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1
Ishaq, I. M. "Fibre-optic long period gratings with nano-structured overlays." Thesis, Cranfield University, 2006. http://dspace.lib.cranfield.ac.uk/handle/1826/10725.
Full textAbstract:
The influence of nano-structured
overlays on the properties of fibre optic Long Period
Gratings (LPGs) has been investigated. The presence of overlays of thickness of order
100 m is shown to
significantly alter the response of the LPG to environmental
parameters, such as the surrounding refractive index. A LPG with a nano-structured
overlay was observed to exhibit enhanced sensitivity to refractive indices lower than
silica, and was observed to exhibit sensitivity to refractive indices greater than that of
the silica
cladding, not observed in the absence of the overlay. A theoretical model
predicts the observed behaviour. The observation was exploited to enhance the
sensitivity of a LPG based chemical concentration sensor.
The
response of the transmission spectrum of concatenated long period gratings
(LPGs) to ' the deposition of nano-structured overlays was also investigated.
Concatenated LPGs act as a Mach-Zehnder interferometer and the
phase of the
interference
fringes that appear within the LPGs° attenuation bands were shown to be
highly sensitive to the optical thickness of the overlay, for thicknesses of order 100
mn. Several devices were fabricated with
increasing path lengths to demonstrate
effect of overlay thickness and refractive index on the transmission spectrum of the
LPG.
2
Ishaq, Imran M. "Fibre optic Long Period Gratings with nano-structured overlays." Thesis, Cranfield University, 2006. http://dspace.lib.cranfield.ac.uk/handle/1826/10725.
Full textAbstract:
The influence of nano-structured overlays on the properties of fibre optic Long Period Gratings (LPGs) has been investigated. The presence of overlays of thickness of order 100 m is shown to significantly alter the response of the LPG to environmental parameters, such as the surrounding refractive index. A LPG with a nano-structured overlay was observed to exhibit enhanced sensitivity to refractive indices lower than silica, and was observed to exhibit sensitivity to refractive indices greater than that of the silica cladding, not observed in the absence of the overlay. A theoretical model predicts the observed behaviour. The observation was exploited to enhance the sensitivity of a LPG based chemical concentration sensor. The response of the transmission spectrum of concatenated long period gratings (LPGs) to ' the deposition of nano-structured overlays was also investigated. Concatenated LPGs act as a Mach-Zehnder interferometer and the phase of the interference fringes that appear within the LPGs° attenuation bands were shown to be highly sensitive to the optical thickness of the overlay, for thicknesses of order 100 mn. Several devices were fabricated with increasing path lengths to demonstrate effect of overlay thickness and refractive index on the transmission spectrum of the LPG.
3
Cleary, Justin. "Surface Plasmon Hosts for Infrared Waveguides and Biosensors, and Plasmons in Gold-Black Nano-Structured Films." Doctoral diss., University of Central Florida, 2010. http://digital.library.ucf.edu/cdm/ref/collection/ETD/id/3562.
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Applications of surface plasmon polaritons (SPPs) have thus far emphasized visible and near-infrared wavelengths. Extension into the long-wave infrared (LWIR) has numerous potential advantages for biosensors and waveguides, which are explored in this work. A surface plasmon resonance (SPR) biosensor that operates deep into the infrared (3-11 µm wavelengths) is potentially capable of biomolecule recognition based on both selective binding and characteristic vibrational modes. The goal is to operate such sensors at wavelengths where biological analytes are strongly differentiated by their IR absorption spectra and where the refractive index is increased by dispersion, which will provide enhanced selectivity and sensitivity. Potentially useful IR surface plasmon resonances are investigated on lamellar gratings formed from various materials with plasma frequencies in the IR wavelength range including doped semiconductors, semimetals, and conducting polymers. One outcome of this work has been the demonstration of a simple analytic formula for calculating the SPP absorption resonances in the angular reflectance spectra of gratings. It is demonstrated for Ag lamellar gratings in the 6-11 µm wavelength range. The recipe is semi-empirical, requiring knowledge of a surface-impedance modulation amplitude, which is found here by comparison to experiment as a function of the grating groove depth and the wavelength. The optimum groove depth for photon-to-SPP energy conversion was found by experiment and calculation to be ~10-15% of the wavelength. Hemicylindrical prism couplers formed from Si or Ge were investigated as IR surface plasmon couplers for the biosensor application. Strong Fabry-Perot oscillations in the angular reflectance spectra for these high index materials suggest that grating couplers will be more effective for this application in the LWIR. A variety of materials having IR plasma frequencies were investigated due to the tighter SPP mode confinement anticipated in the IR than for traditional noble metals. First doped-Si and metal silicides (Ni, Pd, Pt and Ti) were investigated due to their inherent CMOS compatibility. Rutherford backscattering spectroscopy, x-ray diffraction, scanning electron microscopy, secondary ion mass spectrometry and four point probe measurements complemented the optical characterization by ellipsometry. Calculation of propagation length and mode confinement from measured permittivities demonstrated the suitability for these materials for LWIR SPP applications. Semimetals were also investigated since their plasma frequencies are intermediate between those of doped silicon and metal silicides. The semimetal antimony, with a plasma frequency ~80 times less than that of gold was characterized. Relevant IR surface plasmon properties, including the propagation length and penetration depths for SPP fields, were determined from optical constants measured in the LWIR. Distinct resonances due to SPP generation were observed in angular reflection spectra of Sb lamellar gratings in the wavelength range of 6 to 11 µm. Though the real part of the permittivity is positive in this range, which violates the usual condition for the existence of bound SPP modes, calculations based on experimental permittivity showed that there is little to distinguish bound from unbound SPP modes for this material. The SPP mode decays exponentially away from the surface on both sides of the permittivity sign change. Water is found to broaden the IR plasmon resonances significantly at 9.25 micron wavelength where aqueous extinction is large. Much sharper resonances for water based IR SPR biosensor can be achieved in the 3.5 to 5.5 µm range. Nano-structured Au films (Au-black) were investigated as IR absorbers and possible solar cell enhancers based on surface plasmon resonance. The characteristic length scales of the structured films vary considerably as a function of deposition parameters, but the absorbance is found to be only weakly correlated with these distributions. Structured Au-black with a broad range of cluster length scales appear to be able to support multiple SPP modes with incident light coupling to the corrugated surface as seen by photoelectron emission microscopy (PEEM) and SPR experiments, supporting the hypothesis that Au-black may be a suitable material for plasmon-resonance enhancement solar-cell efficiency over the broad solar spectrum.Ph.D.
Department of Physics
Sciences
Physics PhD
4
Lowder, Tyson Lee. "Surface Relief D-Fiber Bragg Gratings for Sensing Applications." Diss., CLICK HERE for online access, 2008. http://contentdm.lib.byu.edu/ETD/image/etd2644.pdf.
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5
Khanfar, Hazem. "Polarizing Optical Devices Based on Embedded One-Dimensional Subwavelength-Structured Photonic-Crystal Layers." ScholarWorks@UNO, 2009. http://scholarworks.uno.edu/td/1022.
Full textAbstract:
Quarter-wave retarders (QWR) that employ total internal reflection (TIR) and interference of light in a transparent thin-film coating at the base of a prism are presented. Explicit equations that guide the optimal design are provided. The optimal refractive index and normalized thickness of QWR coatings on glass and ZnS prisms are determined as functions of the internal angle of incidence from 45o to 75o. An achromatic QWR that uses an Si3N4- coated N-BK10-Schott glass prism is also presented with retardance error of 3o over the 400-600 nm wavelength range. An iterative procedure for the design of a polarizing beam splitter (PBS) that uses a form-birefringent, subwavelength-structured, one-dimensional photonic-crystal layer (SWS 1-D PCL) embedded in a high-index cubical prism is presented. The PBS is based on index matching and total transmission for the p polarization and total internal reflection for the s polarization at the prism-PCL interface at a 45o angle of incidence. A high extinction ratio in reflection ( 50 dB) over the 4-12 μm IR spectral range is achieved using a SWS 1-D PCL of ZnTe embedded in a ZnS cube within an external field of view (FOV) of ±6.6o and in the presence of grating filling factor errors of up to ±10%. Comparable results, but with a wider field of view, are also obtained with a Ge PCL embedded in a Si prism. A design for visible spectrum (553–713 nm) PBS SWS 1-D PCL of ZnTe embedded in a ZnS cube is also presented. The PBS shows a FOV of ±7o. A circular polarizing beam splitter (CPBS) with equal throughput for p and s polarization using SWS 1-D PCL embedded in a high-index cubical prism is introduced. A dual QWR in transmission and reflection with 50–50% CPBS is designed using the PCL. Such a CPBS shows large deviation from the design point as a result of small changes in the design parameters; e.g. a change of 10% in the filling factor results in 12o shift from the 90o phase shift between p and s polarizations, which limits the practical utility of the device.
6
Cetnar, John. "Full Wave Electromagnetic Simulations of Terahertz Wire Grid Polarizers and Infrared Plasmonic Wire Gratings." Wright State University / OhioLINK, 2014. http://rave.ohiolink.edu/etdc/view?acc_num=wright1398356024.
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Greenwell, Andrew. "RIGOROUS ANALYSIS OF WAVE GUIDING AND DIFFRACTIVE INTEGRATED OPTICAL STRUCTURES." Doctoral diss., University of Central Florida, 2007. http://digital.library.ucf.edu/cdm/ref/collection/ETD/id/4346.
