Graduate Thesis Or Dissertation
 

Subwavelength light confinement and quantum chaos in micro- and nano-structured metamaterials

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https://ir.library.oregonstate.edu/concern/graduate_thesis_or_dissertations/rf55zb453

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  • This dissertation concerns a broad range of unique phenomena related to the light propagation at nano- and micro-scales. To access the nano-domain, we introduce anisotropy-based waveguides with positive- and negative-index modes. These novel structures allow energy propagation in subwavelength regions and, in contrast to surface waves, have the mode structure identical to that of telecom fibers. We design multilayered meta-materials for far-IR to visible frequencies and develop analytical homogenization techniques for light transmission through these systems. Our numerical simulations demonstrate that tapered waveguides with anisotropic cores can efficiently transfer energy to and from regions as small as 1/45-th of the wavelength, substantially outperforming conventional techniques. We analyze the behavior of volume and surface modes in nano-waveguides and demonstrate theoretically that subwavelength geometry enables the unique control over modes' dispersive properties, unavailable in diffraction-limited systems. In particular, the inter-scale transition between "photonic-funnel" and "photonic-compressor" regimes in nano-structures allows versatile management of the group velocity of light pulses ranging from slow to superluminal values. As a control mechanism, we employ the material gain, previously suggested for loss compensation, and develop an analytical description of the relevant physics. We further study the prospects of gain-assisted dispersion management in passive and active negative index structures and formulate a universal approach for defining the causal direction of the wave vector of modes in optical metamaterials. This approach also determines signs of the refractive index and impedance. We employ the developed formalism to demonstrate a broadband dispersion-less index and impedance matching in the nanowire-based negative index materials. Finally, we address light scattering phenomena in asymmetric micro-cavity resonators. We introduce a novel class of chaotic ratchet-shaped cavities with broken angular momentum symmetry and study mode dynamics in such systems. This study shows that such resonators have dynamically localized mode structure and benefit a fundamentally distinct in- and out-coupling mechanisms. In contrast to "symmetric" systems featuring same evanescent trapping and escape, incident light couples directly to high-Q modes of a ratchet, while the escape remains evanescent. Application of the presented results include ultra high-density energy focusing, near-field microscopy, nm-resolution imaging, high-performance optical sensing, pulse-routing, and all-optical computing.
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