Planar waveguides obtained on commercial glass substrates by sol-gel and laser irradiation methods

The aim of the thesis is the fundamental study, design, fabrication and characterisation of photonic structures for spatial optic and, particulary, the interconnexion of optical devices. The research explored technologies and substrates for the fabrication of photonic structures based on the guided propogation of light and its application to research and development of integrated optical devices and improving the functionality of communication systems, which realises intelligent optical operations based on Fourier spatial transformed and image formation properties.At the same time, aims to explore new technologies for fabrication ofphotonic structures; which are repeatibility and not contaminants; and the product of well-defined charactericstics and low price

Understanding the Role of Gravity in the Crystallization Suppression of ZBLAN Glass

Fluorozirconate glasses, such as ZBLAN (ZrF4-BaF2-LaF3-AlF3-NaF), have the potential for optical transmission from 0.3 μm in the UV to 7 μm in the IR region. However, crystallites formed during the fiber drawing process prevent this glass from achieving its low loss-capability. Other researchers have shown that microgravity processing leads to suppressed crystal growth in ZBLAN glass, which can lead to lower transmission loss in the desired mid-IR range. However, the mechanism governing crystal growth suppression has not been thoroughly investigated. In the present research multiple ZBLAN samples were subjected to a heating and quenching test apparatus on a parabolic aircraft under controlled μ-g and hyper-g environments and compared with 1-g ground tests. Optical microscopy (transmission and polarized) along with SEM examination elucidates that crystal growth in ZBLAN is suppressed when processed in a microgravity environment. Hence crystallization occurs at a higher temperature in μ-g and the working temperature range at which the fiber can be manufactured has been extended. We postulate that the fundamental process of nano-scale mass transfer (lack of buoyancy driven convection) in the viscous glass is the mechanism responsible for crystal growth suppression in microgravity. Suppressing molecular mobility within the semi-molten glass starves nucleating crystallites and prevents any further growth. A COMSOL Multi-Physics model was developed to show the velocity contours due to convection processes in a 1-g, μ-g, and hyper-g environment. Analytical models show that while suppressing convection is relevant at fiber drawing temperatures (360°C), mass transfer due to diffusion dominates at higher temperatures leading to crystal growth at temperatures 65400°C. ZBLAN fibers are also known for their poor handling ability. Therefore an analysis of the thermal degradation of ZBLAN optical fibers based on fracture mechanics was also conducted. Conditions of crack initiation and stable versus unstable crack growth leading to fiber fracture were analyzed to explain behavior observed from controlled flexure tests of ZBLAN optical fibers exposed to various temperatures

Nonlinear propagation of incoherent white light in a photopolymerisable medium: From single self-trapped beams to 2-D and 3-D lattices

Optical beams that travel through a material without undergoing divergence are known as self-trapped beams. Self-trapping occurs when a beam induces a suitable index gradient in the medium that is capable of guiding the original beam. An incoherent light consists of femtosecond scale speckles, due to random phase fluctuations and were not thought to self-trap until recently. In 1997, Mitchell et al., showed that white light can self-trap, provided the medium cannot respond fast enough to form index gradients to these speckles individually. However, detailed studies have been hampered by a lack of suitable materials and strategies for enabling such a response. In 2006, our group showed that a photopolymer is suitable for incoherent self-trapping, since the index change is governed by an inherently slow rate of polymerization (of the order of milliseconds). This has enabled further studies of various phenomena with white light self-trapping. The studies here show (i) the first direct experimental evidence of interactions of two incoherent white light self-trapped beams, as well as fission, fusion and repulsion. Existence of dark self-trapping beams with incoherent white light was also shown, counter intuitively in a positive nonlinear medium. (iii) Lattices were formed with multiple ordered bright as well as dark self-trapping filaments using optochemical self-organization. (iv) Woodpile-like 3D lattices with bright and dark beams were also demonstrated and simulations showed theoretical band gaps. (v) Self-trapping of a co-axial beam of incoherent white light was also shown experimentally and through simulations.Doctor of Philosophy (PhD

