Abstract
We examined the crystallization behavior of double clad fiber composed by BaO-TiO2-GeO2-SiO2 based glasses in detail. Formation of needle-like fresnoite-type Ba2Ti(Ge,Si)2O8 were observed at the interface between the first and second clad. In addition, we employed the two-step heat-treatment (i.e., 728°C, 20 h + 749°C, 1 h) in fabrication of the crystallized fiber in order to obtain the highly-oriented fresnoite phase in the fiber structure. The first treating temperature, 728°C, which gives the maximum nucleation rate, was determined by differential thermal analysis. It was demonstrated that the two-step heat-treatment was effective for improvement of the orientation of fresnoite-type phase in the first clad of the double clad fiber.
