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Browsing by Subject "Waveguide"

Now showing 1 - 2 of 2
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    Generation of Gradient Index Optics with Subwavelength Metamaterials
    (2019-07) Borowiak, Andrew
    A GRIN optic is a useful device for modern optics but is not frequently used outside of niche applications due to the difficulty of fabricating any arbitrary gradient index. One potential solution to this fabrication problem is to use subwavelength metamaterials generated using lithography. A process was developed to generate a subwavelength waveguide which leverages effective medium theory to behave like a GRIN optic. This process was tested by generating waveguides as well as mode converters for converting from gaussian beams to supergaussian beams. The results from these experiments show that this technique could produce mode converters with average Strehl ratios of 0.997 and an average transmission of 94.8% on the scale of tens of microns; however, it was found that these designs are not viable for modern lithographic fabrication techniques. There is much to explore still with this topic such as the lower size limits of these designs or whether modern lithography could make a mode converter with this structure.
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    A Single-Element Fiber Transducer for All-Optical Ultrasound and Photoacoustic Sensing
    (2019-12) Vilanguppam Thathachary, Supriya
    The past few decades have seen a rapid rise in minimally invasive medical procedures performed around the globe. These procedures have been made possible largely because of innovations in medical imaging and sensing to guide physicians in performing the interventions safely. Ultrasound technology has remained highly popular through this transition due to its safety and efficacy. However, the demand for miniature flexible devices for increased accessibility has prompted a shift toward all-optical ultrasound devices. Additionally, photoacoustic imaging and sensing have emerged as a promising technology with abilities to enhance diagnostic capabilities in several clinical applications, most significantly in the imaging of atherosclerotic plaque. The Fabry-perot ultrasound detector, being one of the more widespread optical ultrasound detection technologies, has been explored significantly in this context. This thesis presents a novel wave-guided configuration for fiber Fabry-Perot ultrasound detectors. This work demonstrates 16 times higher sensitivity than traditional piezoelelectric technology at comparable size scales. The chapters that follow present the simulations and experiments conducted around (a) optimizing the fabrication of the wave-guided fiber Fabry-Perot devices, (b) the complete optical and acoustic characterization of the fabricated devices, and (c) the potential improvements that can be made with incorporating dielectric mirrors. The thesis concludes with a discussion on the possible configurations for creating a complete ultrasound and photoacoustic probe for guiding minimally invasive interventions.