A novel sensor using a polymer coated long-period grating (LPG) has been proposed for monitoring levels of organic contaminants in air or water systems. The sensor operates by detecting refractive index changes in the polymer coating as analytes partition in. Polymer coatings used must be able to reversibly and reproducibly absorb contaminants of interest from the sample and have a refractive index just below that of the fiber cladding. The synthesis and characterization of several chemically selective polysiloxanes is described. Pre-polymer materials are made through the catalyzed condensation of silane monomers. Different functional groups are incorporated either through polymerizing functionalized monomers, or by post-functionalizing the polymer through a platinum-catalyzed hydrosilylation reaction. The pre-polymer materials are crosslinked into elastomeric films using titanium(IV) tetraisopropoxide. The polymer refractive index is controlled through altering the ratios of functional groups within the polymer or changing the loading levels of titanium. Four polymers were made, having different functional groups and optimized refractive indices for use on the proposed sensor. The partition coefficients for the polymers with a variety of solvents are calculated and compared. Each polymer was found to have a slightly different chemical selectivity pattern, demonstrating that a set of polymers could be used to generate a sensor array. Partition coefficient data was calculated from the gas phase by considering the change in polymer refractive index as the solvents partitioned into the polymer. The Lorentz-Lorenz equation was used to model the relationship between the change in refractive index and the solvent concentration within the polymer. Finally, polymers were applied to LPGs and used to successfully detect various solvents from the gas phase. This was accomplished by monitoring the entire LPG spectrum, and also by considering loss at a single wavelength using fiber-loop ring-down spectroscopy. / Thesis (Ph.D, Chemistry) -- Queen's University, 2008-09-26 15:28:35.603

A long period fiber grating (LPFG) is formed by inducing the periodic refractive index variation along a fiber. A lot of work has been done to fabricate the LPFGs in the photonic crystal fibers (PCFs) to function as all-fiber band-rejection filters, interferometers, and sensing applications. In this thesis, we propose a novel LPFG based on the gel-filled PCF. The PCF filled with the UV gel was exposed to the high-intensity UV light through the mask. The periodic index variation is formed along the fiber in the cladding region, resulting in the LPFG. By measuring the propagation losses of our LPFG, three spectral dips in the transmission bands are observed at 872 nm, 1309 nm, and 1418 nm as the grating period is 600 £gm, which indicates the mode coupling from the fundamental core mode to the higher order modes (HOMs) of the gel-filled PCFs. By using a full-vector finite-difference frequency-domain (FDFD) method, we numerically calculate the phase match condition for our LPFGs. The calculated resonant wavelengths are 875 nm, 1319 nm, and 1415 nm. Very good agreement between the measured resonant wavelengths and the numerical results is obtained. We also fabricate the selectively gel-filled LPFGs to reduce the propagation losses by utilizing a simple selectively blocking technique. In addition, we measure and discuss the sensing sensitivities of the UV-induced LPFGs, including the temperature, strain, curvature, torsion, and surrounding refractive index (SRI) sensitivities. The measured sensitivity to temperature is 1.7 nm/¢XC from 25 ¢XC to 45 ¢XC. As the surrounding refractive index is increased to 1.377, the dip position has a maximum shift of 2 nm. Compared with other LPFGs, the UV-induced LPFGs are more insensitive to bending and strain due to the complete cladding structure. This could benefit the stability of the temperature sensors, based on our UV-induced LPFGs.

Equipped with advanced field instruments in the past few decades, oceanographers have been able to comprehend some characteristics of the internal waves(IWs), such as the generation, propagation and energy dissipation, as well as to promote understanding in oceanography and marine ecology affected by IWs in the world ocean. Although surface gravity wave and internal wave are two of the most common natural phenomena in the ocean, the interaction between them has not been fully investigated, despite limited theoretical derivations in the literature, nor using laboratory experiments to verify the theory. A series of laboratory experiments were conducted at the National Sun Yen-sen University to study the waveform evolution of continuous IWs propagation on the flat bottom and across a trapezoidal obstacle. Surface waves were generated on a density stratified fluid system in a wave flume, from which IWs were induced indirectly to investigate their wave properties associated with their propagation . The experimental results are then used to determine the maximum depth which could be affected by surface waves in different wave conditions(wave height and period), as well as the amplitude of the IWs induced. The relationship between them are then presented in graphic form. Experiments were also conducted in uniform density and stratified fluid system with a trapezoidal obstacle. The results reveal that (1)long-period surface waves were susceptible to the interaction with the IWs in a stratified system, thus rendering wave height reduction, and (2)short-period surface waves interactions with their IWs counterparts was insignificant, hence yielded wave height similar to that in uniform density fluid system. Moreover, experiments were also conducted to study for long and short period IW propagated over pseudo slope-shelf(using trapezoidal obstacle). The results show that the variation in the IWs significantly affected the strength of internal hydraulic jump and vortices on the front slope and subsequent waveform inversion on the horizontal plateau. For IWs with short period, the horizontal distance on the plateau affected by the IWs was shirter and the total time of wave-topography interaction decreased.

