Ion beam modification of single crystal sapphire for high temperature optical waveguiding.

摘要

High temperature environments (>1000°C) provide a significant challenge for fiber optic based sensing due to the poor physical properties of silica fiber at elevated temperature. Not only does silica soften above 1000°C, but the dopants that are responsible for the refractive index change between the core and cladding diffuse, reducing the fibers effectiveness as a waveguide. Single-crystal sapphire fiber has the potential to supplement fiber sensing at high temperature however sapphire fiber is unclad and no cladding methods exist that withstand high temperatures. In addition to higher losses the lack of a cladding also leads to decreased sensitivity due to the large number of modes. This thesis explores a cladding method for sapphire based on ion beam modification and annealing, which initial results indicate is suitable for high temperature applications. Ion beam modification of planar sapphire using hydrogen is conducted and analyzed using Rutherford backscattering spectroscopy (RBS), nuclear reaction analysis (NRA), and transmission electron microscopy (TEM) to determine the structural changes and prism coupling, spectroscopic ellipsometry (SE), and UV absorption to determine the optical effects. Sapphire fibers are modified through the use of a rotating implant holder and examined using end face coupling. Substantial change in refractive index does not occur until annealing above 600°C and persists to at least 1700°C. From the measurements of planar sapphire the root cause of the refractive index change at high temperature is determined and verified through finite element simulations. Modified sapphire fibers exhibit increased containment of light to the core region and a novel annular waveguide is fabricated with potential for sensing applications. This work adds to the understanding of the optical effects of ion beam modification and high temperature annealing of sapphire, and provides a foundation for future high temperature sensing applications of single-crystal sapphire fiber.