Negative refraction by photonic nanostructures.

摘要

Artificially engineered optical materials composed of nano-structures have unique optical properties which are not available with naturally occurring materials. Thanks to the rapid development in nano-fabrication and numerical modeling technologies, photonic nano-structures such as metamaterials and photonic crystals and various optical devices made by these optical materials create many novel applications and offer new prospects for manipulating light. For instance, both metamaterials and photonic crystals can exhibit negative refraction and negative refractive indexes. As a result, superlens with the capability of achieving imaging with sub-wavelength resolution can be realized.;In this dissertation, a new negative index metamaterial architecture based on metallic nanoclusters, negative refraction phenomena in photonic crystals and optical devices implemented with negative index photonic crystals for imaging applications are presented. The nanocluster based metamaterials, which utilizes the magnetic Mie resonances of clusters of metallic inclusions, allow us to achieve negative index materials at optical frequency region. Meanwhile, bottom-up fabrication techniques such as self-assembly can be used, which is suitable for large-scale manufacturing and applicable to 3D structures. On the other hand, negative refraction and sub-wavelength imaging by a mechanically tunable photonic crystal structure were investigated. Using a honeycomb lattice photonic crystal composed of a silicon-polyimide membrane, a mechanically tunable superlens with a tunable frequency bandwidth was numerically demonstrated. Additionally, a graded negative index lens made of photonic crystals, which is capable of focusing plane waves, exhibits superior focusing properties such as low chromatic aberrations and broadband operation. Prisms structures made of negative index photonic crystals can offer useful imaging properties such as image inversion and magnification. These devices have the potential to form compact optical imaging systems, therefore enhance the functionalities of superlenses and broaden the applications of negative index materials.