Full textAbstract:
The realization of wavelength scale and sub-wavelength scale fabrication of integrated optical devices has led to a concurrent need for computational design tools that can accurately model electromagnetic phenomena on these length scales. This dissertation describes the physical, analytical, numerical, and software developments utilized for practical implementation of two particular frequency domain design tools: the modal method for multilayer waveguides and one-dimensional lamellar gratings and the Rigorous Coupled Wave Analysis (RCWA) for 1D, 2D, and 3D periodic optical structures and integrated optical devices. These design tools, including some novel numerical and programming extensions developed during the course of this work, were then applied to investigate the design of a few unique integrated waveguide and grating structures and the associated physical phenomena exploited by those structures. The properties and design of a multilayer, multimode waveguide-grating, guided mode resonance (GMR) filter are investigated. The multilayer, multimode GMR filters studied consist of alternating high and low refractive index layers of various thicknesses with a binary grating etched into the top layer. The separation of spectral wavelength resonances supported by a multimode GMR structure with fixed grating parameters is shown to be controllable from coarse to fine through the use of tightly controlled, but realizable, choices for multiple layer thicknesses in a two material waveguide; effectively performing the simultaneous engineering of the wavelength dispersion for multiple waveguide grating modes. This idea of simultaneous dispersion band tailoring is then used to design a multilayer, multimode GMR filter that possesses broadened angular acceptance for multiple wavelengths incident at a single angle of incidence. The effect of a steady-state linear loss or gain on the wavelength response of a GMR filter is studied. A linear loss added to the primary guiding layer of a GMR filter is shown to produce enhanced resonant absorption of light by the GMR structure. Similarly, linear gain added to the guiding layer is shown to produce enhanced resonant reflection and transmission from a GMR structure with decreased spectral line width. A combination of 2D and 3D modeling is utilized to investigate the properties of an embedded waveguide grating structure used in filtering/reflecting an incident guided mode. For the embedded waveguide grating, 2D modeling suggests the possibility of using low index periodic inclusions to create an embedded grating resonant filter, but the results of 3D RCWA modeling suggest that transverse low index periodic inclusions produce a resonant lossy cavity as opposed to a resonant reflecting mirror. A novel concept for an all-dielectric unidirectional dual grating output coupler is proposed and rigorously analyzed. A multilayer, single-mode, high and graded-index, slab waveguide is placed atop a slightly lower index substrate. The properties of the individual gratings etched into the waveguide's cover/air and substrate/air interfaces are then chosen such that no propagating diffracted orders are present in the device superstrate and only a single order is present outside the structure in the substrate. The concept produces a robust output coupler that requires neither phase-matching of the two gratings nor any resonances in the structure, and is very tolerant to potential errors in fabrication. Up to 96% coupling efficiency from the substrate-side grating is obtained over a wide range of grating properties.Ph.D.
Optics and Photonics
Optics and Photonics
Optics PhD
8
Girard, Jules. "Microscopies de fluorescense et de diffraction super-résolues par éclairement multiple." Thesis, Aix-Marseille 3, 2011. http://www.theses.fr/2011AIX30031.
Full textAbstract:
Ce travail de thèse concerne l'amélioration du pouvoir de résolution de la microscopie optique en champ lointain. Nous avons développé des techniques qui tirent profit de la relation liant le champ électromagnétique émis par un objet à l’éclairement utilisé. En utilisant plusieurs images obtenues pour différents éclairements, et à l’aide d’un algorithme d'inversion approprié, il est possible d'accéder à des fréquences spatiales de l'objet habituellement filtrées par le microscope.Ce concept est d’abord appliqué à une technique de microscopie cohérente : la tomographique optique de diffraction. Elle permet d’obtenir numériquement une carte quantitative de la permittivité diélectrique de l'objet, avec une résolution supérieure à celle d'un microscope classique, à partir de plusieurs hologrammes de l'échantillon. Dans ce cadre, nous montrons que le phénomène de diffusion multiple permet d’atteindre des résolutions encore plus spectaculaires s’il est pris en compte. Nous étudions ensuite la microscopie de fluorescence par éclairement structuré, que nous proposons d’améliorer de deux manières différentes. Dans la première, nous utilisons un algorithme d’inversion capable de retrouver simultanément la densité de fluorescence et les éclairements utilisés. Grâce à celui-ci, nous pouvons remplacer l’illumination périodique et contrôlée généralement utilisée, par des speckles aléatoires formés avec un montage remarquablement simple. Nous montrons expérimentalement l'efficacité de cette approche. Dans un second temps, nous proposons de remplacer la lamelle de verre sur laquelle est repose l’échantillon par un réseau diélectrique nanométrique. Celui-ci crée à sa surface une grille de lumière de période inférieure à la limite de diffraction, ce qui permet d’améliorer d’avantage la résolution finale de l’image reconstruite. Nous détaillons la conception, la fabrication et la caractérisation expérimentale de ce substrat nanostructuréThis PhD work focuses on the resolution improvement of far-field optical microscopy. We have studied and developed different techniques that take advantage of the relationship between the sample, the illumination and the diffracted (or emitted) field, in order to increase final band-pass of the image beyond that imposed by the diffraction phenomenon. In In these approaches, several images of the same sample are recorded under different illuminations. An inversion algorithm in then used to reconstruct a super-resolved map of the sample from the set of measurements.This concept is first applied to coherent microscopy. In tomographic diffraction microscopy, many holograms of the same unstained sample are obtained under various incidences, then used to numerically reconstruct a quantitative map of permittivity of the sample. The resolution is usually better than that of classical wide-field microscopy. We show theoretically and experimentally that, far from being a drawback, the presence of multiple scattering within the sample can, if properly accounted for, lead a to an even better resolution.We then study structured illumination fluorescence microscopy. We present two different ways for improving this method. The first one takes advantage of an inversion algorithm, which is able to retrieve the fluorescence density without knowing the illumination patterns. This algorithm permits one to replace the periodic light pattern classically used in structured illumination microscopy by unknown random speckle patterns. The implementation of the technique is thus considerably simplified while the resolution improvement remains. In the second approach, we propose to replace the coverslip on which the sample usually lays, by a sub-lambda grating. The latter is used to form, in near field, a light grid with sub-diffraction period that is able to probe the finest details of the sample. The design, fabrication and optical characterization of this key structure are detailed
9
Bisaillon, Eric. "Distributed diffractive structures for micro-optical systems." Thesis, McGill University, 2007. http://digitool.Library.McGill.CA:80/R/?func=dbin-jump-full&object_id=103366.
Full textAbstract:
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.
10
Ehrlich, Jeffrey Ellis. "Nonlinear grating structures in indium antimonide waveguides." Diss., The University of Arizona, 1989. http://hdl.handle.net/10150/184914.
Full textAbstract:
This dissertation describes various nonlinear grating coupling phenomena in InSb waveguides. InSb exhibits an opto-thermal, diffusive nonlinearity at 9.6μm. This nonlinearity strongly modifies the growth of a guided wave via the grating coupling of an incident, Gaussian signal. In particular, optical limiting and bistability in the coupled power were demonstrated for a detuned grating coupler. The limits on the detunings were also investigated. The experimental results showed qualitative agreement with a theory based upon a diffusive nonlinearity in the grating coupling process. Also demonstrated and theoretically explained was a new form of "butterfly" bistability in the output coupled signal from a nonlinear waveguide. In this situation, nonlinear interference effects in the substrate modified the proportion of power outcoupled into the cover and the substrate. The effects of a thermal nonlinearity on the response of a distributed feedback grating (DFB) were also studied. The DFB reflection response of an incident guided wave was modified either by varying the power of the incident guided wave or that of a second guided wave. Also, the effects of the DFB reflection were shown to enhance the bistable input grating coupling process by providing an additional feedback. This enhancement resulted in a smaller incident switching power required to obtain bistability in the input coupler.
11
Darbyshire, Paul Mark. "The analytical structure of wave mixing problems in nonlinear optical media." Thesis, King's College London (University of London), 1996. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.244080.
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Chuang, Chin-Jung. "Proximity projection grating structured illumination microscopy." Thesis, University of Nottingham, 2011. http://eprints.nottingham.ac.uk/12262/.
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Structured illumination has been employed in fluorescence microscopy to extend its lateral resolution. It has been demonstrated that a factor of 2 improvement can be achieved. In this thesis, we introduce a novel optical arrangement, which we call Proximity Projection Grating Structure Illumination Microscopy (PGSIM). Although the method is based on the original structured illumination, the present technique can further improve the lateral resolution of the microscope. The technique makes use of a fine grating held in close proximity to the sample, with a layer of high refractive index optical thin film sandwiched between the two. The fringe pattern thus projected onto the sample contains grating vectors substantially higher than those that are possible with the original structured illumination setup. The presence of these very high grating orders is the basis for the significant improvement in the system resolution. In this thesis, the principle behind the PGSIM will be explained. The optical system used to demonstrate the technique will be described, with particular attention paid towards the construction and alignment of the unit containing the fine grating. Experimental results will be presented to demonstrate the characteristics of the grating unit and the operation of the system. Further results obtained with the system applied to fine particles will be given, showing the resolution improvement of greater than a factor of 2 compared to a conventional optical microscope. The thesis also contains detailed analysis of the performance of the system. From this analysis, it is concluded that greater resolution improvement can be achieved by using appropriate material for the optical thin film.
