Master's Theses

Date of Award

2014

Document Type

Thesis

Department

Engineering

First Advisor

Sang-Woo Seo

Keywords

nanofabrication, ultrasound, pressure

Abstract

Resonance waveguide grating structures have been a subject of interest for several decades. This optical technique offers unique advantages when compared with other optical components. This stems from their relatively simple structure comprised of layers, as well as their high reflection efficiency within a narrow spectral bandwidth. Typical resonance waveguide grating structures that exhibit these characteristics are cost effective and fabricated with fewer materials than conventional multilayer resonance structures. Essentially, only a grating, waveguide, and substrate layer are required for its operation. In addition, unique spectral characteristics can be obtained by varying the grating and layer structure. Among these characteristics are symmetric low sideband reflections over large wavelength ranges, variable spectral bands, and polarization dependent or independent reflections. In the research presented, the basis for the resonance waveguide grating structure is developed. The diffraction gratings are fabricated using a photolithographic process. A custom setup employing Lloyd’s Mirror Interferometer allows the fabrication of gratings with a wide period range. This technique renders uniform and continuous one-dimensional and twodimensional structures. The gratings are successfully implemented into a resonance waveguide iii grating structure. First, an elastomeric polymer resonant waveguide grating structure is demonstrated to work effectively as a pressure sensor. The external applied pressure is measured optically by the spectrum resonance peak shift the developed sensor incurs. The sensitivity of the demonstrated sensor can be tuned to different pressure ranges by adjusting the layer thickness of the fabricated waveguide and cladding layers, and also by selecting polymers with certain elastic properties. Secondly, an acousto-optic sensor based on the resonance waveguide grating structure is presented. The sensor is fabricated utilizing low Young’s modulus polymer-based materials allowing the sensor to achieve good sensitivity to ultrasound pressure waves. The sensor structural parameters are altered under ultrasound pressure waves that results in an optical resonance shift of the sensor characteristics. This process successfully translates into a light intensity modulation. Ultimately, the planar structure geometry of the demonstrated sensors in this research, allows its potential use for two-dimensional optical pressure imaging applications such as ultrasound imaging and pressure wave detection and mapping.

 
 

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