This research reports a simple and novel method to fabricate microlens arrays by soft stamping the unexposed SU-8 photoresist. A SU-8 based stamp composed of micro-nozzle arrays with a reservoir structure on a glass substrate is first fabricated using a process of dosage control exposure. The unexposed SU-8 is then encapsulated in the cross-linked SU-8 shell and was used as the ¡§ink¡¨ for the stamping process. The proposed SU-8 microlens array is then formed by stamping the formed SU-8 structure on a bare glass substrate at a temperature higher than the glass transition temperature (Tg) of the unexposed SU-8 microlens array. Lenses with various radii of curvature can be formed by controlling the working temperature during the stamping process. In addition, this work also employed a simple electric static pulling scheme to manipulate the fabricated lenses profiles. Aspherical SU-8 microlens arrays with a wide range of tunable focal lengths were fabricated with this approach. Furthermore, we develop an advanced localize E-field control technique to fabricate microlenses with various focus length and microlenses with different tilt angle in a single lens array sheet. A novel grayscale mask fabrication technique is also proposed first. This low cost and rapid method is applied on stepwise and continuous tilt plane fabrication for produces a gradually changed E-field. Hetero axes and focus lengths microlenses are fabricated with this approach. In order to farther understand the real E-field distribution, a novel PCF based E-field sensor fabrication technique is also proposed. This technique also shows the potential on various PCF based devices fabrications.

Rapid development of fiber-optic communications network requirements increasing in recent years, The WDM technology and invention of anhydrous optical fiber open the possibility for optical fiber transmission bands broaden form 1.3 £gm to 1.6 £gm. Chromium doped yttrium aluminum garnet crystal fiber has characteristic of 300 nm broadband. Therefore, it¡¦s strongly desirable to develop a broadband fiber amplifier, laser or other active components for extending the flexibility of system architecture design in optical fiber communication. A few-mode chromium doped yttrium aluminum garnet double-clad crystalline fibers has been demonstrated by employing a modified version of LHPG technique, means using silica-YAG crystal co-drawing and multiple core-tuning process by precisely controlled inter-diffusion between YAG core and silica tube. In this thesis, electron probe x-ray micro-analysis, energy dispersive spectroscopy and transmission electron microscopy were utilized to confirm this fiber structure and composition. This fiber has gross gain about 2.3 dB with dual pumped by few hundred mini Watt. Significantly reduce the pump power threshold. Compared with the last large core size, few-mode (small core size) chromium doped yttrium aluminum garnet double-clad crystalline fibers has lower heat effect and higher power efficiency. To enhance the optical properties towards few modes or even single mode, not only reduce the transmission loss, but improve the device efficiency. Key words: Laser heated pedestal growth, Cr4+:YAG, Double-clad Crystal Fiber, gain

Due to the fast expansion and development in the optical communication industry, the demand for the broad-band laser light source as used to the optical transmission network system has correspondingly increased. Cr4+ doped YAG crystal fibers, with its broad-band spectral property, is thus becoming more and more indispensable to the growth of the industry. However, the Cr4+:YAG crystal fiber in its own repetitive growth process brings with itself one problem: after each re-growth, the concentration of Cr2O3 and Cr4+ ions would reduce appreciatively. Hence, finding sound solutions for effectively raising the concentration of Cr4+ is now becoming an essential issue in the field. The thesis mainly focuses on the development of using Cr4+:YAG as the laser gain medium. Thin layers of CaO, MgO, and Cr2O3 was coated on the circumference of the Cr:YAG crystal fiber. The LHPG method was then employed to re-grow the coated samples, during which the doped concentration of CaO, MgO and Cr2O3 can in-diffuse. And the effect of charge compensation would go further to simultaneously raise the concentration of Cr4+ ions. Now we have successfully enhance the concentration of Cr4+ ions to 4.86x10-3 wt.%. This study, with the use of the E-Gun coating machine and the IAD (ion-beam assisted deposition) system, also probes the technical side of how to better improve the quality of the crystal fiber laser. Both end faces of the Cr4+:YAG crystal fiber were coated with optical thin films by TiO2 and SiO2 targets. In addition to raise the quality of the thin films, the IAD system also functions to create a laser cavity in which both the anti-reflectance (AR) effect (for pumping the light source) and the high reflectance (HR) effect (for stimulating the light source) are achieved. The accompanied benefits would be the reduction of transmission loss, the increased laser efficiency, and thus a more successful and more stable crystal fiber laser.