13
Yeung, Wings T. "Accurate characterization of nanophotonic grating structures." Thesis, Massachusetts Institute of Technology, 2020. https://hdl.handle.net/1721.1/129848.
Full textAbstract:
Thesis: M. Eng., Massachusetts Institute of Technology, Department of Electrical Engineering and Computer Science, February, 2020Cataloged from student-submitted PDF of thesis.
Includes bibliographical references (page 75).
Augmented reality waveguides are designed to have grating regions to in-couple, out-couple, and propagate light from a light engine to the user. This thesis develops two reliable systems to qualify manufactured waveguides. The first system determines grating quality by measuring grating pitch and orientation uniformity across grating regions. The system uses scatterometry in Littrow configuration and captures both the reflected zeroth and first order diffracted light. The second system determines the overall quality of a waveguide by measuring the resolution of the device using a Modulation Transfer Function, MTF, technique. MTF is commonly measured using either the line pair method or the slant edge method. This thesis proposes a new method to measure MTF using single pixel illumination and point spread function. Results from the two systems are presented, and the capabilities and limitations of each system are explored.
by Wings T. Yeung.
M. Eng.
M.Eng. Massachusetts Institute of Technology, Department of Electrical Engineering and Computer Science
14
Amyot-Bourgeois, Maude. "Plasmon Polariton Bragg Gratings and IR-140 Doped PMMA for Active Bragg Structures." Thesis, Université d'Ottawa / University of Ottawa, 2016. http://hdl.handle.net/10393/35060.
Full textAbstract:
This thesis contributes to the realisation of plasmonic lasers based on plasmon polariton Bragg gratings. The scope of this thesis is twofold. In the first section, entitled Passive plasmonic Bragg grating characterization, the results of the testing and characterization of a new design of plasmonic Bragg gratings in the near-infrared are presented. The reflection and transmission responses expected from plasmon-polariton Bragg gratings (PPBGs) are treated theoretically using the transfer matrix method (TMM) and the numerical model is validated experimentally. The experimental setup and procedures are then described in detail. Results show that the near-infrared plasmon polariton Bragg gratings possess a Bragg reflection at a wavelength close to the Bragg wavelength predicted by TMM. In the second section, Gain optimisation and bleaching of IR-140 doped PMMA, an in-depth analysis of the gain medium (IR-140 dye doped poly(methyl methacrylate) better known as PMMA) is performed. This gain medium was selected as a gain layer for active plasmonic gratings and distributed feedback lasers designed by a colleague Ph.D. candidate. The optimized molecular weight of IR-140 in PMMA was found to be 0.9% to obtain a material gain of 81 cm-1.
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Chen, Zhuo. "Grating coupled surface plasmons in metallic structures." Thesis, University of Exeter, 2007. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.441770.
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Major, Huw E. "QPM grating design for novel PPLN structures." Thesis, University of Southampton, 2009. https://eprints.soton.ac.uk/301306/.
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This thesis describes a series of theoretical and experimental studies into modifying the phasematching characteristics of nonlinear parametric interactions, specifically second harmonic generation, using quasi-phase-matched structures. The use of quasi-phase-matching by periodic poling affords a flexibility in designing tailored phase-matching characteristics not offered by alternative techniques. In this work phase matching characteristics are modified to provide enhanced acceptance bandwidths, compensation for focusing effects and high power operation. The first result of this work describes the design and manufacture of 20mm long LiNbO3 aperiodic quasi-phase matched devices for the generation of stable second harmonic power across wide temperature ranges. Theoretical simulations have demonstrated constant power output over a range of 9C. Providing over 35 times the bandwidth of equivalent length periodic structures, whilst offering almost an order of magnitude efficiency enhancement over periodic devices with the same bandwidth. Experimental verification of these devices has shown that stable power can be obtained across wide temperature ranges with only slight deviation from theory. Additionally, an investigation into the effects of focusing on second harmonic generation is undertaken. In this work the Gouy phase of a focused beam has been analytically identified as the source of dephasing in bulk nonlinear interactions, causing such effects as back conversion, reduced efficiency and errors in the phase matching condition. A method to negate these effects, using a modified QPM structure has been proposed and experimentally demonstrated. Finally, simultaneous compensation of both the Gouy phase and focused intensity variation has been applied to aperiodic, wide temperature bandwidth devices. Removal of these deleterious effects has been shown theoretically to correct the experimentally observed bandwidth errors, resulting in the focused interactions performing identically to plane-wave simulations.
17
Ibsen, Morten. "Advanced fibre Bragg grating structures : design and application." Thesis, University of Southampton, 2004. https://eprints.soton.ac.uk/46110/.
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This thesis presents experimental and computational work on a variety of advanced fibre Bragg grating structures covering long dispersion compensating chirped Bragg gratings, superstructured Bragg gratings for identical multiple channel operation, Bragg gratings for pulse-shaping applications and Bragg gratings for add-drop applications in high bit-rate systems. Development of the fabrication-technique developed and analysed as a part of this work has led to a number of experimentai 'firsts', including the meter-long Bragg gratings with dispersion-characteristics designed to compensate simultaneous linear and higher order dispersion. Upon transfer of this technology to our industrial partners, a number of field-trial experiments utilising gratings written using this fabrication technique have been successfully performed. Some of the requirements identified from customers led to the discovery of the importance and understanding of high-quality reflection and time-delay profiles. Another product ofthe high flexibiiity provided by the developed fabrication technique have led to demonstrations of superstructured Bragg gratings for a number of exciting applications such as multiple-channel filters obtained through a periodic sinc modulation of the refractive index-profile in fibre Bragg gratings and pulse-reshaping from a soliton to square-pulse with applications in high-speed demultiplexing. Additionally, it is discussed how uniform apodised Bragg gratings filters for application in dense WDM networks, despite their near ideal spectral performance, suffer from non-linear phase attributes in the stop-band, that could limit their use in high bit-rate systems (10Gbit/s and above). Linear phase-filters for dispersion-free filtering are proposed and demonstrated as a solution to this problem for bit-rates up to 40Gbit/s and channel spacings as narrow as 25GHz.
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Kim, Kyoung Joon. "Thermo-structural influences on optical characteristics of polymer Bragg gratings." College Park, Md. : University of Maryland, 2006. http://hdl.handle.net/1903/3368.
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Thesis (Ph. D.) -- University of Maryland, College Park, 2006.Thesis research directed by: Mechanical Engineering. Title from t.p. of PDF. Includes bibliographical references. Published by UMI Dissertation Services, Ann Arbor, Mich. Also available in paper.
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Lin, Shaohua. "Analysis of Electron Wave Scattering by Nano Grating Structure." Honors in the Major Thesis, University of Central Florida, 2005. http://digital.library.ucf.edu/cdm/ref/collection/ETH/id/768.
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This item is only available in print in the UCF Libraries. If this is your Honors Thesis, you can help us make it available online for use by researchers around the world by following the instructions on the distribution consent form at http://library.ucfBachelors
Engineering and Computer Science
Electrical Engineering
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Chisholm, Karen E. "Fabrication and application of short and novel structure in-fibre Bragg gratings." Thesis, Aston University, 2000. http://publications.aston.ac.uk/7993/.
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This thesis presents details on progress made in the fabrication and application of short and novel structure fibre Bragg gratings. The basic theoretical concepts of in-fibre Bragg gratings and photosensitive mechanisms are introduced together with an overview of fabrication methods and applications presented to date. The fabrication of fibre Bragg gratings using a quadrupled Nd:YAG laser is presented and some of the issues of grating fabrication using a fabrication using a phasemask are investigated, including the variation of the separation of the fibre and phasemask, and other alignment issues. A new apodisation technique is presented, enabling the production of gratings with a wide range of spectral profiles. The technique is used to investigate the design and fabrication of length limited fibre Bragg gratings for use in telecommunication systems as filters. Application to devices designed for use in WDM systems is presented. The use of fibre Bragg gratings as high spatial resolution distributed sensors is investigated. Grating sensing arrays comprising very short apodised gratings are demonstrated and Chirped Moiré gratings are implemented as distributed sensors achieving high spatial resolution with miniature point sensing sub-elements. A novel grating sensing element designed to imitate an interferometer is also presented. Finally, the behaviour of gratings fabricated in Boron-Germania-co-doped fibre is investigated, revealing atypical behaviour of the Bragg wavelength during ageing.
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Badmos, Abdulyezir. "Advanced optical fibre gratings for nano-structural characterisation and biosensing applications." Thesis, Aston University, 2017. http://publications.aston.ac.uk/30869/.
