Optoelectronic materials for subwavelength imaging and laser beam maniupulation.

摘要

Metamaterials are artificially engineered materials for providing properties which are not readily available in nature. In the last decade, research activity in the field of metamaterials has led to diverse applications including remote sensing, lithography, communication, and biological imaging. For instance, researchers have shown that a class of metamaterials exhibit negative refraction and have also utilized this phenomenon to enable a super lens for beating the diffraction limit of light. Other fascinating developments include optical cloaking devices which involves bending of the electromagnetic waves completely around the objects. Therefore, metamaterials have become an important subject for study.;The central focus of this thesis is primarily on two applications of metamaterials: sub-wavelength imaging and laser beam manipulation. The proof-ofconcept of sub-wavelength imaging has been demonstrated in the mid-infrared regime. A tapered array of step-index cylindrical waveguides is the basis for the magnifying infrared fiberscope. Optimized designs have been presented for the proposed infrared fiberscope by numerical modeling. The fabrication of the fiberscope is based on a high pressure chemical fluid deposition technique to deposit precisely defined periodic arrays of semiconductor waveguides within the holes of a microstructured optical fiber made of silica. The optical properties of various waveguides (germanium, silicon, zinc selenide, silicon nitride) fabricated by this method have been characterized in the infrared regime. The basic essential features of an imaging fiber bundle such as isolation between adjacent pixels, magnification, optical throughput and near-field image transfer characteristics have been investigated. The imaging concept is demonstrated at 1.55 mum, 3.39 mum and 10.64 mum using appropriate materials for fabricating the tapered array of waveguides to maximize the optical throughput.;Manipulation of the laser beam has been demonstrated using patterned ferroelectric domains in lithium tantalate. The linear electro-optic effect in ferroelectrics was utilized to demonstrate the proof of concept of two dimensional dynamic focusing, optical switching and laser beam shaping. The beam propagation method was employed to design the required domain pattern. The domain pattern was fabricated by well established electric field assisted poling techniques. The performance of these devices is found to closely agree with theory.