Growth of tetragonal BaTiO 3 single crystal fibers
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F. A. Thiel AT&T Bell Laboratories, Murray Hill, New Jersey 07974 (Received 7 February 1986; accepted 25 March 1986) With the increasing use of optical fibers in the telecommunication network, there is need for fiber geometry compatible optical devices such as optical amplifiers, switches, couplers, and isolators. These active devices are based on field-dependent material properties, such as electrooptic and magneto-optic effects, which are stronger in single crystal than in amorphous materials. Single crystal fibers can be grown by the laser heated pedestal growth (LHPG) technique. In this paper we report the growth of single crystal fibers of ferroelectric barium titanate from sintered ceramic rods of stoichiometric barium titanate. Barium titanate is one of the most extensively investigated ferroelectric materials. However, its growth from stoichiometric melt always results in its hexagonal nonferroelectric phase. Using LHPG, single crystal strontium titanate seed, and sintered ceramic barium titanate rods, we have succeeded in growing single crystal fibers ( ~ 100/mi diameter) of pure barium titanate with tetragonal (ferroelectric) crystal structure. This paper discusses growth and characterization of these fibers.
I. INTRODUCTION The rapid deployment of the optical fiber as transmission medium has created an interest in fiber compatible optical devices such as in-line optical amplifiers, modulators, optical isolators, signal processors, and couplers. These active devices are based on field-dependent material properties such as electro-optic, magnetooptic, photorefractive, or nonlinear susceptibilities. The material for these devices can be suitably doped glass fibers or single crystal fibers. However, the field-dependent properties are stronger in single crystals than in amorphous materials. Single crystal fibers of ferroelectric materials like barium titanate, lithium niobate, and barium strontium niobate are of special interest. In the ferroelectric phase, these materials possess large electro-optic coefficients1 and with suitable doping can be made photorefractive2 or conductive.3 Because of high field intensities and improved phase matching conditions in the fibers,4 they can provide high efficiency for second harmonic generation. Barium titanate is one of the most extensively investigated ferroelectric materials,5 and numerous techniques have been used to grow single crystals.6"1' In this paper we report the growth of tetragonal and hexagonal barium titanate single crystal fibers from stoichiometric sintered ceramic rods using the laser heated pedestal growth (LHPG) method. II. GROWTH TECHNIQUE The LHPG method is based on a modification of the floating zone melting process and utilizes a laser 452
J. Mater. Res. 1 (3), May/Jun 1986
http://journals.cambridge.org
beam as heat source. This method was first reported by Gasson and Cockayne12 and Haggerty et al.13 for growing single crystal fibers of several refractory materials. Burrus and Stone demonstrated lasing action in single crystal fibers of Nd-dop
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