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This thesis presents detailed investigation on the fabrication, spectral characterisation and applications of UV-inscribed optical fibre gratings devices. Of prominent significance is the characterisation of the optical fibre gratings devices with nanoparticles and biological recognition elements for novel developments in the field of optical biosensing. A major contribution detailed in this thesis is the systematic study on fabrication, spectral characterisation and applications of different UV-inscribed in-fibre gratings. Specifically, uniform and apodized Fibre Bragg gratings (FBGs), normal and dual-peak long period fibre gratings (LPFGs), small-angle tilted fibre gratings (S-TFGs) and excessively tilted fibre gratings (Ex-TFGs) are presented. The holographic, phase-mask scanning and point-by-point methods are employed to fabricate these advanced optical fibre gratings using 244nm frequency-doubled Ar+ laser. Particular emphasis is laid on fabrication of dual-peak LPFGs in SMF-28 and thin-cladding single mode fibres of grating periods 140μm and 300μm respectively. Also, Ex-TFGs of different tilt angles are inscribed in single mode fibres using amplitude masks of different periods: 5.0μm, 6.6μm and 25μm. Another important contribution from this study is the nano-structural characterisation of the in-fibre gratings with nanoparticles such as carbon nanotubes (CNT), zinc oxide (ZnO) and gold nanoparticles for power demodulation, sensitivity enhancement and polarisation dependent SPR excitation respectively. Refractive index (RI) sensors based on 81° Ex-TFGs with carbon nanotube (CNT) overlay deposition have been investigated. The CNT, a dark material, with high absorption of light and high RI is responsible for the power demodulation of the attenuation band while the 81°-TFG induces the wavelength shift as the surrounding medium RI changes. Results show high sensitivities of 557.29 nm/RIU and 95.54 dB/RIU for the wavelength shift and power demodulation respectively. Also, nano-deposition of zinc oxide (ZnO) on Ex-TFGs inscribed in two different fibre types has been investigated using dissimilar morphologies (direct ZnO overlay and PSZnO overlay) for enhanced RI sensing. Significant improvement in sensitivity of ~ 21% (~ 522 nm/RIU) is obtained. The polarisation dependence of Au-coated S-TFGs on excitation of surface plasmon resonance (SPR) has also been investigated. Finally, the in-fibre gratings are surface-functionalized with bioreceptor elements such as enzymes (glucose oxidase) and antibody/antigen (Trx, IL-6). Enzyme functionalized biosensor based on dual-peak LPFG has been investigated for sugar concentration level and specific glucose detection and high sensitivities of ~4.67 nm/% and 12.21 ± 0.19 nm/ (mg/ml) are obtained respectively. Also, fibre optic biosensors based on antibodyfunctionalized 81º-TFGs have been presented for label-free specific recognition of interleukin-6 (IL-6) and thioredoxin (Trx) proteins. High saturation values (∧λ max ) of 35.05nm and 33.19nm are obtained respectively. The specificity validation of the biosensors in the presence of other interfering proteins is investigated using human plasma and results show high specificity.
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Boonruang, Sakoolkan. "TWO-DIMENSIONAL GUIDED MODE RESONANT STRUCTURES FOR SPECTRAL FILTERING APPLICATIONS." Doctoral diss., University of Central Florida, 2007. http://digital.library.ucf.edu/cdm/ref/collection/ETD/id/3940.
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Guided mode resonant (GMR) structures are optical devices that consist of a planar waveguide with a periodic structure either imbedded in or on the surface of the structure. The resonance anomaly in GMR structures has many applications as dielectric mirrors, tunable devices, sensors,and narrow spectral band reflection filters. A desirable response from a resonant grating filter normally includes a nearly 100% narrowband resonant spectral reflection (transmission), and a broad angular acceptance at either normal incidence or an oblique angle of incidence. This dissertation is a detailed study of the unique nature of the resonance anomaly in GMR structures with two-dimensional (2-D) periodic perturbation. Clear understanding of the resonance phenomenon is developed and novel 2-D GMR structures are proposed to significantly improve the performance of narrow spectral filters. In 2-D grating diffraction, each diffracted order inherently propagates in its distinct diffraction plane. This allows for coupled polarization dependent resonant leaky modes with one in each diffraction plane. The nature of the interaction between these non-collinear guides and its impact on spectral and angular response of GMR devices is investigated and quantified for 2-D structures with rectangular and hexagonal grids. Based on the developed understanding of the underlying phenomenon, novel GMR devices are proposed and analyzed. A novel controllable multi-line guided mode resonant (GMR) filter is proposed. The separation of spectral wavelength resonances supported by a two-dimensional GMR structure can be coarse or fine depending on the physical dimensions of the structure and not the material properties. Multiple resonances are produced by weakly guided modes individually propagating along multiple planes of diffraction. Controllable two-line and three-line narrow-band reflection filter designs with spectral separation from a few up to hundreds of nanometers are exhibited using rectangular-lattice and hexagonal-lattice grating GMR structures, respectively. Broadening of the angular response of narrow band two-dimension guided mode resonant spectral filters, while maintaining a narrow spectral response, is investigated. The angular response is broadened by coupling the diffracted orders into multiple fundamental guided resonant modes. These guided modes have the same propagation constant but propagating in different planes inherent in multiple planes of diffraction of the 2-D gratings. The propagation constants of the guided resonant modes are determined from the physical dimensions of the grating (periodicity and duty cycle) and the incident direction. A five-fold improvement in the angular tolerance is achieved using a grating with strong second Bragg diffraction in order to produce a crossed diffraction. A novel dual grating structure with a second grating located on the substrate side is proposed to further broaden the angular tolerance of the spectral filter without degrading its spectral response. This strong second Bragg backward diffraction from the substrate grating causes two successive resonant bands to merge producing a resonance with symmetric broad angular response.Ph.D.
Optics and Photonics
Optics and Photonics
Optics PhD
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Wosinski, Lech. "Technology for photonic components in silica/silicon material structure." Doctoral thesis, KTH, Microelectronics and Information Technology, IMIT, 2003. http://urn.kb.se/resolve?urn=urn:nbn:se:kth:diva-3556.
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The main objectives of this thesis were to develop a lowtemperature PECVD process suitable for optoelectronicintegration, and to optimize silica glass composition forUV-induced modifications of a refractive index in PECVDfabricated planar devices. The most important achievement isthe successful development of a low temperature silicadeposition, which for the first time makes it is possible tofabricate good quality low loss integrated components whilekeeping the temperature below 250oC during the entirefabrication process. Two strong absorption peaks thatappear at1.5 mm communication window due to N-H and Si-H bonds have beencompletely eliminated by process optimization. This openspossibilities for monolithic integration with other,temperature sensitive devices, such as semiconductor lasers anddetectors, or polymer-based structures on the common siliconplatform. PECVD technology for low loss amorphous silicon inapplication to SiO2/Si based photonic crystal structures hasbeen also optimized to remove hydrogen incorporated during thedeposition process, responsible for the porosity of thedeposited material and creation of similar to silica absorptionbands.
Change of the refractive index of germanium doped silicaunder UV irradiation is commonly used for fabrication of UVinduced fiber Bragg gratings. Here we describe our achievementsin fabrication of fiber Bragg gratings and their application todistributed sensor systems. Recently we have built up a laserlab for UV treatment in application to planar technology. Wehave demonstrated the high photosensitivity of PECVD depositedGe-doped glasses (not thermally annealed) even without hydrogenloading, leading to a record transmission suppression of 47dBin a Bragg grating photoinduced in a straight buried channelwaveguide. We have also used a UV induced refractive indexchange to introduce other device modifications or functions,such as phase shift, wavelength trimming and control ofpolarization birefringence.The developed low temperature technology and the UVprocessing form a unique technology platform for development ofnovel integrated functional devices for optical communicationsystems.
A substantial part of the thesis has been devoted tostudying different plasma deposition parameters and theirinfluence on the optical characteristics of fabricatedwaveguides to find the processing window giving the besttrade-off between the deposition rate,chamber temperatureduring the process, optical losses and presence of absorptionbands within the interesting wavelength range. The optimalconditions identified in this study are low pressure (300-400mTorr), high dilution of silane in nitrous oxide and high totalflow (2000 sccm), low frequency (380 KHz) RF source and high RFpower levels (800-1000 W).
The thesis provides better understanding of the plasmareactions during the deposition process. RF Power is the keyparameter for increasing the rate of surface processes so as toaccommodate each atomic layer in the lowest energy statepossible. All the process conditions which favor a moreenergetic ion bombardment (i.e. low pressure, low frequency andhigh power) improve the quality of the material, making it moredense and similar to thermal oxide, but after a certain pointthe positive trend with increasing power saturates. As theenergy of the incoming ion increases, a competing effect setsin at the surface: ion induced damage and resputtering.
Finally, the developed technologies were applied for thefabrication of some test and new concept devices for opticalcommunication systems including multimode interference (MMI)-based couplers/splitters, state-of-the-art arrayed waveguidegrating-based multi/ demultiplexers, the first Bragg gratingassisted MMI-based add-drop multiplexer, as well as moreresearch oriented devices such as a Mach-Zehnder switch basedon silica poling and a Photonic Crystal-based coupler.
Keywords:silica-on-silicon technology, PECVD, plasmadeposition, photonic integrated circuits, planar waveguidedevices, UV Bragg gratings, photosensitivity, arrayed waveguidegratings, multimode interference couplers, add-dropmultiplexers.
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Blockey, James Craig. "Feasibility in developing smart structures for use in wind turbine blades." Thesis, Montana State University, 2008. http://etd.lib.montana.edu/etd/2008/blockey/BlockeyJ0808.pdf.
