Thesis (M. Phil.)--University of Hong Kong, 2006. / Title proper from title frame. Also available in printed format.

This thesis investigates a novel optoelectronic platform based on the integration of superconductive structures, such as thin films and micro-constrictions, with optical waveguides for ultra-fast and ultra-sensitive devices with applications including high-speed optical communications, quantum optical information processing, and terahertz (THz) devices and systems. The kinetic-inductive photoresponse of superconducting thin films will be studied as the basic optoelectronic process underlying the operation of these novel devices. Analytical formulation for the non-bolometric response is presented, and experimental photodetection in YBCO meander-line structures will be demonstrated. A set of superconducting coplanar waveguides (CPW) are designed and characterized, which support the operation of the devices at microwave frequencies. Microwave-photonic devices comprising a microwave transmission line and a light-sensitive element, such as a meander-line structure, are designed and measured for implementation of optically tunable microwave components. In order to support low-loss and low-dispersion propagation of millimeter-wave and THz signals in ultra-fast and wideband kinetic-inductive devices, surface-wave transmission lines are proposed, incorporating long-wavelength Surface Plasmon Polariton (SPP) modes in planar metal-dielectric waveguides. The theory of superconducting optical waveguides, including analytical formulation and numerical methods, is developed in detail. The implementation of superconducting optical waveguides is discussed thoroughly, employing conventional dielectric-waveguide techniques as well as optical SPP modes. Superconductive traveling-wave photodetectors (STWPDs) are introduced as a viable means for ultra-fast and ultra-sensitive photodetection and photomixing. A modified transmission line formalism is developed to model STWPDs, where light is guided through an optical waveguide and photodetection is distributed along a transmission line. As an appendix, a systematic approach is developed for the analysis of carrier transport through superconducting heterostructures and micro-constrictions within the Bogoliubov-de Gennes (BdG) framework. The method is applied to study the role of Andreev reflection and Josephson-like phenomena in the current-voltage characteristics of inhomogeneous superconducting structures. I-V characteristics are experimentally demonstrated in YBCO micro-constrictions with potential applications in millimeter-wave and THz devices.

In this study, we study polymer-dispersed blue-phase liquid-crystal (PDBPLC)films. The PDBPLC film is fabricated by using BPLC instead of nematic LC in a PDLC film. The experimental results show that the PDBPLC films and can be switchable as the conventional PDLC. The polymer morphology of the PDBPLC is affected by the concentration of monomer in the BPLC/monomer mixture. The PDBPLC exhibits a good contrast ratio with monomer concentration of 39.17 wt%. The rise time of PDBPLC films decreases as the polymer concentration increases. Moreover, the results also show that a complete phase separation occurs with the exposure time of 20 minutes. For the future work, we will improve the high driving voltage and low ratio of the PDBPLC film.

Thesis (Ph. D.)--University of Texas at Austin, 1999. / Vita. Includes bibliographical references (leaves 147-151). Available also in a digital version from Dissertation Abstracts.

Thesis (Ph. D.)--University of Texas at Austin, 2000. / Vita. Includes bibliographical references (leaves 88-91). Available also in a digital version from Dissertation Abstracts.

Thesis (Ph. D.)--University of Texas at Austin, 2000. / Vita. Includes bibliographical references (leaves 100-110). Available also in a digital version from Dissertation Abstracts.