In this thesis, we have compared between dual-core fiber coupler with photonic crystal fiber coupler. From Surface Integral Equation Method derived from Maxwell¡¦s equations, we can simulate tapered fiber coupler, dual-core fiber coupler and photonic crystal fiber coupler. By analyzing the propagating characteristics and performance of these couplers, we hope to discuss between their advantages and dis-advantages. We have found that at the same parameters, conventional fiber coupler¡¦s coupling length is roughly half compared to photonic crystal coupler. In terms of bandwidth, photonic crystal coupler aided by air-hole tuning can achieve multiples times larger than conventional fiber coupler. So, we believe that in communication networks with a lust of bandwidth, photonic crystal coupler can definitely live up its expectations.

Though Nd:YAG has been widely used as the traditional high power solid-state laser gain medium, Yb:YAG has more advantages such as lower quantum defect, wider absorption and emission bandwidth, and longer fluorescence lifetime, which can be used in Q-switched lasers to storage more energy. In addition, a higher doping concentration Yb:YAG with thinner thickness reduces the shift of optical path, which reduces the ring cavity stability. Therefore Yb:YAG is an eminently suitable gain medium for the two-mirror ring laser. Due to the quasi-three-level characteristic of Yb:YAG, the thermal effect influences the re-absorption loss and deteriorates the laser performance, i.e. lower slope efficiency of laser. In this thesis, we improve the laser efficiency by using Yb:YAG crystal with proper thickness, and various round-trip transmittances with different output couplers were tried. The slope efficiency with 50.3 % has been achieved. We also tried to reduce the thermal loading of Yb:YAG by crystal fiber with Cu-Al alloy package. The fabrication process of Yb:YAG crystal fiber, including sample preparation, and coating design, and the experiment result of Yb:YAG crystal fiber ring laser will be presented in detail. Furthermore, we use numerical analysis to modify the passively Q-switched Yb:YAG ring laser rate equation with FDTD (finite difference time domain) method. The simulated repetition rate, pulse width and peak power were compared to the experimental results in order to optimaize laser performance.

Abstract During the last decade, the fast-growing communication need has promoted the development of the wavelength of 1.3 mm~1.6 mm laser light source. The Cr4+ doped YAG solid-state laser has potential to meet this super wideband demand. In addition, solid state laser has the merits of high laser beam quality, long lifetime, compact, and simple structure. In this thesis, crystal fiber was used as the laser gain medium, and coated with optical thin film at its end facets as the laser cavity. Using this configuration, the volume and cost of the laser can be appreciatively reduced, and the heat dissipation can be improved. The laser-heated-pedestal-growth method was used to grow crystal fiber, which can obtain small diameter at very fast rate and accurate control. High quality Cr4+:YAG crystal fiber with the smallest diameter of 50 mm was grown. A glass-packaged technique clothes the crystal fiber with a core diameter as small as 11 mm. Outside the glass clad Cr4+:YAG crystal fiber, Al-Cu alloy was employed as the heat sink to improve heat dissipation. After grinding, polishing, and coating of this device, the Cr4+:YAG crystal fiber laser was fabricated. Some characteristics of Cr4+:YAG crystal fiber, such as the distribution of Cr2O3 and CaO doping concentration, fluorescence intensity, refraction index, propagation loss, and absorption coefficient were measured and analyzed. In the meanwhile, some simulations of the laser output power depending on the absorption coefficient, propagation loss, output coupling, crystal fiber diameter, and crystal boundary temperature were discussed.