Full textAbstract:
Recently the use of wind as an alternative energy source has developed quickly. The length of the blades is a leading factor in the power output of a wind turbine and as a result, blade length has grown at a similar pace to the growth of the industry. The rapid expansion in use and size of wind turbines is not without its problems, though. As the industry has changed and grown, the overall design of the blades has remained relatively stagnant. This is evident in two primary areas, power control and health monitoring. Power control mechanisms are generally unchanged, utilizing either pitch control or active stall designs. While effective, these systems are neither efficient nor fast acting and can contribute to higher maintenance requirements. Current wind turbine blades also have no sensors built into them. The nacelle and tower utilize many sensors, but the blades themselves have none, leading to blades which are incapable of any real time health monitoring. The application of smart structures will enable the in situ monitoring of the blade and allow the blade to adapt to changing wind loadings Smart structures are those which apply an array of sensors to continuously monitor the state of the structure and are capable of using those sensors to appropriately react to achieve a desired state. This paper will examine the application of smart structures to the wind energy industry. It will be shown that a fiber optic, Fiber Bragg Grating sensor is the best type of sensor for wind energy. One of the main contributing factors is the capability of the sensors to multiplex, which means many sensors can be located along a single optical fiber and different types of sensors can be run on the same optical fiber. The blades will \'react\' to changing conditions through the use of an actuated Gurney style flap. The flap will be used to shed the wind loads from the blade in high wind scenarios. These systems working together will provide an effective and efficient method of advancing the design of the wind turbine blade to a level appropriate for the systems expected today and in the future.
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Chen, Lawrence R. "Applications of compound fiber Bragg grating structures in lightwave communications." Thesis, National Library of Canada = Bibliothèque nationale du Canada, 2000. http://www.collectionscanada.ca/obj/s4/f2/dsk1/tape4/PQDD_0020/NQ53720.pdf.
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Silva, Susana Ferreira de Oliveira. "Fibre Bragg grating based structures for optical sensing and filtering." Dissertação, Porto : edição do autor, 2007. http://catalogo.up.pt/F?func=find-b&local_base=FCB01&find_code=SYS&request=000091906.
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Lombardo, David. "Design and Fabrication of Suspended Waveguides With Photonic Grating Structures." University of Dayton / OhioLINK, 2020. http://rave.ohiolink.edu/etdc/view?acc_num=dayton1591796311145344.
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Shengnan, Geng, Wang Xinglai, and Feng Hui. "FIBER BRAGG GRATING SENSOR SYSTEM FOR MONITORING COMPOSITE AEROSPACE STRUCTURES." International Foundation for Telemetering, 2016. http://hdl.handle.net/10150/624242.
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To investigate strain-sensitive characteristics of fiber Bragg grating (FBG) sensors, a minimal
sensing system consisting of multiplex FBG sensors and signal demodulating and processing
instruments was constructed. FBG sensors were designed with different package structures for
respectively sensing strain or temperature parameters, and they returned
measurand-dependent wavelengths back to the interrogation system for measurement with
high resolution. In this paper, tests were performed on structure samples with step-wise
increase of deformations. Both FBG sensing system and strain gages were tested and
compared. Experimental work proved that the FBG sensing system had a good level of
accuracy in measuring the static response of the tested composite structure. Moreover the
additional advantages such as damp proofing, high sampling rates and real-time inspection
make the novel system especially appropriate for load monitoring and damage detection of
aerospace structures.
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Silva, Susana Ferreira de Oliveira. "Fibre Bragg grating based structures for optical sensing and filtering." Master's thesis, Porto : edição do autor, 2007. http://hdl.handle.net/10216/64131.
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Hemingway, John-Paul J. "Numerical investigation of novel structures of nonlinear optical fibre loop mirrors including Bragg gratings." Thesis, Manchester Metropolitan University, 1999. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.284903.
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Ghiringhelli, Fabio. "Fundamental properties of Bragg gratings and their application to the design of advanced structures." Thesis, University of Southampton, 2003. https://eprints.soton.ac.uk/15468/.
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This thesis presents the analysis of the local properties of Bragg gratings and their applicationto the improvement of standard designs and advanced structures. The time spent by light inside each grating section is derived in terms of complex-valued quantities, and clear meaning is given to both the real and imaginary parts. Improved physical understanding of propagation and energy distributions inside periodic structures is obtained. Local properties also explain in a more intuitive way well understood features of different gratings, which improves intuition of new complex designs. The analysis of the effect of perturbations is immediate using this approach and has important practical applications. Independent confirmation of the theory is obtained, and experimental measurement of the imaginary part of the local time delay is given. Phase errors affect the grating writing techniques, and the related sensitivity is analysed in detail. The robustness of different designs is discussed with respect to such manufacturing errors. Fine tuning of standard or advanced grating designs by means of suitable error distributions is also proposed, and optimised characteristics either in the reflectivity or in the dispersive response are obtained. This method is integrated with inverse scattering designs to further boost their performances. Improved complex designs are also proposed in case losses affect propagation in the grating. Cladding mode losses are compensated using an iterative layer-peeling algorithm. The design of the first wide-band dispersion-compensating grating realised with a standard single mode fibre is shown. Background losses and UV-induced losses in gratings are also compensated using a modified layer-peeling method. The physical limitations related to grating design in lossy media are explained using the derived understanding of local properties. New advanced designs are also considered that fully exploit the theoretical potentialities and manufacturing capabilities of Bragg gratings. The performance of code-division multiple access systems based on superstructured gratings is improved by combining encoding, bandwidth filtering, and dispersion compensation in the same high reflectivity grating.
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SORIA, DARWIN GRAMER FALCON. "MONITORING CORROSION DEFECTS IN PLANAR STRUCTURES WITH FIBER BRAGG GRATING SENSORS." PONTIFÍCIA UNIVERSIDADE CATÓLICA DO RIO DE JANEIRO, 2011. http://www.maxwell.vrac.puc-rio.br/Busca_etds.php?strSecao=resultado&nrSeq=19352@1.
Full textAbstract:
CONSELHO NACIONAL DE DESENVOLVIMENTO CIENTÍFICO E TECNOLÓGICOO foco do presente trabalho é a detecção e o monitoramento de defeitos tais como perda de espessura por corrosão ou dano produzido por impacto em painéis metálicos planos. O sistema proposto emprega sensores de deformação a fibra óptica baseados em redes de Bragg, que possuem alta capacidade de multiplexação. O campo de deformações produzido na superfície da placa por um mesmo carregamento, cuja amplitude pode variar, é continuamente comparado a um mapa de referência, obtido com a estrutura íntegra ou na presença um defeito previamente detectado. Variações nos gradientes de deformações são associadas ao surgimento ou crescimento de um ou mais defeitos. Neste estudo, a metodologia foi preliminarmente avaliada através da análise de campos de deformação produzidos por carregamentos de tração em corpos de alumínio contendo defeitos superficiais. Esses defeitos exemplificam danos causados por corrosão, e são monitorados através de sensores a fibra óptica baseados em redes de Bragg. Os sensores são posicionados ao longo de uma das superfícies da placa, medindo deformações em duas direções ortogonais, que neste estudo corresponderam às direções principais de deformação. A abordagem do problema fundamenta-se na análise de dados experimentais e modelagem numérica por elementos finitos. Os resultados numéricos para as deformações são comparados com os obtidos em experimentos em laboratório. A técnica é utilizada para avaliar qualitativamente os defeitos em estruturas submetidas a carregamento estático. A correlação entre resultados numéricos e experimentais mostraram-se satisfatórias, indicando que o método apresenta potencial para ser estendido para aplicações mais complexas.
The present work is focused on detecting and monitoring damage such as loss of thickness due to corrosion or other planar defects in flat metallic panels. The proposed method employs fiber optic sensors that, due to their high multiplexing capability, are capable of mapping the strain fields in the panel surfaces produced by the same, controlled, loading, which are then continuously compared to a reference map obtained with the structure free of defects or with a previously detected damage. Changes in the strain gradient are attributed to the appearance or growth of structural damage. The proposed approach for structural health monitoring has been preliminarily evaluated in this dissertation by analyzing the strain fields produced on an aluminum plate under in plane tensile loads. Artificial, localized surface defects, simulating a loss of thickness due to corrosion where the investigated defects. A mesh of fiber Bragg grating sensors was installed on one of the panel surfaces measuring its principal strains. The strain fields obtained with the plate containing defects with different depths and sizes were compared to a reference measurement with the panel without defects. Experimental data was compared with numerical simulations based on the Finite Element method. The correlation between numerical and experimental results was satisfactory indicating that the method can be further developed in order to be applied in implementations of structural health monitoring systems.
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Nicolas, Matthew James. "Structural analysis and testing of a carbon-composite wing using fiber Bragg gratings." Thesis, Mississippi State University, 2013. http://pqdtopen.proquest.com/#viewpdf?dispub=1536133.
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The objective of this study was to determine the deflected wing shape and the out-of-plane loads of a large-scale carbon-composite wing of an ultralight aerial vehicle using Fiber Bragg Grating (FBG) technology. The composite wing was instrumented with an optical fiber on its top and bottom surfaces positioned over the main spar, resulting in approximately 780 strain sensors bonded to the wings. The strain data from the FBGs was compared to that obtained from four conventional strain gages, and was used to obtain the out-of-plane loads as well as the wing shape at various load levels using NASA-developed real-time load and displacement algorithms. The composite wing measured 5.5 meters and was fabricated from laminated carbon uniaxial and biaxial prepreg fabric with varying laminate ply patterns and wall thickness dimensions. A three-tier whiffletree system was used to load the wing in a manner consistent with an in-flight loading condition.
