Fiber amplifiers with high power and high pulse energy are strongly in demand for both scientific research and industrial applications. Ytterbium-doped fiber has been an outstanding choice for its broad-gain bandwidth and excellent power conversion efficiencies. In this dissertation, we introduced a compact high power high pulsed energy laser system with chirally coupled core (3C) Yb-doped fibers as the gain media. Traditional standard fibers and photonic crystal fibers are not suitable for compact high power high pulse energy laser systems because of poor higher order modes (HOMs) management and complicated air-hole structure. Newly invented 3C silica fibers solve these problems. A helical side-core around the Yb-doped central core extracts the HOMs from the central core. By adjusting this chirally structure, the core of the 3C fiber can be enlarged and the transverse mode of the fiber can be single mode at certain wavelengths. To simulate the amplification process with high power high pulse energy better, a new modeling method based on a combination of the rate equations and the nonlinear Schrödinger equations is invented. The gain was calculated from rate equations and the pulse evolution was analyzed using nonlinear Schrödinger equation. The simulation provided a good guidance for building compact high power high pulse energy laser systems. To achieve high power and high pulse energy, the system is designed as a two-stage structure. The laser

A stable dual-wavelength Tm:Ho co-doped fiber laser operating above 2 mu m based on cascaded single mode-multimode-single mode (SMS) all-fiber structures has been proposed and experimentally demonstrated for the first time.

Cladding pumped single-frequency Yb3+-doped fiber amplifiers at 976 nm were investigated. Over 4 W output power was obtained and further power scaling can be achieved by reducing the cladding diameter of the Yb3+-doped fiber.

No description available.

Allier de fortes puissances moyennes et crêtes donne accès à un champ applicatif très large pour un système laser ultrarapide. Une technique qui s’est avérée capable de satisfaire ces exigences est la combinaison cohérente de faisceaux (CBC). Elle permet de séparer spatialement les faisceaux avant l’amplification pour les recombiner ensuite d’une manière cohérente en un unique faisceau. Afin d’obtenir une recombinaison efficace, les propriétés spatiales et spectrales de tous les faisceaux doivent être parfaitement en accord.Pour des applications comme l’accélération de particules, le recours à plusieurs milliers de fibres doit être envisagé. Il est donc nécessaire d’étudier des architectures CBC fortement évolutives en termes de canaux amplificateurs.Le projet XCAN vise à une première démonstration d’un tel système en réalisant la combinaison cohérente de 61 fibres amplificatrices. Afin d’étudier les défis scientifiques et techniques d’une telle architecture, une version de taille réduite comprenant sept fibres a été mise en place.La conception et la réalisation de ce prototype sont le sujet de cette thèse.Dans un premier temps, des simulations ont été effectués afin d’estimer les désaccords tolérables entre les propriétés spatiales et spectrales des différents faisceaux.Basé sur ce travail de modélisation, un système laser de combinaison cohérente de sept fibres a été ensuite assemblé et caractérisé. Les résultats obtenus sont très prometteurs et montrent que notre architecture est bien adaptée pour accueillir les 61 fibres du démonstrateur final XCAN. / Future applications of high power ultrafast laser systems require simultaneously high average and peak powers. A technique which has proved to be capable of meeting these demands is coherent beam combining (CBC).In this technique, the beam is spatially split prior to amplification, and coherently recombined in one single beam afterwards. In order to achieve an efficient recombination, the spatial and spectral properties of all beams need to be perfectly matched.For applications such as particle acceleration, the coherent combining of several thousands of fibers needs to be considered. It is thus necessary to investigate highly scalable CBC architectures.The XCAN project aims at a first demonstration of such a scalable setup by coherently combining 61 fiber amplifiers. In order to study the scientific and technical challenges of such a system, a downscaled version consisting of seven fibers has been implemented.The design and characterization of this prototype is the subject of this thesis.As a starting point, numerical simulations have been performed in order to estimate the maximum tolerable mismatches between the spatial and spectral properties of the beams.Based on this modeling work, a seven fiber CBC system has been assembled and characterized. The obtained results are very promising and imply that our setup is well suited for the accommodation of all 61 fibers of the final XCAN demonstrator.

