Defects and Optical Property of Single-crystal Sapphire Fibers Grown by Edge-defined Film-fed Growth Method

Single-crystal sapphire fibers with diameter of 400-1000 m and length of 500 mm were successfully grown by the edge-defined film-fed growth (EFG) method. The cross section is roughly circular without noticeable faceting on the lateral surface of the fiber. The diameter variation was within 40 m in the whole fiber. Crystal defects such as micro-bubbles, inclusions and growth stripes were observed and analyzed. Most micro bubbles in the crystal are spherical and exist on the periphery of the fiber. A small amount of Mo inclusions were observed on the periphery of the fiber. The new dies produce greater number of Mo inclusions at the first several uses, and Mo inclusions decrease after several uses. Size and distribution of micro-bubbles in sapphire fiber have been studied by experimental and numerical simulation of the fluid flow in the meniscus. Results of experimental and numerical simulation presented excellent agreement. The micro-bubbles distribution depends on the fluid flow in the meniscus. Vortex of the fluid flow drove these micro-bubbles to move to the atmosphere under thermo-capillary convection. Absorption loss at 633 nm was 9 dB/m. Inclusions and surface irregularities increase the scattering losses.