Rozprawy doktorskie na temat „Chalcogenide Waveguides”

The growing speed and bandwidth requirements of telecommunication systems demand all-optical on-chip solutions. Microphotonic devices can deliver low power nonlinear signal processing solutions. This thesis looks at the slow light photonic crystals in chalcogenide glasses to enhance low power nonlinear operation. I demonstrate the development of new fabrication techniques for this delicate class of materials. Both, reactive ion etching and chemically assisted ion beam etching are investigated for high quality photonic crystal fabrication. A new resist-removal technique was developed for the chemical, mechanical and light sensitive thin films. I have developed a membraning method based on vapor phase etching in combination with the development of a save and economical etching tool that can be used for a variety of vapour phase processes. Dispersion engineered slow light photonic crystals in Ge₃₃As₁₂Se₅₅ are designed and fabricated. The demonstration of low losses down to 21±8dB/cm is a prerequisite for the successful demonstration of dispersion engineered slow light waveguides up to a group index of around n[subscript(g)] ≈ 40. The slow light waveguides are used to demonstrate highly efficient third harmonic generation and the first advantages of a pure chalcogenide system over the commonly used silicon. Ge₁₁.₅As₂₄24Se₆₄.₅ is used for the fabrication of photonic crystal cavities. Quality factors of up to 13000 are demonstrated. The low nonlinear losses have enabled the demonstration of second and third harmonic generation in those cavities with powers up to twice as high as possible in silicon. A computationally efficient model for designing coupled resonator bandpass filters is used to design bandpass filters. Single ring resonators are fabricated using a novel method to define the circular shape of the rings to improve the fabrication quality. The spectral responses of the ring resonators are used to determine the coupling coefficient needed for the design and fabrication of the bandpass filters. A flat top bandpass filter is fabricated and characterized as demonstration of this method. A passive all-optical regenerator is proposed, by integrating a slow-light photonic crystal waveguide with a band-pass filter based on coupled ring resonators. A route of designing the regenerator is proposed by first using the dispersion engineering results for nonlinear pulse propagation and then using the filter responses to calculate the nonlinear transfer function.

Compact optical frequency comb sources with gigahertz repetition rates are desirable for various important applications including arbitrary optical waveform generation, microwave synthesis, spectroscopy and advanced telecommunications. This thesis investigates the exploitation of the interplay of two distinct nonlinear optical effects for the generation of gigahertz repetition rate frequency combs: stimulated Brillouin scattering (SBS) and the optical Kerr-effect. This interplay can lead to the generation of Brillouin frequency combs (BFCs) with repetition rates that are equal to the acoustic resonance associated with SBS. This resonance frequency is about 8 GHz, making BFCs ideal for the advanced photonic applications of interest. In this thesis, we experimentally demonstrate BFCs with equally spaced comb modes that exhibit a stable and repeatable spectral phase. The BFCs are generated in chalcogenide fibre and in chalcogenide waveguides on photonic chips. Through theoretical and numerical investigations we show that, whilst SBS provides the high repetition rate of the combs, the Kerr-nonlinearity plays an important role in achieving equally spaced and phase-coherent spectral components. We also study the interplay of BFCs and photosensitivity via multiphoton absorption in chalcogenide fibres and photonic chips. We show that this interplay can be used to internally inscribe multiwavelength gratings that exhibit several stopbands that are spaced by the acoustic resonance frequency. We then use these gratings in an SBS configuration and demonstrate a significant enhancement of BFC generation by exploiting the slow light effects associated with the grating band edges. This body of work represents an advance in the understanding of BFCs. We study the physics behind phase-coherent BFC generation. The demonstration of chip-based BFC generation is a step towards an all integrated, gigahertz repetition rate, optical frequency comb source. We also demonstrate a novel and flexible method for enhancing chip-based BFC generation that can potentially be extended to other nonlinear effects.