This thesis focuses on simulating, designing, and characterizing a narrow-linewidth continuous-wave (CW) Ytterbium (Yb) master oscillator fiber amplifier (MOFA) system. The primary goal was to achieve a watt-level output at 1087 nm with a narrow 1 GHz linewidth, making the MOFA well-suited for serving as a pump source in Terahertz (THz) generation experiments. This system can essentially be divided into two main parts: a narrow-linewidth Yb fiber seed laser (master oscillator), responsible for delivering a stable and narrow-linewidth signal power, and a Yb fiber amplifier for scaling this signal power.The all-fiber Yb seed laser produced a maximum output power of 11.31 mW at 1087.39 nm with a narrow linewidth of approximately 1.86 GHz. The narrow-linewidth operation was achieved by incorporating a fiber Bragg grating (FBG) as a resonator mirror and an intracavity FBG based Fabry-Perot interferometer as a bandpass filter, allowing only specific portion of the FBG reflected spectrum to pass through. A simulation was subsequently developed to identify the optimal Yb gain fiber lengths and pump powers required to realize an efficient Yb fiber amplifier with high gains. Finally, by employing a 10-meter Yb fiber amplifier, seed laser’s output power was boosted to 0.86 W, resulting in a 23.1 dB gain, achieved with a notable power conversion efficiency of 33 %. The final amplified spectrum exhibited a Gaussian-like profile centered at 1087.12 nm, with a bandwidth of less than 12.7 GHz. By further scaling the output power to watt-level range, this Yb MOFA system has the potential to be utilized as a pump source in Terahertz (THz) generation research. / I detta examensarbete presenteras simuleringar, konstruktion och karaktärisering av en kontinuerlig smalbandig Ytterbium (Yb) fiberlaser och förstärkare. Målet med arbetet är att uppnå en effekt runt en watt med en centervåglängd på 1087 nm och en bandbredd på 1 GHz som kan användas vid generation av terahertzstrålning (THz-strålning). Systemet kan delas in i två delar: en Yb fiberlaser som levererar en stabil och smalbandig signal och den andra är en Yb fiber baserad förstärkare för amplifikation av signalen. Yb fiberlasern hade en maxeffekt på 11.31 mW med en centervåglängd på 1087.39 nm och en bandbredd på 1.86 GHz. Den smalbandiga operationen var uppnådd genom att inkorporera en fiber bragg-gitter (FBG) som formade en resonator, med två ytterligare FBG element som agerade som en intra-kavitär Fabry-Perot interferometer vilket begränsar vilka våglängder som kan propagera. Ett program för att simulera den optimala längden på Yb fiberförstärkaren samt vilken pumpeffekt som maximerade den förstärkta signalen togs fram för projektet. Det resulterade i en förstärkare med en 10 m lång Yb fiber som kunde förstärka fiberlasern till 0.86 W, vilket motsvarade till en 23.1 dB förstärkning med en effektivitet på 33%. Den slutgiltiga signalen hade ett spektrum med gaussisk profil och en bandbredd under 12.7 GHz. Med ytterligare skalning på effekten genom fler förstärkare kan system som helhet användas vid generation av THz strålning.

The aim of this thesis is to develop both Yb and Tm fiber laser sources with all fiber cavities. Both wavelength ranges provide useful laser sources for optical pumping of helium. The goal is to develop Tm laser sources operating at 2058 nm to optically quench 3He (2058.63 nm) and 4He (2058.69 nm) singlets (21S0). We also have developed Yb laser sources at 1083 nm to optical pump the triplet states of helium and laser cool an atomic beam of helium.

Mid-infrared (IR) lasers (2-12 μm) have found tremendous applications in medical surgeries, spectroscopy, remote sensing, etc. Nowadays, mid-IR emissions are usually generated from semiconductor lasers, gas lasers, and solid-state lasers based on nonlinear wavelength conversion. However, they usually have disadvantages including poor beam quality, low efficiency, and complicated configurations. Mid-IR fiber lasers have the advantages of excellent beam quality, high efficiency, inherent simplicity, compactness, and outstanding heat-dissipating capability, and have attracted significant interest in recent years. In this dissertation, I have studied and investigated Q-switched and mode-locked fiber lasers in the mid-IR wavelength region. My dissertation includes six chapters: In Chapter 1, I review the background of mid-IR lasers and address my motivation on the research of mid-IR fiber lasers; In Chapter 2, I present the experimental results of microsecond and nanosecond Er³⁺-doped and Ho³⁺-doped fiber lasers in the 3 μm wavelength region Q-switched by Fe²⁺:ZnSe and graphene saturable absorbers. In Chapter 3, Q-switched 3 μm laser fiber amplifiers are investigated experimentally and theoretically and their power scaling are discussed. In Chapter 4, a graphene mode-locked Er³⁺-doped fiber lasers at 2.8 μm with a pulse width < 50 ps is presented. In Chapter 5, extending the spectral range of mid-IR fiber lasers by use of nonlinear wavelength conversion is addressed and discussed. I have proposed 10-watt-level 3-5 μm Raman lasers using tellurite fibers as the nonlinear gain medium and pumped by our Er³⁺-doped fiber lasers at 2.8 μm. In the last chapter, the prospect of mid-IR fiber laser is addressed and further research work is discussed.

