Sensing and interferometry, including design and characterisation of special optical fibres

This thesis presents my work in the area of optical fibre sensing, and optical fibre design and characterisation along with the interferometric and signal processing techniques that were developed along the way

Sensing and interferometry, including design and characterisation of special optical fibres

This thesis presents my work in the area of optical fibre sensing, and optical fibre design and characterisation along with the interferometric and signal processing techniques that were developed along the way

Recent Progress in Optical Fiber Research

This book presents a comprehensive account of the recent progress in optical fiber research. It consists of four sections with 20 chapters covering the topics of nonlinear and polarisation effects in optical fibers, photonic crystal fibers and new applications for optical fibers. Section 1 reviews nonlinear effects in optical fibers in terms of theoretical analysis, experiments and applications. Section 2 presents polarization mode dispersion, chromatic dispersion and polarization dependent losses in optical fibers, fiber birefringence effects and spun fibers. Section 3 and 4 cover the topics of photonic crystal fibers and a new trend of optical fiber applications. Edited by three scientists with wide knowledge and experience in the field of fiber optics and photonics, the book brings together leading academics and practitioners in a comprehensive and incisive treatment of the subject. This is an essential point of reference for researchers working and teaching in optical fiber technologies, and for industrial users who need to be aware of current developments in optical fiber research areas

Novel materials for silicon based photonics

Thesis: Ph. D., Massachusetts Institute of Technology, Department of Materials Science and Engineering, 2018.This electronic version was submitted by the student author. The certified thesis is available in the Institute Archives and Special Collections.Cataloged from student-submitted PDF version of thesis.Includes bibliographical references.A complete photonic chip must include the following components: a light source, usually lasers, an isolator, a waveguide, a modulator and a photodetector. Limited by material intrinsic properties, silicon alone cannot realize all the above mentioned functions. The development of silicon photonics has found its way through exploiting novel materials as hybrid platforms to manufacture various devices and systems. In this thesis, we focus on the development of novel material in emerging needs of broadband coherent light source and optical isolators. Chalcogenide glass stands out among the candidates for light generation and sensing due to its large non-linear figure of merit and wide transparency window in the IR spectral range, while magnetic garnet still presents the best device performance among magneto-optical isolators owing to the ease of phase formation and relatively low material absorption. We first investigated the fabrication technology of chalcogenide glass and developed a process flow to produce low loss planar chalcogenide glass waveguides. Using electron beam lithography to minimize sidewall roughness and reactive ion etch to achieve vertical sidewalls. We managed to demonstrate a record low loss of 0.5 dB/cm in single mode core chalcogenide waveguides. Based on this low loss platform, we integrated a supercontinuum light source onto a sensor chip. Our work presented a step forward towards miniaturization photonic sensor chips. Next, we focused on a hybrid platform of chalcogenide glass and magnetic garnet. By carefully designing device architecture, a monolithically integrated TM polarized magneto-optical (MO) isolator with 3 dB insertion loss and 40 dB isolation ratio was demonstrated. Both parameter sets record among current monolithically integrated on-chip MO isolators. Meanwhile, we also demonstrated a monolithically integrated MO isolator with TE polarization featuring 11.5 dB insertion loss and 20 dB isolation ratio. Lastly, we leveraged cavity enhanced spectroscopy platform to study radiation induced effect on SiNx, a-Si and SiC materials. We found a refractive index modulation to the order of 10⁻³ after receiving 10 Mrad Gamma radiation dose.by Qingyang Du.Ph. D

Towards an integrated atom chip

The field of atom chips is a relatively new area of research which is rapidly becoming of great interest to the scientific community. It started out as a small branch of cold atom physics which has quickly grown into a multidisciplinary subject. It now encompasses topics from fundamental atomic and quantum theory, optics and laser science, to the engineering of ultra sensitive sensors.In this thesis the first steps are taken towards a truly integrated atom chip device for real world applications. Multiple devices are presented that allow the trapping, cooling, manipulation and counting of atoms. Each device presents a new component required for the integration and miniaturisation of atom chips into a single device, capable of being used as a sensor.Initially, a wire trap was created capable of trapping and splitting a cloud of BoseEinstein condensate (BEC) for use in atom interferometry. Using this chip a BEC has been successfully created, trapped and coherent splitting of this cloud has been achieved.Subsequently, the integration and simplification of the initial trapping process was approached. In all the experiments to date, atoms are initially collected from a warm vapour by a magneto-optical trap (MOT). This thesis presents a new approach in which microscopic pyramidal MOTs’ are integrated into the chip itself. This greatly reduces the number of optical components and helps to simplify the process significantly.Also presented is a method for creating a planar-concave micro-cavity capable of single atom detection. One such cavity consists of a concave mirror fabricated in silicon and the planar tip of an optical fibre. The performance of the resonators is highly dependent on the surface roughness and shape profile of the concave mirrors therefore a detailed study into the fabrication technique and its effects on these parameters was undertaken. Using such cavities single atom detection has been shown to be possible. These cavities have also been sccessfully integrated into an atom wire guide.Finally a co-sputtered amorphous silicon/titanium (a-Si/Ti) nanocomposite material was created and studied for its use as a novel structural material. This material is potentially suitable for integrated circuitry (IC)/Micro-electromechanical- systems (MEMS) integration. The material’s electrical and structural properties were investigated and initial results suggest that a-Si/Ti has the potential to be a compelling structural material for future IC/MEMS integration.To build all of these devices, a full range of standard microfabrication techniques was necessary as well as some non standard processes that required considerable process development such as the electrochemical deposition.This thesis presents a tool box of fabrication techniques for creating various components capable of different tasks that can be integrated into a single device. Each component has been successfully demonstrated in laboratory conditions. This represents a significant step toward a real world atom chip device

