<p>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.</p><p>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.</p><p>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).</p><p>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.</p><p>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.</p><p><b>Keywords:</b>silica-on-silicon technology, PECVD, plasmadeposition, photonic integrated circuits, planar waveguidedevices, UV Bragg gratings, photosensitivity, arrayed waveguidegratings, multimode interference couplers, add-dropmultiplexers.</p>

Temporal pulse shaping based on integrated Bragg gratings is investigated in this work to achieve arbitrary output waveforms. The grating structure is simulated based on the sidewall-etching geometry in an AlGaAs platform. The inverse scattering employin the Gel'fan-Levithan-Marchenko theorem and the layer peeling method provides a tool to determine grating structures from a desired spectral reflection response. Simulations of pulse shaping considered flat-top and triangular pulses as well as one-to-one and one-to-many pulse shaping. The suggested grating profiles revealed a compromise between performance and grating length. The integrated grating, a few hundred microns in length, could generate flat-top pulses with pulse durations as short as 500 fs with rise/fall times of 200 fs; the results are comparable to previous work in free-space optics and fiber optics. The theories and the devised algorithms could serve as a design station for advanced grating devices for, but not restricted to, optical pulse shaping.

Temporal pulse shaping based on integrated Bragg gratings is investigated in this work to achieve arbitrary output waveforms. The grating structure is simulated based on the sidewall-etching geometry in an AlGaAs platform. The inverse scattering employin the Gel'fan-Levithan-Marchenko theorem and the layer peeling method provides a tool to determine grating structures from a desired spectral reflection response. Simulations of pulse shaping considered flat-top and triangular pulses as well as one-to-one and one-to-many pulse shaping. The suggested grating profiles revealed a compromise between performance and grating length. The integrated grating, a few hundred microns in length, could generate flat-top pulses with pulse durations as short as 500 fs with rise/fall times of 200 fs; the results are comparable to previous work in free-space optics and fiber optics. The theories and the devised algorithms could serve as a design station for advanced grating devices for, but not restricted to, optical pulse shaping.

Made available in DSpace on 2016-03-15T19:37:34Z (GMT). No. of bitstreams: 1 Claudia Barros dos Santos.pdf: 3294972 bytes, checksum: b848d69d9c6a8c824e5142a4e3659d37 (MD5) Previous issue date: 2011-01-21 / In this work, we inserted two Arrayed Waveguide Gratings (AWGs), in an Erbium doped fiber ring cavity laser, where a single gain medium at room temperature can emit laser in multiples wavelengths, simultaneous and individualy controlled. The setup allowed us to check different functions in the ring cavity. Here we show emission in CW regime, Passive Mode-Locking, using Carbon Nanotubes as saturable absorbers and finally Active mode-locking at 7GHz, simultaneously. / Neste trabalho, fez-se a inserção de duas grades de difração matriciais com guias de onda, ou AWGs (Arrayed Waveguide Gratings) em uma cavidade laser de fibra dopada com Érbio, onde um único meio de ganho em temperatura ambiente pode gerar ação laser em múltiplos comprimentos de onda, com emissões simultâneas e controladas individualmente. A configuração utilizada permitiu o teste com diferentes regimes de operação simultâneos dentro da cavidade. Mostramos a possibilidade de emissão laser em regime CW, em regime de mode-locking passivo, com o uso de nanotubos de carbono como absorvedor saturável e, por último, em regime de modelocking ativo com uma freqüência de modulação de 7 GHz.

Made available in DSpace on 2016-03-15T19:37:35Z (GMT). No. of bitstreams: 1 Claudia Barros dos Santos.pdf: 3294972 bytes, checksum: b848d69d9c6a8c824e5142a4e3659d37 (MD5) Previous issue date: 2011-01-21 / In this work, we inserted two Arrayed Waveguide Gratings (AWGs), in an Erbium doped fiber ring cavity laser, where a single gain medium at room temperature can emit laser in multiples wavelengths, simultaneous and individualy controlled. The setup allowed us to check different functions in the ring cavity. Here we show emission in CW regime, Passive Mode-Locking, using Carbon Nanotubes as saturable absorbers and finally Active mode-locking at 7GHz, simultaneously. / Neste trabalho, fez-se a inserção de duas grades de difração matriciais com guias de onda, ou AWGs (Arrayed Waveguide Gratings) em uma cavidade laser de fibra dopada com Érbio, onde um único meio de ganho em temperatura ambiente pode gerar ação laser em múltiplos comprimentos de onda, com emissões simultâneas e controladas individualmente. A configuração utilizada permitiu o teste com diferentes regimes de operação simultâneos dentro da cavidade. Mostramos a possibilidade de emissão laser em regime CW, em regime de mode-locking passivo, com o uso de nanotubos de carbono como absorvedor saturável e, por último, em regime de modelocking ativo com uma freqüência de modulação de 7 GHz.

