Photonic devices for integrated optical applications

work presented in this thesis encompasses an investigation into the use of ultrafast laser inscription in the fabrication of glass based photonic devices for integrated optical applications. Waveguide fabrication and characterisation experiments were carried out in three categories of glass substrate. Firstly, waveguides were inscribed in an erbium doped glass with the aim of fabricating optical amplifiers and lasers operating in the 1.5 μm spectral region. Low loss waveguides were fabricated in substrates with different dopant concentrations. Fibre to fibre net gain was achieved from one substrate composition, however it was found that ion clustering limited the amount of achievable gain. Laser action was demonstrated by constructing an optical fibre based cavity around the erbium doped waveguide amplifier. Waveguides were also inscribed in bismuth doped glass with the aim of fabricating optical amplifiers and lasers operating in the 1.3 μm spectral region. Low loss waveguides were fabricated, however the initial composition was incapable of providing gain. A proven substrate material was employed, demonstrating ultra-broadband gain spanning more than 250 nm. High losses prevented the achievement of net gain, however the broad potential of the substrate material was highlighted. Finally, waveguides were inscribed in a Chalcogenide glass. Strong refractive index contrasts were observed, with a wide range of waveguiding structures produced. Supercontinuum experiments were carried out in order to confirm the nonlinear behaviour of the waveguides. A spectrally smooth supercontinuum spanning 600 nm was generated, providing a potentially useful source for optical coherence tomography

Femtosecond Transient Bragg Gratings

Fiber Bragg gratings (FBGs) have found numerous applications in fiber lasers, sensors, telecommunication, and many other fields. Traditionally, they are fabricated using UV laser sources and a phase mask or other interferometric techniques. In the past two decades, FBGs have been fabricated with femtosecond lasers in either the point-by-point method or by using a phase mask, in a similar configuration as with UV laser sources. In the following, we briefly review the advantages of femtosecond fabrication of fiber Bragg gratings. We then focus on transient FBGs; these are FBGs that exist for a short duration only, for the purpose of all-optical, in-fiber switching and modulation and the possible mechanism to implement them with a high-power femtosecond laser. The theory behind transient grating switching is outlined, and we discuss related experimental results achieved by our group on both permanent grating inscription and the generation of transient (dynamic) fiber Braggs gratings

The ultrafast laser inscription of photonic devices for integrated optical applications

A study of some key areas in which ultrafast laser inscription may usefully be employed is presented. The thesis includes waveguide inscription in a variety of substrates including passive glass, doped glass and a nonlinear crystal. The work contained can be split into three studies, with some overlap between them. Firstly fused silica glass is used, both in planar substrates and as flat fibre, for the inscription of two sensing elements. The planar substrate is used for a device similar in design to a side-polished fibre and the flat fibre is used for the fabrication of a Bragg grating waveguide array. In the second study, waveguides are inscribed in the nonlinear crystal monoclinic bismuth borate, and used for guided mode second harmonic generation. A novel waveguide design is employed to increase overlap between the pump and second harmonic waveguide modes. The remainder of the thesis investigates the applicability of ultrafast laser inscription to the fabrication of compact modelocked lasers. Lasing is demonstrated, both continuous wave and modelocked, using a laser inscribed erbium doped bismuthate glass waveguide as the gain element. A study is then undertaken into methods of integrating carbon nanotubes, used as saturable absorbers to modelock lasers, into laser inscribed waveguides