Orientadores: Luiz Carlos Barbosa, Cristiano Monteiro de Barros Cordeiro / Dissertação (mestrado) - Universidade Estadual de Campinas, Instituto de Fisica Gleb Wataghin / Made available in DSpace on 2018-08-11T19:12:29Z (GMT). No. of bitstreams: 1 Santos_ElianeMourados_M.pdf: 4020531 bytes, checksum: 57766702771129e7f4bfe1d0c7852f67 (MD5) Previous issue date: 2007 / Resumo: Este trabalho apresenta estudos de como inserir fluidos (líquidos e gases) em fibras ópticas microestruturadas, especialmente fibras de cristal fotônico, também conhecidas como PCF¿s (do inglês Photonic Crystal Fibers). Estas fibras possuem buracos de ar que percorrem todo seu comprimento. Elas podem ser divididas em dois grandes grupos: as de núcleo sólido que guiam luz por reflexão interna total e as de núcleo oco que guiam luz por um mecanismo conhecido como photonic bandgap. Ambos os tipos de fibras permitem várias aplicações em áreas como óptica e fotônica e nos dedicamos aqui à área de sensoriamento a fibra. Nesta área, usamos os microburacos para inserir fluido e dessa maneira manipular as propriedades de guiamento (em fibras de núcleo líquido), deixar a fibra mais sensível a algum parâmetro externo ou para sensoriar o fluido em questão. Nos três casos, precisamos estudar os processos de preenchimentos de fibras microestruturadas. Para este fim, estudamos e desenvolvemos maneiras de inserir fluidos em fibras de núcleos sólidos ou ocos. Usando preenchimento seletivo, produzimos fibras com núcleo líquido, criando uma região de alta interação entre luz e material. Neste trabalho, estudamos diferentes técnicas de preenchimento. A primeira, para fibras de núcleo líquido, é um preenchimento seletivo que pode ser feito usando uma máquina de emendas (splicer) ou um polímero para bloquear os microburacos. O outro consiste em manter as pontas das fibras livres (para medidas ópticas) enquanto o preenchimento é feito. Por fim, usamos o conhecimento desses processos em aplicações como sensoriamento de fluidos ou parâmetros externos e manipulação de propriedades de guiamento da luz / Abstract: This work presents studies of how to insert fluids (liquid and gas) into microstructured optical fibers, especially photonic crystal fibers, also known as PCF¿s. These optical fibers possess air holes that run along its entire length. They can be divided into two major groups: solid core fibers that guide light by total internal reflection and hollow core fibers that guide light by photonic bandgap. Both types of fibers allow several applications in areas such as optics and photonics and we dedicated this work to the fiber-sensing field. In this area we use the micro holes to insert fluids and in this way to manipulate the guidance properties in liquid core fibers, to leave the fiber more sensitive to some external parameter or to sensing the fluid. In these three cases we need to study the filling procedures in microstructured fibers. For this purpose, we studied and developed ways of inserting fluids in hollow and solid core fibers. We produced liquid core fibers, creating a high light-material overlap, using a selective filling technique. In this work we studied different filling techniques. The first one, for liquid core fibers, is a selective filling, which can be done by using a splicer machine or a polymer to block the fiber micro holes. The last one consists of keeping the fiber tips free (for optical measurements) while the filling is done. And finally we used the filling process knowledge in applications like sensing of fluids or external parameters and manipulation of guidance properties / Mestrado / Física Geral / Mestre em Física

