  The 3D nano-structuring on the <10nm scale allows the refractive index of
functional sensory materials(n>2) to be reduced and matched with the cladding
of optical fiber(n~1.46) for low-loss integration. A high temperature capable
hydrogen sensor composed of D-shaped optical fiber with palladium nanoparticles
infused nanoporous (~5nm) TiO2 film is demonstrated. The behavior of the
developed sensor was characterized by examining the wavelength of an
incorporated Fiber Bragg Grating and by observing the transmission losses at
temperatures up to 700C. In addition, with frequency domain reflectometry the
distributed sensing potential of the developed sensor for hydrogen
concentrations of up to 10% is examined. The results show the possibility of
detecting chemical gradients with sub-cm resolution at very high
temperatures(>500C).
