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UBC Theses and Dissertations

Spectral control of total internal reflection for novel information displays Mossman, Michele Ann

Abstract

A new method for creating a reflective image device has been devised based on total internal reflection (TIR). This technique has the potential to yield a brighter, highercontrast image than those of current reflective displays by incorporating polymeric micro-prismatic sheets that reflect by means of TIR. High surface reflectance is achieved by efficiently redirecting ambient light toward the viewer, and an image is generated by controllably preventing, or "frustrating", the reflection in selected regions through absorption of light in the very thin evanescent wave region near the TIR interface. The transition between the reflective and absorptive state requires a motion of less than a micron of the absorber, and therefore it can occur quickly and efficiently. A fundamental problem in this approach - interfacial adhesion - was ameliorated through the use of liquid phase backing material, instead of gas. However, this complicated the optical requirements by substantially reducing the refractive index ratio at the TIR interface. To maintain TIR over an acceptable angular range, a low refractive index perfluorinated hydrocarbon was identified as an ideal liquid, and an optical configuration was devised to enhance the effective refractive index ratio at the interface. Detailed Monte Carlo ray tracing verified that high reflectance and a high contrast ratio are achievable with these designs over a useful range of viewing directions. Electrophoresis of pigment particles in a perfluorinated hydrocarbon has been shown to be a practical method for modulating TIR. The observed photometric performance is consistent with a numerical model developed to describe the interaction of an incident light ray with a density distribution of particles near the interface. Colour pigment suspensions have yielded, for the first time, spectrally selective control of TIR, which requires the particles to be essentially non-scattering but selectively absorptive. The results presented here demonstrate the feasibility of this TIR-based approach in practical reflective image device applications, and are suggestive that further development work in this area is warranted.

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