Preparation of crystallized glass for application in fiber-type devices
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Seiki Ohara Department of Applied Physics, Tohoku University, Aoba, Sendai, 980-8579, Japan; and Research Center, Asahi Glass Co. Ltd., Kanagawa-ku, Yokohama, 211-8755, Japan
Yuki Kondo and Naoki Sugimoto Research Center, Asahi Glass Co. Ltd., Kanagawa-ku, Yokohama, 211-8755, Japan (Received 7 August 2008; accepted 20 October 2008)
We have demonstrated that 30BaO–15TiO2–30GeO2–25SiO2 (BTGS25) glass is a candidate for fiber-type nonlinear optical devices using crystallization of glass matrix. We determined the glass composition is suitable for crystallized fiber using partial substitution of Ge in 30BaO–15TiO2–55GeO2 (BTG55) by Si. The BTGS25 satisfied both thermal stability for fiber drawing and electronic polarizability for nonlinear optical property. After crystallization, the BTGS25 bulk crystallized glass showed surface crystallization behavior with the polar c-orientation of fresnoite phase, which was favorable for large second-order optical susceptibility. Following the results of the bulk glass, we prepared the BTGS25 glass fiber without precipitation of fresnoite crystallites. The BTGS25 crystallized fiber also showed c-oriented surface crystallization of fresnoite and second harmonic generation, which shows that the crystallized fiber is a promising material for fiber-type optical active devices.
I. INTRODUCTION
Fresnoite (Ba2TiSi2O8) is a noteworthy mineral, because Ti (IV) ion in fresnoite can take up an unusual square pyramid (TiO5) structure.1–3 In the fresnoite structure, TiO5 is connected to Si2O7 to form a layered titanosilicate structure and possesses a spontaneous polarization along the c axis. Since fresnoite shows ferroelectric,4 pyroelectric,5 piezoelectronic,6,7 and second-order optical nonlinear properties,8 it has attracted attention for various applications. Our group has focused on the second-order optical nonlinear property of BaO– TiO2–GeO2 (BTG) crystallized glass, in which fresnoite Ba2TiGe2O8 nano-crystallites were precipitated after heat treatment.9–12 We have reported second-harmonic generation (SHG) of the transparent BTG crystallized glasses using a Maker fringe technique. In particular, transparent 30BaO–15TiO2–55GeO2 (BTG55) crystallized glass showed the second-order nonlinear optical susceptibility, d33 24 p.m./V,11 which was comparable to the value of LiNbO3. In the BTG55 crystallized glass, crystal growth of Ba2TiGe2O8 was observed from the surface to inside of bulk glasses with c orientation, and the orientation is the origin of large nonlinear optical susceptibility. a)
Address all correspondence to this author. e-mail: [email protected] DOI: 10.1557/JMR.2009.0021
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J. Mater. Res., Vol. 24, No. 1, Jan 2009
Recently, Hane et al. reported fabrication of BTG55 glass fibers made by just pulling up glass melt and crystallization of the BTG55 glass fiber.13 In the transparent BTG55 crystallized fiber, precipitated Ba2TiGe2O8 crystallites grew from the surface to the center of fibers with the c-axis orientation. Although the BTG55 was of a nonstoichiometric
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