This research work presents numerical simulations of supercontinuum (SC) generation in optical waveguides based on Ge11.5As24Se64.5 chalcogenide (ChG) material. Rigorous numerical simulations were performed using finite-element and split-step Fourier methods in order to optimize the waveguides for wideband SC generation. Through dispersion engineering and by varying dimensions of the 1.8-cm-long ChG nanowires, we have investigated dispersion curves for a number of nanowire geometries and identified a promising one which can be used for generating a SC with 1300 nm bandwidth pumped at 1550 nm with a low peak power of 25 W. It was observed through successive inclusion of higher-order dispersion coefficients during SC simulations that there is a possibility of obtaining spurious results if the adequate number of dispersion coefficients is not considered. We then investigate MIR SC in dispersion-tailored, air-clad, ChG channel waveguide employing either Ge11.5As24S64.5 or MgF2 glass and ChG rib waveguide employing MgF2 glass for their lower claddings. We study the effect of waveguide parameters on the bandwidth of the SC at the output of 1-cm-long waveguides. Our results show that output can vary over a wide range depending on their design and the pump wavelength employed. At the pump wavelength of 2 μm the SC never extended beyond 4.5 μm for any of our designs. However, SC could be extended to beyond 5 μmfor a pump wavelength of 3.1 μm. A broadband SC spanning from 2 to 6 μm and extending over 1.5 octave could be generated with a moderate peak power of 500 W at a pump wavelength of 3.1 μm using an air-clad, all-ChG, channel waveguide. We show that SC can be extended even further covering the wavelength ranges 1.8-7.7 μm and 1.8-8 μm (> 2 octaves) when MgF2 glass is used for the lower claddings of ChG channel waveguide and rib waveguide, respectively. By employing the same pump source, we show that SC spectra can cover a wavelength range of 1.8-11 μm (> 2.5 octaves) in a channel waveguide and 1.8-10 μm in a rib waveguide employing MgF2 glass for their lower claddings with a moderate peak power of 3 kW. Finally we present microstrucured fibre based design made with same glass to generate SC spectra in the MIR region. Numerical simulations show that such a 1-cm-long fibre can produce a spectrum extending from 1.3 μm to beyond 11 μm (> 3 octaves) with the same pump and peak power applied before. We consider three fibre structures with microstrucured air-holes in their cladding and find their optimum designs through dispersion engineering. Among these, equiangular-spiral microstrucured fibre is found to be the most promising candidate for generating ultrawide SC in the MIR region.

Chalcogenide glasses offer transmission from the far visible to the far - infrared (IR) wavelength range. They exhibit photosensitivity and have high linear and nonlinear refractive indices. There are many potential applications involving near- and mid- infrared light such as laser delivery, optical data storage and all-optical switching. Two types of optical waveguides based on chalcogenide glasses were developed in this project: (1) The fabrication of planar optical waveguides in thin As40Se60 glass films was carried out via a hot embossing pressing technique. Previous work had shown it possible to fabricate optical waveguides in polymers using hot embossing techniques. Nevertheless using hot embossing to pattern waveguides in a thin chalcogenide glass film did not receive much success. In the present work, single-mode optical rib waveguides operating at telecommunication wavelengths were successfully patterned in a thermally evaporated As40Se60 glass thin film on a Ge17As18Se65 chalcogenide glass substrate. This experimental line demonstrated a fast and economic way of producing planar waveguides in thin chalcogenide glass films. (2) For the first time, a one-layer, solid micro-structured optical fibre (MOF) was successfully drawn from As40Se60 and Ge10As23.4Se66.6 (atomic %) chalcogenide glasses for operation in the near- to mid-infrared. This experimental line showed a new and flexible route to micro-structuring of mid-infrared fibre for operation in the near- to mid-infrared, presenting an all-solid (i.e. glass-glass) alternative to air-glass micro-structuring. The principal advantage of the new approach is mechanical rigidity. A sufficiently large refractive index step between the component glasses exists to enable structures that rely on photonic bandgap effects for their operation to be realised in future work. Underpinning the development of these optical waveguides, the refractive index dispersion of bulk chalcogenide glasses As40Se60, Ge10As23.4Se66.6 and Ge17As18Se65 was measured using ellipsometry from 0.3 μm to 2.3 μm wavelength in this project. Also, the refractive index of thin As40Se60 films was measured and compared with that of bulk As40Se60 samples. Finally a Se precursor purification process was developed to enhance the purity of the end-glasses.

Chalcogenide glasses and their use in a wide range of optical, electronic and memory applications, has created a need for a more thorough understanding of material property variation as a function of composition and in geometries representative of actual devices. This study evaluates compositional dependencies and photo-induced structural mechanisms in As-S-Se chalcogenide glasses. An effective fabrication method for the reproducible processing of bulk chalcogenide materials has been demonstrated and an array of tools developed, for the systematic characterization of the resulting material's physical and optical properties. The influence of compositional variation on the physical properties of 13 glasses within the As-S-Se system has been established. Key structural and optical differences have been observed and quantified between bulk glasses and their corresponding as-deposited films. The importance of annealing and aging of the film material and the impact on photosentivity and long term behavior important to subsequent device stability have been evaluated. Photo-induced structures have been created in the thin films using bandgap cw and sub-bandgap femtosecond laser sources and the exposure conditions and their influence on the post-exposure material properties, have been found to have different limitations and driving mechanisms. These mechanisms largely depend on both structural and/or electronic defects, whether initially present in the chalcogenide material or created upon exposure. These defect processes, largely studied previously in individual binary material systems, have now been shown to be consistently present, but varying in extent, across the ternary glass compositions and exposure conditions examined. We thus establish the varying photo-response of these defects as being the major reason for the optical variations observed. Nonlinear optical material properties, as related to the multiphoton processes used in our exposure studies, have been modeled and a tentative explanation for their variation in the context of composition and method of evaluation is presented.
Ph.D.
Other
Optics and Photonics
Optics