Motivated by an increasing demand for functionality and reliability of systems operating in harsh, ionizing-radiation environments, the core of the present research is an investigation of the response of rare-earth-doped, aluminosilicate fibers to ionizing radiation. These rare-earth-doped fibers, consisting of fibers doped with ions of erbium (Er³⁺) and ytterbium (Yb³⁺) designed for use in amplifier systems, reveal average specific losses in response to ⁶⁰Co gamma radiation to be in the range of 0.0285 - 0.193 dB/(m•krad(Si)) at wavelengths from 1300 nm to 1400 nm. An ionizing dose rate dependence was identified in which high dose rates of approximately 40 rad(Si)/s invariably lead to higher induced losses than lower dose rates of approximately 14 rad(Si)/s, indicating the possibility of complex radiation-related phenomena underlying the observed absorption. Data clearly show that Er³⁺-doped fibers are more sensitive to ionizing-radiation in comparison to Yb³⁺-doped fibers, while Er³⁺/Yb³⁺ co-doped fibers are found to be the least sensitive to radiation of all the fibers examined. Evidence of color center formation associated with the dopant aluminum is found in results of visible spectroscopy conducted on gamma-irradiated preform samples and on fibers flown in low-Earth orbit. Near infrared spectroscopic data is consistent with absorption derived from this dopant as well, with the interpretation of band-tailing from the visible portion of the spectrum. Evidence of the formation of a defect intrinsic to the silicate host matrix, the Non-Bridging Oxygen Hole Center (NBOHC), is also found following ionizing radiation of the optical fiber preforms. Since the observed ionizing-radiation-induced absorption is concentrated in the visible portion of the spectrum, the performance of actively operated rare-earth-doped amplifiers is largely impacted by the pump wavelength, which is located at higher energies within the near-infrared portion of the spectrum and therefore closer to the visible portion of the spectrum than the lasing wavelength. Experimental results stemming from rare-earth-doped amplifiers operated under ionizing radiation substantiate the importance of the pumping wavelength, and suggest the presence of cascaded pump photon absorption processes. Based on these results, pumping at longer wavelengths is advised to reduce the effect of color center absorption on this crucial aspect of active fiber amplifier operation.

Made available in DSpace on 2016-03-15T19:38:16Z (GMT). No. of bitstreams: 1 Marcelo Leme Mamud.pdf: 1194376 bytes, checksum: 159feb30c5e6a599335f280e27316dbc (MD5) Previous issue date: 2010-03-03 / Fundo Mackenzie de Pesquisa / In recent years there have been some proposals to develop educational tools using multimedia and interactive resources. However, most of them just transpose the traditional materials to the computer screen. The reason for this work is the gap of didactic materials to explore important subjects about photonics and optical communication systems, specially the lack of tools related to Erbium Doped Fiber Amplifier (EDFA) learning. The aim of this research is to provide at the LCMS MOODLE open platform an Intelligent Learning Resource to support EDFA study, providing a set of Learning Objects more suitable for the study of the base concepts needed to optimise the use of the computer simulation tool. For so, this research presents the development of an Intelligent Learning Resource for Electric Engineering, Physics, and related fields, in which students can learn about optical communications, in particular EDFA. The proposal is to give autonomy to the students, which manage their own study time, and fulfill the basement and prerequisites needed to understand the subject and complete the tasks proposed. Moreover, the learning resource proposes the navigation through a concept map based on a multiagent system architecture, providing an individual treatment according to each student profile. The insertion of a society of agents in the concept map, in order to observe, collect information about the user background profile, and also act in the virtual environment, suggesting the study of the most appropriate learning objects. The learning resource developed can stimulate the students to understand how amplifiers are designed for a practical application, and the parameters that should be considered in a project. The Artificial Intelligence techniques used for the development of the learning resource consider the learner differences in a way to adapt the system actions according to each student background. / Nos últimos anos foi possível observar o desenvolvimento de propostas de ferramentas digitais de ensino, utilizando interatividade, recursos multimídia, entre outros. Entretanto, parte destas propostas reflete as deficiências características das metodologias de ensino tradicionais. Este trabalho apresenta o desenvolvimento de um Recurso Digital de Aprendizagem, baseado em técnicas de Inteligência Artificial, com aplicação no campo de comunicações ópticas. São apresentadas as técnicas e aplicativos de suporte para a construção deste recurso, incluindo as estratégias para adaptação da navegação de acordo com os prérequisitos e perfis dos aprendizes. Foi utilizada a tecnologia de mapas conceituais e sistemas multiagentes, integrados a Objetos de Aprendizagem. Os agentes computacionais, inseridos em cada nó do mapa, têm a missão de atuar sobre o ambiente de aprendizagem, sugerindo o estudo e acesso aos Objetos de Aprendizagem mais apropriados, conforme os resultados sobre o perfil do usuário. Trata-se de uma abordagem pedagógica, que conta com interatividade, recursos audiovisuais e disponibilidade para o aluno administrar seu próprio tempo e da maneira mais flexível, aumentando a eficiência dos estudos. A partir da observação das dificuldades encontradas por estudantes da área, foi possível determinar os requisitos do projeto. A motivação para o desenvolvimento, na área de amplificadores ópticos de fibras dopadas por érbio (EDFA), surgiu pela dificuldade e carência de materiais didáticos no campo de pesquisa de engenharia de telecomunicações. Um dos principais problemas no estudo de EDFA é a abordagem matemática utilizada na literatura da área, exigindo domínio de conceitos avançados em cálculo. A partir do Recurso de Aprendizagem implantado, é possível verificar a estratégia de extrair a partir de diversos recursos tecnológicos como, por exemplo, interatividade, multimídia, mapas conceituais, inteligência artificial e simulação computacional, maneiras para estimular a aprendizagem significativa sobre os conceitos abordados.