Using Long-Period Fiber Gratings as component of Gain-Flattening filter ofOptical Amplifier, and discuss spectrum of different struture of Long-Period Fiber Gratings. To investigate the spectra characteristics of Long-Period fiber Gratings for designing reference resources. Aiming at different Gain-Flattening filter uses different struture of fiber grating, and the decision of parameter of fiber grating using Genetic Algorithm. Finally delcaring the dataflow of designing filter using Long-Period Fiber Grating and conclusion.In this paper , gain flatttening Cr:YAG optical amplifier spectrum and Erbium-doped optical amplifier spectrum,one achieve 300nm bandwidth and another achieve 40nm.

Distributed sensing is highly desirable in a wide range of civil, industrial and military applications. The current technologies for distributed sensing are mainly based on the detection of optical signals resulted from different elastic or non-elastic light-matter interactions including Rayleigh, Raman and Brillouin scattering. However, they can measure temperature or strain only to date. Therefore, there is a need for technologies that can further expand measurement parameters even to chemical and biological stimuli to fulfill different application needs. This dissertation presents a fully-distributed fiber-optic sensing technique based on a traveling long-period grating (T-LPG) in a single-mode fiber. The T-LPG is generated by pulsed acoustic waves that propagate along the fiber. When there are changes in the fiber surrounding medium or in the fiber surface coating, induced by various physical, chemical or biological stimuli, the optical transmission spectrum of the T-LPG may shift. Therefore, by measuring the T-LPG resonance wavelength at different locations along the fiber, distributed measurement can be realized for a number of parameters beyond temperature and strain. Based on this platform, fully-distributed temperature measurement in a 2.5m fiber was demonstrated. Then by coating the fiber with functional coatings, fully-distributed biological and chemical sensing was also demonstrated. In the biological sensing experiment, immunoglobulin G (IgG) was immobilized onto the fiber surface, and the experimental results show that only specific antigen-antibody binding can introduce a measurable shift in the transmission optical spectrum of the T-LPG when it passes through the pretreated fiber segment. In the hydrogen sensing experiment, the fiber was coated with a platinum (Pt) catalyst layer, which is heated by the thermal energy released from Pt-assisted combustion of H2 and O2, and the resulted temperature change gives rise to a measurable T-LPG wavelength shift when the T-LPG passes through. Hydrogen concentration from 1% to 3.8% was detected in the experiment. This technique may also permit measurement of other quantities by changing the functional coating on the fiber; therefore it is expected to be capable of other fully-distributed sensing applications. / Ph. D.

No description available.

