Acousto-optic modulation of optical reflection properties in fiber Bragg gratings and the application in fiber lasers

This thesis aims to investigate the interaction of acoustic waves and fiber Bragg gratings (FBGs) in standard and suspended-core fibers (SCFs), to evaluate the influence of the fiber, grating and modulator design on the increase of the modulation efficiency, bandwidth and frequency. Initially, the frequency response and the resonant acoustic modes of a low frequency acousto-optic modulator (f < 1.2 MHz) are numerically investigated by using the finite element method. Later, the interaction of longitudinal acoustic waves and FBGs in SCFs is also numerically investigated. The fiber geometric parameters are varied and the strain and grating properties are simulated by means of the finite element method and the transfer matrix method. The study indicates that the air holes composing the SCF cause a significant reduction of the amount of silica in the fiber cross section increasing acousto-optic interaction in the core. Experimental modulation of the reflectivity of FBGs inscribed in two distinct SCFs indicates evidences of this increased interaction. Besides, a method to acoustically induce a dynamic phase-shift in a chirped FBG employing an optimized design of modulator is shown. Afterwards, a combination of this modulator and a FBG inscribed in a three air holes SCF is applied to mode-lock an ytterbium doped fiber laser. To improve the modulator design for future applications, two other distinct devices are investigated to increase the acousto-optic interaction, bandwidth and frequency (f > 10 MHz). A high reflectivity modulation has been achieved for a modulator based on a tapered fiber. Moreover, an increased modulated bandwidth (320 pm) has been obtained for a modulator based on interaction of a radial long period grating (RLPG) and a FBG inscribed in a standard fiber. In summary, the results show a considerable reduction of the grating/fiber length and the modulator size, indicating possibilities for compact and faster acousto-optic fiber devices. Additionally, the increased interaction efficiency, modulated bandwidth and frequency can be useful to shorten the pulse width of future all-fiber mode-locked fiber lasers, as well, to other photonic devices which require the control of the light in optical fibers by electrically tunable acoustic waves.

Proposta de um processo de transferência de tecnologia para as instituições públicas de pesquisa: o caso da Embrapa

The Brazilian agricultural research agency has, over the years, contributed to solve social problems and to promote new knowledge, incorporating new advances and seeking technological independence of the country, through the transfer of knowledge and technology generated. However, the process of transfering of knowledge and technology has represented a big challenge for public institutions. The Embrapa is the largest and main brazilian agricultural research company, with a staff of 9.790 employees, being 2.440 researchers and an annual budget of R$ 2.52 billion. Operates through 46 decentralized research units, and coordinate of the National Agricultural Research System - SNPA. Considering that technology transfer is the consecration of effort and resources spent for the generation of knowledge and the validity of the research, this work aims to conduct an assessment of the performance of Embrapa Swine and Poultry along the production chain of broilers and propose a technology transfer model for this chain, which can be used by the Public Institutions Research – IPPs. This study is justified by the importance of agricultural research for the country, and the importance of the institution addressed. The methodology used was the case study with a qualitative approach, documentary and bibliographic research and interviews with use of semi-structured questionnaires. The survey was conducted in three stages. In the first stage, there was a diagnosis of the Technology Transfer Process (TT), the contribution of the Embrapa Swine and poultry for the supply chain for broiler. At this stage it was used bibliographical and documentary research and semi- structured interviews with agroindustrial broiler agents, researchers at Embrapa Swine and Poultry, professionals of technology transfer, from the Embrapa and Embrapa Swine and Poultry, managers of technology transfer and researchers from the Agricultural Research Service - ARS. In the second step, a model was developed for the technology transferring poultry process of Embrapa. In this phase, there were made documentary and bibliographic research and analysis of information obtained in the interviews. The third phase was to validate the proposed model in the various sectors of the broilers productive chain. The data show that, although the Embrapa Swine and Poultry develops technologies for broiler production chain, the rate of adoption of these technologies by the chain is very low. It was also diagnosed that there is a gap between the institution and the various links of the chain. It was proposed an observatory mechanism to approximate Embrapa Swine and Poultry and the agents of the broiler chain for identifying and discussing research priorities. The proposed model seeks to improve the interaction between the institution and the chain, in order to identify the chain real research demands and the search and the joint development of solutions for these demands. The proposed TT model was approved by a large majority (96.77%) of the interviewed agents who work in the various links in the chain, as well as by representatives (92%) of the entities linked to this chain. The acceptance of the proposed model demonstrates the willingness of the chain to approach Embrapa Swine and Poultry, and to seek joint solutions to existing problems.

Proposta de uma matriz de decisão em energia hidrelétrica com o uso do método multicritério, para formulação de políticas públicas no estado do Paraná

Brazil is internationally acknowledged for its renewable sources, most notably, hydroelectric power plant projects which correspond to 65% of electricity production supply to the National Interconnected System. The main question behind this research is: what are the weights and the relative importance of the variables which have influence on the decision making process for the expansion of hydroelectric generation projects in Parana? The main objective is to propose a multi-criteria decision procedure, in association with water sources options that take into consideration the weight and relative importance of the alternatives having influence on the decision by enterprises in the generation of electricity in the state of Paraná. As far as the approach to the problem is concerned, this research can be classified as having mixed methodologies, applying Content Analysis, Delphi technique and the Analytic Hierarchy Process. Following Delphi methodology, a group of 21 was selected for data collection, all of those linked to Paranaense hydroelectricity market. And the main result was the construction of a decision tree in which it was possible to identify the importance and relative weight of the elements associated with the four dimensions of energy. In environmental dimension, the highest relative weight was placed on the loading capacity of Parana system; the economic dimension, the amortization of investment; in social dimension, the generation of direct work places and in institutional dimension, the availability of suitable sources of financing. Policy makers and business managers make their decisions based on specific criteria related to the organization segment, market information, economic and political behavior among other indicators that guide them in dealing with the typical tradeoffs of projects in hydropower area. The results obtained in the decision tree show that the economic bias is still the main factor in making investment decisions. However, environmental impacts on the State loading capacity, income generation, providing opportunities for direct as well as indirect jobs. And at an institutional level, the absence of funding sources show that the perception of experts is focused on other issues beyond the logic behind development per se. The order of priority of variables in this study indicates that in the current environment of uncertainty in the Brazilian economy as many variables must be analyzed and compared in order to optimize the scarce resources available to expand local development in relation to Paranaense water matrix.