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.ucf.edu/Systems/DigitalInitiatives/DigitalCollections/InternetDistributionConsentAgreementForm.pdf You may also contact the project coordinator, Kerri Bottorff, at kerri.bottorff@ucf.edu for more information.
Bachelors
Arts and Sciences
Physics

Femtosecond laser has been an essential tool for nonlinear optics and materials processing at micrometer scale, in which chalcogenide and heavy metal oxide glasses have received special attention not only for their high third-order optical nonlinearities but also due to their transparency up to the infrared regions. Although metallic nanoparticles are expected to improve the optical properties of glasses, there are no enough experimental researches about their influence on the nonlinear refractive index (n2) and nonlinear absorption coefficient (β), moreover at femtosecond regime. Based on the scientific and technological interests on highly nonlinear glasses, the goal of this thesis was to apply femtosecond laser pulses in two main domains: (i) at the basis of fundamental science, to study the effect of metallic nanoparticles in the third-order nonlinear optical properties of glasses; and (ii) at the field of applied science, aiming the development of photonic devices, performed by the fabrication of 3D optical waveguides containing metallic nanoparticles. This aim was achieved through the techniques of z-scan and femtosecond laser micromachining, which provided the nonlinear optical characterization and waveguides development, respectively. First, we analyzed the third-order nonlinear optical properties of the GeO2-Bi2O3 glass containing gold nanoparticles, which promoted saturation of the absorption in the region of the surface plasmon resonance band. On the other hand, these gold nanoparticles did not affect the n2 that kept constant in the wavelength range of 480 - 1500 nm. The same features were investigated for a Pb2P2O7-WO3 matrix doped with copper nanoparticles. In contrast to the gold doped ones, these samples showed a slight enhancement of the nonlinear refractive index when the energy of the excitation approaches the surface plasmon band. We also found out that the Pb2P2O7-WO3 matrix is a good host to grow silver nanoparticles by fs-laser micromachining. Similarly, copper nanoparticles were produced in a borosilicate glass using single-step laser processing. The explanation for metallic nanoparticle formation is addressed in this thesis, as well as, its application in waveguides. Thus, we demonstrated the functionality of optical waveguides containing Cu0 or Ag0 nanoparticles. Still based on the technological interests on glasses doped with nanoparticles, we showed a single-step synthesis of silver sulfide nanoparticles in chalcogenide glass, which was carried in partnership with researches at Princeton University. The materials investigated in this PhD work are of great importance for photonics, in which the synthesis of nanoparticles, fabrication of waveguides and nonlinear optical characterization have been performed.
O laser de femtossegundos tem sido uma ferramenta essencial tanto para a óptica não-linear quanto para o processamento de materiais na escala micrométrica, na qual os vidros calcogenetos e óxidos de metais pesados têm recebido atenção especial, não apenas pelas suas elevadas não-linearidades ópticas de terceira ordem, mas também devido à sua transparência até o infravermelho. Embora seja esperado que nanopartículas metálicas melhorem as propriedades ópticas dos vidros, não existe investigações experimentais suficientes sobre a sua influência no índice de refração não linear (n2) e no coeficiente de absorção linear (β), sobretudo no regime de femtossegundos. Com base nos interesses científicos e tecnológicos de vidros altamente não-lineares, o objetivo deste trabalho foi aplicar pulsos laser de femtossegundos em dois domínios principais: (i) na campo da ciência fundamental, para estudar o efeito de nanopartículas metálicas nas propriedades ópticas não lineares de terceira ordem destes materiais; e (ii) no domínio da ciência aplicada, visando o desenvolvimento de dispositivos fotônicos, realizado pelo fabricação de guias de onda tridimensionais contendo nanopartículas metálicas. Este objetivo foi alcançado através das técnicas de varredura-z e microfabricação com laser de femtossegundos, que proporcionaram a caracterização óptica não-linear e o desenvolvimento de guias de onda, respectivamente. Primeiramente, foram investigadas as propriedades ópticas não-lineares de terceira ordem do vidro GeO2-Bi2O3 contendo nanopartículas de ouro, as quais promoveram saturação da absorção na região da banda de ressonância de plásmon. Por outro lado, essas nanopartículas não afetaram o n2, que se manteve constante no intervalo de comprimento de onda 480 - 1500 nm. As mesmas características foram investigadas para uma matriz Pb2P2O7-WO3 dopada com nanopartículas de cobre. Em contraste com os vidros dopados com ouro, estas amostras apresentaram um ligeiro aumento do índice de refração não linear quando a energia de excitação está próxima da banda de ressonância de plásmon. Observou-se ainda que a matriz Pb2P2O7-WO3 é ideal para a obtenção de nanopartículas de prata através da microfabricação com laser de femtossegundos. Similarmente, nanopartículas de cobre foram produzidas em vidro de borosilicato usando somente uma varredura a laser. A explicação para a formação de nanopartículas metálicas é abordada nesta tese, bem como sua aplicação em guias de onda. Deste modo, demonstrou-se a funcionalidade de guias de onda ópticos compostos por nanopartículas de Cu0 e Ag0. Ainda com base nos interesses tecnológicos em vidros dopados com nanopartículas, demonstrou-se uma síntese de nanopartículas de sulfeto de prata em vidro calcogeneto usando o processamento de única etapa, realizada em parceria com pesquisadores da Universidade de Princeton. Os materiais investigados neste trabalho de doutorado são de grande importância para aplicações em fotônica, em que a síntese de nanopartículas, a fabricação de guias de onda e a caracterização óptica não-linear foram realizadas.