Este trabalho visa dar uma importante contribuição à pesquisa de novos materiais, através da determinação de condições otimizadas para obtenção pela técnica LHPG de fibras monocristalinas de compostos óxidos. Com esse objetivo fibras foram obtidas com êxito para compostos que podem ser utilizados como meios ativos para lasers de estado sólido (CaNb2O6 e GdTaO4), em aplicações de óptica de raios X (cristais gradientes dos sistemas GdTaO4-ErTaO4 e GdTaO4-YbTaO4) e também compostos que apresentam supercondutividade (EuNbO3, Yb2NbO5, Sm2NbO5 e Er2NbO5). A preparação dos pedestais se mostrou uma etapa muito importante na preparação das várias fibras. A caracterização estrutural por técnicas de difração de raios X mostrou que fibras monocristalinas de CaNb2O6 e GdTaO4 podem ser obtidas rapidamente e com alta qualidade cristalina sendo altamente adequadas para aplicações em óptica. Adicionalmente resultados de medidas espectroscópicas mostraram que as fibras CaNb2O6 dopadas com Nd+3 são boas candidatas para desenvolvimento de micro-lasers. Monocristais com gradiente controlado de parâmetro de rede foram obtidos pela primeira vez para os sistemas GdTaO4- ErTaO4 e GdTaO4-YbTaO4. A estratégia aplicada aqui possibilitou a obtenção de um gradiente composicional e de parâmetros de rede com ótima linearidade. Para o sistema GdTaO4- ErTaO4 foi obtido um gradiente de espaçamento de rede de 1,24%/cm para a reflexão (4 -4 4). Para os cristais GdTaO4- ErTaO4 um gradiente de 2,9%/cm para a reflexão (6 -4 0) foi obtido, sendo este o maior valor já observado em cristais gradientes. Através de uma inovação, utilizando Nb metálico em pó na preparação dos pedestais, fibras do composto EuNbO3 foram obtidas pela primeira vez, ao nosso conhecimento, através de uma técnica utilizando fusão. A aplicação desta mesma inovação buscando a obtenção de fases com esta mesma estrutura para outras terras raras, proporcionou a descoberta de três fases inéditas, Yb2NbO5, Sm2NbO5 e Er2NbO5. A estrutura destas novas fases foi determinada e através de caracterizações magnéticas e elétricas iniciais observou-se que estas apresentam supercondutividade com temperaturas de transição, Tc, iguais a 12,5K, 6,5K e 14,9K respectivamente para Yb2NbO5, Sm2NbO5 e Er2NbO5 / This work aims to give an important contribution to the research of new materials, by determining optimized conditions for obtaining of single crystal fibers of oxide compounds by LHPG technique. With this objective fibers were successfully obtained for compounds which can be used as solid state lasers (CaNb2O6 e GdTaO4), for X-ray optics applications (gradient crystals of GdTaO4-ErTaO4 e GdTaO4-YbTaO4 systems) and also as superconducting compounds. The preparation of the pedestals was a very important stage in the obtaining of the various fibers, with influence in growth experiments and quality of the fibers. The structural characterization by X-ray diffraction techniques showed that CaNb2O6 and GdTaO4 single crystal fibers presenting high crystalline quality can be quickly obtained. These fibers can be highly suitable for optics applications. In addiction the results of spectroscopic measurements showed Nd+3 doped CaNb2O6 fibers are good candidates for development of micro-lasers. Single crystals with controlled lattice parameter gradient were obtained for the first time for GdTaO4- ErTaO4 e GdTaO4-YbTaO4 systems. The applied approach in here enabled to obtain a compositional and lattice parameters gradient presenting optimized linear behavior. For the GdTaO4- ErTaO4 system a lattice spacing gradient of 1.24%/cm for (4 -4 4) reflection was obtained. For GdTaO4-YbTaO4 crystals a gradient of 2.9%/cm was observed. This is the largest value of lattice spacing gradient up to this moment. By an innovation, using metallic Nb in the form of powder in preparing the pedestals, fibers of the EuNbO3 compound were obtained, being the first report by a fusion technique. The application of this innovation to obtain phases with this structure for others rare earth enabled the discovery of three new phases, namely Yb2NbO5, Sm2NbO5 and Er2NbO5. The structure of these new phases was determined and by magnetic and electric characterizations it was observed that the phases are superconductor materials with transition temperatures, Tc, equals to 12,5K, 6,5K and 14,9K respectively for Yb2NbO5, Sm2NbO5 and Er2NbO5. compounds

