This thesis is an exploration of the properties of engineered defects in self-assembled photonic crystals, with particular attention paid to the complete band gap of the a-Si inverse opal. The potential of this metamaterial for optical signal processing in telecommunications is studied using a pair of complementary simulation techniques; one is a frequency-domain code, while the other is in the time domain. Calculations of photonic states associated with isolated point defects are performed, and their cavity modes, losses and field distributions are calculated. The equivalence of two classes of defects is demonstrated, and a robust, single-mode point defect microcavity is proposed. A linear defect waveguide, comprised of coupled chain of such point defects, is analyzed. Transmission around sharp bends is demonstrated, and some simple devices are considered. Several potential approaches to fabrication of the defects, the properties of various candidate materials, and more complex devices are discussed.

Femtosecond laser processes were optimized for nonlinear interactions with optical materials to develop a novel biophotonic lab-on-a-chip device that integrates laser-formed waveguides, microfluidic channels and photonic crystals (PCs). Such integration seeks the novel demonstration of dual PC functionalities: (1) efficient chromatographic separation and filtration of analytes through a porous PC embedded inside a microfluidic channel and (2) optofluidic spectroscopy through embedded waveguides that probe PC stop band shifts as varying analyte concentrations flow and separate. The building blocks for such integration were demonstrated through the accelerated analyte flow rates measured through the embedded porous PC and the optical characterization of a PC’s stop band via integrated waveguides. Together, these laboratory results give promise for achieving simultaneous chromatographic and spectroscopic capabilities in a single PC optofluidic device. Future improvements in the laser process and possible new research directions are also offered.

Slow photon, or light with reduced group velocity, is a unique phenomenon found in photonic crystals that theoreticians have long suggested to be invaluable for increasing the efficiency of light-driven processes. This thesis demonstrates experimentally the feasibility of using slow photons to optically amplify photochemistry of both organic and inorganic systems. The effect of photonic properties on organic photochemistry was investigated by tracing out the wavelength-dependent rate of photoisomerization of azobenzene anchored on silica opals. The application of slow photons to inorganic photochemical processes was realized by molding nanocrystalline titania into an inverse opal structure and investigating its photodegradation efficiency in relation to the photonic properties. Changes in the photodegradation efficiency were directly linked to modifications of the electronic band gap absorption as a result of the photonic properties. The highest enhancement of twofold was achieved when the energy of the slow photons overlaps with the electronic band gap absorption, such that the loss of light due to photonic stop-band reflection was significantly reduced. In addition, the strength of slow-photon amplification with respect to the macroscopic structural order was studied by introducing controlled disorder via the incorporation of guest spheres into the opal templates. For the first time, a correlation between structural order, photonic properties and a photochemical process was established. The ability to combine slow-photon optical amplification with chemical enhancement was further achieved by incorporating platinum nanoparticles in inverse titania opals where the platinum nanoparticles increased the lifetimes of the higher population of electron-hole pairs arising from slow photon. Overall, various important factors governing the slow photon enhancement were investigated in detail, including the energy of the photonic stop band, angle dependence, thickness of the film, degree of structural order, filling fraction of the dielectric material and diffusion of a second medium if present. Theoretical calculations based on scalar-wave approximation in support of the experimental findings were provided wherever possible. The findings provide a blueprint for achieving optical amplification using slow photons in the broad range of photochemical or photophysical processes.

This thesis is an exploration of the properties of engineered defects in self-assembled photonic crystals, with particular attention paid to the complete band gap of the a-Si inverse opal. The potential of this metamaterial for optical signal processing in telecommunications is studied using a pair of complementary simulation techniques; one is a frequency-domain code, while the other is in the time domain. Calculations of photonic states associated with isolated point defects are performed, and their cavity modes, losses and field distributions are calculated. The equivalence of two classes of defects is demonstrated, and a robust, single-mode point defect microcavity is proposed. A linear defect waveguide, comprised of coupled chain of such point defects, is analyzed. Transmission around sharp bends is demonstrated, and some simple devices are considered. Several potential approaches to fabrication of the defects, the properties of various candidate materials, and more complex devices are discussed.

Femtosecond laser processes were optimized for nonlinear interactions with optical materials to develop a novel biophotonic lab-on-a-chip device that integrates laser-formed waveguides, microfluidic channels and photonic crystals (PCs). Such integration seeks the novel demonstration of dual PC functionalities: (1) efficient chromatographic separation and filtration of analytes through a porous PC embedded inside a microfluidic channel and (2) optofluidic spectroscopy through embedded waveguides that probe PC stop band shifts as varying analyte concentrations flow and separate. The building blocks for such integration were demonstrated through the accelerated analyte flow rates measured through the embedded porous PC and the optical characterization of a PC’s stop band via integrated waveguides. Together, these laboratory results give promise for achieving simultaneous chromatographic and spectroscopic capabilities in a single PC optofluidic device. Future improvements in the laser process and possible new research directions are also offered.