Cette thèse est une contribution au domaine de recherche de la plasmonique nonlinéaire, domaine émergent de l'optique. L'objectif principal est de démontrer expérimentalement l'autofocalisation d'une onde plasmonique.L'étude débute avec la fabrication et la caractérisation de guides plans en verre de chalcogénure de composition Ge-Sb-Se. Une technique basée sur la formation de solitons spatiaux est développée afin d’estimer leurs non-linéarités Kerr. Les propriétés optiques linéaires et non linéaires de ces guides sont étudiées aux longueurs d’onde de 1200 nm et 1550 nm.Des structures plasmoniques sont ensuite conçues pour propager des ondes hybrides plasmon-solitons avec des pertes de propagation modérées. Elles sont constituées des guides précédents recouverts de nanocouches de silice et d'or.Les caractérisations optiques par couplage plasmon-soliton révèlent une forte autofocalisation subie par l’onde qui se propage à l'intérieur de la structure plasmonique. Comme prévu par la théorie, le comportement est présent uniquement pour une lumière polarisée TM. Des résultats expérimentaux détaillés de cette autofocalisation exaltée par effet plasmonique sont présentés pour différentes configurations. Des simulations confirment les résultats expérimentaux obtenus.Cette démonstration fondamentale vient confirmer le concept d’autofocalisation assistée par plasmon tout en révélant un effet nonlinéaire très efficace. Cela ouvre de nouvelles perspectives pour le développement de dispositifs photoniques non linéaires intégrés ainsi que de nouveaux phénomènes physiques
This dissertation contributes to the research area of nonlinear plasmonics an emerging field of optics. The main goal is to demonstrate experimentally the spatial self-trapping of a plasmonic wave.The study begins with the fabrication and the characterization of slab Ge-Sb-Se chalcogenide waveguides. A technique based on the formation of spatial solitons is developed to estimate their Kerr nonlinearities. Linear and nonlinear optical properties of the waveguides are studied at the wavelengths of 1200 nm and 1550 nm.Plasmonic structures are then designed to propagate hybrid plasmon-soliton waves with moderate propagation losses. They are constituted of the previous waveguides covered with nanolayers of silica and gold.Optical characterizations reveal a giant self-focusing undergone by the wave that propagates inside the plasmonic structure. The behavior is present only for TM polarized light as expected from theory. Detailed experimental results of this plasmon enhanced nonlinear self-trapping corresponding to different configurations are presented. Simulations confirm the obtained experimental results.This fundamental demonstration confirms the concept of plasmon-assisted self-focusing while revealing a very efficient nonlinear effect. This opens new perspectives for the development of integrated nonlinear photonic devices as well as new physical phenomena

There are many applications for small scale, solid state lasers in the near infrared, where conversely there are very few such devices. A lasing device in a rare earth doped gallium-lanthanum-sulphide thin film is attractive due to emission at wavelengths in the 2 to 5 µm region where many gasses and liquids have fundamental vibrations and overtones and so are detectable. This region also covers the 3 to 5 µm atmospheric 'windows'. Some examples of such detection is presented in this thesis. Using Pulsed Laser Deposition, a relatively new deposition technique, we are able to grow thin films of the chalcogenide glass; gallium-lanthanum-sulphide, gallium-sodium-sulphide and variations of oxysulphides, on a variety of substrates. EXAFS measurements have shown that some of the elements in the glass structure change their bonding arrangement when grown at different energy density producing 'wrong bonds'. This points to the origin of the increased absorption and shift of the optical bandgap which is seen in the materials. It is this tail absorption which ultimately prevented the production of an actual solid state, rare earth laser device. These amorphous semiconductors have a transmission range from the visible through to the mid infrared part of the spectrum. Chalcogenides can be photomodified. i.e. they have an ability to change refractive index when illuminated with photons whose energies lie in the optical bandgap of the material. This process can be reversible or irreversible depending on post deposition treatment and so gives them potential applications such as optical memory, holographic recording media, lithographically written waveguide structures and potentially laser mediums. For such uses a detailed knowledge of the chalcogenide materials optical parameters is needed. A novel technique for the optical characterisation of the thin films has been developed which has is able to measure differences in refractive index to an accuracy of 8.5 x 105. We are able to map refractive index changes across an entire surface and more uniquely whilst they are occurring during, and after, photomodification or heating.