Development Of Carbon Based Neural Interface For Neural Stimulation/recording And Neurotransmitter Detection

Electrical stimulation and recording of neural cells have been widely used in basic neuroscience studies, neural prostheses, and clinical therapies. Stable neural interfaces that effectively communicate with the nervous system via electrodes are of great significance. Recently, flexible neural interfaces that combine carbon nanotubes (CNTs) and soft polymer substrates have generated tremendous interests. CNT based microelectrode arrays (MEAs) have shown enhanced electrochemical properties compared to commonly used electrode materials such as tungsten, platinum or titanium nitride. On the other hand, the soft polymer substrate can overcome the mechanical mismatch between the traditional rigid electrodes (or silicon shank) and the soft tissues for chronic use. However, most fabrication techniques suffer from low CNT yield, bad adhesion, and limited controllability. In addition, the electrodes were covered by randomly distributed CNTs in most cases. In this study, a novel fabrication method combining XeF2 etching and parylene deposition was presented to integrate the high quality vertical CNTs grown at high temperature with the heat sensitive parylene substrate in a highly controllable manner. Lower stimulation threshold voltage and higher signal to noise ratio have been demonstrated using vertical CNTs bundles compared to a Pt electrode and other randomly distributed CNT films. Adhesion has also been greatly improved. The work has also been extended to develop cuff shaped electrode for peripheral nerve stimulation. Fast scan cyclic voltammetry is an electrochemical detection technique suitable for in-vivo neurotransmitter detection because of the miniaturization, fast time response, good sensitivity and selectivity. Traditional single carbon fiber microelectrode has been limited to single detection for in-vivo application. Alternatively, pyrolyzed photoresist film (PPF) is a good candidate for this application as they are readily compatible with the microfabrication process for precise fabrication of microelectrode arrays. By the oxygen plasma treatment of photoresist prior to pyrolysis, we obtained carbon fiber arrays. Good sensitivity in dopamine detection by this carbon fiber arrays and improved adhesion have been demonstrated

Photonic devices for sensing and security applications

The main aim of this thesis is the numerical and experimental verification of structured micro- and nano-scaled optical devices fabricated with e-beam, photolithography, reactive ion etching and embossing. Two separate themes were addressed; sensing of electromagnetic pulses by electro-optic non-linear guided wave photonic devices and free space photonic devices for security and anti-counterfeiting in polymer banknotes. The first theme was led by a comparison between two photonic devices used as extrinsic fibre optic sensors for the detection of short duration electromagnetic pulses (EMPs). A suitable electro-optic substrate was used for the fabrication of both micron sized waveguide-based evanescent coupling photonic devices, modelled using beam envelope methods, and its nano-structured surface Plasmon enhanced counterpart, modelled using FDTD. Both devices are capable of detecting EMPs with field strengths ranging from 50 – 500kV/m with pulse durations from 200ns – 2000ns. The surface enhanced plasmonic device showed improved device sensitivity and tunability, with a more linearized response along with greater ease of integration with optical fibres. In the second theme the photonic devices were used for image formation through diffractive optical methods with a view to polymeric mass replication. Multilevel 2μm - 8μm feature size diffractive optical elements, designed for dual colour operation in the scalar domain, were compared to 250nm feature size binary phase modulated Bragg gratings for single colour operation in the resonance domain. Both devices are capable of generating high fidelity images under appropriate illumination. The scalar domain elements, designed for 450nm and 650nm illumination, showed measured diffraction efficiencies of 37% and 55% in the 0th order for each of the respective illumination wavelengths. Operating at 532nm, the diffraction efficiency of the resonance domain element was measured to be 70%. The resonance domain element is significantly shallower than the scalar domain device with a reduced number of phase levels (2 compared to 16). With the final aim of this application area being replication on a flexible base substrate, the elements with larger feature sizes would represent challenging replication process (in terms of linearization of depth profile) whereas the smaller feature sizes would be more challenging in lateral dimensions. In both cases the potential for counterfeiting would be reduced and the addition of a second image at a different illumination wavelength for the scalar domain element would lead to a further enhanced degree of security

Characterization and modification of electrospun fiber mats for use in composite proton exchange membranes