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Fievre, Ange Marie P. "Uniquely Identifiable Tamper-Evident Device Using Coupling between Subwavelength Gratings." FIU Digital Commons, 2015. http://digitalcommons.fiu.edu/etd/1762.
Full textAbstract:
Reliability and sensitive information protection are critical aspects of integrated circuits. A novel technique using near-field evanescent wave coupling from two subwavelength gratings (SWGs), with the input laser source delivered through an optical fiber is presented for tamper evidence of electronic components. The first grating of the pair of coupled subwavelength gratings (CSWGs) was milled directly on the output facet of the silica fiber using focused ion beam (FIB) etching. The second grating was patterned using e-beam lithography and etched into a glass substrate using reactive ion etching (RIE). The slightest intrusion attempt would separate the CSWGs and eliminate near-field coupling between the gratings. Tampering, therefore, would become evident.
Computer simulations guided the design for optimal operation of the security solution. The physical dimensions of the SWGs, i.e. period and thickness, were optimized, for a 650 nm illuminating wavelength. The optimal dimensions resulted in a 560 nm grating period for the first grating etched in the silica optical fiber and 420 nm for the second grating etched in borosilicate glass. The incident light beam had a half-width at half-maximum (HWHM) of at least 7 µm to allow discernible higher transmission orders, and a HWHM of 28 µm for minimum noise. The minimum number of individual grating lines present on the optical fiber facet was identified as 15 lines. Grating rotation due to the cylindrical geometry of the fiber resulted in a rotation of the far-field pattern, corresponding to the rotation angle of moiré fringes. With the goal of later adding authentication to tamper evidence, the concept of CSWGs signature was also modeled by introducing random and planned variations in the glass grating.
The fiber was placed on a stage supported by a nanomanipulator, which permitted three-dimensional displacement while maintaining the fiber tip normal to the surface of the glass substrate. A 650 nm diode laser was fixed to a translation mount that transmitted the light source through the optical fiber, and the output intensity was measured using a silicon photodiode. The evanescent wave coupling output results for the CSWGs were measured and compared to the simulation results.
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CHENG, JI. "FOCUSED ION BEAM FABRICATION OF PHOTONIC STRUCTURES FOR OPTICAL COMMUNICATIONS." University of Cincinnati / OhioLINK, 2002. http://rave.ohiolink.edu/etdc/view?acc_num=ucin1023127713.
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Stockermans, Raymond Joseph. "Resonant grating waveguide structures and their application as high-quality narrowband filters." Thesis, National Library of Canada = Bibliothèque nationale du Canada, 1998. http://www.collectionscanada.ca/obj/s4/f2/dsk1/tape11/PQDD_0007/MQ44921.pdf.
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Wang, Yunmiao. "A Quasi-distributed Sensing Network Based on Wavelength-Scanning Time-division Multiplexed Fiber Bragg Gratings." Diss., Virginia Tech, 2012. http://hdl.handle.net/10919/39324.
Full textAbstract:
Structural health monitoring (SHM) has become a strong national interest because of the need of reliable and accurate damage detection methods for aerospace, civil and mechanical engineering infrastructure. Health monitoring of these structures usually requires the sensors to have such features as large area coverage, maintenance free or minimum maintenance, ultra-low cost per measurement point, and capability of operation in harsh environments. Fiber Bragg grating (FBG) has attracted considerable interest for this application because of its compactness, electromagnetic immunity, and excellent multiplexing capability. Several FBG multiplexing techniques have been developed to increase the multiplexing number and further reduce the unit cost. To the authorâ s best knowledge, the current demonstrated maximum multiplexing number are 800 FBG sensors in a single array using optical frequency domain reflectometry (OFDR), whose maximum fiber span is limited by the coherence length of light source.
In this work, we proposed and demonstrated a wavelength-scanning time-division multiplexing (WSTDM) of 1000 ultra-weak FBGs for distributed temperature sensing. In comparison with the OFDR method, the WSTDM method distinguishes the sensors by different time delays, and its maximum operation distance, which is limited by the transmission loss of the fiber, can be as high as tens of kilometers. The strong multiplexing capability and low crosstalk of the ultra-weak FBG sensors was investigated through both theoretical analysis and experiment. An automated FBG fabrication system was developed for fast FBG fabrication. With this WSTDM method, we multiplexed 1000 ultra-weak FBGs for distributed temperature sensing. Besides the demonstrated temperature measurement, the reported method can also be applied to measure other parameters, such as strain, pressure.Ph. D.
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Li, Chien-Hsing, and 李建興. "Strain and Biomedical Sensing by Structured Long Period Fiber Gratings Sensor." Thesis, 2014. http://ndltd.ncl.edu.tw/handle/60518135747417905597.
Full textAbstract:
碩士國立高雄應用科技大學
機械與精密工程研究所
102
In the present study, a novel packaged long-period fiber grating (PLPFG) strain sensor is first presented. The Micro Electro Mechanical Systems(MEMS) process was utilized to fabricate the packaged optical fiber strain sensor. The sensor structure consisted of etched optical fiber sandwiched between two layers of thick photoresist SU-8 3050 and then packaged with poly(dimethylsiloxane) (PDMS) polymer material to construct the PLPFG strain sensor. The PDMS packaging material was used to prevent the glue effect, wherein glue flows into the LPFG structure and reduces coupling strength, in the surface bonding process. Because the fiber grating was packaged with PDMS material, it was effectively protected and made robust. The resonance attenuation dip of PLPFG grows when it is loading. This study explored the size effect of the grating period and fiber diameter of PLPFG via tensile testing. The experimental results found that the best strain sensitivity of the PLPFG strain sensor was -0.0365 dB/, and that an R2 value of 0.97 was reached. The present study, proposes an experimental approach of using photolithography process to produce Comb-Microchannel Long Period Fiber Grating(CM-LPFG), which used as an immune protein sensor. In the sensor, SU-8 3050 photoresist is used as a structure, and coupled with fiber after buffered oxide etch (BOE) to obtain long period effect. This allows the sensor to generate hydroxyl group (O-H) through using sodium hydroxide (NaOH) solution, then the sensor is soaked in (3-Aminopropyl)triethoxys (APTES) liquid to generate the bonding of amine group (N-H) with O-H to achieve the purpose of surface silylation and to be used as the bridge for bio-binding. After processing cultured SK-Hep1 and Mahlavu cell with cell lysis buffer, then impurities such as cell membrane from the cell are isolated through using a low temperature centrifugation at 4ºC to obtain total proteins of the cells, followed by carrying out specific sensing experiment on the extracted proteins with HDAC6 antibodies. Through the experiment, it is proved that, when using HDAC6 antibodies against the total proteins of Mahlavu cells, there is no any drift amount, and the maximum energy loss is -0.44 dB; but when using HDAC6 antibodies against the total proteins of SK-Hep1 cells, the energy loss reaches is a significant -14.07 dB. From this result, it can be found that the experimental approach of using a CM-LPFG sensor to detect the expressed amount of specific protein is feasible.
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You-DaDai and 戴佑達. "Reconfiguration of Optical CDMA Network Codecs Structured over composite M-signatures Waveguide Gratings." Thesis, 2011. http://ndltd.ncl.edu.tw/handle/76175467391684392136.
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Tseng, Shin-Pin, and 曾信賓. "Several Optical CDMA Spectral Codecs Structured Over Arrayed-Waveguide and Fiber-Bragg Gratings." Thesis, 2003. http://ndltd.ncl.edu.tw/handle/84859259601780868328.
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碩士國立成功大學
電機工程學系碩博士班
91
Fiber-optic CDMA techniques provide a flexible solution for asynchronous, high capacity communication, which are the most suitable application in local area networks (LAN). Several code families can be used in the SAC OCDMA systems recently, including maximal-length sequence (M-sequence) codes, Walsh-Hadamard codes, modified quadratic congruence (MQC) codes, and so on. In this thesis, optical code-division multiple-access (OCDMA) systems of spectral amplitude coding (SAC) is presented, which uses the proposed novel optical encoder/decoder based on arrayed-waveguide grating (AWG) routers and fiber Bragg gratings (FBGs). First we propose two SAC CDMA systems adopting the cyclic properties of AWG routers. By adopting the cyclic properties of M-sequence codes over AWG routers, the encoder/decoder pair can encode/decode multiple codewords simultaneously. By using complementary Walsh Hadamard (CWH) code over AWG router, each user only need an AWG router as the encoder to implement complement keying. Next, the new code family is proposed to construct based on a series of FBG for SAC OCDMA system. Due to lower weight of proposed codes, we can construct the encoder/decoder with only a few FBGs. Therefore, it is very easy to implement. The information signal is employing either on-off keying (OOK) or complement keying with low cost incoherent sources, then AWG router or FBG is used to control the amplitude spectra of broadband incoherent optical sources. AWG routers will spectrally slice incoming broadband optical spectrum into several spectral chips are distributed over the different output ports of AWG router. FBGs are used as filters that will make a series of code chips by method of selectively reflecting to broadband incoherent optical source spectrum with information signal. Then, each wavelength chip has different central wavelength and is distributed over the spectrum of the incoming light source. These configurations not only preserve the ability of multiple user interference (MUI) cancellation in SAC OCDMA system, but also result in a cheap system with reduced system complexity.