Orientadores: Cristiano Monteiro de Barros Codeiro, Marcos Antonio Ruggieri Franco / Dissertação (mestrado) - Universidade Estadual de Campinas, Instituto de Física Gleb Wataghin / Made available in DSpace on 2018-08-20T13:14:05Z (GMT). No. of bitstreams: 1 ValenzuelaEspinel_YovannyAlexander_M.pdf: 51370027 bytes, checksum: 2f925ea5d4b6a8642e1244ad21e8e82b (MD5) Previous issue date: 2011 / Resumo: Foram realizados estudos sobre o controle de propriedades ópticas, por meio de pressão, e sensibilidade à pressão com fibras de cristal fotônico (PCF). No primeiro caso foi demonstrado por meio de simulações, uma nova forma para obter e sintonizar com pressão hidrostática externa o estado monomodo e única polarização em fibras PCF de polimetilmetacritalo (PMMA). Em relação à sensibilidade à pressão hidrostática, o comportamento espectral do coeficiente de sensibilidade de varias fibras PCF em sílica, Cs = (?? / ?P) (onde ?? é a variação num mínimo do espectro de transmissão de uma fibra PCF que acontece quando a pressão hidrostática externa muda em LlP), é calculado teoricamente e corroborado experimentalmente. Com a finalidade de estudar teoricamente o coeficiente Cs, a birrefringência de grupo e a sensibilidade da birrefringência modal de fase à pressão são simuladas para as fibras. Expressões analíticas do coeficiente Cs na aproximação de primeira e segunda ordem são calculadas. Nas duas aproximações é confirmado um aumento do Cs para comprimentos de onda no visível devido à birrefringência de grupo. Para baixas pressões, tal comportamento é corroborado experimentalmente. Segundo a literatura apresentada até agora a possibilidade de otimizar o coeficiente Cs, fazendo uso da birrefringência de grupo no visível e ao mesmo tempo incorporando geometrias com uma alta anisotropia geométrica para aumentar a sensibilidade da birrefringência modal de fase à pressão, não tem sido explorada. Na aproximação de segunda ordem do coeficiente Cs são incorporadas as mudanças do comprimento de onda e da pressão e são comparadas com a aproximação de primeira ordem. Cálculos analíticos foram feitos e apresentados nos Apêndices B e C. As equações do efeito fotoelástico, determinantes para realizar as simulações com o software (COMSOL 3.5a), são apresentadas no Apêndice B, relações que descrevem o coeficiente Cs de fibras PCF são apresentadas no (Apêndice C) / Abstract: Abstract Studies about both the active control of optical properties by means of external hydrostatic pressure and pressure sensitivity in photonic crystal fibers (PCFs) were made. In the first case, a new form to obtain and tune, by using pressure, the single-mode single-polarization state in microstructured polymer optical fibers (mPOFs) is demonstrated by simulations. In relation to pressure sensitivity, the spectral behavior of the sensitivity coefficient of some PCFs in silica, Cs = (?? / ?P) (where ?? é is the change in a minimum of the transmission spectrum for a PCF as a consequence of the change in the external hydrostatic pressure 11P that is applied on the fiber), is calculated and corroborated experimentally. In order to investigate the coefficient Cs, the group birefringence and the sensitivity of phase modal birefringence to pressure are calculated in the fibers. Analytical expressions for the coefficient Cs in the first and second order approximation are calculated. In these two approximations an increase of the coefficient Cs is confirmed to wavelengths in the visible. To low pressures this behavior is corroborated experimentally. At the best of our knowledge, the possibility to optimize the coefficient (Cs) by using the group birefringence and geometries with high geometric anisotropy to enhancing the sensitivity of phase modal birefringence to pressure has not been investigated. In the coefficient Cs with the second order approximation are incorporated the changes of the wavelength and pressure and are compared with the first approximation. On the other hand, analytic calculates are realized in the Appendixes B and C. The equations related to the photoelastic effect were calculates (Appendix B). Finally, the relations that describing the behavior of pressure sensitivity also were calculates (Appendix C) / Mestrado / Física / Mestra em Física