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.

This dissertation presents the novel creation of a surface relief fiber Bragg grating on the flat surface of a D-shaped optical fiber. In order to produce an efficient surface relief grating the grating must be etched into the surface of the glass fiber close to the core. A short etch that removes the cladding above the core is performed in order to decrease the core-to-flat distance and allow the light to interact with the grating on the flat surface. Due to the unique D-shape of the optical fiber the mechanical integrity of the fiber remains high even after the fabrication process. For traditional fiber Bragg gratings the index modulation occurs in the core of the optical fiber. While this method can produce highly reflective gratings they are not well suited for many sensing applications. For example, the operating temperature range is limited to a few hundred degrees Celsius before the index modulation returns to a more uniform index profile. Also because the gratings are created in the core of the fiber, interaction with the surrounding environment is limited. The surface relief fiber Bragg grating created for this work overcomes some of the sensing challenges of traditional gratings. The major accomplishments of this dissertation show a dramatic increase in operating temperature to over 1000 degrees Celsius, the ability to measure multi-dimensional bend, the ability to measure material changes around the fiber such as chemical concentration, and the ability to use a Vernier effect to dramatically increase the sensors sensitivity. In addition to the sensing applications of this work a more thorough understanding of the reflection and transmission properties of the surface relief grating is also presented. Implementation of the transfer matrix method for simulation of the gratings is also shown to be a fast and accurate modeling tool for predicting the grating response.

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

Volume phase holographic (VPH) gratings have been designed for use in many areas of science and technology such as optical communication, medical imaging, spectroscopy and astronomy. The goal of this dissertation is to design a volume phase holographic grating that provides diffraction efficiencies of at least 70% for the entire visible wavelengths and higher than 90% for red, green, and blue light when the incident light is unpolarized. First, the complete design, simulation and optimization of the volume hologram are presented. The optimization is done using a Monte Carlo analysis to solve for the index modulation needed to provide higher diffraction efficiencies. The solutions are determined by solving the diffraction efficiency equations determined by Kogelnik's two wave coupled-wave theory. The hologram is further optimized using the rigorous coupled-wave analysis to correct for effects of absorption omitted by Kogelnik's method. Second, the fabrication or recording process of the volume hologram is described in detail. The active region of the volume hologram is created by interference of two coherent beams within the thin film. Third, the experimental set up and measurement of some properties including the diffraction efficiencies of the volume hologram, and the thickness of the active region are conducted. Fourth, the polarimetric response of the volume hologram is investigated. The polarization study is developed to provide insight into the effect of the refractive index modulation onto the polarization state and diffraction efficiency of incident light.

This thesis proposes a metallic hole array of a rectangular converging-diverging channel (RCDC) shape with extraordinary transmission. We use a three-dimensional (3D) finite element method to analyze the transmission characteristics of two-dimensional metallic hole arrays (2D-MHA) with RCDC. For a straight channel MHA, when the aperture size is reduced, the transmission peaks have a blue-shift. The same result is observed for a smaller gap throat for the RCDC structure. For the rectangular holes with a high length-width ratio, a similar blue-shift in the transmission peaks as well as a narrower full width at half maximum (FWHM) are observed. The asymmetry from the rectangular shape gives this structure high selectivity for light with different polarizations. Furthermore, the RCDC shape gives extra degrees of geometrical variables to 2D-MHA for tuning the location of the transmission peak and FWHM. The tunable transmission property of this structure shows promise for applications in tunable filters, photonic circuits, and biosensors. / text