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.ucf.edu/Systems/DigitalInitiatives/DigitalCollections/InternetDistributionConsentAgreementForm.pdf You may also contact the project coordinator, Kerri Bottorff, at kerri.bottorff@ucf.edu for more information.
Bachelors
Arts and Sciences
Physics

Stimulated Brillouin scattering (SBS) involves nonlinear interaction of an optical wave with material, which under the phase-matching condition results in generation of an acoustic wave. In turns, part of the optical wave is scattered by the acoustic wave through an inelastic scattering process. SBS enables unique applications in optical fibers and more recently in on-chip photonic waveguides, ranging from RF-signal processing to lasing, frequency combs, RF sources, and light storage. Harnessing on-chip SBS paves the way to photonic integration by enabling powerful functionalities in an integrated, scalable, energy-efficient and potentially CMOS-compatible platform. In this thesis, we explore the possibility of enabling SBS in a silicon-based platform by designing, fabricating and characterizing a hybrid silicon-chalcogenide waveguide, which shows significant improvement in terms of nonlinear losses and SBS gain compared to a standard silicon waveguide. The SBS response in photonic waveguides including the silicon-chalcogenide platform is subject to spectral broadening which influences the quality of the devices whose performance are relying on the narrow linewidth of SBS. The spectral broadening is mainly due to structural non-uniformities along the waveguides which affect the local SBS response and consequently deteriorates the strength of the integrated SBS response. Therefore, characterizing those waveguides is of great importance. To address this issue, we employed the principle of distributed SBS sensing to monitor the on-chip waveguides. However, since the waveguides length is on the order of cm and mm, the spatial resolution of the distributed technique needs to be very high, preferably in the sub-mm regime, which is the main goal of this thesis.

The advent of ultrafast lasers has enabled micromachining schemes that cannot be achieved by other current techniques. Laser direct writing has emerged as one of the possible routes for fabrication of optical waveguides in transparent materials. In this thesis, the advantages and limitations of this technique are explored. Two extended-cavity ultrafast lasers were built and characterized as the laser sources for this study, with improved performance over existing systems. Waveguides are fabricated in oxide glass, chalcogenide glass, and polymers, these being the three major classes of materials for the telecommunication industry. Standard waveguide metrology is performed on the fabricated waveguides, including refractive index profiling and mode analysis. Furthermore, a finite-difference beam propagation method for wave propagation in 3D-waveguides is proposed. The photo-structural modifications underlying the changes in the material optical properties after exposure are investigated. The highly nonlinear processes of the light/matter interaction during the writing process are described using a free electron model. UV/visible absorption spectroscopy, photoluminescence spectroscopy and Raman spectroscopy are used to assess the changes occurring at the atomic level. Finally, the impact of laser direct writing on nonlinear waveguide applications is discussed.
Ph.D.
Other
Optics and Photonics
Optics

In recent years, chalcogenide glasses have established their usefulness as attractive candidates for the fabrication of all-optical devices and mid infra-red lasers. These glasses possess low phonon energy and hence high luminescence quantum efficiency, which make them suitable for fabricating active photonic devices. Further, chalcogenide glasses exhibit a variety of photo-induced phenomena upon irradiation with energies above band gap under suitable conditions; the energy deposited at the focal point creates a localized refractive index change which can be used to fabricate a dielectric channel waveguide by translating the material through the laser focus. In this thesis work, different chalcogenide glasses have been prepared by melt quenching technique and their response to irradiation with ultrafast laser pulses has been studied. Photosensitivity studies undertaken have shown that the shape and magnitude of the index profile strongly vary with irradiation conditions. An optimal waveguide by ULI is the result of the successful interplay of a variety of inscription parameters that depend on the inscription laser, steering & focusing optics, translational stage parameters and the material under study. Thus, the waveguide properties can be tailored by optimizing these inscription parameters. The optical characterization of ultrafast laser inscribed, single-scan, as well as multi-scan waveguides, has been carried out at 1550 nm. The multi-scan technique reduces the number of scattering and absorbing defects induced in the modified material by the inscription process, hence reducing the optical losses. Mechanical and structural characterization has been carried out on ultrafast laser inscribed waveguides by nanoindentation and micro-Raman spectroscopy. Nanoindentation studies on single-scan waveguides show a position dependent mechanical behavior in the photo-modified region. At the laser focus, the photo-modified region exhibits same mechanical properties as those of bulk glass. This observation indicates that the material is getting quenched during re-solidification after waveguide inscription. At top of the waveguide, which is away from the focus, the elastic modulus and hardness are reported to be lower than bulk indicating the material is getting annealed at this region. This position dependent mechanical behaviour is correlated with the structural changes using micro-Raman studies. Nanoindentation studies undertaken on multi-scan waveguides reveal lower elastic modulus and hardness values compared to the bulk glass. The lower pulse energy and longer thermal accumulation during multiple passes cause annealing in the photo-modified region. Micro-Raman studies show a decrease in network connectivity in the photo-modified region resulting in lower mechanical properties. The change in mechanical properties in the photo-modified region is found to be greatly influenced by the net-fluence used for waveguide fabrication. The waveguides fabricated at different net-fluence show different local structures as a result of different rates of localized heating/cooling, which determine bond order and the local structure in a glassy network.