Periodic fibre devices for advanced applications in all-optical systems

The main objective of this work is to investigate advanced applications of fibre gratings with the combination of nonlinear fibre optical effects, including the stimulated Raman scattering (SRS), Kerr effects, four-wave mixing (FWM) and second-harmonic generation. A Raman distributed-feedback (R-DFB) fibre laser formed in a passive optical fibre by using Raman gain is considered as the most promising route to generate a single-frequency and narrow-linewidth laser source at any wavelength given a proper pump source.In this thesis, the R-DFB fibre laser has been intensively studied both numerically and experimentally. Simulation results of centre pi phase-shifted R-DFB fibre lasers show that the longer length of the DFB grating, the higher Raman gain coefficient and the lower background loss of the host fibre are always beneficial for achieving low threshold R-DFB fibre lasers. 30 cm long centre pi phase-shifted R-DFB fibre lasers have been respectively demonstrated in two types of commercially available Ge/Si fibres of PS980 and UHNA4. Both un-polarised and linearly polarised CW Yb-doped fibre lasers at ~1.06 µm were used as the pump sources. The R-DFB fibre lasers are single-frequency operation at around 1.11 µm and have 3 dB linewidth less than 2.5 kHz; lasing thresholds down to sub-watt power levels; total output powers up to ~2 W; and total conversion efficiencies against incident pump power around 13%. Ultra-wide range (>110 nm) wavelength conversion by using FWM in these 30 cm-long R-DFB fibre lasers have been observed and up to ~-25 dB FWM conversion efficiency has been obtained.The nonlinearities and photosensitivity of several high-index non-silica glasses and fibres are also studied in order to incorporate fibre Bragg gratings (FBGs) with the highly nonlinear fibres to form R-DFB fibre lasers with lower thresholds. In particular, the Raman gain coefficient of a house-made tellurite glass fibre has been found to be ~35 times higher than the silica fibre and a SRS-assisted supercontinuum from ~1.1-1.7 µm has been observed in the fibre with a length of ~1.35 m by pumping at ~1.06 µm in the normal dispersion region of the fibre.Preliminary investigations into concatenating periodic poled silica fibres (PPSFs) to improve the frequency-doubling conversion efficiency are also presented

Novel Specialty Optical Fibers and Applications

Novel Specialty Optical Fibers and Applications focuses on the latest developments in specialty fiber technology and its applications. The aim of this reprint is to provide an overview of specialty optical fibers in terms of their technological developments and applications. Contributions include:1. Specialty fibers composed of special materials for new functionalities and applications in new spectral windows.2. Hollow-core fiber-based applications.3. Functionalized fibers.4. Structurally engineered fibers.5. Specialty fibers for distributed fiber sensors.6. Specialty fibers for communications

Fiber Optic Sensors and Fiber Lasers

The optical fiber industry is emerging from the market for selling simple accessories using optical fiber to the new optical-IT convergence sensor market combined with high value-added smart industries such as the bio industry. Among them, fiber optic sensors and fiber lasers are growing faster and more accurately by utilizing fiber optics in various fields such as shipbuilding, construction, energy, military, railway, security, and medical.This Special Issue aims to present novel and innovative applications of sensors and devices based on fiber optic sensors and fiber lasers, and covers a wide range of applications of optical sensors. In this Special Issue, original research articles, as well as reviews, have been published

Three-Dimensional Integrated Photonics in Transparent Substrates Enabled by Femtosecond Laser Fabrication

Unlike integrated electronic circuits that are built mostly on silicon wafers, integrated photonic devices involve a great variety of materials and platforms. The development of integrated photonic devices in both 2-D and 3-D architectures in each material and platform presents distinct fabrication challenges. The research in this dissertation explores the femtosecond laser as a versatile cross-platform manufacturing tool to fabricate 3-D photonic structures in transparent optical substrates. This dissertation first presents the fabrication of multiplexable and distributed optical sensors in silica and sapphire optical fiber with high radius of curvature surfaces. Using a diffraction-limited oil-immersion fabrication setup, a reel-to-reel laser direct writing system was established to deposit laser energy inside optical fibers with micrometer precision. Through careful tuning of laser-matter interaction to form nanograting in fiber core, Intrinsic Fabry-Perot Interferometer arrays were fabricated with a high fringe visibility of 0.49 and low insertion loss of 0.002 dB per sensor. The temperature sensitivity, cross-talk, and spatial multiplexability of sensor arrays were investigated in detail. By continuously introducing nanograting as artificial Rayleigh scattering centers, femtosecond laser-fabricated Rayleigh scattering enhanced section could achieve an optimized propagation loss of 0.01 dB/cm with drastic improvement of the signal-to-noise ratio of over 35 dB for Optical Frequency-Domain Reflectometry-based distributed sensing. Long-term high-temperature performance was successfully demonstrated with improved thermal stability. This dissertation also explores the fabrication of high-density 3-D topological photonic circuits in glass substrates with flat surfaces. Inspired from solid-state physics, topological photonics has found potential applications such as quantum information processing and defect-resistant lasing devices. Through careful control of the multiphoton laser-matter interaction in the femtosecond time scale and nanometer spatial scale, we demonstrate the fabrication of high-density coupled and low-loss 3-D waveguide arrays with varying index profiles. This dissertation presents the experimental verification of lattice braiding, Thouless pumping under the presence of disorder, and the topological pumping in a higher-order system. In sum, the dissertation studies the optics science of femtosecond laser-matter interaction and unveil the potentials of femtosecond laser as a powerful fabrication tool for 3-D photonic device fabrication for studies in optics science and for photonics applications in communication and sensing