Material Properties of Anderson Localizing Optical Fiber

Over half a century ago, the paper entitled “Absence of Diffusion in Certain Random Lattices” was published by P. Anderson and described a metal-to-insulator transition phenomenon where electron diffusion does not occur in disordered semiconductors. This phenomenon is now commonly referred to as “Anderson localization” (AL). Since the AL detailed in Anderson’s paper arose from the wave nature of electrons, similar behavior should be observed in other wave systems, more specifically in optics. Given the utility of optical fibers, extensive theoretical treatment has been conducted on transverse Anderson localization (TAL, disorder in x- and y-directions, with the z-direction remaining invariant) in such systems. Only recently has it been experimentally observed, paving the way for studies into the influence of fiber material on linear and nonlinear TAL. This Dissertation represents the first materials study of doped silicate transverse Anderson localizing optical fibers (TALOFs) and their corresponding passive and active optical properties. More specifically, Chapter I reviews microstructured and multicore optical fiber, and methods of their fabrication, in order to develop an understanding of the impact of the core microstructure on waveguide properties. Then, an overview of TALOFs is developed to provide insights into the different materials and fabrication methods used to develop the few TALOFs reported to date. The former fiber systems are well studied; therefore, this research Dissertation will be focused on the novel effects and material influences on the latter (Anderson) systems. Chapter II begins the development of these novel fibers through in situ phase separation in optical fibers drawn using the molten core method (MCM). Limitations in the resulting fibers were studied, and adaptations to the fabrication method were made to elongate the already formed microphases through development and subsequent use of a two-tier MCM. Chapter III introduces an alternative fiber fabrication technique, namely the stack-and-draw method, specifically adapted to utilize MCM-derived precursor fibers in the stack. The resulting fibers are characterized to understand the effects of processing on the core microstructure, and ultimately to understand how the core microstructure leads to TAL. Chapters IV and V investigate the material properties and potential applications of the TALOFs that resulted from the fabrication technique developed in Chapter III. Specifically, Chapter IV investigates both Yb3+ and Er3+ doped TALOFs for solid-state lasing and amplification respectively. The resulting experimental observations and present limitations of these fibers for active applications are discussed. In Chapter V, the first nonlinear optical TALOFs are explored. Even though the higher refractive index phases possessed an estimated nonlinear refractive index (n2) similar to silica, small modal effective areas were demonstrated due to the strong localization in certain regions of these TALOFs. As a result, nonlinear optical frequency shifts were demonstrated for the first time in a TALOF, attributed to Raman and four-wave mixing (FWM), concomitantly. While not decisive into the underlying nature of TAL in the presence of optical nonlinearities, this suggests that the two are not mutually exclusive. Finally, Chapter VI summarizes the findings of this Dissertation, discusses the challenges with further fiber development in these TALOFs, and provides examples for future efforts in improving both the fibers themselves, and ultimately the understanding of these fibers

Laser induced modifications and waveguides writing inside silicon

Doctor of PhilosophyDepartment of Industrial & Manufacturing Systems EngineeringShuting LeiSilicon is the basic material for semiconductor industry and laser direct writing in the bulk of silicon has attracted people’s attention since 20 years ago. However, the research of laser-matter interaction inside silicon is limited and the formation process of the subsurface modification is not clear enough. In addition, the attempts in the past decade to generate waveguides inside silicon are not satisfactory. Based on this situation, this dissertation has two objectives. The first one is to study the fundamental process of laser-matter interaction and have a better understanding of the material modification process inside silicon, and the second one is to write straight and curved waveguides inside silicon and characterize these waveguides. The first objective will be achieved through a comprehensive experimental study on the physics behind the nanosecond (ns) laser writing process. The experimental study will involve generating subsurface modifications inside silicon and characterize the modifications by optical microscopy, SEM, TEM, and Raman spectroscopy. The second objective will be achieved through laser transverse writing and by shaping the laser beam through a pair of cylindrical lenses and focusing the shaped beam inside the silicon. It is found that permanent modifications are made with tightly focused ns pulses at 1.55 μm wavelength inside silicon without damaging the front surface. Examinations of the modified zone using Raman spectroscopy and TEM reveal a disturbed crystal structure with defects and strained areas. For the first time, high resolution TEM images show a direct evidence of amorphous silicon inside ns laser induced modifications. A quantitative analysis based on Raman spectra of the modified zone indicates that the amorphous silicon accounts for only a small percentage of the total modification. More work is needed to determine the effects of laser parameters on the amorphous transition inside silicon. Nanosecond laser transverse writing of different types of waveguides inside silicon are demonstrated, such as straight waveguides, curved waveguides with different radii, and straight-curved waveguides. A nearly circular transverse guide-profile is formed with the shaped beam. The waveguides are found to support single-mode propagation for 1.55 μm wavelength light. The loss is found to be about 3 dB/cm for straight waveguide and can be larger for curved waveguides depending on the curvature. The knowledge gained from this research will enable us to have a better understanding of laser-matter interaction inside silicon and pave the way for its future applications in the semiconductor field

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