in the capital Tripoli, in order to identify pathogens, pathologies or other health issues that might pose a hazard to cultured populations but also to remaining wild dusky grouper stocks. To achieve these aims, twelve field surveys spanning the period of 2013-2015 were conducted. From these surveys, it was established that the dusky grouper is captured throughout the year, including the spawning season. Fish sizes offered for sale ranged between 20-92 cm total length (TL), with the fish being sold from local fishing grounds around Tripoli, but also from as far as Benghazi, 1300 km to the east of Tripoli. The dusky grouper is principally caught in artisanal fisheries and by spearfishing, with approximately 300 spear-fishermen serving one particular fish market in Tripoli that was a focus in this study, and with dusky grouper being one of their main targets. Over the period of the survey, 267 landed dusky grouper were inspected for visible lesions prior to sampling. A total of 50 dusky grouper with sizes ranging from 27- 66 cm TL including the gonads from a further five fish measuring 66-92 cm TL that were sampled separately and examined to assess the stage of sexual maturity and to look for the presence of parasitic infections mainly affecting the gills, skin and gonads. The spawning season was found to extend from May to early September, with females ranging between 39-68 cm TL, males measuring 57-92 cm TL, and transient fish measuring 58-68 cm TL. From otolith readings of 8 fish, the youngest fish was a 3 year old juvenile of 28 cm TL and the oldest was an 8-9 year old 56 cm TL female. Whilst the highest prevalence of parasitic infection was found to be monogenean infection of the gills, with 100% prevalence, followed by gnathiid isopods infecting the oral cavity with 92% prevalence, it was the nematode Philometra sp. infecting post-spawning ovaries at 52% prevalence, that gave the highest apparent pathological impact. Necrosis potentially attributed to Philometra sp. in one particular ovary, was at a level likely to have caused complete parasitic castration, while others showed varying levels of probable functional reduction. The pathologies described need further investigation, especially in relation to possible synergies between Philometra sp. and bacteria in causing the necrosis. From the 267 inspected dusky grouper, 55 fish ranging in size from 42-92 cm TL were observed to be affected by external skin lesions of unknown aetiology. Twenty-six of these fish were sampled, having lesions at various stages of severity, and 5 further unaffected fish were used for histological assessment of the skin as negative controls. Histopathologically, the lesions comprised a multifocal, unilateral or bilateral dermatitis, involving the epidermis, superficial dermis and scale pockets, and sometimes, in severe cases, the hypodermis. Severe lesions had marked epidermal spongiosis progressing to ulceration. Healing was observed in some fish. Bacteria and fungi could be isolated from severe lesions, although they were not seen histopathologically in early-stage lesions. By contrast, metazoan parasite eggs were observed in the dermis and epidermis of some fish with mild and moderate dermatitis. Unidentified gravid digenean trematodes, carrying similar eggs, were also seen within the blood vessels of the deep and superficial dermis. The newly described condition was termed dusky grouper dermatitis (DGD). DGD’s geographical distribution along the Libyan coastline was investigated using a novel application of the social media network Facebook. Using Facebook, it was possible to document skin lesions of dusky grouper in Libyan waters from images attached to the entries of spear-fishermen. Thirty two Facebook accounts and 8 Facebook groups posting from 23 Libyan coastal cities provided a retrospective observational dataset comprising a total of 382 images of dusky grouper caught by spearfishing from December 2011-December 2015. Skin lesions were observable on 57 / 362 fish, for which images were of sufficient quality for analysis, giving a minimal prevalence for lesions of 15.75%. Only dusky grouper exceeding an estimated 40 cm total length exhibited lesions. The ability to collect useful data about the occurrence and geographical distribution of pathological conditions affecting wild fish using social media networks, demonstrates their potential utility as a tool to support epidemiological studies and monitor the health of populations of aquatic animals. The gravid digenean trematode described from mild lesions of five fish was identified using reconstruction through histological sectioning as belonging to the Family Aporocotylidae Odhner, 1912. This is the first description of a blood fluke from the dusky grouper, as well as from dermal blood vessels. The parasite was relatively long; the longest section of the parasite that could be measured was 1500 µm and 20-80 µm in width, while the total length of the parasite was estimated at 1500-2000 µm. Minute tegumental spines, possibly covering only a few parts of the parasite, were seen from some cross-sections. The parasite had one post-testicular ovary, which might overlap the testis, a pre-ovarian ascending uterus, and a post-ovarian descending uterus. It also possessed an oesophagus surrounded by oesophageal glandular cells and a pre-ovarian and pre-testicular extension of the vitelline cells, mostly at the level of the ascending uterus. The parasite was observed to be intra-vascular, the uterine lumen varies in size to accommodate between 1-7 eggs. The uterine eggs were embryonated and observed to span several stages of maturation. Eggs were also found in the dermal blood vessels, in the dermis, and in the epidermis, with the latter appearing to provide a potential route of egress of eggs into the environment. The extra-uterine eggs were 23.5 to 37.52 µm long and contained a ciliated miracidium. The eggs seemed to elicit a mixed inflammatory reaction, with degranulation of eosinophilic granular cells attached to the external surface of some of the eggs within the blood vessels but also the dermis. From observations made in the current study, this parasite appears to be a new species, most closely allied to none of the currently described Aporocotylidae genera. / In summary, the present study has demonstrated that the dusky grouper is extensively fished in Libya without discrimination to sizes and season, by both artisanal and spearfishing, with the latter as one of the main fishing methods, posing treats to the spawning potential and conservation of dusky grouper in Libya. The philometrid infecting the ovaries has a potential to reduce fecundity or to result in parasitic castration of wild broodstock. Gill-infecting monogeneans might represent a hazard for all stages of dusky grouper production. Dusky grouper dermatitis is a skin lesion, although there are no indications that infections may result in mortalities. Under culture conditions, however, this might change due to increase bacterial loads, which might lead to secondary bacterial infection. The presence of skin lesions would undoubtedly reduce the market value of whole fish. These findings are important for existing wild stocks, and for future plans regarding the aquaculture of dusky grouper. Future studies need to focus on the pathology of DGD, describing the disease process and aetiology using laboratory techniques such as TEM and virology as well as using morphology and molecular-based tools to describe the blood fluke and to determine their potential role in the initiation the disease. The novel approach to disease surveillance using social media Facebook posts could be further expanded by attracting citizen scientists, for future research assessing disease in wild fish, for sightings of mortality events and/or the appearance of disease outbreaks, or, for mapping marine mammal stranding’s and/or turtle nesting activity.