导模法生长蓝宝石单晶光纤的缺陷和光学特性研究

doi:10.15541/jim20190573

摘要/Abstract

摘要：

通过导模法(EFG)成功生长了蓝宝石单晶光纤(直径400~1000 μm, 长度500 mm)。光纤的横截面大致为圆形, 侧面无明显的小面, 直径变化小于40 μm。本研究对晶体缺陷, 例如微气泡, 包裹物和生长条纹等进行观察与分析, 得出: 大多数微气泡是球状的, 且存在于光纤的外侧缘; 在蓝宝石光纤外侧面也观察到少量的钼包裹物元素; 新模具在前几次使用中往往会产生更多的钼夹杂物, 在多次使用后降低。通过对熔体膜流体流动的实验和数值模拟, 研究蓝宝石光纤中微气泡尺寸和分布, 实验和数值模拟的结果显示出良好的一致性。微气泡的分布取决于熔体膜处的流体流动模式, 流体流动的涡流使微气泡在热毛细对流作用下移动到蓝宝石光纤外侧缘。633 nm处的吸收损耗为9 dB/m, 包裹物和表面不规则性会增加散射损耗。

关键词: 蓝宝石光纤, 导模法(EFG), 微气泡, 钼包裹物

Abstract:

Single-crystal sapphire fibers with diameter of 400-1000 μm 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 μm 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.

Key words: sapphire fibers, edge-defined film-fed growth method, micro bubble, Mo inclusion

中图分类号:

TQ174

王东海,侯文涛,李纳,李东振,徐晓东,徐军,王庆国,唐慧丽. 导模法生长蓝宝石单晶光纤的缺陷和光学特性研究[J]. 无机材料学报, 2020, 35(9): 1053-1058.

WANG Donghai,HOU Wentao,LI Na,LI Dongzhen,XU Xiaodong,XU Jun,WANG Qingguo,TANG Huili. Defects and Optical Property of Single-crystal Sapphire Fibers Grown by Edge-defined Film-fed Growth Method[J]. Journal of Inorganic Materials, 2020, 35(9): 1053-1058.

图/表 12

Fig. 1 Schematic experimental device 1-Melt; 2-Crucible; 3-Die; 4-Meniscus; 5-Sapphire fiber; 6-Seed

Fig. 2 View of as-grown sapphire in which fibers with irregular shape (a) and regular shape (b)

Fig. 3 Schematic diagram of the boundary conditions used in the numerical simulation

Fig. 4 Growth stripes in the crystal structure caused by slight vibrations above the die, v=30 mm/h

Fig. 5 Cross section morphology and bubbles' distribution in the cross section of the sapphire fibers

Fig. 6 Principles of capillary shaping for EFG fiber growth method Rm-Vertical curvature of the meniscus; Rd-Die radius; Rc-Radius of the crystal; Hm-Meniscus height

Table 1 Parameter φo for different crystals

Materials	Orientation	φ_o/(o)	Ref.
Si	[111]	11	[10]
YAG	[100]	11	[11]
Sapphire	[0001]	17	[12]
Sapphire	$[10\bar{1}0]$	35	[12]

Fig. 7 Relationship between theoretical meniscus shapes Z(R) and different fiber radii R

Fig. 8 Bubbles’ distribution observed on the lateral periphery of the fiber

Fig. 9 Decrease in total Mo inclusion length with die life (a) and Mo concentration as a function of time from a sapphire melt (b)

Fig. 10 Flow field in the meniscus (fiber radius 0.5 mm) and corresponding bubbles in the crystals

Fig. 11 Absorption spectrum of the EFG sapphire fiber

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