With the progress of microfabrication and nanofabrication technologies, there has been a reawakened interest in the possibility of controlling the propagation of light in various materials periodically structured at a scale comparable to, or slightly smaller than the wavelength. We can now engineer materials with periodic structures to implement a great variety of optical phenomena. These include well known effects, such as dispersing a variety of wavelength to form a spectrum and diffracting light and controlling its propagation directions, to new ones such as prohibiting the propagation of light in certain directions at certain wavelengths and localizing light with defects in some artificially synthesized dielectric materials. Advances in this field have had tremendous impact on modern optical and photonic technologies. This doctoral research was aimed at investigating some of the physics and applications of periodic structures for building blocks of the optical communication and interconnection system. Particular research emphasis was placed on the exploitation of innovative periodic structure-based optical and photonic devices featuring better functionality, higher performance, more compact size, and easier fabrication. Research topics extended from one-dimensional periodic-structure-based true-time delay module, to two-dimensional periodic-structure-based silicon photonic-crystal electro-optic modulators. This research was specifically targeted to seek novel and effective solutions to some long-standing technical problems, such as slow switching speed, large device size, and high power consumption of silicon optical modulators, among others. For each subtopic, research challenges were presented and followed by the proposed solutions with extensive theoretical analysis. The proposals were then verified by experimental implementations. Experimental results were carefully interpreted and the future improvements were also discussed. / text

published_or_final_version / abstract / Electrical and Electronic Engineering / Master / Master of Philosophy

In modern communications systems, the components supporting wavelength division for increased density are rapidly becoming small compared with the wavelength of light being manipulated. As the size of these devices shrinks there comes a point when the features of interest become smaller than the wavelength and thereby the fundamental properties of light interaction with such structures change dramatically. In these structures and materials, resonances, effective properties, and band-gaps arise and offer designers a new realm of possibilities for the design of high quality factor resonators, filters and switches. / The study of structures comprising two different scales compared with the wavelength of light promises interesting optical possibilities for future devices. In these structures a subwavelength size feature is used in conjunction with a super-wavelength size feature. This thesis will show how the resulting optical behavior for such structures arises from the combination of the sub- and super-wavelength diffractive effects. / Two application examples of these two-scale devices will be studied: the distributed echelle grating and the subwavelength based Fabry-Perot cavity. Both of these applications can be thought, of as distributed diffractive structures, a structure in which diffraction and subwavelength scale interference combine to produce high efficiency and versatile new devices.

This thesis investigates a novel optoelectronic platform based on the integration of superconductive structures, such as thin films and micro-constrictions, with optical waveguides for ultra-fast and ultra-sensitive devices with applications including high-speed optical communications, quantum optical information processing, and terahertz (THz) devices and systems. The kinetic-inductive photoresponse of superconducting thin films will be studied as the basic optoelectronic process underlying the operation of these novel devices. Analytical formulation for the non-bolometric response is presented, and experimental photodetection in YBCO meander-line structures will be demonstrated. A set of superconducting coplanar waveguides (CPW) are designed and characterized, which support the operation of the devices at microwave frequencies. Microwave-photonic devices comprising a microwave transmission line and a light-sensitive element, such as a meander-line structure, are designed and measured for implementation of optically tunable microwave components. In order to support low-loss and low-dispersion propagation of millimeter-wave and THz signals in ultra-fast and wideband kinetic-inductive devices, surface-wave transmission lines are proposed, incorporating long-wavelength Surface Plasmon Polariton (SPP) modes in planar metal-dielectric waveguides. The theory of superconducting optical waveguides, including analytical formulation and numerical methods, is developed in detail. The implementation of superconducting optical waveguides is discussed thoroughly, employing conventional dielectric-waveguide techniques as well as optical SPP modes. Superconductive traveling-wave photodetectors (STWPDs) are introduced as a viable means for ultra-fast and ultra-sensitive photodetection and photomixing. A modified transmission line formalism is developed to model STWPDs, where light is guided through an optical waveguide and photodetection is distributed along a transmission line. As an appendix, a systematic approach is developed for the analysis of carrier transport through superconducting heterostructures and micro-constrictions within the Bogoliubov-de Gennes (BdG) framework. The method is applied to study the role of Andreev reflection and Josephson-like phenomena in the current-voltage characteristics of inhomogeneous superconducting structures. I-V characteristics are experimentally demonstrated in YBCO micro-constrictions with potential applications in millimeter-wave and THz devices.