  A method to engineer the refractive indices of functional materials (TiO2,
ZnO, SnO2, SiO2), by nanostructuring in the deep sub-wavelength regime (<20nm),
is presented. Block-copolymer templating combined with a wet processing route
is used to realize 3D functional nanostructures with continuously adjustable
refractive indices from 1.17 to 2.2. Wet processing accessed refractive index
engineering can be applied to address a variety of realizability concerns in
attaining design specified refractive index values and refractive index
gradients in 1D, 2D, and 3D that arise as the results of optical design
techniques such as thin film optimization methods, transformation optics and
conformal mapping. Refractive index optimized multi-layer anti-reflection
coatings on crystalline silicon, which reduce light reflections from 38% down
to ~3% with a wide angular span, are demonstrated with the developed wet
processing route. A high temperature oxygen free fiber optic hydrogen sensor
realized by accessing nano-engineering enabled refractive indices is also
presented. The functionality of the sensor is characterized with a fiber Bragg
grating, transmission based interrogation, and optical frequency domain
reflectometry. The latter demonstrates the potential of the developed sensor
for the detection of chemical gradients for applications such as in high
temperature hydrogen driven fuel cells.