A key factor in the vertical integration of optical waveguide devices is the uniformity of the surface across which the coupling takes place. This thesis focuses on the fabrication of annealed proton-exchanged (APE) waveguides vertically integrated with chalcogenide waveguides. While titanium diffused waveguides form a surface bump that is approximately twice the size of the originally deposited film, an annealed proton-exchange process produces waveguides with surfaces having 90% less deformation. The theory behind wave guiding devices is explored in this work along with the modeling and simulation of APE waveguides. The results obtained from the simulations are used to aid in the fabrication of these devices. A detailed review of the fabrication process of APE waveguides and chalcogenide waveguides is provided with results obtained from measurements. The first known coupling results for vertically integrated chalcogenide waveguides on top of annealed proton-exchanged waveguides are recorded. This work is concluded with future directions for this research including lowering losses by obtaining better simulation parameters and vertically integrating ring resonators along with ways in which to do this.

Chalcogenide glasses are highly nonlinear optical materials which can be used for fabricating active and passive photonic devices. This thesis work deals with the fabrication of buried, three dimensional, channel waveguides in chalcogenide glasses, using ultrafast laser inscription technique. The femtosecond laser pulses are focused into rare earth ions doped and undoped chalcogenide glasses, few hundred microns below from the surface to modify the physical properties such as refractive index, density, etc. These changes are made use in the fabrication of active and passive photonic waveguides which have applications in integrated optics. The first chapter provides an introduction to the fundamental aspects of femtosecond laser inscription, laser interaction with matter and chalcogenide glasses for photonic applications. The advantages and applications of chalcogenide glasses are also described. Motivation and overview of the present thesis work have been discussed at the end. The methods of chalcogenide glass preparation, waveguide fabrication and characterization of the glasses investigated are described in the second chapter. Also, the details of the experiments undertaken, namely, loss (passive insertion loss) and gain measurements (active) and nanoindentation studies are outlined. Chapter three presents a study on the effect of net fluence on waveguide formation. A heat diffusion model has been used to solve the waveguide cross-section. The waveguide formation in GeGaS chalcogenide glasses using the ultrafast laser, has been analyzed in the light of a finite element thermal diffusion model. The relation between the net fluence and waveguide cross section diameter has been verified using the experimentally measured properties and theoretically predicted values. Chapter four presents a study on waveguide fabrication on Er doped Chalcogenide glass. The active and passive characterization is done and the optimal waveguide fabrication parameters are given, along with gain properties for Er doped GeGaS glass. A C-band waveguide amplifier has been demonstrated on Chalcogenide glasses using ultrafast laser inscription technique. A study on the mechanical properties of the waveguide, undertaken using the nanoindentation technique, is presented in the fifth chapter. This work brings out the close relation between the change in mechanical properties such as elastic modulus and hardness of the material under the irradiation of ultrafast laser after the waveguide formation. Also, a threshold value of the modulus and hardness for characterizing the modes of the waveguide is suggested. Finally, the chapter six provides a summary of work undertaken and also discusses the future work to be carried out.

Chalcogenide glasses are highly nonlinear optical materials which can be used for fabricating active and passive photonic devices. This thesis work deals with the fabrication of buried, three dimensional, channel waveguides in chalcogenide glasses, using ultrafast laser inscription technique. The femtosecond laser pulses are focused into rare earth ions doped and undoped chalcogenide glasses, few hundred microns below from the surface to modify the physical properties such as refractive index, density, etc. These changes are made use in the fabrication of active and passive photonic waveguides which have applications in integrated optics. The first chapter provides an introduction to the fundamental aspects of femtosecond laser inscription, laser interaction with matter and chalcogenide glasses for photonic applications. The advantages and applications of chalcogenide glasses are also described. Motivation and overview of the present thesis work have been discussed at the end. The methods of chalcogenide glass preparation, waveguide fabrication and characterization of the glasses investigated are described in the second chapter. Also, the details of the experiments undertaken, namely, loss (passive insertion loss) and gain measurements (active) and nanoindentation studies are outlined. Chapter three presents a study on the effect of net fluence on waveguide formation. A heat diffusion model has been used to solve the waveguide cross-section. The waveguide formation in GeGaS chalcogenide glasses using the ultrafast laser, has been analyzed in the light of a finite element thermal diffusion model. The relation between the net fluence and waveguide cross section diameter has been verified using the experimentally measured properties and theoretically predicted values. Chapter four presents a study on waveguide fabrication on Er doped Chalcogenide glass. The active and passive characterization is done and the optimal waveguide fabrication parameters are given, along with gain properties for Er doped GeGaS glass. A C-band waveguide amplifier has been demonstrated on Chalcogenide glasses using ultrafast laser inscription technique. A study on the mechanical properties of the waveguide, undertaken using the nanoindentation technique, is presented in the fifth chapter. This work brings out the close relation between the change in mechanical properties such as elastic modulus and hardness of the material under the irradiation of ultrafast laser after the waveguide formation. Also, a threshold value of the modulus and hardness for characterizing the modes of the waveguide is suggested. Finally, the chapter six provides a summary of work undertaken and also discusses the future work to be carried out.