Thesis (Ph. D.)--Massachusetts Institute of Technology, Dept. of Materials Science and Engineering, 2013.This electronic version was submitted by the student author. The certified thesis is available in the Institute Archives and Special Collections.Cataloged from student-submitted PDF version of thesis.Includes bibliographical references.Electrostatic fiber formation, or electrospinning, offers a particularly simple and robust method to create polymeric nanofibers of various sizes and morphologies. In electrospinning, a viscoelastic fluid is charged so that a liquid jet is ejected from the surface of the fluid (typically in the form of a drop supplied by a needle or spinneret) and collected on a grounded plate, creating a nonwoven fiber mat. Modification of the diameter of the fibers as well as the porosity, specific surface area, and mechanical properties of the mat allows one to tailor electrospun mats for specific applications. Despite the widespread and rapidly growing use of electrospinning in the fabrication of novel nanomaterials, there are no simple, universal methods of predicting, a priori, the properties of electrospun fibers from knowledge of the polymer solution properties and electrospinning operating conditions alone. Changing a single fluid or processing parameter can affect the jet and fiber formation through several mechanisms. For example, using a different solvent can change several properties of the electrospinning fluid, such as the dielectric constant, conductivity, surface tension, and solute-solvent interaction. The work in this thesis seeks to develop a simple relation for predicting terminal jet diameter during electrospinning, which accounts for solution viscoelasticity as well as solution conductivity and operating parameters that can be easily measured and controlled. The mechanical and tribological properties of electrospun fiber mats are of paramount importance to their utility as components in a variety of applications. Although some mechanical properties of these mats have been investigated previously, reports of their tribological properties are essentially nonexistent. In this thesis, electrospun nanofiber mats of poly(trimethyl hexamethylene terephthalamide) (PA 6(3)T) and poly(hexamethylene adipamide) (PA 6,6) are characterized mechanically and tribologically. Post-spin thermal annealing was used to modify the fiber morphology, inter-fiber welding, and crystallinity within the fibers. Morphological changes, in-plane tensile response, friction coefficient, and wear rate were characterized as functions of the annealing temperature. The Young's moduli, yield stresses and toughnesses of the PA 6(3)T nonwoven mats improved by two- to ten-fold when annealed slightly above the glass transition temperature, but at the expense of mat porosity. The mechanical and tribological properties of the thermally annealed PA 6,6 fiber mats exhibited significant improvements through the Brill transition temperature, comparable to the improvements observed for amorphous PA 6(3)T electrospun mats annealed near the glass transition temperature. The wear rates for both polymer systems correlate with the yield properties of the mat, in accordance with a modified Ratner-Lancaster model. The variation in mechanical and tribological properties of the mats with increasing annealing temperature is consistent with the formation of fiber-to-fiber junctions and a mechanism of abrasive wear that involves the breakage of these junctions between fibers. A mechanically robust proton exchange membrane with high ionic conductivity and selectivity is an important component in many electrochemical energy devices such as fuel cells, batteries, and photovoltaics. The ability to control and improve independently the mechanical response, ionic conductivity, and selectivity properties of a membrane is highly desirable in the development of next generation electrochemical devices. In this thesis, the use of layer-by-layer (LbL) assembly of polyelectrolytes is used to generate three different polymer film morphologies on highly porous electrospun fiber mats: webbed, conformal coating, and pore-bridging films. Specifically, depending on whether a vacuum is applied to the backside of the mat or not, the spray-LbL assembly either fills the voids of the mat with the proton conducting material or forms a continuous fuel-blocking film. The LbL component consists of a proton-conducting, methanolimpermeable poly(diallyl dimethyl ammonium chloride)/sulfonated poly(2,6-dimethyl 1,4- phenylene oxide) (PDAC/sPPO) thin film. The electrospun fiber component consists of PA 6(3)T fibers of average diameter between 400 and 800 nm, in a nonwoven matrix of 60-90% porosity depending on the temperature of thermal annealing utilized to improve the mechanical properties. This thesis demonstrates the versatility and flexibility of this fabrication technique, since any ion conducting LbL system may be sprayed onto any electrospun fiber mat, allowing for independent control of functionality and mechanical properties. The mechanical properties of the spray coated electrospun mats are shown to be superior to the LbL-only system, and possess intrinsically greater dimensional stability and lower mechanical hysteresis than Nafion under hydration cycling. The electrochemical selectivity of the composite LbL-electrospun membrane is found to be superior to Nafion, which makes them a viable alternative proton exchange membrane for fuel cell applications. The composite proton exchange membranes fabricated in this work were tested in an operational direct methanol fuel cell, with results showing the capability for higher open circuit voltages (OCV) and comparable cell resistances when compared to Nafion.by Matthew Marchand Mannarino.Ph.D

Eighteenth Space Simulation Conference: Space Mission Success Through Testing

The Institute of Environmental Sciences' Eighteenth Space Simulation Conference, 'Space Mission Success Through Testing' provided participants with a forum to acquire and exchange information on the state-of-the-art in space simulation, test technology, atomic oxygen, program/system testing, dynamics testing, contamination, and materials. The papers presented at this conference and the resulting discussions carried out the conference theme 'Space Mission Success Through Testing.