Technical Readiness and Gaps Analysis of Commercial Optical Materials and Measurement Systems for Advanced Small Modular Reactors

This report intends to support Department of Energy’s Office of Nuclear Energy (DOE-NE) Nuclear Energy Research and Development Roadmap and industry stakeholders by evaluating optical-based instrumentation and control (I&C) concepts for advanced small modular reactor (AdvSMR) applications. These advanced designs will require innovative thinking in terms of engineering approaches, materials integration, and I&C concepts to realize their eventual viability and deployability. The primary goals of this report include: 1. Establish preliminary I&C needs, performance requirements, and possible gaps for AdvSMR designs based on best available published design data. 2. Document commercial off-the-shelf (COTS) optical sensors, components, and materials in terms of their technical readiness to support essential AdvSMR in-vessel I&C systems. 3. Identify technology gaps by comparing the in-vessel monitoring requirements and environmental constraints to COTS optical sensor and materials performance specifications. 4. Outline a future research, development, and demonstration (RD&D) program plan that addresses these gaps and develops optical-based I&C systems that enhance the viability of future AdvSMR designs. The development of clean, affordable, safe, and proliferation-resistant nuclear power is a key goal that is documented in the Nuclear Energy Research and Development Roadmap. This roadmap outlines RD&D activities intended to overcome technical, economic, and other barriers, which currently limit advances in nuclear energy. These activities will ensure that nuclear energy remains a viable component to this nation’s energy security

Glassy Materials Based Microdevices

Microtechnology has changed our world since the last century, when silicon microelectronics revolutionized sensor, control and communication areas, with applications extending from domotics to automotive, and from security to biomedicine. The present century, however, is also seeing an accelerating pace of innovation in glassy materials; as an example, glass-ceramics, which successfully combine the properties of an amorphous matrix with those of micro- or nano-crystals, offer a very high flexibility of design to chemists, physicists and engineers, who can conceive and implement advanced microdevices. In a very similar way, the synthesis of glassy polymers in a very wide range of chemical structures offers unprecedented potential of applications. The contemporary availability of microfabrication technologies, such as direct laser writing or 3D printing, which add to the most common processes (deposition, lithography and etching), facilitates the development of novel or advanced microdevices based on glassy materials. Biochemical and biomedical sensors, especially with the lab-on-a-chip target, are one of the most evident proofs of the success of this material platform. Other applications have also emerged in environment, food, and chemical industries. The present Special Issue of Micromachines aims at reviewing the current state-of-the-art and presenting perspectives of further development. Contributions related to the technologies, glassy materials, design and fabrication processes, characterization, and, eventually, applications are welcome