A chalcogenide glass (arsenic-trisulfide, As2S3) optical waveguide is vertically integrated onto titanium-diffused lithium-niobate (Ti:LiNbO3) waveguides to add optical feedback paths and to create more compact optical circuits. Lithium-niobate waveguides are commonly used as building blocks for phase and amplitude modulators in high speed fiber communication networks due to its high electrooptic coefficient and low mode coupling loss to single-mode optical fibers. Although it can easily be modulated using an RF signal to create optical modulators, it lacks the intrinsic trait to create optical feedback loops due to its low core-to-cladding index contrast. Ring resonators are main building blocks of many chip-scale optical filters that require these feedback loops and are already demonstrated with other material systems. We have, for the first time, incorporated As2S3 as a guiding material on Ti:LiNbO3 and fabricated s-bends and ring resonators. We have examined As2S3-on-Ti:LiNbO3 waveguides at simulation, microfabrication, and optical characterization levels.

Bright, broadband, mid-infrared (MIR) sources are useful for microscopy and spectroscopy as well as many other areas of science and technology. Among the available sources, supercontinuum (SC) sources stand out because of their high brightness and continuous spectral coverage. SC generation involve a range of nonlinear optical effects including self-phase modulation, four-wave mixing, stimulated Raman scattering, etc. Anomalous dispersion plays a major role and interacts with nonlinearity leading to the creation of optical solitons that are essential to create a broad spectrum. The goal of this PhD was to generate practical, octave-spanning MIR SC sources spanning at least 2-10 μm using optical waveguides. To achieve this, firstly, it was necessary to identify the best nonlinear materials for SC generation. Chalcogenide glasses were chosen due to their high third-order optical nonlinearity, low nonlinear absorption and good transparency in the MIR. The potential of chalcogenides for SC generation was first demonstrated using bulk samples leading to a SC spectrum covering more than one octave. A challenge with chalcogenides is that they typically have long zero dispersion wavelengths (ZDWs) (beyond 5 μm) and this makes it difficult to pump them directly in the anomalous dispersion region. Two approaches were used to overcome this: 1) the dispersion was engineered via waveguide design to shift the anomalous region to shorter wavelengths; and 2) long-wavelength femtosecond pump sources were developed with appropriate powers to pump them. Both optical fibers and planar waveguides were explored and the measured SC spectra were compared with simulations based on the split-step Fourier method. Dispersion-engineered, step-index fibers were drawn by collaborators in China whilst dispersion-engineered rib waveguides were fabricated in house. Both allowed the first ZDWs to be shifted to wavelengths around 3 μm, however, ZDW below 3 μm was incompatible with the need for the waveguide to operate to beyond 10 μm. Simulations showed that MIR SC generation required a pump pulses in the 3-5 μm band with duration of a few hundred fs. We developed laser-seeded optical parametric amplifiers (OPA) pumped with femtosecond pulses from mode-locked Yb lasers, to create either 330 fs or 200 fs pulses tunable around 4 μm. In addition, we demonstrated a method for chirping and compressing the OPA pulses down to <60 fs which is needed to create a coherent SC spectrum. Combining the dispersion design and the femtosecond MIR OPA system, SC spectra more than two octaves wide with moderate average output powers (10s mW) were obtained from both fibers and waveguides. For the step-index chalcogenide fibers, typical experimental SC spectra covered the ranges of 2-10 μm or 2.2-12 μm depending on the fiber composition, however, due to their circular symmetry, the output was generally unpolarised. The fibers were also multimode over some of the SC spectrum. Both these deficiencies could be overcome by moving to a planar waveguide design. A tri-layer rib waveguide allowed the production of a linearly-polarized SC spanning from 2.0 μm to 10.8 μm. This source was used successfully for demonstrations of MIR spectroscopy.

