REFRACTIVE INDEX ENGINEERING BY 3D SUB-WAVELENGTH NANOSTRUCTURING FOR APPLICATIONS IN OPTICS AND OPTICAL SENSING

In photonics, the flow of light in light-wave circuits is molded by optical materials and structures with different refractive indices. The ingenuities of photonic engineering are often curbed by the limited range in the refractive indices of naturally occurring optical materials. In this dissertation, sub-wavelength 3D nano-engineering is explored to create artificial optical materials with tunable optical properties. Block-copolymer templating coupled with a wet processing route was applied to realize 3D functional metal oxides with nanostructure features in the sub-50nm regime. Using this low-cost and scalable manufacturing method, high quality films of TiO2, SnO2, ZnO, and SiO2, with refractive indices continuously tunable in the range of 1.17 to 2.2, is demonstrated. These new optical materials open new opportunities in a wide range of applications. This dissertation explores applications for optical fiber sensing, solar cell anti-reflection technology, along with other suggested avenues for exploration.\ud An expansion of the sensory capability of optical fiber type sensors to include the detection of chemical species, from low to high temperatures, is demonstrated. The merger of functional metal oxides with optical fiber is not well explored both theoretically and experimentally. Full wave simulations were performed that provide valuable insight in the design of these sensors along with experiments to identify the type of the sensory responses. Measurements performed using Optical Frequency Domain Reflectometry demonstrate the use of the developed sensors for the distributed type detection of hydrogen at very high temperatures, for applications in hydrogen driven Fuel Cells. With distributed sensing a single sensor can function as a linear combination of hundreds of sensor and can be used to analyze existing gradients across the sensor element.\ud Optical anti-reflection technology can benefit substantially from the extensive broadening of the available refractive indices. Optimal anti-reflection coatings predicted by theory rely on continuous gradual changes in the refractive indices which are too difficult to manufacture conventionally, if at all. The use of the developed refractive index engineering scheme for the realization of low cost and practical, broad-band and omnidirectional anti-reflection coatings with an improved efficiency, is also demonstrated