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Yan, Lu. "Stimulated emission depletion microscopy with optical fibers." Thesis, 2017. https://hdl.handle.net/2144/20853.
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Imaging at the nanoscale and/or at remote locations holds great promise for studies in fields as disparate as the life sciences and materials sciences. One such microscopy technique, stimulated emission depletion (STED) microscopy, is one of several fluorescence based imaging techniques that offers resolution beyond the diffraction-limit. All current implementations of STED microscopy, however, involve the use of free-space beam shaping devices to achieve the Gaussian- and donut-shaped Orbital Angular Momentum (OAM) carrying beams at the desired colors –-- a challenging prospect from the standpoint of device assembly and mechanical stability during operation. A fiber-based solution could address these engineering challenges, and perhaps more interestingly, it may facilitate endoscopic implementation of in vivo STED imaging, a prospect that has thus far not been realized because optical fibers were previously considered to be incapable of transmitting the OAM beams that are necessary for STED.
In this thesis, we investigate fiber-based STED systems to enable endoscopic nanoscale imaging. We discuss the design and characteristics of a novel class of fibers supporting and stably propagating Gaussian and OAM modes. Optimization of the design parameters leads to stable excitation and depletion beams propagating in the same fiber in the visible spectral range, for the first time, with high efficiency (>99%) and mode purity (>98%).
Using the fabricated vortex fiber, we demonstrate an all-fiber STED system with modes that are tolerant to perturbations, and we obtain naturally self-aligned PSFs for the excitation and depletion beams. Initial experiments of STED imaging using our device yields a 4-fold improvement in lateral resolution compared to confocal imaging. In an experiment in parallel, we show the means of using q-plates as free-space mode converters that yield alignment tolerant STED microscopy systems at wavelengths covering the entire visible spectrum, and hence dyes of interest in such imaging schematics.
Our study indicates that the vortex fiber is capable of providing an all-fiber platform for STED systems, and for other imaging systems where the exploitation of spatio-spectral beam shaping is required.
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Madhav, Kalaga Venu. "All-Fiber Sensing Techniques For Structural Health Monitoring And Other Applications." Thesis, 2007. http://hdl.handle.net/2005/644.
Full textAbstract:
In this thesis, we explore the four aspects of fiber Bragg grating sensors: mathematical modeling of Fiber Bragg Grating response/spectral characteristics, fabrication using phase mask, application and interrogation. Applications of fiber Bragg gratings, also known as in-fiber gratings, with emphasis on their sensing capabilities, interrogation of an array of sensors and their performance in structural health monitoring scenario are documented.
First, we study the process of photosensitivity phenomenon in glasses, in particular GeO2:SiO2 glasses. For mathematical modeling we consider the 1-D refractive index profile along the propagation axis of an optical fiber drawn from the preform of such glasses. These 1-D index structures exhibit a bandgap for propagation along the fiber axis. We show how the bandgap is dependent on the two structural parameters: index periodicity and effective refractive index. The mathematical model provides the characteristics of three sensor parameters -resonance wavelength also known as the Bragg wavelength (λB ), filter bandwidth (ΔλB ), and reflectivity (R). We show that the evolution of the index structure in germanosilicate glasses is dependent on the inscription parameters such as exposure time, intensity of the laser used for inscribing, the interference pattern, and coherence of the laser system. In particular, a phase mask is used as the diffffacting element to generate the required interference pattern, that is exposed on the photosensitive fiber. We present a mathematical model of the electromagnetic diffraction pattern behind the phase mask and study the effect of the limited coherence of the writing laser on the interference pattern produced by the diffracting beams from the mask.
Next, we demostrate the sensing capabilities of the fiber Bragg gratings for measuring strain, temperature and magnetic fields. We report linearity of 99.7% and sensitivity of 10.35pm/◦C for the grating temperature sensor. An array of gratings assigned with non-overlapping spectral windows is inscribed in a single fiber and applied for distributed sensing of structural health monitoring of an aircraft’s composite air-brake panel. The performance of these sensors is compared with the industry standard resistance foil gauges. We report good agreement between the two gauges (FBG and RSG).
In some applications it is more desirable to know the spectral content, rather than the magnitude of perturbation. Fiber Bragg gratings sensors can be used to track events that occur in a very small span of time and contain high frequencies. Such applications demand very high speed wavelength demodulation methods. We present two interrogation techniques: wavelength-shift time-stamping (WSTS) and reflectivity division multiplexing (RDM). WSTS interrogation method employs the multiple threshold-crossing technique to quantize the sensor grating fluctuations and in the process produces the time stamps at every level-cross. The time-stamps are assembled and with the a priori knowledge of the threshold levels, the strain signal is reconstructed. The RDM methodology is an extension of the WSTS model to address multiple sensors. We show that by assigning unique reflectivities to each of the sensors in an array, the time-stamps from each of the sensors can be tagged. The time-stamps are collected by virtue of their corresponding pulse heights, and assembled to reconstruct the strain signal of each of the array sensor. We demonstrate that the two interrogation techniques are self-referencing systems, i.e., the speed at which the signals are reconstructed is instantaneous or as fast as the signal itself.
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Roberson, Craig Valentine. "An investigation into performance criteria for Fibre Bragg Grating sensors embedded in composite structures." Thesis, 2014. http://hdl.handle.net/10210/12124.
Full textAbstract:
M.Ing. (Mechanical Engineering)The dissertation explores the applications and limitations of optic Fibre Bragg Grating (FBG) sensors for the purpose of structural health monitoring of high performance composite aerospace structures. The absence of a set of stringent performance criteria governing the form and function of a sensory system for embedded high performance applications highlights the major hurdle to be overcome before widespread acceptance of these technologies becomes apparent. The dissertation therefore develops through an extensive literature study a basic framework of performance criteria to be met by the sensory system upon which a prototype Structural Health Monitoring (SHM) system can be further developed. The resolution of the performance criteria into categories of mechanical and non-mechanical performance allows independent evaluation of factors that directly affect the performance of the sensor (in terms of strength, embeddability and load carrying ability) as well as its functional performance (in terms of orientation, spatial resolution and measurement philosophy). The literature study uses the non-mechanical performance limitations as a guideline for the selection of Fibre Bragg Grating (FBG) sensors as the sensory mechanism. The mechanical performance limitations of these specific sensors are then called into question and evaluated. Independent experiment campaigns are therefore developed to evaluate the mechanical and non-mechanical performance limitations such that a set of performance criteria can be developed governing the use of embedded sensory systems. Non mechanical performance with particular emphasis on sensor placement and orientation is investigated by simulating a fixed-free Euler Bernoulli cantilever using the Finite Element Method (FEM). The ability of the sensor to identify structural changes by measuring changes in modal response shows good results. Furthermore the inability of modal based monitoring to identify structural changes in the vicinity of modal inflection points is identified as an opportunity to locate structural deficiencies by monitoring multiple modes with known inflection point positions. The method also provides recommendations of sensor placement and orientation (close to the beam fixture and parallel with the neutral axis) such that the effectiveness of strain component measurements from all measurable modes is maximised. Mechanical performance of embedded FBG sensors is evaluated through an extensive fracture testing program which measures the fracture strains of fibre samples subjected to two-point bending. The fracture test program allows the quantification of the effects of the presence of the fibre’s protective polymer coating on fibre embeddability in composites, the consequent effects that the removal of this coating has on the mechanical performance and fracture behaviour of FBG sensors. These effects are qualified and mitigatory measures developed to improve the mechanical performance. A system of crack masking, hydrofluoric acid etching and fibre treatment is developed and statistical data analysis methods are employed and refined such that improvements in the mechanical properties of the FBG sensors can be quantified. An evaluation of the effectiveness of the proposed mechanical performance improvements yields good results culminating in the development of a comprehensive set of mechanical performance criteria to facilitate further development of a reliable SHM system.
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Kung, Li-Ti, and 龔豊迪. "Multi-grating structures of dielectric waveguides." Thesis, 2016. http://ndltd.ncl.edu.tw/handle/8g2yz8.
Full textAbstract:
碩士義守大學
電機工程學系
104
In this thesis, we use Floqiet-Bloch theory to analyze the gratings with Multi-grating sections. We develop a software to solve the effective index of periodic dielectric waveguides. The transmission, reflection and radiation spectrum of first Bragg and second Bragg condition of gratings are simulated. In addition, we focus on three grating structures: the combination structure of gratings, Liner structures and Oracle structures. The simulated results show that the second Bragg of the composited grating structures is similar to the first Bragg gratings, while the composited gratings have large attenuation constants and wide 3dB bandwidth. Moreover, we successful simulate three linear structures of gratings, where the properties of linear grating structures are similar to the composited grating structures. Finally, the properties of commercial Oracle structure are calculated.
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Siregar, Priska-Rouli, and 欣芮佳. "Polarization Splitters Using Subwavelength Grating Structures." Thesis, 2019. http://ndltd.ncl.edu.tw/cgi-bin/gs32/gsweb.cgi/login?o=dnclcdr&s=id=%22107NCHU5198007%22.&searchmode=basic.