Comunicações avançadas com fibra óptica plástica

Nowadays, fiber to the Home/Curb/Building/Cabinet (FTTx) services that interconnect homes with a standard glass optical fiber cables to the core/access optical networks have brought the optical fiber at the doorsteps of our homes. However, the last few miles in home access network is still based on the limited bandwidth electronic component which supports by the cooper wires e.g. Cat-5, 6. The rapid growth of personal smart/mobile electronic devices with new developments such as video on demand, High Definition (HD) and three-Dimension (3D) television (TV), cloud computing, video conferences, etc. has been proposed new challenges for the next generation high bandwidth demand required for subscribers in home access network. In order to meet the more demanding expectations of the end user with new developments, it is necessary to improve the physical infrastructure of the existing in home networks in order to obtain the best ratio between quality of service and price of implementation. Plastic optical fibers (POFs) are point out as a promising transmission medium for short-range communication in compare to the “classic” single/multimode glass optical fibers and current cooper wire technology developments. The main advantages of POF are its easy to install, easy splicing and the possibility of using low cost optical transceivers, capability of being robust, and immunity to electromagnetic noise interference. However, the benefits of large-core POFs come at the expense of a less bandwidth and a higher attenuation than silica-based solution. The main objective of this doctoral dissertation is to explore the possibilities and develop low cost, short reach, high data rate POF-links for in home networks applications. This thesis investigates the use of multilevel modulation in particular, pulse amplitude modulation (PAM in combination of the receiver equalizer in order to overcome the bandwidth limitations of the graded index POFs. The possibility of the using multiple channels over a single fiber to increase the capacity of POF systems using commercially available multimode components is also analyzed in this dissertation. Moreover, a low cost Digitised radio signal over plastic fiber system is proposed and evaluated to deliver digital baseband data for wireline and wireless users in home access network. The deployment will be specified in terms of performance, maximum rates and any degradation that might appear in the network. Furthermore, the possibilities of the microstructured fibers in telecommunication application will be studied with main emphasis on their structural design. The photonic crystal fibers made of different highly nonlinear materials with different structures are optimized to achieve ultra-flat dispersion, high nonlinearity and low confinement loss over a broad range of wavelengths in the perspective of their usage in telecommunication applications.Hoje em dia, a possibilidade de a fibra óptica até casa (FTTH) para a transmissão simultânea de diferentes serviços como internet, telefone, televisão digital é uma realidade. No entanto, para satisfazer as expectativas mais exigentes do usuário final com novos desenvolvimentos, tais como vídeo sob demanda, de alta definição (HD) e tridimensional (3D) de televisão (TV), computação em nuvem, vídeo conferências, etc., é necessário melhorar a infra-estrutura física da existente em redes domésticas, a fim de obter a melhor relação entre a qualidade do serviço e preço de implementação. Fibra óptica de plástico (POF) é considerada um meio de transmissão promissor para comunicações de curto alcance, queando comparadas com a clássica fibra óptica de silica (tanto monomodo como multimodo) e com as tecnologias atuais baseadas em fio de cobre. As principais vantagens da POF encontramse na sua facilidade de instalação e conecção, possibilidade de uso de fontes e detectores de baixo custo, robustez e imunidade electromagnética. No entanto, o uso da POF de elevado diâmetro têm também desvantagens uma vez que esta oferece uma menor largura de banda e uma atenuação superior à fibra de sílica convêncional. Esta dissertação de doutoramento tem como principal objetivo explorar as possibilidades de desemvolvimento de componentes de baixo custo baseados em POF para redes de curto alcance, com alta taxa de transmisssão de dados. Esta tese investiga a utilização de vários formatos de modulação combinados com equalizador e receptor, de maneira a superar as limitações de largura de banda em sistemas de comunicação óptica de curto alcance. Em particular, a modulação em amplitude de impulso (PAM) é proposta e investigada a fim de aumentar a capacidade de tais sistemas. Além disso, a possibilidade de usar múltiplos canais, utilizando uma única fibra óptica, também conhecido por multiplexagem por divisão de comprimento de onda (WDM), será analisada neste trabalho. A viabilidade das tecnologias de redes de acesso tanto a nível individual como em sistemas WDM serão analisadas usando componentes multimodo disponíveis comercialmente. A implementação será especificada em termos de desempenho tanto a nível da taxas máximas de transmissão, bem como na degradação do sinal que possa ocorrer na rede. No capitulo 5 desta dissertação é apresentado sistema de radio através de fibra. Este tipo de sistemas permite a simplificação das estações base providenciando também uma elevada manutenção de custos. O principal objectivo deste estudo prende-se com a investigação do impacto da amostragem na preformance de digitalização de rádio através de fibra e também como a introdução de fibra óptica de plástico pode afetar o sistema. Além disso, a possibilidade da aplicação de fibras óticas microestruturadas em redes de telecomunicações serão estudadas com ênfase principal na sua concepção estrutural. As fibras de cristal fotônico feitas de diferentes materiais altamente não-lineares com diferentes estruturas serão otimizadas a fim de alcançar uma dispersão ultra-plana, elevada não linearidade e baixa perda de confinamento em uma vasta gama espectral, na perspectiva de seu uso em aplicações de telecomunicações.Programa Doutoral em Engenharia Eletrotécnic