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  • About
  • The Global ETD Search service is a free service for researchers to find electronic theses and dissertations. This service is provided by the Networked Digital Library of Theses and Dissertations.
    Our metadata is collected from universities around the world. If you manage a university/consortium/country archive and want to be added, details can be found on the NDLTD website.
1

Fabrication of Hollow Optical Waveguides on Planar Substrates

Barber, John P. 16 October 2006 (has links) (PDF)
This dissertation presents the fabrication of hollow optical waveguides integrated on planar substrates. Similar in principle to Bragg waveguides and other photonic crystal waveguides, the antiresonant reflecting optical waveguide (ARROW) is used to guide light in hollow cores filled with liquids or gases. Waveguides with liquid or gas cores are an important new building block for integrated optical sensors. The fabrication method developed for hollow ARROW waveguides makes use of standard microfabrication processes and materials. Dielectric layers are deposited on a silicon wafer using plasma-enhanced chemical vapor deposition (PECVD) to form the bottom layers of the ARROW waveguide. A sacrificial core material is then deposited and patterned. Core materials used include aluminum, SU-8 and reflowed photoresist, each resulting in a different core geometry. Additional dielectric layers are then deposited, forming the top and sides of the waveguide. The sacrificial core is then removed in an acid solution, resulting in a hollow ARROW waveguide. Experiments investigating the mechanical strength of the hollow waveguides and the etching characteristics of the sacrificial core suggest design rules for the different core types. Integration of solid-core waveguides is accomplished by etching a ridge into the top dielectric layer of the ARROW structure. Improved optical performance can be obtained by forming the waveguides on top of a raised pedestal on the silicon substrate. Loss measurements on hollow ARROW waveguides fabricated in this manner gave loss coefficients of 0.26 cm-1 for liquid-core waveguides and 2.6 cm-1 for air-core waveguides. Fluorescence measurements in liquid-core ARROW waveguides have achieved single-molecule detection sensitivity. Integrated optical filters based on ARROW waveguides were fabricated, and preliminary results of a capillary electrophoresis separation device using a hollow ARROW indicate the feasibility of such devices for future investigation.
2

Fundamental Components for Lamina Emergent Mechanisms

Jacobsen, Joseph O. 22 February 2008 (has links) (PDF)
This thesis introduces lamina emergent mechanisms (LEMs) and presents components that can be used as building blocks to create LEMs capable of more complex motion. As the name suggests, lamina emergent mechanisms are fabricated out of planar materials (the lamina) but their motion is out of that plane (emergent). Lamina emergent mechanisms can provide benefits that include reduced manufacturing costs and minimal volume when in the planar state. The compact initial state of LEMs is beneficial in reducing shipping costs, especially in volume critical applications. LEMs also exhibit the potential benefits of compliant mechanisms, namely increased precision, reduced weight, reduced wear, and part count reduction. The LEM components presented in this thesis include flexible segments, fundamental mechanisms, and a new complaint joint, the lamina emergent torsional (LET) Joint. The flexible segments are developed through changes in geometry, boundary/loading conditions, and material. The fundamental mechanisms presented have motion similar to planar change-point four-bar and six-bar mechanisms, and spherical change-point mechanisms. The LET Joint is presented as a compliant joint suited for applications where large angular rotation is desired, but high off-axis stiffness is not as critical. The joint is introduced and the equations necessary for determining the force-deflection characteristics and stress are presented. Since the LET Joint can be fabricated from a single planar layer, it is well suited for macro and micro applications. Illustrative examples of the LET Joint are provided with devices fabricated from materials as diverse as steel, polypropylene, and polycrystalline silicon.

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