Arsenic trisulfide (As₂S₃) waveguide devices on lithium niobate substrates (LiNbO₃) provide a set of compact and versatile means for guiding and manipulating optical modes in infrared integrated optical circuits, including the integrated trace gas detection system. As a member of the chalcogenide glass family, As₂S₃ has many properties superior to other materials, such as high transparency up to 10 [mu]m, large refractive index and high nonlinear coefficient. At the wavelength of 4.8[mu]m, low-loss As₂S₃ waveguides are achieved: The propagation loss is 0.33 dB/cm; the coupling efficiency is estimated to be 81 %; and less than 3 dB loss is measured for a 90-degree bent waveguide of 250 [mu]m bending radius. They offer an ideal solution to the optical interconnection -- the fundamental element of an optical circuit. LiNbO₃ is a birefringent crystal that has long been studied as the substrate material. Titanium diffused waveguides in lithium niobate substrate (Ti: LiNbO₃) have excellent electro-optical properties, based on which, on-chip polarization converters are demonstrated. New benefits can be obtained by integrating As₂S₃ and Ti: LiNbO₃ to form a hybrid waveguide, which benefits from the high index contrast of As₂S₃ and the electro-optical properties of Ti: LiNbO₃ as well as its easy connection with commercial single mode fibers. For hybrid waveguides, the mode coupling is key. A taper coupler is preferred owing to its simplicity in design and fabrication. Although preliminary experiments have shown the feasibility of such integration, the underlying mechanism is not well understood and guidelines for design are lacking. Therefore, a simulation method is first developed and then applied to the taper coupler design. Devices based on taper couplers are then fabricated and characterized. The study reveals that in the presence of mode beating, it is not necessarily the longer taper that is the better coupling. There exists an optimum length for a taper with fixed width variation. A two-stage taper design can largely reduce the total length, e. g. by 64%, while keeping the coupling efficiency above 90%. According to the frequency domain analysis, these practical taper couplers work for a wavelength range instead of a single wavelength.

Chalcogenide glass waveguide devices have received a great deal of attention worldwide in the last few years on account of their excellent properties and potential applications in mid-infrared (MIR) sensing and all-optical signal processing. Waveguide propagation losses, however, currently limit the potential for low power nonlinear optical processing, and the lack of suitable on chip integrated MIR sources is one of the major barriers to integrated optics based MIR sensing. One approach to overcome the losses is to employ rare-earth ion doped waveguides in which the optical gain can compensate the loss, in such a way that the conversion efficiency of nonlinear effects is increased significantly. For infrared applications, the long wavelengths potentially attainable from rare-earth ion transitions in chalcogenide hosts are unique amongst glass hosts. New rare-earth ion doped chalcogenide sources in the MIR range could benefit molecular sensing, medical laser surgery, defence etc. Despite these promising applications, until now, no one has succeeded in fabricating rare-earth ion doped chalcogenide amplifiers or lasers in planar devices. This work develops high quality erbium ion doped chalcogenide waveguides for amplifier and laser applications. Erbium ion doped As2S3 films were fabricated using co-thermal evaporation. Planar waveguides with 0.35 dB/cm propagation loss were patterned using photolithography and plasma etching on an erbium ion doped As2S3 film with an optimised erbium ion concentration of 0.45x1020 ions/cm3. The first demonstration of internal gain in an erbium ion doped As2S3 planar waveguide was performed using these waveguides. With different film deposition approaches, promising results on intrinsic lifetime of the Er3+ 4I13/2 state were achieved in both ErCl3 doped As2S3 films (2.6 ms) and radio frenquency sputtered Er3+:As2S3 films (2.1 ms), however, no waveguide was fabricated on these films due to film quality issues and photopumped water absorption issues. The low rare-earth ion solubility of As2S3 is considered the main factor limiting its performance as a host. Gallium-containing chalcogenide glasses are known to have good rare-earth ion solubility. Therefore, a new glass host material, the Ge-Ga-Se system, was investigated. Emission properties of the bulk glasses were studied as a function of erbium ion doping. A region between approximately 0.5 and 0.8 at% of Er3+ ion was shown to provide sufficient doping, good photoluminescence and adequate lifetime to envisage practical planar waveguide amplifier devices. Ridge waveguides based on high quality erbium ion doped Ge-Ga-Se films were patterned. Significant signal enhancement at 1540 nm was observed and 50 % erbium ion population inversion was obtained, in waveguides with Er3+ concentration of 1.5x1020 ion/cm3. To the Author's knowledge, this is the highest level of inversion ever demonstrated for erbium ions in a chalcogenide glass host and is an important step towards future devices operating at 1550 nm and on the MIR transitions of erbium ions in chalcogenide glass hosts. Photoinduced absorption loss caused by upconversion products in the waveguides is the remaining hurdle to achieving net gain. Further research is needed to find suitable compositions that possess high rare-earth ion solubility whilst avoiding the detrimental photoinduced losses.

A novel photonic frequency discriminator has been developed. The discriminator utilizes a Mach Zehnder interferometer-assisted ring resonator to achieve enhanced linearity. A numerical frequency-domain two-tone test is performed to evaluate the unique design of the discriminator, particularly for suppression of the third order intermodulation distortion. The discriminator is switchable between linear-intensity and linear-field regimes by adjusting a phase delay on one arm of the Mach Zehnder interferometer. Through the simulation, the linear