Designing Optical Properties in Infrared Glass

Chalcogenide glasses (ChGs) are well-known for their attractive optical properties, such as high refractive index and transparency in across infrared wavelengths. ChGs also possess the ability to compositionally tune properties such as the refractive index, the thermo-optic coefficient, and other non-optical properties. Chalcogenide glasses with compositionally tailored physical and optical properties will provide optical designers with new materials necessary to create novel infrared imaging systems requiring new or expanded functionality. This dissertation has evaluated the relationship between glass composition, the resulting atomic structure, and resulting optical and thermo-optical properties, with specific focus on the infrared refractive index and the thermo-optic coefficient (dn/dT). To create these linkages, a series of GeAsSe glasses with increasing Ge content were fabricated across three tielines, and evaluated for their chemical and physical attributes. A novel infrared refractometer was constructed to provide supplemental refractive index and dn/dT data. Findings in this dissertation showed a correlation between the Ge content of the glass composition and several non-optical properties. Namely, as the Ge content increases, the glass transition temperature and Vickers Hardness increase, while the coefficient of thermal expansion decreases. These physical changes are due to the cross-linking of the glassy network by the 4-coordinated Ge additions. In contrast, optical property data showed a strong dependence on the appearance and/or disappearance of specific atomic structures within the glassy network as the glass composition changes. Overall, this study aimed to answer key questions that have not been systematically studied within multi-component chalcogenide glasses. These questions include: • How will compositional variations for the sake of optical tunability affect the physical properties which dictate a materials’ response to manufacturing processes? • Are there links between optical properties, such as the index and dn/dT, and non-optical properties that can allow for easier prediction of the difficult to measure optical properties? • Are there compositions within the GeAsSe ternary that can produce a zero dn/dT that will offer better thermo-mechanical stability to the current commercial options? Finally, this work presented a new phenomenon of a thermally-induced, sub-Tg index hysteresis and subsequent room temperature structural relaxation in chalcogenide glasses. This process resulted in a maximal change in the room temperature refractive index of 0.0030. Over the course of 2 months the structural relaxations returned the refractive index to the initial state, with a characteristic relaxation time ranging from τ = 70,000s to τ = 300,000s

Characterization of catalytic chemical vapor-deposited SiCN thin film coatings

Silicon carbonitride thin films of 480 to 730-nm thicknesses were grown on silicon substrate using ammonia and hexamethyldisilazane gas sources using catalytic chemical vapor deposition process. Compositions of silicon, carbon and nitrogen in the SiCN films were varied by changing the flow rate of ammonia gas. The effect of deposition conditions on the structural, optical and mechanical properties of SiCN thin films was examined. X-ray photoelectron spectroscopy analysis indicated that the higher flow rate of ammonia gas results in higher nitrogen and lower carbon content in the deposited thin films. The measurement of stress as a function of substrate temperature in the SiCN film showed that the stress changes from compressive to tensile in the range of 275°C to 325°C. With these preliminary characterization tests, it is expected that SiCN nano-thin films can be used for developing sensors for harsh environment

Solid immersion lens at the aplanatic condition for enhancing the spectral bandwidth of a waveguide grating coupler

We report a technique to substantially boost the spectral bandwidth of a conventional waveguide grating coupler by using a solid immersion cylindrical lens at the aplanatic condition to create a highly anamorphic beam and reach a much larger numerical aperture, thus enhancing the spectral bandwidth of a free-space propagating optical beam coupled into a single-mode planar integrated optical waveguide (IOW). Our experimental results show that the broadband IOW spectrometer thus created almost doubles (94% enhancement) the coupled spectral bandwidth of a conventional configuration. To exemplify the benefits made possible by the developed approach, we applied the technique to the broadband spectroscopic characterization of a protein submonolayer; our experimental data confirm the enhanced spectral bandwidth (around 380–nm) and illustrate the potentials of the developed technology. Besides the enhanced bandwidth, the broadband coupler of the single-mode IOW spectrometer described here is more robust and user-friendly than those previously reported in the literature and is expected to have an important impact on spectroscopic studies of surface-adsorbed molecular layers and surface phenomena