Nanophotonics is an emerging research field that deals with interaction between light and matter in a sub-micron length scale. Nanophotonic devices have found an increasing number of applications in many areas including optical communication, microscopy, sensing, and solar energy harvesting especially during the past two decades. Among all nanophotonic devices, three main areas, namely photonic crystals, optical metamaterials and plasmonic devices, gain dominant interest in the photonic society owning to their potential impacts. This thesis studies the fabrication and characterization of three types of novel devices within the above-mentioned areas. They are respectively photonic-crystal (PhC) surface-mode microcavities, optical metamaterial absorbers, and plasmonic couplers. The devices are fabricated with modern lithography-based techniques in a clean room environment. This thesis particularly describes the critical electron-beam lithography step in detail; the relevant obstacles and corresponding solutions are addressed. Device characterizations mainly rely on two techniques: a vertical fiber coupling system and a home-made optical transmissivity/reflectivity setup. The vertical fiber coupling system is used for characterizing on-chip devices intended for photonic integrations, such as PhC surface-mode cavities and plasmonic couplers. The transmissivity/reflectivity setup is used for measuring the absorbance of metamaterial absorbers. This thesis presents mainly three nanophotonic devices, from fabrication to characterization. First, a PhC surface-mode cavity on a SOI structure is demonstrated. Through a side-coupling scheme, a system quality-factor of 6200 and an intrinsic quality-factor of 13400 are achieved. Such a cavity can be used as ultra-compact optical filter, bio-sensor and etc. Second, an ultra-thin, wide-angle metamaterial absorber at optical frequencies is realized. Experimental results show a maximum absorption peak of 88% at the wavelength of ~1.58μm. The ultra-fast photothermal effect possessed by such noble-metal-based nanostructure can potentially be exploited for making better solar cells. Finally, we fabricated an efficient coupler that channels light from a conventional dielectric waveguide to a subwavelength plasmonic waveguides and vice versa. Such couplers can combine low-loss dielectric waveguides and lossy plasmonic components onto one single chip, making best use of the two. / QC 20110524

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Porous silicon (PSi) photonic crystals have aroused research interest as label-free chemical and biological sensing transducers owing to the ease of fabrication, high quality optics and a sensitive optical response to changes in efractive index. A major impediment to using PSi materials as sensors is the relative instability of the silicon surface to oxidation in ambient air and aqueous environments. This thesis reports methods for derivatising PSi towards realisation of 1-D silicon-based photonic materials for applications in biology and medicine. Narrow-linewidth rugate filters, a class of photonic crystal, are fabricated on silicon to display a high reflectivity resonant line in the reflectance spectrum. The position of the resonance is sensitive to changes in refractive index, thus allowing quantification of infiltrating biological species. The efficacy of rugate filters as biosensing transducers requires 1) protection from aqueous degradation, 2) resistance to non-specific adsorption and 3) distal reactivity for coupling of biorecognition molecules. Two chemical strategies based on hydrosilylation of functional alkenes are compared for stabilising the PSi structure against oxidation whilst resisting non-specific adsorption of biomolecules. Immobilisation of peptides to the organic layers is demonstrated for optical detection of protease enzymes. Introduction of protease results in cleavage of the immobilised peptides within the rugate filters, detected by an optical blue-shift to shorter wavelengths. To increase the sensitivity to proteolysis, covalent mmobilisation of biopolymers is evaluated using gelatin as a model substrate. Digestion of gelatin is detected down to 37 attomoles of protease. Furthermore, the surface chemistry allows specific capture of live cells and incubation with stimulated macrophages in tissue culture results in optical detection of released gelatinase enzymes. The generality of the surface chemistry allows for a range of other biological applications to be investigated. An alternative biorecognition interface, hybrid lipid bilayer membranes, containing specific recognition elements for cholera toxin allows optical detection of affinity capture and concentration within the PSi. In addition, the suitability of chemically modified photonic crystals as reservoirs for mass spectrometry is evaluated towards biomolecule quantification after optical detection. A robust and flexible surface chemistry on PSi photonic crystals is critical to performance in a range of biological assays and a necessary requirement for wide-scale employment.

Thesis (M.S.)--West Virginia University, 2008. / Title from document title page. Document formatted into pages; contains vi, 120 p. : ill. (some col.). Includes abstract. Includes bibliographical references (p. 91-100).