In this dissertation, high-power ytterbium-doped fiber amplifiers designed with advanced waveguide concepts are characterized and power scaled. Fiber waveguides utilizing cladding microstructures to achieve wave guidance via the photonic bandgap (PBG) effect and a combination of PBG and modified total internal reflection (MTIR) have been proposed as viable single-mode waveguides. Such novel structures allow larger core diameters (>35 μm diameters) than conventional step-index fibers while still maintaining near-diffraction limited beam quality. These microstructured fibers are demonstrated as robust single-mode waveguides at low powers and are power scaled to realize the thermal power limits of the structure. Here above a certain power threshold, these coiled few-mode fibers have been shown to be limited by modal instability (MI); where energy is dynamically transferred between the fundamental mode and higher-order modes. Nonlinear effects such as stimulated Brillouin scattering (SBS) are also studied in these fiber waveguides as part of this dissertation. Suppressing SBS is critical towards achieving narrow optical bandwidths (linewidths) necessary for efficient fiber amplifier beam combining. Towards that end, new effects that favorably reduce acoustic wave dispersion to increase the SBS threshold are discovered and reported. The first advanced waveguide examined is a Yb-doped 50/400 µm diameter core/clad PBGF. The PBGF is power scaled with a single-frequency 1064 nm seed to an MI-limited 410 W with 79% optical-to-optical efficiency and near-diffraction limited beam quality (M-Squared < 1.25) before MI onset. To this author's knowledge, this represents 2.4x improvement in power output from a PBGF amplifier without consideration for linewidth and a 16x improvement in single-frequency power output from a PBGF amplifier. During power scaling of the PBGF, a remarkably low Brillouin response was elicited from the fiber even when the ultra large diameter 50 µm core is accounted for in the SBS threshold equation. Subsequent interrogation of the Brillouin response in a pump probe Brillouin gain spectrum diagnostic estimated a Brillouin gain coefficient, gB, of 0.62E-11 m/W; which is 4x reduced from standard silica-based fiber. A finite element numerical model that solves the inhomogenous Helmholtz equation that governs the acoustic and optical coupling in SBS is utilized to verify experimental results with an estimated gB = 0.68E-11 m/W. Consequently, a novel SBS-suppression mechanism based on inclusion of sub-optical wavelength acoustic features in the core is proposed. The second advanced waveguide analyzed is a 35/350 µm diameter core/clad fiber that achieved wave guidance via both PBG and MTIR, and is referred to as a hybrid fiber. The waveguide benefits mutually from the amenable properties of PBG and MTIR wave guidance because robust single-mode propagation with minimal confinement loss is assured due to MTIR effects, and the waveguide spectrally filters unwanted wavelengths via the PBG effect. The waveguide employs annular Yb-doped gain tailoring to reduce thermal effects and mitigate MI. Moreover, it is designed to suppress Raman processes for a 1064 nm signal by attenuating wavelengths > 1110 nm via the PBG effect. When seeded with a 1064 nm signal deterministically broadened to ~1 GHz, the hybrid fiber was power scaled to a MI-limited 820 W with 78% optical-to-optical efficiency and near diffraction limited beam quality of M_Squared ~1.2 before MI onset. This represents a 14x improvement in power output from a hybrid fiber, and demonstrates that this type of fiber amplifier is a quality candidate for further power scaling for beam combining.