Full textAbstract:
碩士國立中興大學
物理學系所
107
Polarization beam splitter (PBS) is an essential component in the photonic integrated circuits (PICs). It is used to separate transverse electric (TE) and transverse magnetic (TM) polarizations while using high-contrast of refractive index materials to build up optical devices based on a silicon-on-insulator (SOI) platform. We know that there are several kinds of waveguide structures such as, strip/channel, rib/ridge, hybrid plasmonic, photonic crystal, slot, and subwavelength grating (SWG) waveguides. Among them, the SWG structures open up unique possibilities of advancing the integration of complex functionalities in PICs, and many high-performance PICs have been proposed in the SOI platform. SWG waveguides consist of periodic segments of low and high refractive index materials, with a pitch less than the operating wavelength. In this work, we propose a PBS operated at a wavelength of 1550 nm using SWG structures as the coupling waveguide between two Si waveguides guiding TE and TM modes. The TM mode propagates along a bar channel while the TE mode couples to another the cross channel by matching the phases of the two Si channels. The upper cladding is air and the substrate is SiO2. The height and width of the two Si waveguides are set to be 340 nm and 240 nm, respectively. We design the middle SWG waveguide to optimize the performances of the proposed PBS by analyzing the dimension of the SWG structure. The polarization extinction ratios (PERs) achieve 24 dB and 7 dB for TM and TE, respectively, while the insertion losses (ILs) are 0.2 dB and 2.9 dB for TM and TE, respectively.
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Fang, Chun-Yu, and 方鈞宥. "Luminescent Solar Concentrators Using Slanted Grating Structures." Thesis, 2014. http://ndltd.ncl.edu.tw/handle/24071113260606861780.
Full textAbstract:
碩士國立中興大學
機械工程學系所
102
This study uses slanted grating structures to fabricate the luminescent solar concentrator (LSC) which is designed for guiding the incident light to the optical receiver in a specific direction and reducing the solar cell area. By coating the waveguide bottom with the fluorescent dyes, the LSC can convert specific wavelengths of light into the wavelengths of solar cell absorbing band. It will be expected to efficiently enhance the waveguide efficiency of LSCs and apply this device to the building-integrated photovoltaics. With the use of optical ray tracing software (ZEMAX), the sunlight passing through the waveguide with grating structures was simulated at the mixed sequential and non-sequential modes. According to the behaviors and paths of light guiding in the waveguide, the grating period for generating the total internal reflection was obtained. Based on the period, the diffraction efficiencies of the slanted grating were simulated by using the grating analysis software (G-solver). The grating’s parameters which can make a maximum efficiency difference between the positive first diffraction order and the negative first diffraction order were also discussed. Because the simulated grating period is too small, it is difficult to be fabricated by general equipments. Thus, the experiment was focused on the fabrication of slanted gratings of the thicker line width. The element fabrication of this study was focused on fabricating slanted gratings with the period of 4 μ m. The quartz glass and ITO glass were adopted as waveguide materials to conduct the photolithography process. Then, the inductively coupled plasma reactive ion etching (ICP-RIE) was used for etching the waveguide. Referring to many papers, different process parameters, like process pressure, electrode power, gas type, and gas flow rate, were tried. By making discussions and improvement after every experiment result, the purpose of fabricating slanted gratings has been achieved. Finally, the diffraction efficiencies of the fabricated grating elements were measured under positive first order, zero order, and negative first order. They were compared with the simulation results. When the wavelength of the light was 532nm and the depth of the slanted grating was 1500nm, the efficiency of positive first order was 4.6% and the efficiency of negative first order was 2.3%. The results were close to the simulation. Besides, the spectrum change of the light after passing through the slanted grating with fluorescent dyes was measured to verify whether the device can reduce the area of solar concentrator and enhance the efficiency or not.
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Chang, Chao-Jan, and 張超然. "Investigation of Subwavelength Grating (SWG) Waveguide Structures." Thesis, 2014. http://ndltd.ncl.edu.tw/handle/16823041824507948127.
Full textAbstract:
碩士國立交通大學
光電工程研究所
103
We propose an efficient and accurate mode solver for three dimensional subwavelength grating (3D SWG) waveguides with straight and bend structures. Based on the approximated linear dispersion relation of the SWG structures, we utilize the transfer matrix method (TMM) to obtain the equivalent effective index of a SWG structure, and then a 3D SWG waveguide is equivalent to the conventional 3D waveguide. At last, we use the finite element method (FEM) to realize the modal distributions and related properties of this SWG waveguide. To confirm our mode solver, we investigate several straight and bent SWG waveguides with different geometric parameters and compare to the modes calculated by 3D finite difference time domain (FDTD) method by using the overlap integral. We observe the values of overlap integrals are larger than 96 %, showing that our mode solver is highly accurate. Besides, we apply this mode solver to design tapered waveguides and ring resonators. We propose two SWG tapered waveguides by varying the filling factors along the structures. Then the effective medium indices along the structures are varied and thus the mode is converted along the SWG tapered waveguides. The simulated results show that the taper with its length larger than 2 m has its taper loss of less than 0.14 dB. On the other hand, we use the obtained effective indices of a partial SWG bending structure with a radius of 3 m to calculate the resonant wavelengths and the free spectral range (FSR) of the corresponding PSWG ring resonator. The FDTD simulated results show this PSWG ring resonator has extinction ratio of 25.72 dB, quality factor (Q factor) of 1062.3, FWHM of 1.45 nm and FSR of 33 nm.
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Keulen, Casey James. "Process and structural health monitoring of composite structures with embedded fiber optic sensors and piezoelectric transducers." Thesis, 2012. http://hdl.handle.net/1828/4170.
Full textAbstract:
Advanced composite materials are becoming increasingly more valuable in a plethora of engineering applications due to properties such as tailorability, low specific strength and stiffness and resistance to fatigue and corrosion. Compared to more traditional metallic and ceramic materials, advanced composites such as carbon, aramid or glass reinforced plastic are relatively new and still require research to optimize their capabilities. Three areas that composites stand to benefit from improvement are processing, damage detection and life prediction. Fiber optic sensors and piezoelectric transducers show great potential for advances in these areas. This dissertation presents
the research performed on improving the efficiency of advanced composite materials through the use of embedded fiber optic sensors and surface mounted piezoelectric transducers.
Embedded fiber optic sensors are used to detect the presence of resin during the injection stage of resin transfer molding, monitor the degree of cure and predict the remaining useful life while in service. A sophisticated resin transfer molding apparatus was developed with the ability of embedding fiber optics into the composite and a glass viewing window so that resin flow sensors could be verified visually. A novel technique for embedding optical fiber into both 2- and 3-D structures was developed. A theoretical model to predict the remaining useful life was developed
and a systematic test program was conducted to verify this model.
A network of piezoelectric transducers was bonded to a composite panel in order
to develop a structural health monitoring algorithm capable of detecting and locating
damage in a composite structure. A network configuration was introduced that
allows for a modular expansion of the system to accommodate larger structures and
an algorithm based on damage progression history was developed to implement the
network.
The details and results of this research are contained in four manuscripts that are
included in Appendices A-D while the body of the dissertation provides background
information and a summary of the results.Graduate
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Yan, Yu-Tsung, and 顏宇聰. "Asynchronous Optical CDMA Networks Structured on Cascaded Fiber Bragg Grating and Arrayed Waveguide Grating Devices." Thesis, 2002. http://ndltd.ncl.edu.tw/handle/zv4kxx.
Full textAbstract:
碩士國立成功大學
電機工程學系碩博士班
90
In this thesis, an asynchronous optical code-division multiple-access (CDMA) network, which is based on cascaded fiber Bragg grating (FBG) and arrayed waveguide grating (AWG) devices, is proposed, and it allows more users to access the network. In this system, an optical spectrally encoding scheme is devised for CDMA networks, and we use the maximal-length sequence (M-sequence) to perform balanced detection to acquire information of users at the receiver. The multiple FBGs are cascaded in the system to encode the signals. However, when the number of users increases, length of M-sequence becomes longer and the length of total FBGs required becomes longer too. Therefore, some non-ideal properties, which can be neglected at the short-length code system, become serious. Another alternative is to treat some users as a group, insert a stage of AWG structure, and encode the signal of group by the AWG combined with delay lines. On the other hand, delay characteristic will affect the performance. Different distribution causes the signals of interference group spread on different time slot. Seeking better code family to reduce the interference of other users will be our future improvement.
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蔡孟璋. "Chromatic Dispersion Measurement and Structure Reconstruction of Fiber Bragg Gratings." Thesis, 2003. http://ndltd.ncl.edu.tw/handle/28827588824561854806.
Full textAbstract:
碩士國立交通大學
光電工程所
91
In this thesis we measure the time delay spectrum of fiber gratings by the use of a Michelson interferometer. The advantages of the method are the short measurement time and the low cost experimental setup. Both reflective and transmissive optical components can be measured and we only need standard components and setups including a broadband lightsource ,an optical spectrum analyzer,couplers, mirrors and collimators. The light emitting from the broadband lightsource enter the fiber grating and then be reflected.Different frequency components of the reflected light from the fiber grating obtain different phase shifts which can be infered form the change of the interference pattern on the frequency domain. We obtain the phase delay spectrum by performing a Fourier transform and by differentating the phase with respect to the wavelength we get the time delay spectrum finally. After obtaining the phase shift and reflectivity sprectra of the fiber Bragg grating we then use the “Discrete Layer Peeling Method” to find out the coupling coefficient of the fiber grating.The knowledge about the actual distribution of coupling coefficient can be used to achieve higher accuracy of the fabraction process and to provide us more information about the fabricated fiber gratings.