Integrated waveguide and nanostructured sensor platform for surface-enhanced Raman spectroscopy

Limitations of current sensors include large dimensions, sometimes limited sensitivity and inherent single-parameter measurement capability. Surface-enhanced Raman spectroscopy can be utilized for environment and pharmaceutical applications with the intensity of the Raman scattering enhanced by a factor of 106. By fabricating and characterizing an integrated optical waveguide beneath a nanostructured precious metal coated surface a new surface-enhanced Raman spectroscopy sensing arrangement can be achieved. Nanostructured sensors can provide both multiparameter and high-resolution sensing. Using the slab waveguide core to interrogate the nanostructures at the base allows for the emission to reach discrete sensing areas effectively and should provide ideal parameters for maximum Raman interactions. Thin slab waveguide films of silicon oxynitride were etched and gold coated to create localized nanostructured sensing areas of various pitch, diameter, and shape. These were interrogated using a Ti:Sapphire laser tuned to 785-nm end coupled into the slab waveguide. The nanostructured sensors vertically projected a Raman signal, which was used to actively detect a thin layer of benzyl mercaptan attached to the sensors

An infrared integrated optic astronomical beam combiner for stellar interferometry at 3-4 microns

Integrated-optic, astronomical, two-beam and three-beam, interferometric combiners have been designed and fabricated for operation in the L band (3 - 4 microns) for the first time. The devices have been realized in titanium-indiffused, x-cut lithium niobate substrates, and on-chip electro-optic fringe scanning has been demonstrated. White light fringes were produced in the laboratory using the two-beam combiner integrated with an on-chip Y-splitter.Comment: This paper was published in Optics Express and is made available as an electronic reprint with the permission of OSA. The paper can be found at the following URL on the OSA website: http://www.opticsinfobase.org/oe. Systematic or multiple reproduction or distribution to multiple locations via electronic or other means is prohibited and is subject to penalties under la

Energy and greenhouse gas emissions implications of alternative housing types for Australia

Many cities around the world are looking for ways to reduce their per capita greenhouse gas emissions. The outward growth of cities from a central business district, typical of many cities around the world, is often seen as working against this goal and as unsustainable. This is especially the case in circumstances where this growth is not supported by the necessary infrastructure, often resulting in an increase in the use of private transport. However, alternative scenarios to contain the outward growth are being proposed. This paper provides a comparison of the energy demand and greenhouse gas emissions between typical detached outer-suburban housing currently being built in Australia\u27s major cities and inner-city and -suburban apartments, which are increasingly seen as a legitimate alternative to the housing that is currently being built on our outer city fringes. By analysing the energy demand associated with the construction and operation of each housing type and for occupant travel it was found that the location of the housing and its size are the dominant factors determining energy use and greenhouse gas emissions. The findings from this analysis provide useful information for policy-makers in planning the development of our cities into the future, when faced with a growing population and an increasing need to minimise greenhouse gas emissions

Data-driven design of glasses with desirable optical properties using statistical regression

In this study, we used a data-driven approach to build models for assisting the design of new glasses with high refractive index and low dispersion. Our models, which are based on multiple linear regression and kernel ridge regression, achieved high accuracy in predicting optical properties of glasses based on their composition alone. Using the predictions of these models as a guide, we fabricated new glasses in our laboratory. In agreement with model predictions, these glasses had promising optical properties. This work therefore demonstrates a successful example of data-driven materials design and can be used as a template for designing glasses or other materials with other desirable properties

A machine learning approach to the prediction of the dispersion property of oxide glass

In this study, we built a model for predicting the optical dispersion property of oxide glasses via machine-learning techniques such as kernel ridge regression, neural networks, and random forests. The models precisely predicted the optical property. Based on the predictions for glasses with doped oxides, we prepared new glasses in our laboratory. The experiments agreed well with the predictions made using kernel ridge regression and neural networks but not with those made using random forests. The results of this study demonstrate that the data-driven approach is a promising route for new material design