Ionic self-assembled multilayers (ISAMs) can be formed by alternately dipping a substrate in anionic and cationic polyelectrolytes. Each immersion deposits a monolayer via electrostatic attraction, allowing for nanometer-scale control over film thickness. Additionally, ISAM films can be applied to arbitrary substrate geometries and can easily incorporate a variety of polymers and nanoscale organic or inorganic inclusions. The ISAM technique was used to tune and functionalize a rapid, sensitive fiber optic biosensor for textit{Brucella}, a family of bacteria that are detrimental to livestock and can also infect humans. The sensor was based on a turn-around point long period fiber grating (TAP-LPG). Unlike conventional LPGs, in which the attenuation peaks shift wavelength in response to environmental changes, TAP-LPGs have a highly sensitive single wavelength peak with variable attenuation. ISAMs were applied to a TAP-LPG to tune it to maximum sensitivity and to facilitate cross-linking of receptor molecules. Biotin and streptavidin were used to attach biotinylated hybridization probes specific to distinct species of textit{Brucella}. The sensor was then exposed to lysed cell cultures and tissue samples in order to evaluate its performance. The best results were obtained when using samples from textit{Brucella} infected mice, which produced a transmission change of 6.0 ± 1.4% for positive controls and 0.5 ± 2.0% for negative controls. While the sensor was able to distinguish between positive and negative samples, the relatively short dynamic range of the available fiber limited its performance. Attempts to fabricate new TAP-LPGs using a CO2 laser were unsuccessful due to poor laser stability. A second application of the ISAM technique was as a source of second-harmonic generation (SHG). SHG is a nonlinear optical process in which light is instantaneously converted to half its wavelength in the presence of intense electric fields. Localized surface plasmons (LSPs) in metal nanoparticles produce strong electric field enhancements, especially at sharp tips and edges, that can be used to increase SHG. Colloidally grown silver nanoprisms were deposited onto nonlinear ISAM films and conversion of 1064 nm Nd:YAG radiation to its 532 nm second-harmonic was observed. Little enhancement was observed when using nanoprisms with LSP resonance near 1064 nm due to their large size and low concentration. When using shorter wavelength nanoprisms, enhancements of up to 35 times were observed when they were applied by immersion, and up to 1380 times when concentrated nanoprisms were applied via dropcasting at high enough densities to broaden their extinction peak towards the excitation wavelength. A maximum enhancement of 2368 times was obtained when concentrated silver nanoprisms with LSP resonance around 900 nm were spincast with an additional layer of PCBS. / Doctor of Philosophy / Polyelectrolytes are long molecules composed of chains of charged monomers. When a substrate with a net surface charge is dipped into an oppositely charged polyelectrolyte solution, a single layer of molecules will be electrostatically deposited onto the substrate. Because the surface charge now appears to match the charge of the solution, no further deposition occurs. However, the process can be repeated by rinsing the substrate and immersing in a solution with the opposite charge. This technique forms ionic self-assembled multilayers (ISAMs), which can be assembled with nanometer-level control over thickness. The flexibility of polymer chemistry allows ISAMs to be formed from polyelectrolytes with a wide variety of properties. Additionally, the technique can easily incorporate other nanoscale materials, such as nanoparticles, clay platelets, and biological molecules, and has been investigated for applications ranging from dye-sensitized organic solar cells to drug delivery and medical implant coatings. This dissertation presents two applications of ISAM films. In one, ISAM films were used to tune and functionalize an optical biosensor for Brucella. Brucellosis primarily infects livestock, in which it causes significant reproductive problems leading to economic losses, but can also cause flu-like symptoms and more serious complications in humans. A rapid, sensitive test for Brucella is required to monitor herds and adjacent wild carriers, such as elk and bison. Optical biosensors, which operate by detecting changes due to the interaction between light and the stimulus, could satisfy this need. Long period fiber gratings (LPGs) are periodic modulations induced in the core of an optical fiber that cause transmitted light to be scattered at a resonant wavelength, resulting in attenuation. Conventional LPGs respond to changes in strain, temperature, or external refractive index by shifting their resonant wavelength. When special conditions are met, an LPG may exhibit a turn-around point (TAP), where dual peaks coalesce into a single peak with a constant wavelength but variable attenuation depth. TAP-LPGs are more sensitive than ordinary LPGs, and could be developed into inexpensive sensors with single-wavelength light sources and detectors. In this work, ISAMs were deposited onto an LPG to tune it near its TAP. Segments of single-stranded DNA, called hybridization probes, that were specific to individual species of Brucella were attached to the ISAM film before the sensor was exposed to lysed bacterial cultures. It was found that the sensor could distinguish between Brucella and other types of bacteria, but was less successful at distinguishing between Brucella species. The project was limited by the available TAP-LPGs, which had less dynamic range than those used in prior work by this group. Attempts were made to establish a new supply of TAP-LPGs by fabrication with a CO2 laser, but these efforts were unsuccessful due to poor laser stability. The second project discussed in this dissertation investigated ISAM films as a source of second-harmonic generation (SHG), a nonlinear optical process in which light is converted to half its fundamental wavelength in the presence of intense electric fields. Nonlinear ISAMs were constructed by choosing a polyelectrolyte with a hyperpolarizable side group in which SHG can occur. The SHG efficiency was increased by factors of several hundred to several thousand by the addition of silver nanoprisms. Metal nanoparticles can produce strong electric field enhancements, especially at their tips and edges, when incident light causes resonant collective oscillations in their electrons called localized surface plasmons (LSPs). It was found that while silver nanoprisms whose LSP resonant wavelength matched the fundamental wavelength were too dilute to produce noticeable enhancement, better results could be obtained by depositing shorter wavelength nanoprisms at sufficient density to broaden their extinction peak via interparticle interactions. The best enhancement observed was for a sample where concentrated silver nanoprisms with LSP resonance around 900 nm were dropcast onto an ISAM film and coated with an additional polymer layer, resulting in 2368 times more SHG than the plain ISAM film.

No description available.

Recently, long-period fiber gratings (LPFGs) based on PCFs have been demonstrated by using heating or a mechanically pressure to induce periodic index variations along the fibers. However, LPFGs fabricated by these two methods suffer the structure damage. In this thesis we propose novel optically controllable LPFGs based on the photoresponsive photonic liquid crystal fibers (PLCFs) and no structure damage occurs during the fabrication process. The photoresponsive PLCF was filled with a LC mixture consisting of the nematic LC E7 and the photoresponsive 4MAB. The properties of the photoresponsive PLCF can be modulated by using laser irradiation. In addition, the transmission bands of the photoresponsive PLCF can also be tuned by controlling the 4MAB concentration or operation temperature. An optically controllable LPFG was fabricated based on the photoresponsive PLCF by using blue-laser irradiation through a mask with 700-£gm grating period. The measured resonant wavelength appeared at 1539 nm with the FWHM was 27 nm, and the maximum dip depth was about −15 dB with a 6.5-dB insertion loss. The LPFG was shown to be erasable by using a green laser. In addition, we have also investigated the effects of the number of grating period, 4MAB concentrations, operation temperatures, thermal recovery properties, and irradiation intensity on the LPFGs. Our proposed optically controllable LPFGs possess reversible property and are quite useful to be applied in tunable optical devices.

Thesis (Ph. D.)--Miami University, Dept. of Chemistry and Biochemistry, 2006. / Title from first page of PDF document. Includes bibliographical references.